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Division of parental care and reproductive success in the zebra finch (Taeniopygia guttata ).
Behavioural Processes, Elsevier
12 (1986) l-22
DIVISION OF PARENTAL CARE AND FINCH (TAENIOPYGIA GUTTATA). -------------VERONIOUE
ANNIE
REPRODUCTIVE
SUCCESS
IN THE
ZEBRA
DELESALLE
Biology Department, lB1, Canada.
MC Gill
University,
Montreal,
Quebec,
Present Address: Department of Ecology and Evolutionary University of Arizona, Tucson, AZ 85721, USA.
H3A
Biology,
(Accepted 21 March 1985) ABSTRACT Delesalle, V.A., 1986. Division success in the Zebra finch Processes, 12: l-22.
of parental (Taenioel@a ------
care and reproductive Behav. guttata).
Variation in reproductive success among pairs of Zebra finches bred in captivity under time- rather than (Taenioeyea guttata), _--_ arose primarily because of differences energy-limited conditions, in number of clutches per reproductive bout. Division of parental care between mates during the time-constrained incubation phase, rather than the fledging phase, affected their fitness and future behavior. Pairs where the males assumed a greater fraction of the pooled incubation time were more likely to breed together again than pairs where males did not share in this activity as equally. In addition, males remated with familiar mates increased their time investment in incubation.
INTRODUCTION In species
with
quantity
and quality
parental
duties
mates
may
component
of mate
Trivers, not
an
of their
parental
a pair's choice
efficient when
the offspring is
forager
paired
with
(Burley
should
when
that have
an individual
two
or
success
and Moran,
a bird
is a good
in the
the division
and
may
be
a
1978;
incubator
a greater
of
between
Erickson,
but
reproductive
is good
at incubating.
more
0376-6357/86/$03.50 0 1986Elsevier Science Publishers
1979;
that
good
vary
complementarity)
reproductive
but not necessarily
necessary
behaviors,
of behavioral
1972). For example,
success
labor
care,
(or degree
affect
if individuals
biparental
at feeding Division
parental
tasks
B.V. (Biomedical
Division)
must
of be
carried
out
nest
(e.g., may
be
and
construction
advantageous
mates
and
in it
success
one
(Laridae), birds
swans
and
1970).
Early
found
in
unpredictable the
breeding
the
nest
is
My
own
in
performance set
aviary
out
conditions
care.
of
the
mates,
lifetime over
birds:
crows
and
and and
1972;
more
doves
gulls
terns
related
Coulson
and
and
constant
have
determine:
(1) study
Cody,
what (fitness
factors was
and
fairly
bonds
adaptations are one
within
limited operationally
as to
scarce,
parent
Serventy,
considerable
between
for
Butterfield, pair
of
1971;
is
pair
been
resources
presence
revealed
duties
1965; extended
where
to
have
be
Zebra
species
appear
to
of
in
grassfinch
Immelmann,
1980;
effects
success
believed
and
the
physiology
environments,
parental
for
Birds
and
are
(Carey,
this
test
maturity
observations
of
especially
bonding
Coulson,
This
1954;
short
required
to
Pair
reproductive
ecology
harsh
of
(Emlen
influencing
and
to on
finches
season
be of
a number
1970;
reproductive
or
longer
should
(Anatidae),
(Morris,
Zebra
together
(Estrildidael,
biparental
behavior,
documented
between
in
guttata).
has
their
burden
breed
in
undertaken
(Taeniopygia
life,
energetic
1983).
was
and
duties
affiliation
found
sequential
parental
individuals.
complementarity
monogamous
I
these is
Rowley,
study
finches
well
important
(Butterfield,
1983;
behavioral
more
are
sharing
complementarity long-term
and
(Corvidae)
This
and
grassfinches
geese
Thomas,
survive
season
(Columbidae),
the
with
of
breeding
pigeons
the
be
activities
incubation)
Behavioral
should
the
equalizes
to
species
reproductive than
it
them
1977).
important
and if
allows
Oring,
since
When
simultaneously.
at
1971).
variability pairs. fitness
under measured
3
as
the
total
number
experiment); fitness
(did
higher and
(2)
of
how
pairs
the that
reproductive mate
familiarity
reproductive
success.
MATERIALS
AND METHODS
Subjects--
and ---
-exerimental -_--
fledglings patterns divided
success?); affected
produced of
parental
parental and
by
(3)
behavioral
a pair
during
investment care
how
more breeding
the
affected equally
have
experience
complementarity
and
design -~-
Twenty-six domesticated zebra finches, approximately 6 months old and with no prior breeding experience, were paired randomly isolated physically and visually but not auditorily in and Pairs were provided with a domed nest cages (45 x 25 x 30 cm). skeleton, nesting material, food (a commercial finch seed mixture and an oatmeal wheat germ mix for the nestlings) and water ad libidum and cuttlebone. Once a week they were given hard--_-9 gravel boiled eggs and spinach. Birds were kept on a 14 hour daylight cycle, at a room temperature of 25 + 2 C. Pairs were observed for a period of 18 weeks which will be referred to as the pairing ‘trial’. At the end of the first pairing trial, males and females were visually isolated for 5 long enough for the pair bond to dissolve and for the weeks, birds to be ready to remate (Butterfield, 19701. The birds were Four of the original pairs were then paired for a second trial. experimental pairs were kept together (controls) and nine new Pairs could be divided into 4 groups: control formed randomly. pairs during the first pairing trial (Cl) and during the second experimental pairs during the first (El) and second trial (C2), (E2) trials. There were no initial differences in breeding ability between the two groups since none of the comparisons between Cl and El groups were significant (Mann-Whitney U tests). were made to test for the effects of Appropriate comparisons breeding experience and mate familiarity (Cl versus C21, of breeding experience only (El versus E2), and of mate familiarity per - -se (E2 versus C2). Reproductive -------
data ----
Nests were checked daily or every other day to obtain the following information: (1) The number of successful clutches (i.e., at least one young fledged) per trial. Pairs that had only one breeding cycle during to multiple a trial were called single clutchers as opposed clutchers, pairs that bred two or three times. (2) Clutch size. (3) Hatching efficiency, the proportion of eggs in a clutch that hatched. than number of hatchlings) Hatching efficiency (rather
4
was used as a measure of success during incubation since it measures only egg fertility and incubation success, while number of hatchlings reflects both these factors and clutch size. (4) Fledging efficiency, the percentage of young fledged from This is a measure of the pair’s ability and hatchlings. willingness to feed the offspring. Young were considered fledged when they left the nest willingly and were able to fly between the nest and the bottom of the cage. No post-fledging mortality was observed and, since fledglings could not leave their cage, the post-fledging phase was standardized to two weeks. The number of fledglings per clutch is equal to clutch size x hatching efficiency x fledging while all four efficiency, variables determine total number of fledglings during a pairing trial. Hatching date of the first egg and fledging date of the last young of the first breeding cycle were determined for each pair. Most fledglings were weighed on the day they fledged and all were aged. Fledging age and weights were similar to those of young bred in our aviary (unpubl. data). One control pair during both pairing trials and four experimental pairs (two during each trial) failed to fledge young no eggs hatched or all hatchlings died within two days of (i.e., hatching). Except for one possibly infertile female, all other birds successfully fledged at least one young in their other mating. By excluding these pairs, I hoped that the variation in reproductive success between the remaining pairs could be explained by behavioral decisions independent (at least to a greater extent) of genetic incompatibility of the mates or of failure to breed under experimental conditions. Behavioral _---_-
data ----
Time expenditures in incubation and in feeding of offspring, as a brood or individually, were used as measures of parental investment by each sex. Behaviors were coded and recorded using an electronic data recorder. Half-hour observations were equally distributed all through the day and represented all portions of the breeding cycle for each pair. Observer was in full view of the birds, sitting approximately 2.5 m away. No evidence of diurnal variations of the sexes was noted. phase. Three to six (1) Observations during the incubation observation sessions were made per pair per trial during this period (number of observations varied depending on number of clutches per pair). Total time spent incubating by each mate was recorded and the mean incubation time for each member of the pair calculated. Time spent incubating by the pair was taken as the sum of the male’s and female’s time expenditures; this value could exceed 30 min since both birds could be sitting on the nest at the same time and were assumed to provide heat or maintain nest temperature. During the first trial, incubating birds were scored every hour for two days for presence in the nest. This measure of nest attendance correlated to time was strongly expenditure (Spearman rank correlation, r E 0.882, n = 18, p < suggesting the latter was an appropriate measure of 0.005). investment in incubation. Because of mechanical problems with the data recorder, I have no incubation data for one control pair.
5
(2) Observations during the fledging and post-fledging phases. Time investment in feeding the young included both time spent regurgitating to the offspring and ‘extra’ time spent foraging by the parents, assuming this foraging was done to meet the energetic requirements of fledging the young. A measure of this extra time was obtained by subtracting the mean time expenditure of an individual during this phase from the average time spent feeding during the non-breeding period. Thus the term ‘feeding’ refers here to both regurgitation and ‘extra’ foraging by the parents. Number of observation sessions varied from six to 12 per pair per trial. Mean time expenditures were calculated for the male, the female and the pair. Time spent feeding individual offspring by parents was determined by dividing mean time expenditure in feeding by number of mouths being fed. If the fledging efficiency was 100% or if number of the nestlings died 1 to 3 days after hatching, fledglings equalled number of offspring being fed. To account for the number of mouths being fed other mortality during this phase, was taken as the average between the number of hatchlings and of fledglings. Analysis--_-One control and four experimental pairs during the first trial and three control and three experimental pairs during the second trial were multiple clutchers. Over both trials, there were 9 single clutch pairs (and 9 breeding cycles) and 11 multiple clutchers (for a total of 23 breeding cycles, since 1 pair fledged 3 clutches in one trial). An individual that was a single clutcher in one pairing could be compared to itself as a multiple clutcher in another pairing or could contribute twice to the sample size of its group if, for example, it was a multiple clutcher during both of its pairings. The trials were treated independently since correlations of the time expenditures of significant the two trials were never individuals between (Spearman rank correlation; for incubation, r = -0.107; for feeding, r I 0.050; n = 18, both ns). Similarly, multiple clutchers varied in both reproductive success and time investment breeding cycles were during each breeding cycle within a trial: considered independent events in some of the analyses. Since I expected breeding experience or mate familiarity to reproductive statistical tests appropriate to increase success, this hypothesis were one-tailed. Other tests were two-tailed unless otherwise indicated. Kendall rank correlations and MannWhitney Ll tests were performed unless otherwise specified. Means + standard deviations are reported.
RESULTS Factors -----
limiting --------
Multiple +
1.7)
than
re=oductive ----_-_
clutchers single
produced clutchers
success _-----significantly (2.4
+
1.2)
more (U
q
5,
fledglings n,m
= 9,11,
(5.7 p
<
6
0.001);
but they
of fledglings 1.1 versus
per clutch
(69 + 27% versus
14% versus
86 + 28%)
88; for clutch for fledging Single
attempt
U = 102;
clutchers
at about
same
cycle
hatched:
22.9 + 4.9 versus
fledged:
45.1 +
both
(single
positive
size
or
clutch
were
not
correlations
were
number clutch
41.8 2
per
egg
their
only
multiple
(90 +
clutch,
U =
U I 96.5;
hatched)
and
successful
clutchers'
clutchers;
10.6 days,
first
first
U = 38;
last
egg young
U = 37.5;
efficiencies of
size
between while
was
(r
(89
(70 + 28%)
n,m
=
-
p
significant
between (Table
per
negative
= 0.030,
n : 32),
ns,
much
n
higher = 32,32,
values
reached
of hatchlings
100%.
I
and
fledging
and
I).
positively
n,m
number
between
fledglings
was
0.108,
were
of
showed
size and both hatching
(U = 298,
fledging
between
number
I). Also,
brood
per clutch
correlations
significant
= 0.234,
19%)
and
clutch
per
=
the
the correlation
not
(r +
while
(Table
of hatchlings
the
of fledglings
efficiency
efficiency
efficiencies
correlation
1.1).
efficiency
first
multiple
and number
found
efficiencies
half
2.7 +
4.3 +
efficiency,
25.6 + 11.4 days,
significant
hatching
than
as the
versus
fledging
efficiencies,
fledging
fledged)
correlation,
fledging
with
1.3 versus
of fledglings
time
11.1 versus
efficiency
clutch
The
clutchers:
ns).
Hatching a strong
(4.6 +
(i.e., when
young
breeding
9.11,
single
in number
U = 103; n,m = 9.23, all ns).
last the
clutchers
for hatching
started
when
versus
size
(for number
size,
single
72 + 30%) or fledging
efficiency,
(i.e.,
from
(multiple
1.2), clutch
2.4 +
hatching
ended
did not differ
correlated but
not
to
32).
Fledging
than
hatching
p = 0.002). A strong
More
positive
and of fledglings
was
7
found
(r = 0.893,
TABLE
1
p < 0.001,
n = 32).
Kendall rank correlation values for the different measures of reproductive success determining number of fledglings per clutch. Two-tailed tests, n I 32 breeding cycles. ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Number of Fledging Hatching fledglings efficiency efficiency ____________________~~~~~~~~~~~~~-~-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Clutch
size
Hatching efficiency
+ 0.063 ns
- 0.308 p < 0.001
+ 0.518 p < 0.001
- 0.159 p = 0.100
- 0.288 p < 0.001 ---
----Fledging + 0.098 efficiency ns ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-~-~-~-
Thus, pairs
most
was
Within
a
due
to
spent
+
17.1
significantly
0.010). These
values
(1966).
spent
significant by either
time
of
sex
reproductive most
was
than
trial.
important
or the
were
pair
and
q
who 317,
to those
by males (r
their
(U =
similar
incubating
correlation
of
time)
in
n,m
found between size
= 31,31,
+
7.8 p
=
by El-Wailly
females
p = 0.028,
showed
a
n : 31). No
spent
(males,
Females
11.7
given
time
parents
incubating,
spent
versus
- 0.242,
clutch
by both
28.8 + 8.3 min.
males,
time)
are very
incubating was
(57%
their
correlations
spent
session
min/session
(39%
negative
between
in -reEfoduction -_ -----
time
observation
min/session
Strong
average
more
Time
per
efficiency
investment -__-_-
The
7.5
clutches
success
of fledglings.
of parental _---_-
a 30 min
in reproductive
of
hatching
number
Incubation. during
number
clutch,
determining
Patterns ----
of the variation
incubating
r z - 0.053;
8
females,
r
females
=
or
hatching
0.031;
pairs, time
pairs,
efficiency n :
0.096; existed
31,
for
both
(r
time
time
spent
(9.2
= -
2.9
min/session)
positive done
(U
=
correlations by
spent
the feeding
feeding
TABLE
male
versus (r
individual
=
273,
the
n,m
=
between
the
female,
either
p
offspring
<
0.001, (r
:
n
0.530,
to
pairs,
r
=
out
with
females
young
than p
the in :
spent
=
(6.9
+
Strong
amount
of
feeding
oftotaltime
or
32)
more
males
0.002).
terms
data
of
p < 0.001,
time n :
spent
32).
2
Kendall rank correlation values between different measures reproductive success and the per-offspring time spent feeding Two-tailed tests, n : 32 breeding cycles. the parents. ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Time spent feeding Fledging efficiency Number of fledglings per young by the: ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Pair - 0.036 - 0.478 ns p < 0.001 Male
-
Female
Time
-
expenditures
in
correlated
positively (pairs,
-
correlation
carried
32,32,
found
For
correlated
for
On average,
were
0.473,
not
ns).
n = 31).
were
feeding
all
negative
analyses
min/session)
31,
= 0.092;
p = 0.010,
young.
=
was
r
0.292,
the
n
a significant
Similar
+ 3.6
0.018;
incubating
but
feeding
-
females,
ns),
males
=
spent
(for
Post-incubation. on
r
r
I
0.361,
0.077 ns
-
0.065
-
feeding with
p
=
0.002;
p
by
0.429 < 0.001 0.415
males,
females
of
fledglings
per
r
P
number males,
=
0.265,
of by
and
pairs
were clutch
=
0.018;
9
females,
r
= 0.374,
feeding
individual
number
of
Comparisons clutchers. incubating
time
Females
of
p
the
0.062,
(m
incubated
(13.1
by
=
males
0.723, p
23,
=
looked
at
brood
of
analyses
the
were
multiple
17.1
t
their +
1.8
days,
U = 51,
the
the
young t
earlier = 2.75,
= 24,
of
than
single
with
3).
clutchers
I
a
Hatching incubating
clutchers,
not
-
hold
r
= -
0.407, if
during
time at
significant
one
their
in
fledging
did
(Student’s I
25,38,
t
ns),
(Student’s n,m
when
expenditure
n = only first
= 29.49,
p
test,
the
same
the
young
differ
test,
but t
feeding
not
9.7
+
multiple 18.1
< 0.050).
q
multiple
males
r
p
+
clutches
spent
clutchers,
were
young
n,m
7.6
ns).
clutchers
= 0.19,
difference
multiple
did
their U = 23,
(U
time
for
multiple
11,
min;
5.6
Table
with
multiple
for
of
with
relationship
by
+
cycles
= 0.032;
correlation; for
during
time
clutchers:
more p
multiple
more
the
breeding
correlated
rank
and
pairs
multiple
significantly
7.5,
performed
and g,
spent
fledging
spent
males,
males
comparisons
single
0.8
to
significance
all
used,
min)
n =
Weights
fledged
are
but
3).
+
from
p < 0.050;
(Table
9.7
data
= 0.287,
None
versus
When
investment
(r
time with
single
15.9
For
3).
approached
2
between
versus
Table
negatively
0.050).
10.3
min)
(7.6
8,
q
relation
pairs
6.9
(Spear-man n
+
(single
+ 7.5
was
no
multiple-clutched
(19.4
23)
clutch
efficiency
of
0.050,
t
3).
clutchers
showed
of
correlated
single-clutched
groups
13.0
Table
single
<
two
versus
amount
negatively
expenditures
females cycle
8.11,
between 7.5
but
of
breeding
was
The
2).
than
z
n = 32).
offspring
(Table
first
0.002;
fledglings
efficiency
n,m
p :
between 0.9
versus
clutchers +
1.4
versus
10
TABLE
3
and multiple clutchers: Compar isons between s ingle Time expenditure data (means + standard deviations in min). M = male; F = female. Sample sizes (number of breeding cycles) are given. ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Feeding Feeding per Incubation offspring x+s x+s (a) x + s (X)
Single
clutchers;
all data
7.6 + 7.5
M F
(n
q
6.1 2 2.9
(28)
19.4 + 10.3 (72) clutchers : data
Multiple
9) (411
3.5 2 2.4
8.9 + 4.0 (59)
4.4 + 2.9
for first
breeding
cycle
(n = 11)
M
13.0
+
6.9
(45)
5.7 + 1.8 (41)
2.5 + 1.2
F
15.9
+
5.6
(55)
8.1 + 2.7
(59)
3.5 + 2.0
Multiple
clutchers : all data
(n = 23)
M
13.1 + 7.5
(451
7.2 + 2.9
(43)
2.9 2 1.2
F
16.3 + 6.3
(551
9.7 + 3.5 (57)
3.9 + 2.0
____________________~~~~~~-~-~~~~~~~~~~~~~~-~-~~~~~~-~~~~~~~~~~~~ * n : 8 for incubation
In conclusion, reproduction.
incubating
Other
measures
were
also
females
by of
with
reproductive
found
to incubate
in association,
Breedi% -----
experience -------on
experience
of the time
and
correlation
hatching in
success.
Males
their
than
mates
was
breeding
from
single
less time
in
time found.
were
of multiple
males
spent
between
efficiency
investments
more
investment
not
clutches clutch
incubating.
and ___ mate ---I---_familiarity --_
reproductive and/or
most
negative
males time
pairs;
Data
assumed
A significant
spent
correlated
data.
mate
success familiarity
of
groups
differing
are presented
in breeding
in Table
4.
TABLE
4
Comparisons of control versus experimental pairs during the two trials: success data (means + standard deviations). Reproductive Sample sizes (n number of pairs, m = number of breeding cycles): for Cl group, n,m = 3,4; for C2 group, n,m = 3,7; for El n,m = 7,ll; for E2 group, n,m = 7,lO. group, q
Control
pairs
Experimental
pairs
-----_-_-_________-_-----_-__-~-----_-_________~_______ Pairing
cycle
Number
of
Clutch
size
1 clutches
1.3
+
0.6
1.6
+
0.5
4.0
+
1.4
4.8
+
1.5
Hatching
efficiency
(5)
79
+
25
54
+
34
Fledging
efficiency
($)
100
2
00
94
+
20
3.0
+
0.8
2.4
+
1.6
4.0
+
2.0
3.7
+ 2.6
2.3
+
0.6
1.4
+
0.5
4.6
+
0.8
4.4
+
1.1
Number of per clutch
fledglings
Total number fledglings Pairing
cycle
Number
of
Clutch
size
of
2 clutches
Hatching
efficiency
(%)
72
+
16
a2
+ 22
Fledging
efficiency
(%I
88
+
15
80
+
20
+
0.7
+
0.8
3.9 + 6.7 + 1.5 Total number of fledglings ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.9
Number of per clutch
More by
in
young
were
experimental
3,7,
p total
control
=
2.9
fledglings
0.0461, number pairs
fledged pairs
by during
while
the
of
fledglings
fledged
2.7
two
control
(pairs
the
second
=
young
23,
kept trial
experimental (U
more
2.7
together) (U
groups n,m
during
did
= 7.72 the
=
2.5,
n,m
not
differ
ns).
second
than
Though pairing
=
12
(U
the
1,
tria
1,
=
sample
n,m
=
clutch,
per
trial,
though
the
pairs
80%)
(Tables
TABLE
q
also
trends
for
experimental
4 and
This
size
decreased
is
or
was
not
of
clutches
fledging
small
number
fledglings per
(from
are
during
72%
efficiency
to (from
of per
trial
increased
only
to
in
of
efficiency pairs
due
differ
number
s ignificant
not
probably
did
number
Hatching
had
groups
groups
clutch
for
control
0.100).
different
direction.
trial
these
p
The
expected
second
between
3.3,
sizes.
clutches
the
difference
in the
82%) 88%
but to
5).
5
Summary of comparisons between control and experimental pairs: Reproductive success data. See text for explanation of abbreviations and Table 4 for data and sample sizes. One-tailed Mann-Whitney U tests. ____________________~~~~~~~~~~~~~~~~~~~~~_~_~_~_~_~_~___~__~~~~~~ Cl E2 Cl E2 Number _--c2
of --
clutches -1----
U= 1 p = 0.100
El
Clutch -----c2
Hatching -----u = 3 p = 0.058
c2
u = 21 ns
El
Fledging-----u = 34.5
ns
Number ----c2
El
u
of --
c2
ns
El
fledglings ------
u = 13.5 ns
per --
11
q
25.5
ns
efficiency ----_-U
= 8 ns
U
= 28 ns
u
=
p < clutch -----
u = 30 ns u
U
U = 28.5 p < 0.050
El
= 54.5 ns
-
u = IlS
size --U = 8.5
efficiency ---------
= 40.5 ns _____________________~_~_~_~_~_~~~_~~~_~_~_~_~_~~~~~~~~~~~~~~~~~~
30 0.050
13
TABLE
6
pairs: Time Comparisons of control versus experimental expenditure data (means + standard deviations in min). Sample size for incubation data for Cl group, n,m I 2,3; for all other cases see Table 4. ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-Experimental pairs Control pairs ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-...~~~~~~~~~~~~ Pairing ------
-1
=cle--
Incubation
by
the
Male
12.1
+
3.2
11.4
+
9.7
Female
14.0
+
6.5
17.3
+
8.3
Male
4.9
2
1.6
6.6
2
2.8
Female
a.2
+
1.2
a.7
t
3.4
by
the
Male
1.9
+
0.4
3.8
+
2.1
Female
3.2
+
0.7
5.0
+
3.0
Male
15.9
+
5.3
a.9
+
7.3
Female
16.6
2
6.1
17.6
+
8.2
7.3
+
1.7
7.6
2
3.8
11.0
+
2.5
9.7
+
4.8
by
the
3.0
+
1.2
2.8
_c 1.3
3.2
+
Feeding
by
Feeding
the
per
----Pairing
offspring
-2
-cycle ---
Incubation
Feeding
by
by
the
the
Male Female Feeding
per
offspring
Male
Female 4.0 + 1.1 ___________________________~__~-~~~~~~~~~~~~~~~~~~~~~~-----------
Males min)
than
of
control experimental
pairs
spent males
more (8.9
time +
7.3
incubating min)
during
1.8
(15.9 the
+
5.3
second
14
but
trial,
16.6
E2:
females +
pairs
spent
trial
(Cl
for
6.1
versus
more
6
and
increased
for
(Student’s
t
0.7
n,m t
g,
TABLE
C2;
of
(Tables
= =
vary
17.6
+
for +
time
all
3.00,
6.5
min)
p n,m
16.8
< =
0.001; 30.33,
(Tables
12.1
_c 3.2 16.6
in weight
from
pairs
+
expenditure
1.2
versus
weight:
9.4
+
+ 5.3 no
at
trial 18.1
other
1.9
the
next
days,
t
versus
0.8
min;
fledging
to +
second
significant
offspring
versus
Control
min); were
first
versus
the
15.9
6.1
feeding
the
7).
during
+
of
(C2
6 and
offspring
versus
and
age:
time
their
males:
Age
38,40,
8.2
expenditure
7).
test;
their
feeding
14.0
comparisons
not
time
versus
females:
3.81,
did
10.0
p = 0.004).
7
control and experimental pairs: Summary of comparisons between See text for explanation of abbreviations Time expenditure data. and Table 6 for data. Two-tailed Mann-Whitney IJ tests. ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Females Males Cl Cl E2 E2 ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Incubation I____c2
U = 8 ns
u = 31.5 ns
El
u = 5 ns
u = 14 p q 0.050 u
u = 53.5 ns
q
51.5
ns
Feed in& ---c2
u = 3 p = 0.058
c2 El
q
31
ns
u = 3.5 p < 0.092
U = 46 ns
El
Feedi= --
u
per -IJ I 4 ns
offeng ---
u = 33.5 rlS
U = 46.5 ns
-U = 23
‘J = 6.5 tlS
u zs39 ns
u = 34 ns Ll q 41 ns
= +
15
Both
breeding
reproductive
experience
success.
clutches
and
spent
more
second
of
In
and association
fledglings
time
mate
familiarity
with
an
produced,
incubating
than
affected
increased
males
of
experimental
number
control
males
of
pairs
during
the
trial.
DISCUSSION Most arose
of
variation
primarily
during per
the
from
a
pairing
clutch
(no
efficiency
differences
account
for
For
example,
first
the
in
Why
did
had
sufficient
Single expenditures clutchers, even
during
females comparison,
the
clutch
size,
ten
of
single
being
second
trial,
females to one
female
only
breed
once,
especially
time
to
breed
again
(both
their
first
and
multiple by
males their invested during
mates incubated first
significantly breeding
more the
than first
males clutch
in
second
out
all and
pairs
times)? time
in In
and
females
multiple
breed
single
3).
of
or
trial.
multiple
single-clutched 6
of
not
differed
In
cycle.
did
similar
more
the
clutchers,
multiple
(Table
one.
during
since
at
during
second
bred
the
only
incubation
in
the
who
during
cycle
clutchers
clutchers
who
pairs
fledging
completely
multiple
clutch
breeding
or
fledged
cannot
during
fledged
ended
one
and
young
clutchers).
multiple so
the
of
had
multiple
quality were
pairs
a pair
hatching and
necessarily
of
number
single
who
between
clutches
trial
some
clutchers
‘from
between
not
success
successful
individual
from
the
not
birds
out
went
first
found
were five
of
in
since
trial
trial
and
in
this
vice-versa, in
be
reproductive
number
differences
Innate
first
the
trial,
could
the
in
less pairs,
8
cases. clutchers,
In
16
females
invested
invested
equally
increased with
the
a
more in
phase
usually
often
result
been
Stauffer, incubation
Rowley,
by
together
each
inference
sample
size
numerous
is
and
to
females remated
the
data
phase,
time
were success
success
whether
the
constraints,
hatching
that
on
was
fledging
though
suggest
or
in
(Best
and
expenditure
they
in
should
male
and
incubation
other
female
is
of
development of
breed
in
their
synchronization (Erickson,
may 1978).
require ring
keep
1980;
nest
previous doves,
of
weight
when
pairs
other
nest
mates;
is
1982;
one
mate
bird
for
presence
within 1981)
not
during
the
by
constant
their
and pairs
requires
may and
with males
of
thermal
this
attendance,
where
is
correlation
the
experience
are
(Welty,
negative
eggs
Vleck,
between of
loss
to
Nearly
to
mate
investment
available
relief
patterns
the
small
there
its
competitors by
foraging.
(Carey,
In
or
and
if
periods
expenditures,
required
nest
as
during
time as
often
synchronization
loss
time
such
parents
such
indicated
determines
activities
specific
activity,
As
only Still,
incubator
predators
1981).
data
cautiously.
the
nest
against
Wittenberger, between
this
correlation
treated to
increased
defended
on
be
costs
share
incubation
range
I
of
fledging
mates
when
energy
the
affected
based
should
possible
willing
the
1983). mate
Since
than
not
incubation
surprising lower
but
Analysis
1).
during
and
again.
This
in
be
cases
incubating
7).
(Table
2
males
suggested
not
to
in
spent
6 and
birds
is
found
1980;
they
study the
males
addition,
already
to
this
In
(Tables
this
important
removed,
not
in
cases,
time
success
limiting
has
of
mate
reproductive
5
4 cases.
amount
familiar
in
be
optimal
one’s were
very
mate mated
17
unfamiliar
with successful
in
other
breeding
these
factors
may
as
still For
hatching
may
most
why
first
brood
expenditure
of
males
pair
again.
incubation
may
efficiency
in
The pairs
high
first
eggs
with
1)
by
to
for
correct
mortality.
strategy have
if led
to
from
egg
by
of
this
increased
of
clutch
size,
or that
affect
last
inbreeding)
of
a
that
would
if
had
an the
with
clutch
coverage
of
incubation larger
clutches
efficiency, is
(e.g.,
or
most
support
lay
hatching
and
female).
imply
improper
females
in
hatching
decrease
possibility common
decreased
inadequate
because
remains
efficiency
either
lower
investment
study
may
of
have
My results
fledge.
a
investment
question
(or
time
whether
paternal
a pair
male
clutchers’
clutchers
of
the
since
time
This
to
efficiency
determine
hatching
efficiency
is
to
of
their
Hatching
failure
and
and
surprising
cost
possible
to
This
is
increased
hatchlin’gs
variables
of
wild
males,
multiple
multiple
fitness
parents,
for
clutchers?
a consequence
the
to
all
due
hatching
increased
don’t
the
increasing
investment
embryo
as
or
the
mostly
than
seems the
limited
alternative. (Table
hold
efficiencies
of
less
respect
One in
was
result
single
determining
already
with
finches
with
incubation
why
outweigh
number
size
This
benefit
fledging
were
optimal
in
were
1972).
more
doesn’t
than the
zebra
correlated
males,
but
unanswered,
Morris,
success
Considering
efficiency
comparable
incubated
known).
multiple-clutched hatching
they
correlation not
females
birds.
negatively
is
breeds
to
hatching
since
this
were
important
clutches,
familiar
and
domesticated
was
(though
but
(Erickson
be
efforts
investment
to
eggs
factors
affect
females’
opposed
an
aviary explain
such
as
appropriate conditions the
lack
Of
18
correlation
between
between
clutch
In
size
and
conclusion,
female, not
clutch
the
that
to
more.
Birds
breeding
may
other
with
mated
in --
Because and
found
fledging
mates from
-the
pairs
were
no
correlation
efficiency
increase
still
spent
more
time
time
expenditure
amount
of
parents
do to
feeding not
not I
offspring
or
time
to
usually
may
have
unwilling
invest
incubate
all
rest
the
decided
to
in
feed,
parents.
stages
of
or
perform
I
expected
and
expenditure. pairs, 2). limiting
to
be
expenditure
Time number
larger much
was results
reproductive
as
of
with
no
to
high
correlation
reinforce success
the and
broods
number
they better
(Royama,
allowing of
increase
mouths with
in
between
these
conclusion
that
that
mouths
individual
investment,
efficiency
the i.e.,
heat
feeding
parental
but 2),
retain
in
to
Increased
of
smaller
by
females
young,
number
different
the
feeding
males.
(Table
broods
efficiency due
the
and
and
more
decreases to
fledglings in
did
fledge
expenditure
pairs
of
fledglings,
than
to
measure
Probably
of
young
as
time
fledging
These
1).
offspring
fed
resources,
number
because
between
there
food
between
with
a better
for
by
proportionally
expected be
limited
per
possibly
had
chase --
necessary
invest
need
to
comparisons
was
of
feeding
is
feed,
do
1966).
(Table
care
and
the
partner,
parental
to
fledglings by
the
unwilling
(Table
does
most
incubation
incapable
loss
not
parents
feed,
in
post-fledging
both
and
in that
of
activities.
Investment
have
time
a mate
with
suffer
number
suggest
more
again
and
investment
data
invested
breed
size
differences
to time
fledging variables incubation between
of
19
pairs
should
easily
be
subtle
in
There
were
found.
investment though
between the
this
also
single
offspring
of
study,
where no
and
food
abundant
differences
multiple
multiple
is
in
clutchers
clutchers
and
feeding (Table
left
the
81,
nest
a day
earlier.
Breedi% -II_
experience --1_1-
Age
and/or
shown
to and
1972;
Erickson
experience
with
(6.7)
trial.
Mate
fledging even
a specific
times by
during
commitment did
not
but
males the
to take
did
(Tables
clutch
an
4 to
to
7).
All
more
numerous
fledge
their
and
C2
versus more second
hatching
to time
breed
or
two
investment
pairs
fledged
increased
heavier time
consequently,
than
experimental
pairs. Experimental
pairs
breeding
experience,
success,
but
efficiency.
this It
is
may as
benefitted
indicated
benefit not
have
obvious
was
by negated
why
these
from
their
previous
their
increased
hatching
by
a decreased
fledging
parents
could
or in
their
and,
young
and
the
size,
brood
In
comparison)
during
increased
egg
1983).
produced
pairs
Controls
trial.
their
longer
affect control
with
second
feed
not
C2
pairs (3.9)
of
familiarity
versus
pairs
been
(Coulson,
E2
while
(Cl
date
Rowley,
versus
control
5):
allowed
together
(El
have
species
1968;
se
mate
size, of
success
and
did
number
per
experimental
efficiency
young
4
the
clutch
Lack,
mate
familiarity
incubation
a
1972;
experience
than
three
in
Morris,
Tables
with
length,
reproductive
comparisons;
young
familiarity
success
breeding increase
-complementara -----
courtship
and
not
E2
and
hatching
study,
did
behavioral -----
experience
influence
laying
this
and ---
not
fledge
20
all
their
familiar
hatchlings.
Studies
and unfamiliar
predict
that
of the division
mates
the effects
when
of mate
food
of
feeding
is limited
familiarity
between
are needed;
on fitness
I
should
be
striking.
CONCLUSIONS I suggest of
that
parental
care
incubation),
because
parental
care
no conflicts
most
simultaneous
be explored
important
necessary phase
results
have
of
time
of
that
success.
division
19801,
a
been
As
a
overlooked:
there
behaviors
since
between
these
of
simple
approximation.
eliminated
does
time
or energy
reproductive to one
to those
and
there
were
restrictions
deal
how
to weigh
no
should
of this
work
also
are more
deserves
different
behaviors
that
complementarity,
the
of these
importance of labor
are
problems
are overall
time-
it will
be
breeding
that
see Chase,
suggestive,
of
To further
of each during
more
phases
are energy-limited?
of division
discussion
the
with
that
constraints
success
compare
of behavioral
and the importance
(for theoretical The
how
to know
an optimal
a first
may
mates
reproductive
(Chase,
importance
trying
importance
with
during
future.
as compared
the
as
were
of whether
When
reproduction,
used
patterns
in determining
attention.
limited
was
The
higher ways
division
(especially
paired
established
behaviors
in the
The question
have
in allocation
limitations.
mates
numerous
be
important
were
by the previous
individuals
of the
design
resu,lt, some
the
behavior
could
experimental
test
that
their
However,
is determined
between
and
complement'
energy
remating
phase
1980).
though
the
21
large
variability
difficult. under
More
are
consequences
of
the
for mate
variables
worthwhile, between
needed.
neglected
important
sample
sizes
long-term
resource-limited
contributions
mostly
extensive,
natural,
pressures
and small
since
pairs
and
that
in field it reveals
and raises
some
are
to
choice.
studies
interpretation on breeding
conditions
There sexes
make
few
data
parental
that
difficulty
situations some
the
and this
of
make
subtle
interesting
on
care
I suggest
the
and under
success predation
relative
the area
possible has been
controlling
this
type
behavioral
more
of
all study
differences
questions.
ACKNOWLEDGEMENTS initially encouraged me to pursue this study. N. N. Burley Burley, G. Bell, C. Erickson, D. Gori, B. Holmes, A. KodricC. Petersen and anonymous reviewers read this Brown, D. Kramer, manuscript at various stages of its preparation and made many program that useful suggestions. B. Beaulieu wrote the computer did all of the compilation of the raw data. This research was supported by a Sigma Xi Grant-in-aid of Research, by McGill's Computer Center and by a NSERC (Canada) grant to N. Burley.
REFERENCES D.F., 1980. Factors affecting nesting Best, L.B. and Stauffer, success in riparian bird commmunities. Condor, 82: 149-158. The significance of age and Burley, N. and Moran, N., 1979. preferences of feral reproductive experience in the mate pigeons, -----Columba --livia. Anim. Behav., 27: 686-698. Butterfield. P.A.. 1970. The pair bond in the zebra finch. In: in Birds and Mammals. (Ed-itor), Social Behaviour J.H. Crook Academic Press, London, pp. 249-275. 30: Carey, C., 1980. The ecology of avian incubation. Bioscience, 819-824. and noncooperative behavior in Chase, I., 1980. Cooperative animals. Am. Nat. 115: 827-857. aspects of reproduction. In: D.S. Cody, M., 1971. Ecological Farner and J.R. King (Editors), Avian Biology, vol. 1. Academic Press, New York, pp. 461-512. of the pair-bond in the Coulson, J.C., 1972. The significance Kittiwake. In: Proc. XVth Int. Ornith. Cong. Brill, Leiden,
22
pp. 424-433. Mate choice in the Coulson, J.C. and Thomas, C.S., 1983. Kittiwake Gull. In: P. Bateson (Editor), Mate Choice. Cambridge University Press, Cambridge, pp. 361-376. for egg laying and El-Wailly, A.J., 1966. Energy requirements incubation in the zebra finch, --_ Taeniougia Condor, ----~castanotis. 68: 582-594. Emlen, S.T. and Oring, L.W., 1977. Ecology, sexual selection, and the evolution of mating systems. Science, 197: 215-223. in animals: Pair bonds Erickson, C.J., 1978. Sexual affiliation and reproductive strategies. In: J.B. Hutchison (Editor), Determinants of Sexual Behavior. Wiley, New York, Biological PP. 697-725. Effects of mate Erickson, C.J. and Morris, R.L., 1972. familiarity on the courtship and reproductive success of the (Streptopelia risoria). Anim. Behav., 20: 341-344. ring dove Immelmann, K., 1965. Australian Finches in Bush and Aviary. Angus and Robertson, Sidney. for Breeding in Birds. Adaptations Lack, D., 1968. Ecological Methuen, London. Morris, D., 1954. The reproductive behaviour of the zebra finch with special reference to pseudofemale (Poehila guttata), -----behaviour and displacement activities. Behaviour, 6: 271-322. in birds. In: P. Bateson (Editor), Rowley, I., 1983. Re-mating Choice. Cambridge Mate University Press, Cambridge, pp. 331360. food Factors governing feeding rate, Royama, T., 1966. requirement and brood size of nestling great tits ----Parus major. Ibis, 108: 313-347. of desert birds. In: D.S. Farner Serventy, D.L., 1971. Biology Avian Biology, vol. 1. Academic and J.R. King (Editors), Press, New York, pp. 287-339. and sexual selection. In: Trivers, R., 1972. Parental investment 8. Campbell (Editor), Sexual Selection and the Descent of Man, 18711971. Aldine, Chigago, pp. 136-179. Energetic Vleck, C.M., 1981. cost of incubation in the zebra finch. Condor, 83: 229-237. College Publ., Welty, J.C., 1982. The Life of Birds. Saunders Philadelphia. Wittenberger, J.F., 1981. Animal Social Behavior. Duxbury Press, New York.
12 (1986) l-22
DIVISION OF PARENTAL CARE AND FINCH (TAENIOPYGIA GUTTATA). -------------VERONIOUE
ANNIE
REPRODUCTIVE
SUCCESS
IN THE
ZEBRA
DELESALLE
Biology Department, lB1, Canada.
MC Gill
University,
Montreal,
Quebec,
Present Address: Department of Ecology and Evolutionary University of Arizona, Tucson, AZ 85721, USA.
H3A
Biology,
(Accepted 21 March 1985) ABSTRACT Delesalle, V.A., 1986. Division success in the Zebra finch Processes, 12: l-22.
of parental (Taenioel@a ------
care and reproductive Behav. guttata).
Variation in reproductive success among pairs of Zebra finches bred in captivity under time- rather than (Taenioeyea guttata), _--_ arose primarily because of differences energy-limited conditions, in number of clutches per reproductive bout. Division of parental care between mates during the time-constrained incubation phase, rather than the fledging phase, affected their fitness and future behavior. Pairs where the males assumed a greater fraction of the pooled incubation time were more likely to breed together again than pairs where males did not share in this activity as equally. In addition, males remated with familiar mates increased their time investment in incubation.
INTRODUCTION In species
with
quantity
and quality
parental
duties
mates
may
component
of mate
Trivers, not
an
of their
parental
a pair's choice
efficient when
the offspring is
forager
paired
with
(Burley
should
when
that have
an individual
two
or
success
and Moran,
a bird
is a good
in the
the division
and
may
be
a
1978;
incubator
a greater
of
between
Erickson,
but
reproductive
is good
at incubating.
more
0376-6357/86/$03.50 0 1986Elsevier Science Publishers
1979;
that
good
vary
complementarity)
reproductive
but not necessarily
necessary
behaviors,
of behavioral
1972). For example,
success
labor
care,
(or degree
affect
if individuals
biparental
at feeding Division
parental
tasks
B.V. (Biomedical
Division)
must
of be
carried
out
nest
(e.g., may
be
and
construction
advantageous
mates
and
in it
success
one
(Laridae), birds
swans
and
1970).
Early
found
in
unpredictable the
breeding
the
nest
is
My
own
in
performance set
aviary
out
conditions
care.
of
the
mates,
lifetime over
birds:
crows
and
and and
1972;
more
doves
gulls
terns
related
Coulson
and
and
constant
have
determine:
(1) study
Cody,
what (fitness
factors was
and
fairly
bonds
adaptations are one
within
limited operationally
as to
scarce,
parent
Serventy,
considerable
between
for
Butterfield, pair
of
1971;
is
pair
been
resources
presence
revealed
duties
1965; extended
where
to
have
be
Zebra
species
appear
to
of
in
grassfinch
Immelmann,
1980;
effects
success
believed
and
the
physiology
environments,
parental
for
Birds
and
are
(Carey,
this
test
maturity
observations
of
especially
bonding
Coulson,
This
1954;
short
required
to
Pair
reproductive
ecology
harsh
of
(Emlen
influencing
and
to on
finches
season
be of
a number
1970;
reproductive
or
longer
should
(Anatidae),
(Morris,
Zebra
together
(Estrildidael,
biparental
behavior,
documented
between
in
guttata).
has
their
burden
breed
in
undertaken
(Taeniopygia
life,
energetic
1983).
was
and
duties
affiliation
found
sequential
parental
individuals.
complementarity
monogamous
I
these is
Rowley,
study
finches
well
important
(Butterfield,
1983;
behavioral
more
are
sharing
complementarity long-term
and
(Corvidae)
This
and
grassfinches
geese
Thomas,
survive
season
(Columbidae),
the
with
of
breeding
pigeons
the
be
activities
incubation)
Behavioral
should
the
equalizes
to
species
reproductive than
it
them
1977).
important
and if
allows
Oring,
since
When
simultaneously.
at
1971).
variability pairs. fitness
under measured
3
as
the
total
number
experiment); fitness
(did
higher and
(2)
of
how
pairs
the that
reproductive mate
familiarity
reproductive
success.
MATERIALS
AND METHODS
Subjects--
and ---
-exerimental -_--
fledglings patterns divided
success?); affected
produced of
parental
parental and
by
(3)
behavioral
a pair
during
investment care
how
more breeding
the
affected equally
have
experience
complementarity
and
design -~-
Twenty-six domesticated zebra finches, approximately 6 months old and with no prior breeding experience, were paired randomly isolated physically and visually but not auditorily in and Pairs were provided with a domed nest cages (45 x 25 x 30 cm). skeleton, nesting material, food (a commercial finch seed mixture and an oatmeal wheat germ mix for the nestlings) and water ad libidum and cuttlebone. Once a week they were given hard--_-9 gravel boiled eggs and spinach. Birds were kept on a 14 hour daylight cycle, at a room temperature of 25 + 2 C. Pairs were observed for a period of 18 weeks which will be referred to as the pairing ‘trial’. At the end of the first pairing trial, males and females were visually isolated for 5 long enough for the pair bond to dissolve and for the weeks, birds to be ready to remate (Butterfield, 19701. The birds were Four of the original pairs were then paired for a second trial. experimental pairs were kept together (controls) and nine new Pairs could be divided into 4 groups: control formed randomly. pairs during the first pairing trial (Cl) and during the second experimental pairs during the first (El) and second trial (C2), (E2) trials. There were no initial differences in breeding ability between the two groups since none of the comparisons between Cl and El groups were significant (Mann-Whitney U tests). were made to test for the effects of Appropriate comparisons breeding experience and mate familiarity (Cl versus C21, of breeding experience only (El versus E2), and of mate familiarity per - -se (E2 versus C2). Reproductive -------
data ----
Nests were checked daily or every other day to obtain the following information: (1) The number of successful clutches (i.e., at least one young fledged) per trial. Pairs that had only one breeding cycle during to multiple a trial were called single clutchers as opposed clutchers, pairs that bred two or three times. (2) Clutch size. (3) Hatching efficiency, the proportion of eggs in a clutch that hatched. than number of hatchlings) Hatching efficiency (rather
4
was used as a measure of success during incubation since it measures only egg fertility and incubation success, while number of hatchlings reflects both these factors and clutch size. (4) Fledging efficiency, the percentage of young fledged from This is a measure of the pair’s ability and hatchlings. willingness to feed the offspring. Young were considered fledged when they left the nest willingly and were able to fly between the nest and the bottom of the cage. No post-fledging mortality was observed and, since fledglings could not leave their cage, the post-fledging phase was standardized to two weeks. The number of fledglings per clutch is equal to clutch size x hatching efficiency x fledging while all four efficiency, variables determine total number of fledglings during a pairing trial. Hatching date of the first egg and fledging date of the last young of the first breeding cycle were determined for each pair. Most fledglings were weighed on the day they fledged and all were aged. Fledging age and weights were similar to those of young bred in our aviary (unpubl. data). One control pair during both pairing trials and four experimental pairs (two during each trial) failed to fledge young no eggs hatched or all hatchlings died within two days of (i.e., hatching). Except for one possibly infertile female, all other birds successfully fledged at least one young in their other mating. By excluding these pairs, I hoped that the variation in reproductive success between the remaining pairs could be explained by behavioral decisions independent (at least to a greater extent) of genetic incompatibility of the mates or of failure to breed under experimental conditions. Behavioral _---_-
data ----
Time expenditures in incubation and in feeding of offspring, as a brood or individually, were used as measures of parental investment by each sex. Behaviors were coded and recorded using an electronic data recorder. Half-hour observations were equally distributed all through the day and represented all portions of the breeding cycle for each pair. Observer was in full view of the birds, sitting approximately 2.5 m away. No evidence of diurnal variations of the sexes was noted. phase. Three to six (1) Observations during the incubation observation sessions were made per pair per trial during this period (number of observations varied depending on number of clutches per pair). Total time spent incubating by each mate was recorded and the mean incubation time for each member of the pair calculated. Time spent incubating by the pair was taken as the sum of the male’s and female’s time expenditures; this value could exceed 30 min since both birds could be sitting on the nest at the same time and were assumed to provide heat or maintain nest temperature. During the first trial, incubating birds were scored every hour for two days for presence in the nest. This measure of nest attendance correlated to time was strongly expenditure (Spearman rank correlation, r E 0.882, n = 18, p < suggesting the latter was an appropriate measure of 0.005). investment in incubation. Because of mechanical problems with the data recorder, I have no incubation data for one control pair.
5
(2) Observations during the fledging and post-fledging phases. Time investment in feeding the young included both time spent regurgitating to the offspring and ‘extra’ time spent foraging by the parents, assuming this foraging was done to meet the energetic requirements of fledging the young. A measure of this extra time was obtained by subtracting the mean time expenditure of an individual during this phase from the average time spent feeding during the non-breeding period. Thus the term ‘feeding’ refers here to both regurgitation and ‘extra’ foraging by the parents. Number of observation sessions varied from six to 12 per pair per trial. Mean time expenditures were calculated for the male, the female and the pair. Time spent feeding individual offspring by parents was determined by dividing mean time expenditure in feeding by number of mouths being fed. If the fledging efficiency was 100% or if number of the nestlings died 1 to 3 days after hatching, fledglings equalled number of offspring being fed. To account for the number of mouths being fed other mortality during this phase, was taken as the average between the number of hatchlings and of fledglings. Analysis--_-One control and four experimental pairs during the first trial and three control and three experimental pairs during the second trial were multiple clutchers. Over both trials, there were 9 single clutch pairs (and 9 breeding cycles) and 11 multiple clutchers (for a total of 23 breeding cycles, since 1 pair fledged 3 clutches in one trial). An individual that was a single clutcher in one pairing could be compared to itself as a multiple clutcher in another pairing or could contribute twice to the sample size of its group if, for example, it was a multiple clutcher during both of its pairings. The trials were treated independently since correlations of the time expenditures of significant the two trials were never individuals between (Spearman rank correlation; for incubation, r = -0.107; for feeding, r I 0.050; n = 18, both ns). Similarly, multiple clutchers varied in both reproductive success and time investment breeding cycles were during each breeding cycle within a trial: considered independent events in some of the analyses. Since I expected breeding experience or mate familiarity to reproductive statistical tests appropriate to increase success, this hypothesis were one-tailed. Other tests were two-tailed unless otherwise indicated. Kendall rank correlations and MannWhitney Ll tests were performed unless otherwise specified. Means + standard deviations are reported.
RESULTS Factors -----
limiting --------
Multiple +
1.7)
than
re=oductive ----_-_
clutchers single
produced clutchers
success _-----significantly (2.4
+
1.2)
more (U
q
5,
fledglings n,m
= 9,11,
(5.7 p
<
6
0.001);
but they
of fledglings 1.1 versus
per clutch
(69 + 27% versus
14% versus
86 + 28%)
88; for clutch for fledging Single
attempt
U = 102;
clutchers
at about
same
cycle
hatched:
22.9 + 4.9 versus
fledged:
45.1 +
both
(single
positive
size
or
clutch
were
not
correlations
were
number clutch
41.8 2
per
egg
their
only
multiple
(90 +
clutch,
U =
U I 96.5;
hatched)
and
successful
clutchers'
clutchers;
10.6 days,
first
first
U = 38;
last
egg young
U = 37.5;
efficiencies of
size
between while
was
(r
(89
(70 + 28%)
n,m
=
-
p
significant
between (Table
per
negative
= 0.030,
n : 32),
ns,
much
n
higher = 32,32,
values
reached
of hatchlings
100%.
I
and
fledging
and
I).
positively
n,m
number
between
fledglings
was
0.108,
were
of
showed
size and both hatching
(U = 298,
fledging
between
number
I). Also,
brood
per clutch
correlations
significant
= 0.234,
19%)
and
clutch
per
=
the
the correlation
not
(r +
while
(Table
of hatchlings
the
of fledglings
efficiency
efficiency
efficiencies
correlation
1.1).
efficiency
first
multiple
and number
found
efficiencies
half
2.7 +
4.3 +
efficiency,
25.6 + 11.4 days,
significant
hatching
than
as the
versus
fledging
efficiencies,
fledging
fledged)
correlation,
fledging
with
1.3 versus
of fledglings
time
11.1 versus
efficiency
clutch
The
clutchers:
ns).
Hatching a strong
(4.6 +
(i.e., when
young
breeding
9.11,
single
in number
U = 103; n,m = 9.23, all ns).
last the
clutchers
for hatching
started
when
versus
size
(for number
size,
single
72 + 30%) or fledging
efficiency,
(i.e.,
from
(multiple
1.2), clutch
2.4 +
hatching
ended
did not differ
correlated but
not
to
32).
Fledging
than
hatching
p = 0.002). A strong
More
positive
and of fledglings
was
7
found
(r = 0.893,
TABLE
1
p < 0.001,
n = 32).
Kendall rank correlation values for the different measures of reproductive success determining number of fledglings per clutch. Two-tailed tests, n I 32 breeding cycles. ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Number of Fledging Hatching fledglings efficiency efficiency ____________________~~~~~~~~~~~~~-~-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Clutch
size
Hatching efficiency
+ 0.063 ns
- 0.308 p < 0.001
+ 0.518 p < 0.001
- 0.159 p = 0.100
- 0.288 p < 0.001 ---
----Fledging + 0.098 efficiency ns ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-~-~-~-
Thus, pairs
most
was
Within
a
due
to
spent
+
17.1
significantly
0.010). These
values
(1966).
spent
significant by either
time
of
sex
reproductive most
was
than
trial.
important
or the
were
pair
and
q
who 317,
to those
by males (r
their
(U =
similar
incubating
correlation
of
time)
in
n,m
found between size
= 31,31,
+
7.8 p
=
by El-Wailly
females
p = 0.028,
showed
a
n : 31). No
spent
(males,
Females
11.7
given
time
parents
incubating,
spent
versus
- 0.242,
clutch
by both
28.8 + 8.3 min.
males,
time)
are very
incubating was
(57%
their
correlations
spent
session
min/session
(39%
negative
between
in -reEfoduction -_ -----
time
observation
min/session
Strong
average
more
Time
per
efficiency
investment -__-_-
The
7.5
clutches
success
of fledglings.
of parental _---_-
a 30 min
in reproductive
of
hatching
number
Incubation. during
number
clutch,
determining
Patterns ----
of the variation
incubating
r z - 0.053;
8
females,
r
females
=
or
hatching
0.031;
pairs, time
pairs,
efficiency n :
0.096; existed
31,
for
both
(r
time
time
spent
(9.2
= -
2.9
min/session)
positive done
(U
=
correlations by
spent
the feeding
feeding
TABLE
male
versus (r
individual
=
273,
the
n,m
=
between
the
female,
either
p
offspring
<
0.001, (r
:
n
0.530,
to
pairs,
r
=
out
with
females
young
than p
the in :
spent
=
(6.9
+
Strong
amount
of
feeding
oftotaltime
or
32)
more
males
0.002).
terms
data
of
p < 0.001,
time n :
spent
32).
2
Kendall rank correlation values between different measures reproductive success and the per-offspring time spent feeding Two-tailed tests, n : 32 breeding cycles. the parents. ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Time spent feeding Fledging efficiency Number of fledglings per young by the: ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Pair - 0.036 - 0.478 ns p < 0.001 Male
-
Female
Time
-
expenditures
in
correlated
positively (pairs,
-
correlation
carried
32,32,
found
For
correlated
for
On average,
were
0.473,
not
ns).
n = 31).
were
feeding
all
negative
analyses
min/session)
31,
= 0.092;
p = 0.010,
young.
=
was
r
0.292,
the
n
a significant
Similar
+ 3.6
0.018;
incubating
but
feeding
-
females,
ns),
males
=
spent
(for
Post-incubation. on
r
r
I
0.361,
0.077 ns
-
0.065
-
feeding with
p
=
0.002;
p
by
0.429 < 0.001 0.415
males,
females
of
fledglings
per
r
P
number males,
=
0.265,
of by
and
pairs
were clutch
=
0.018;
9
females,
r
= 0.374,
feeding
individual
number
of
Comparisons clutchers. incubating
time
Females
of
p
the
0.062,
(m
incubated
(13.1
by
=
males
0.723, p
23,
=
looked
at
brood
of
analyses
the
were
multiple
17.1
t
their +
1.8
days,
U = 51,
the
the
young t
earlier = 2.75,
= 24,
of
than
single
with
3).
clutchers
I
a
Hatching incubating
clutchers,
not
-
hold
r
= -
0.407, if
during
time at
significant
one
their
in
fledging
did
(Student’s I
25,38,
t
ns),
(Student’s n,m
when
expenditure
n = only first
= 29.49,
p
test,
the
same
the
young
differ
test,
but t
feeding
not
9.7
+
multiple 18.1
< 0.050).
q
multiple
males
r
p
+
clutches
spent
clutchers,
were
young
n,m
7.6
ns).
clutchers
= 0.19,
difference
multiple
did
their U = 23,
(U
time
for
multiple
11,
min;
5.6
Table
with
multiple
for
of
with
relationship
by
+
cycles
= 0.032;
correlation; for
during
time
clutchers:
more p
multiple
more
the
breeding
correlated
rank
and
pairs
multiple
significantly
7.5,
performed
and g,
spent
fledging
spent
males,
males
comparisons
single
0.8
to
significance
all
used,
min)
n =
Weights
fledged
are
but
3).
+
from
p < 0.050;
(Table
9.7
data
= 0.287,
None
versus
When
investment
(r
time with
single
15.9
For
3).
approached
2
between
versus
Table
negatively
0.050).
10.3
min)
(7.6
8,
q
relation
pairs
6.9
(Spear-man n
+
(single
+ 7.5
was
no
multiple-clutched
(19.4
23)
clutch
efficiency
of
0.050,
t
3).
clutchers
showed
of
correlated
single-clutched
groups
13.0
Table
single
<
two
versus
amount
negatively
expenditures
females cycle
8.11,
between 7.5
but
of
breeding
was
The
2).
than
z
n = 32).
offspring
(Table
first
0.002;
fledglings
efficiency
n,m
p :
between 0.9
versus
clutchers +
1.4
versus
10
TABLE
3
and multiple clutchers: Compar isons between s ingle Time expenditure data (means + standard deviations in min). M = male; F = female. Sample sizes (number of breeding cycles) are given. ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Feeding Feeding per Incubation offspring x+s x+s (a) x + s (X)
Single
clutchers;
all data
7.6 + 7.5
M F
(n
q
6.1 2 2.9
(28)
19.4 + 10.3 (72) clutchers : data
Multiple
9) (411
3.5 2 2.4
8.9 + 4.0 (59)
4.4 + 2.9
for first
breeding
cycle
(n = 11)
M
13.0
+
6.9
(45)
5.7 + 1.8 (41)
2.5 + 1.2
F
15.9
+
5.6
(55)
8.1 + 2.7
(59)
3.5 + 2.0
Multiple
clutchers : all data
(n = 23)
M
13.1 + 7.5
(451
7.2 + 2.9
(43)
2.9 2 1.2
F
16.3 + 6.3
(551
9.7 + 3.5 (57)
3.9 + 2.0
____________________~~~~~~-~-~~~~~~~~~~~~~~-~-~~~~~~-~~~~~~~~~~~~ * n : 8 for incubation
In conclusion, reproduction.
incubating
Other
measures
were
also
females
by of
with
reproductive
found
to incubate
in association,
Breedi% -----
experience -------on
experience
of the time
and
correlation
hatching in
success.
Males
their
than
mates
was
breeding
from
single
less time
in
time found.
were
of multiple
males
spent
between
efficiency
investments
more
investment
not
clutches clutch
incubating.
and ___ mate ---I---_familiarity --_
reproductive and/or
most
negative
males time
pairs;
Data
assumed
A significant
spent
correlated
data.
mate
success familiarity
of
groups
differing
are presented
in breeding
in Table
4.
TABLE
4
Comparisons of control versus experimental pairs during the two trials: success data (means + standard deviations). Reproductive Sample sizes (n number of pairs, m = number of breeding cycles): for Cl group, n,m = 3,4; for C2 group, n,m = 3,7; for El n,m = 7,ll; for E2 group, n,m = 7,lO. group, q
Control
pairs
Experimental
pairs
-----_-_-_________-_-----_-__-~-----_-_________~_______ Pairing
cycle
Number
of
Clutch
size
1 clutches
1.3
+
0.6
1.6
+
0.5
4.0
+
1.4
4.8
+
1.5
Hatching
efficiency
(5)
79
+
25
54
+
34
Fledging
efficiency
($)
100
2
00
94
+
20
3.0
+
0.8
2.4
+
1.6
4.0
+
2.0
3.7
+ 2.6
2.3
+
0.6
1.4
+
0.5
4.6
+
0.8
4.4
+
1.1
Number of per clutch
fledglings
Total number fledglings Pairing
cycle
Number
of
Clutch
size
of
2 clutches
Hatching
efficiency
(%)
72
+
16
a2
+ 22
Fledging
efficiency
(%I
88
+
15
80
+
20
+
0.7
+
0.8
3.9 + 6.7 + 1.5 Total number of fledglings ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.9
Number of per clutch
More by
in
young
were
experimental
3,7,
p total
control
=
2.9
fledglings
0.0461, number pairs
fledged pairs
by during
while
the
of
fledglings
fledged
2.7
two
control
(pairs
the
second
=
young
23,
kept trial
experimental (U
more
2.7
together) (U
groups n,m
during
did
= 7.72 the
=
2.5,
n,m
not
differ
ns).
second
than
Though pairing
=
12
(U
the
1,
tria
1,
=
sample
n,m
=
clutch,
per
trial,
though
the
pairs
80%)
(Tables
TABLE
q
also
trends
for
experimental
4 and
This
size
decreased
is
or
was
not
of
clutches
fledging
small
number
fledglings per
(from
are
during
72%
efficiency
to (from
of per
trial
increased
only
to
in
of
efficiency pairs
due
differ
number
s ignificant
not
probably
did
number
Hatching
had
groups
groups
clutch
for
control
0.100).
different
direction.
trial
these
p
The
expected
second
between
3.3,
sizes.
clutches
the
difference
in the
82%) 88%
but to
5).
5
Summary of comparisons between control and experimental pairs: Reproductive success data. See text for explanation of abbreviations and Table 4 for data and sample sizes. One-tailed Mann-Whitney U tests. ____________________~~~~~~~~~~~~~~~~~~~~~_~_~_~_~_~_~___~__~~~~~~ Cl E2 Cl E2 Number _--c2
of --
clutches -1----
U= 1 p = 0.100
El
Clutch -----c2
Hatching -----u = 3 p = 0.058
c2
u = 21 ns
El
Fledging-----u = 34.5
ns
Number ----c2
El
u
of --
c2
ns
El
fledglings ------
u = 13.5 ns
per --
11
q
25.5
ns
efficiency ----_-U
= 8 ns
U
= 28 ns
u
=
p < clutch -----
u = 30 ns u
U
U = 28.5 p < 0.050
El
= 54.5 ns
-
u = IlS
size --U = 8.5
efficiency ---------
= 40.5 ns _____________________~_~_~_~_~_~~~_~~~_~_~_~_~_~~~~~~~~~~~~~~~~~~
30 0.050
13
TABLE
6
pairs: Time Comparisons of control versus experimental expenditure data (means + standard deviations in min). Sample size for incubation data for Cl group, n,m I 2,3; for all other cases see Table 4. ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-Experimental pairs Control pairs ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-...~~~~~~~~~~~~ Pairing ------
-1
=cle--
Incubation
by
the
Male
12.1
+
3.2
11.4
+
9.7
Female
14.0
+
6.5
17.3
+
8.3
Male
4.9
2
1.6
6.6
2
2.8
Female
a.2
+
1.2
a.7
t
3.4
by
the
Male
1.9
+
0.4
3.8
+
2.1
Female
3.2
+
0.7
5.0
+
3.0
Male
15.9
+
5.3
a.9
+
7.3
Female
16.6
2
6.1
17.6
+
8.2
7.3
+
1.7
7.6
2
3.8
11.0
+
2.5
9.7
+
4.8
by
the
3.0
+
1.2
2.8
_c 1.3
3.2
+
Feeding
by
Feeding
the
per
----Pairing
offspring
-2
-cycle ---
Incubation
Feeding
by
by
the
the
Male Female Feeding
per
offspring
Male
Female 4.0 + 1.1 ___________________________~__~-~~~~~~~~~~~~~~~~~~~~~~-----------
Males min)
than
of
control experimental
pairs
spent males
more (8.9
time +
7.3
incubating min)
during
1.8
(15.9 the
+
5.3
second
14
but
trial,
16.6
E2:
females +
pairs
spent
trial
(Cl
for
6.1
versus
more
6
and
increased
for
(Student’s
t
0.7
n,m t
g,
TABLE
C2;
of
(Tables
= =
vary
17.6
+
for +
time
all
3.00,
6.5
min)
p n,m
16.8
< =
0.001; 30.33,
(Tables
12.1
_c 3.2 16.6
in weight
from
pairs
+
expenditure
1.2
versus
weight:
9.4
+
+ 5.3 no
at
trial 18.1
other
1.9
the
next
days,
t
versus
0.8
min;
fledging
to +
second
significant
offspring
versus
Control
min); were
first
versus
the
15.9
6.1
feeding
the
7).
during
+
of
(C2
6 and
offspring
versus
and
age:
time
their
males:
Age
38,40,
8.2
expenditure
7).
test;
their
feeding
14.0
comparisons
not
time
versus
females:
3.81,
did
10.0
p = 0.004).
7
control and experimental pairs: Summary of comparisons between See text for explanation of abbreviations Time expenditure data. and Table 6 for data. Two-tailed Mann-Whitney IJ tests. ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Females Males Cl Cl E2 E2 ____________________~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Incubation I____c2
U = 8 ns
u = 31.5 ns
El
u = 5 ns
u = 14 p q 0.050 u
u = 53.5 ns
q
51.5
ns
Feed in& ---c2
u = 3 p = 0.058
c2 El
q
31
ns
u = 3.5 p < 0.092
U = 46 ns
El
Feedi= --
u
per -IJ I 4 ns
offeng ---
u = 33.5 rlS
U = 46.5 ns
-U = 23
‘J = 6.5 tlS
u zs39 ns
u = 34 ns Ll q 41 ns
= +
15
Both
breeding
reproductive
experience
success.
clutches
and
spent
more
second
of
In
and association
fledglings
time
mate
familiarity
with
an
produced,
incubating
than
affected
increased
males
of
experimental
number
control
males
of
pairs
during
the
trial.
DISCUSSION Most arose
of
variation
primarily
during per
the
from
a
pairing
clutch
(no
efficiency
differences
account
for
For
example,
first
the
in
Why
did
had
sufficient
Single expenditures clutchers, even
during
females comparison,
the
clutch
size,
ten
of
single
being
second
trial,
females to one
female
only
breed
once,
especially
time
to
breed
again
(both
their
first
and
multiple by
males their invested during
mates incubated first
significantly breeding
more the
than first
males clutch
in
second
out
all and
pairs
times)? time
in In
and
females
multiple
breed
single
3).
of
or
trial.
multiple
single-clutched 6
of
not
differed
In
cycle.
did
similar
more
the
clutchers,
multiple
(Table
one.
during
since
at
during
second
bred
the
only
incubation
in
the
who
during
cycle
clutchers
clutchers
who
pairs
fledging
completely
multiple
clutch
breeding
or
fledged
cannot
during
fledged
ended
one
and
young
clutchers).
multiple so
the
of
had
multiple
quality were
pairs
a pair
hatching and
necessarily
of
number
single
who
between
clutches
trial
some
clutchers
‘from
between
not
success
successful
individual
from
the
not
birds
out
went
first
found
were five
of
in
since
trial
trial
and
in
this
vice-versa, in
be
reproductive
number
differences
Innate
first
the
trial,
could
the
in
less pairs,
8
cases. clutchers,
In
16
females
invested
invested
equally
increased with
the
a
more in
phase
usually
often
result
been
Stauffer, incubation
Rowley,
by
together
each
inference
sample
size
numerous
is
and
to
females remated
the
data
phase,
time
were success
success
whether
the
constraints,
hatching
that
on
was
fledging
though
suggest
or
in
(Best
and
expenditure
they
in
should
male
and
incubation
other
female
is
of
development of
breed
in
their
synchronization (Erickson,
may 1978).
require ring
keep
1980;
nest
previous doves,
of
weight
when
pairs
other
nest
mates;
is
1982;
one
mate
bird
for
presence
within 1981)
not
during
the
by
constant
their
and pairs
requires
may and
with males
of
thermal
this
attendance,
where
is
correlation
the
experience
are
(Welty,
negative
eggs
Vleck,
between of
loss
to
Nearly
to
mate
investment
available
relief
patterns
the
small
there
its
competitors by
foraging.
(Carey,
In
or
and
if
periods
expenditures,
required
nest
as
during
time as
often
synchronization
loss
time
such
parents
such
indicated
determines
activities
specific
activity,
As
only Still,
incubator
predators
1981).
data
cautiously.
the
nest
against
Wittenberger, between
this
correlation
treated to
increased
defended
on
be
costs
share
incubation
range
I
of
fledging
mates
when
energy
the
affected
based
should
possible
willing
the
1983). mate
Since
than
not
incubation
surprising lower
but
Analysis
1).
during
and
again.
This
in
be
cases
incubating
7).
(Table
2
males
suggested
not
to
in
spent
6 and
birds
is
found
1980;
they
study the
males
addition,
already
to
this
In
(Tables
this
important
removed,
not
in
cases,
time
success
limiting
has
of
mate
reproductive
5
4 cases.
amount
familiar
in
be
optimal
one’s were
very
mate mated
17
unfamiliar
with successful
in
other
breeding
these
factors
may
as
still For
hatching
may
most
why
first
brood
expenditure
of
males
pair
again.
incubation
may
efficiency
in
The pairs
high
first
eggs
with
1)
by
to
for
correct
mortality.
strategy have
if led
to
from
egg
by
of
this
increased
of
clutch
size,
or that
affect
last
inbreeding)
of
a
that
would
if
had
an the
with
clutch
coverage
of
incubation larger
clutches
efficiency, is
(e.g.,
or
most
support
lay
hatching
and
female).
imply
improper
females
in
hatching
decrease
possibility common
decreased
inadequate
because
remains
efficiency
either
lower
investment
study
may
of
have
My results
fledge.
a
investment
question
(or
time
whether
paternal
a pair
male
clutchers’
clutchers
of
the
since
time
This
to
efficiency
determine
hatching
efficiency
is
to
of
their
Hatching
failure
and
and
surprising
cost
possible
to
This
is
increased
hatchlin’gs
variables
of
wild
males,
multiple
multiple
fitness
parents,
for
clutchers?
a consequence
the
to
all
due
hatching
increased
don’t
the
increasing
investment
embryo
as
or
the
mostly
than
seems the
limited
alternative. (Table
hold
efficiencies
of
less
respect
One in
was
result
single
determining
already
with
finches
with
incubation
why
outweigh
number
size
This
benefit
fledging
were
optimal
in
were
1972).
more
doesn’t
than the
zebra
correlated
males,
but
unanswered,
Morris,
success
Considering
efficiency
comparable
incubated
known).
multiple-clutched hatching
they
correlation not
females
birds.
negatively
is
breeds
to
hatching
since
this
were
important
clutches,
familiar
and
domesticated
was
(though
but
(Erickson
be
efforts
investment
to
eggs
factors
affect
females’
opposed
an
aviary explain
such
as
appropriate conditions the
lack
Of
18
correlation
between
between
clutch
In
size
and
conclusion,
female, not
clutch
the
that
to
more.
Birds
breeding
may
other
with
mated
in --
Because and
found
fledging
mates from
-the
pairs
were
no
correlation
efficiency
increase
still
spent
more
time
time
expenditure
amount
of
parents
do to
feeding not
not I
offspring
or
time
to
usually
may
have
unwilling
invest
incubate
all
rest
the
decided
to
in
feed,
parents.
stages
of
or
perform
I
expected
and
expenditure. pairs, 2). limiting
to
be
expenditure
Time number
larger much
was results
reproductive
as
of
with
no
to
high
correlation
reinforce success
the and
broods
number
they better
(Royama,
allowing of
increase
mouths with
in
between
these
conclusion
that
that
mouths
individual
investment,
efficiency
the i.e.,
heat
feeding
parental
but 2),
retain
in
to
Increased
of
smaller
by
females
young,
number
different
the
feeding
males.
(Table
broods
efficiency due
the
and
and
more
decreases to
fledglings in
did
fledge
expenditure
pairs
of
fledglings,
than
to
measure
Probably
of
young
as
time
fledging
These
1).
offspring
fed
resources,
number
because
between
there
food
between
with
a better
for
by
proportionally
expected be
limited
per
possibly
had
chase --
necessary
invest
need
to
comparisons
was
of
feeding
is
feed,
do
1966).
(Table
care
and
the
partner,
parental
to
fledglings by
the
unwilling
(Table
does
most
incubation
incapable
loss
not
parents
feed,
in
post-fledging
both
and
in that
of
activities.
Investment
have
time
a mate
with
suffer
number
suggest
more
again
and
investment
data
invested
breed
size
differences
to time
fledging variables incubation between
of
19
pairs
should
easily
be
subtle
in
There
were
found.
investment though
between the
this
also
single
offspring
of
study,
where no
and
food
abundant
differences
multiple
multiple
is
in
clutchers
clutchers
and
feeding (Table
left
the
81,
nest
a day
earlier.
Breedi% -II_
experience --1_1-
Age
and/or
shown
to and
1972;
Erickson
experience
with
(6.7)
trial.
Mate
fledging even
a specific
times by
during
commitment did
not
but
males the
to take
did
(Tables
clutch
an
4 to
to
7).
All
more
numerous
fledge
their
and
C2
versus more second
hatching
to time
breed
or
two
investment
pairs
fledged
increased
heavier time
consequently,
than
experimental
pairs. Experimental
pairs
breeding
experience,
success,
but
efficiency.
this It
is
may as
benefitted
indicated
benefit not
have
obvious
was
by negated
why
these
from
their
previous
their
increased
hatching
by
a decreased
fledging
parents
could
or in
their
and,
young
and
the
size,
brood
In
comparison)
during
increased
egg
1983).
produced
pairs
Controls
trial.
their
longer
affect control
with
second
feed
not
C2
pairs (3.9)
of
familiarity
versus
pairs
been
(Coulson,
E2
while
(Cl
date
Rowley,
versus
control
5):
allowed
together
(El
have
species
1968;
se
mate
size, of
success
and
did
number
per
experimental
efficiency
young
4
the
clutch
Lack,
mate
familiarity
incubation
a
1972;
experience
than
three
in
Morris,
Tables
with
length,
reproductive
comparisons;
young
familiarity
success
breeding increase
-complementara -----
courtship
and
not
E2
and
hatching
study,
did
behavioral -----
experience
influence
laying
this
and ---
not
fledge
20
all
their
familiar
hatchlings.
Studies
and unfamiliar
predict
that
of the division
mates
the effects
when
of mate
food
of
feeding
is limited
familiarity
between
are needed;
on fitness
I
should
be
striking.
CONCLUSIONS I suggest of
that
parental
care
incubation),
because
parental
care
no conflicts
most
simultaneous
be explored
important
necessary phase
results
have
of
time
of
that
success.
division
19801,
a
been
As
a
overlooked:
there
behaviors
since
between
these
of
simple
approximation.
eliminated
does
time
or energy
reproductive to one
to those
and
there
were
restrictions
deal
how
to weigh
no
should
of this
work
also
are more
deserves
different
behaviors
that
complementarity,
the
of these
importance of labor
are
problems
are overall
time-
it will
be
breeding
that
see Chase,
suggestive,
of
To further
of each during
more
phases
are energy-limited?
of division
discussion
the
with
that
constraints
success
compare
of behavioral
and the importance
(for theoretical The
how
to know
an optimal
a first
may
mates
reproductive
(Chase,
importance
trying
importance
with
during
future.
as compared
the
as
were
of whether
When
reproduction,
used
patterns
in determining
attention.
limited
was
The
higher ways
division
(especially
paired
established
behaviors
in the
The question
have
in allocation
limitations.
mates
numerous
be
important
were
by the previous
individuals
of the
design
resu,lt, some
the
behavior
could
experimental
test
that
their
However,
is determined
between
and
complement'
energy
remating
phase
1980).
though
the
21
large
variability
difficult. under
More
are
consequences
of
the
for mate
variables
worthwhile, between
needed.
neglected
important
sample
sizes
long-term
resource-limited
contributions
mostly
extensive,
natural,
pressures
and small
since
pairs
and
that
in field it reveals
and raises
some
are
to
choice.
studies
interpretation on breeding
conditions
There sexes
make
few
data
parental
that
difficulty
situations some
the
and this
of
make
subtle
interesting
on
care
I suggest
the
and under
success predation
relative
the area
possible has been
controlling
this
type
behavioral
more
of
all study
differences
questions.
ACKNOWLEDGEMENTS initially encouraged me to pursue this study. N. N. Burley Burley, G. Bell, C. Erickson, D. Gori, B. Holmes, A. KodricC. Petersen and anonymous reviewers read this Brown, D. Kramer, manuscript at various stages of its preparation and made many program that useful suggestions. B. Beaulieu wrote the computer did all of the compilation of the raw data. This research was supported by a Sigma Xi Grant-in-aid of Research, by McGill's Computer Center and by a NSERC (Canada) grant to N. Burley.
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22
pp. 424-433. Mate choice in the Coulson, J.C. and Thomas, C.S., 1983. Kittiwake Gull. In: P. Bateson (Editor), Mate Choice. Cambridge University Press, Cambridge, pp. 361-376. for egg laying and El-Wailly, A.J., 1966. Energy requirements incubation in the zebra finch, --_ Taeniougia Condor, ----~castanotis. 68: 582-594. Emlen, S.T. and Oring, L.W., 1977. Ecology, sexual selection, and the evolution of mating systems. Science, 197: 215-223. in animals: Pair bonds Erickson, C.J., 1978. Sexual affiliation and reproductive strategies. In: J.B. Hutchison (Editor), Determinants of Sexual Behavior. Wiley, New York, Biological PP. 697-725. Effects of mate Erickson, C.J. and Morris, R.L., 1972. familiarity on the courtship and reproductive success of the (Streptopelia risoria). Anim. Behav., 20: 341-344. ring dove Immelmann, K., 1965. Australian Finches in Bush and Aviary. Angus and Robertson, Sidney. for Breeding in Birds. Adaptations Lack, D., 1968. Ecological Methuen, London. Morris, D., 1954. The reproductive behaviour of the zebra finch with special reference to pseudofemale (Poehila guttata), -----behaviour and displacement activities. Behaviour, 6: 271-322. in birds. In: P. Bateson (Editor), Rowley, I., 1983. Re-mating Choice. Cambridge Mate University Press, Cambridge, pp. 331360. food Factors governing feeding rate, Royama, T., 1966. requirement and brood size of nestling great tits ----Parus major. Ibis, 108: 313-347. of desert birds. In: D.S. Farner Serventy, D.L., 1971. Biology Avian Biology, vol. 1. Academic and J.R. King (Editors), Press, New York, pp. 287-339. and sexual selection. In: Trivers, R., 1972. Parental investment 8. Campbell (Editor), Sexual Selection and the Descent of Man, 18711971. Aldine, Chigago, pp. 136-179. Energetic Vleck, C.M., 1981. cost of incubation in the zebra finch. Condor, 83: 229-237. College Publ., Welty, J.C., 1982. The Life of Birds. Saunders Philadelphia. Wittenberger, J.F., 1981. Animal Social Behavior. Duxbury Press, New York.