Cultural transmission of song patterns and dialect development in a free-living bird population

Anim. Behav ., 1977, 25, 5 0-78

CULTURAL TRANSMISSION OF SONG PATTERNS AND DIALECT DEVELOPMENT IN A FREE-LIVING BIRD POPULATION BY P . F. JENKINS

Zoology Department, University of Auckland, New Zealand

Abstract . Vocalizations and social organization of a semi-flightless passerine (Philesturnus carunculatus) were studied in a colour-banded population on a densely forested island . Pair bonds and territories were permanent. Males sang from I to 4 highly diverse loud songs . Each song pattern was sung by groups of up to 20 birds occupying contiguous territories . Temporal and spatial continuity of song groups by cultural transmission to new recruits was observed . Song groups overlapped where they met. Development of new song groups arising from errors in song learning, described as cultural mutations, were studied . Father/son song relationships and dispersal of sons of known parentage are discussed in relation to the proposed function of song groups in promoting gene flow in an otherwise extraordinarily static population. Although many field studies of the song behaviour of free-living populations of passerines have been published, very few of them have been carried out with birds rendered individually recognizable by colour marking, and even fewer of them have been based on a knowledge of an area for more than one season . Consequently I planned in this study to investigate the continued and detailed relationships of the songs of a substantial number of individually identifiable saddlebacks (Philesturnus carunculatus rufusater, Passeres) living in contiguous territories . This species has a combination of characteristics that render it particularly suited to lengthy and intimate field study ; it has exceptionally weak powers of flight, forms permanent pair-bonds, holds a life-long territory, has a varied vocal repertoire, is not afraid of close approach by man, and has exceptional longevity for a bird of its size . The distribution of song patterns proved to be so clear-cut and stable from year to year that I was able to study song behaviour of young birds entering the population, and especially the characteristics of the songs of sons in relation to those colour-banded fathers whose songs were already well known . Nice (1943) investigated the songs of sons and grandsons in the field but because of the absence of tape-recordings and because of the extreme variability of the songs of song sparrows (Melospiza melodia) she was unable to establish any kind of rules for that species . Mulligan (1966) likewise did not find any pattern of relationship . Kroodsma (1974) working with a colour-banded population of Bewick wrens reported close similarity between two of the song patterns of one male and the songs of its neigh-

bours. The father of this male did not have those two songs in its repertoire . Cultural transmission of song patterns by learning from older conspecifics occurs under aviary conditions in a number of species (Thorpe 1958 ; Marler & Tamura 1964 ; Immelman 1969) and perhaps dialects arise by a similar process occurring in the field (Marler & Tamura 1962 ; Nottebohm 1970) . Nottebohm & Selander (1972) suggested that the extensive dialect system in the chingolo sparrow may serve to reduce gene flow between locally adapted groups of birds, but the widespread occurrence of song learning (Nottebohm 1972) in other species remains unexplained in terms of selective advantage . In the present study I describe the development of local song traditions and the relationships of the songs of fathers to those of sons and discuss some hypotheses concerning the function of dialects . Study Area, Materials and Methods Most of this study was carried out in the years 1970 to 1974 on Cuvier Island, a small off shore plutonic intrusion of dioritic rock approximately 100 km north-east of Auckland, New Zealand . Smaller studies were made on Fanal Island (Mokohinau group), Lady Alice Island (Hen and Chickens group) and on Hen Island . Cuvier Island lies almost at the edge of the continental shelf, 38 km east of Cape Colville and 24 km south-east of Cape Barrier at approximately 36° 26' south latitude and 175° 64' east longitude (Fig . 1) . The island is approximately 21 km long east to west and 11 km north to south at the widest point, and is divided into two reserves : a Flora and Fauna 50



JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

Reserve, consisting of 171 ha of forested land and 23 . 4 ha of fenced pasture and rough grazing land which makes up the Lighthouse and Radio Beacon Reserve at the eastern end of the island . The topography shows a very marked contrast between the steep almost cliff like coastal fringe rising to about 100 m, and the broad rolling central summit area lying between about 100 and 230 m (Fig . 1) . The study area consisted of the forested hills and valleys within the rectangle of 1 . 2 x 1 km shown in Fig . 5. Until 1959 feral goats and semi-feral cattle had completely eaten out the forest floor vegetation and prevented regeneration in areas bared by erosion . Eradication of goats and cats by the New Zealand Wildlife Service (Blackburn 1967) resulted in vigorous regeneration of the forest below the canopy. The upper surface of the forest is a discontinuous canopy of pohutukawa (Metrosideros excelsa) which allows much light to penetrate so that there is an abundant growth of trees beneath forming a continuous lower canopy . The composition of this second layer of vegetation varies markedly with the slope and

51

aspect of the site . In the damper valleys the understorey takes the form of dense vegetation made up of young kohekohe (Dysoxylum spectabile), mahoe (Melicytus ramiflorus), young puriri (Vitex lucens), kawakawa (Macropiper excelsum), houpara (Pseudopanax lessonii), and nikau palms (Rhopalostylis sapida) In drier sites this lower layer is more open and there is abundant rangiora (Brachyglottis repanda), mapou (Myrsine australis) and raurekau (Coprosma australis) . Where the lower stratum is even more open a species of Gahnia is common . On areas that had in the past been kept as clearings either by Maori occupation or by the goats, there is bracken fern (Pteridium acquilinum manuka (Leptospermum scoparium), or a tight scrub of mahoe, houpara and rangiora . Epiphytes occur on many large trees, especially in damp valleys . All the tree and shrub species mentioned are broad-leaved evergreens, forming a dense subtropical forest. The North Island sub-species of the saddleback, Philesturnus carunculatus rufusater, is a medium-sized passerine bird belonging to the small New Zealand endemic family of Callaeatidae (Fleming 1964) . The plumage is black except for a broad band of bright chestnut i COLVILLE CHANNEL

CAPE COLVILLEy _ T ~ N3

Fig . 1 . Cuvier Island, showing 100-ft contours .

CAPE BARRIER

I

OC~VIER I

52

ANIMAL BEHAVIOUR, 26, 1

extending from the wing coverts on one side across the back to the other wing . Adult females weigh between 65 and 80 g and males about 75 to 90 g. The sexes can be reliably determined by their vocalizations . Saddlebacks have noticeably small rounded wings which cannot support level flight for more than a few metres . The species was formerly common in the North Island but by 1900 it had become extinct almost everywhere on the mainland and only one population survived on Hen (Taranga) Island about 80 km north of Auckland. In January 1968 New Zealand Wildlife Service officers transferred 29 saddlebacks from Hen Island to Cuvier Island where they established well and bred freely . This study commenced 2 years after that liberation . There were 28 pairs living in the study area when the study began. Of these, 12 individuals were survivors from the original liberation while the other 16 were Cuvier-bred birds . The population increased to 50 pairs in 1971 to 72, dropped to 45 pairs in 1972 to 73 and rose again to 48 pairs in 1973 to 74. The two original colonizers which were still living at that time were at least 7 years old . Only two nests with eggs were discovered, both containing three eggs . The reported clutch size is two (Oliver 1945) and in the breeding season of 1970 to 71 the average number of fledglings observed being fed by parents was 1 .9 per pair . Only one pair was ever observed to be double brooded . The numbers and kinds of predators present on Cuvier Island were very low . The only mammal, other than man, was the Pacific rat, Rattus exulans, which is primarily frugivorous but may sometimes eat nestlings . In one season there was a pair of morepork owls (Ninox novaeseelandiae) but whether they predate birds as large as saddlebacks is unknown . It seems very unlikely that any other species present could have any important effect on saddlebacks. Thus this species appears to be relatively long-lived and to have a very low reproductive rate . An account of the population on Cuvier Island will be published elsewhere (Jenkins, in preparation) . A brief account of the social organization is necessary to understand the song groups system and father/son song relationship given here. The pairs are extremely sedentary, carrying out all their activities of feeding, breeding and roosting in the same area of forest all the year

round and also from year to year . With very few exceptions the pairs were always found foraging within this home area but they did not actively defend its boundaries by patrolling or skirmishing . Their `territories' were apparently the product of mutual avoidance behaviour mediated by very loud song, a social system in which the avoidance component in all aggressive events between two birds appears to be greatly elaborated . The pair-bond is very strong and usually it is life-long. The members of each pair forage very close to each other all day and every day for years . Pair formation occurs at any season and mates that die are quickly replaced . Widowed females ordinarily remain in their territory where they are joined by their new mate . At night adult saddlebacks invariably roost separately in a hole in a tree, and consequently each pair-bond paradoxically breaks down every evening and is reformed anew each morning, yet the saddleback must have what is one of the most persistent pair-bonds reliably reported in passerine birds . Thus the saddleback social system is a rather rigid one in which the entire habitat is permanently parcelled out amongst evenly dispersed pairs which are intensely mate-faithful and sitefaithful. Whether this inherently static system resulted from its poor powers of flight, or vice versa, is difficult to say . For capturing post-fledgling and adult birds I used the methods developed by Merton (1965) . Fledglings of known parentage were taken on their roosts at night . Wraparound PVC colour bands size D were used in combination with New Zealand Wildlife Service numbered metal bands . I recorded vocalizations on a Uher 4000 Report L tape recorder with a Uher 514 omnidirectional microphone and to prepare sound spectrographs I used a Kay Sonagraph on the wide-band setting. Only songs from birds which were unequivocally identified by colour-bands were used in the analyses . Vocalizations were recorded and dispersion patterns mapped either by moving from one bird to its nearest singing neighbour or by traversing the area along a predetermined route . Saddleback Songs Saddleback songs were designated as loud or quiet . Loud songs are powerful vocalizations with a characteristic timbre and great carrying power. Two subdivisions were recognized (i) chatter songs (Fig . 2) and (ii) male rhythmical

JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

songs (Figs . 3, 4) . Quiet songs are soft flutelike sounds audible only at closer quarters . They are strictly sexually dimorphic and much simpler and shorter than loud songs . Quiet songs are not considered further here . Chatter songs. The long and short chatter songs are the commonest saddleback vocalizations, being given by both sexes throughout the year . In calm weather these songs can be heard up to 150 m through dense vegetation. Unlike the songs in the next category no regular patterns of variation were observed in chatter songs . Male rhythmical songs . The male rhythmical song (M.R .S .) is used exclusively by siteattached pair-bonded adult males . Each bird sang from one to four patterns, and in the study area on Cuvier Island nine different patterns were studied in detail . This song is typically, but not invariably, divisible into two parts, (a) an `introductory phrase' consisting of two high-pitched puretoned whistles, called here 'zeets', and (b) a `repeated phrase' which is sung from three to seven times (Figs . 3, 4) . This repeated phrase is often complex and is delivered in a very stereotyped pattern and, for any one bird, with a characteristic and unvarying pause between successive notes and phrases . The whole performance conveyed an impression of a carefully contrived and rehearsed rhythmical pattern, contrasting markedly with the stop-start and erratic delivery of the chatter song .

4 3

A

11 111

2

53

The Distribution of Male Rhythmical Song Patterns When the recordings of males living in neighbouring territories were assembled it became clear that the M.R.S . patterns were not distributed randomly . Indeed each song pattern was restricted to a small compact group of birds ranging in number from two to eight . Repeated recordings made of the same birds over a period of months, and later of years, established that the song patterns sung by individual birds were in general constant, both in number of patterns and in form. With a few very rare exceptions a given song pattern was not heard from birds outside the particular song group . However, although each song group was a discrete set of individuals occupying contiguous territories, the sets overlapped to a small extent in the region where they abutted, the birds in the region of overlap singing both song types . Thus of the 28 identifiable males studied in the 1970 to 71 season, 12 males used two M .R .S . patterns and the remaining 16 males only one . In one song group (VPH, SR) all three birds sang both the song patterns, but there was no overlap with other song groups in 1970 to 71 . The number of birds singing 1, 2, etc . songs and the mean number of songs per bird are given in Table I . The increase after the first year was due to the spread of the NE song . Subsequently the mean repertoire size remained very constant .

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Fig . 2 . Sonagrams of a typical long chatter song (above) and two short chatter songs .



54

ANIMAL BEHAVIOUR, 26, 1

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JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

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56

ANIMAL

BEHAVIOUR, 26,

Table I . Changes in Song Repertoire Size No . of song patterns per bird 1 2 3 4 Mean no . of songs per bird

No . of birds 1970-71

1971-72

1972-73

1973-74

16 12 0 0 1 .5

18 24 6 2 1 .8

16 18 9 2 1 .9

18 20 9 1 1 .8

The observations relating to the distribution of M .R.S . patterns are presented in two forms, first in Figs. 5, 6, 7, the sonagrams of songs of the birds constituting each song group are presented with a map showing the location of each singer in 1970 to 71, and secondly, the overlapping of song pattern groups is presented semi-schematically in Figs . 8, 9, 10, 11, for each of the years of the study . Song Pattern Groups, 1970 to 71 On Shooter's Ridge (Fig . 5), three males each sang two patterns, SR and VPH, sonagrams of which are shown in the top left part of the page . Only one song phrase is given for each pattern for each bird, but the similarity between the birds and differences between songs are evident . Although two of these birds were unbanded, recordings were made when both were in sight, and general surveillance of their behaviour left no doubt about their correct identity. The CC song was given by eight birds in a compact area . This pattern was readily recognized in the field, and the structural similarity between songs shows well in the sonagrams (Fig . 5) . In Fig. 6 are shown the birds singing three further song patterns, PH, KS and DC . Six birds sang the PH pattern ; three birds sang the KS song, and four sang the DC pattern. The PH song was clearly distinct to the ear, and sonagrams 1 to 5 show the similarities ; but the version sung by A-RG was not quite typical . The KS songs were quite unmistakeable even when the first note was duplicated as KKS in Y-AR (9 in Fig . 6) . The distribution of birds singing the ZZ pattern and the SE pattern are shown in Fig . 7 . Only one bird (A-GW) regularly sang a song that did not fit into the surrounding song groups . After the first season it shifted into a different song group and modified its song pattern accordingly.

1

The NE song distribution is not shown in the 1970 to 71 maps because recordings suitable for analysis were obtained from only one bird (YR-AG) . The Overlap of Song Pattern Groups The `song group' is the set of birds singing a particular song pattern and Figs . 5, 6, 7, show that where two song groups abut, birds on either side of the meeting line often sing both songs . In Table II the songs sung by each bird in the 1970 to 71 season have been listed to show how the shared songs were distributed and the data are presented in Fig . 8 in which the rectangles represent the song pattern groups . The size of each area is approximately proportional to the number of birds that sang each type of song . The diagram which is semi-schematic, rather than strictly geographic in the representation of song groups is to show the complex way in which the song groups overlapped each other . For example, around the perimeter of the PH song group in 1970 to 71 one bird sang both PH and CC, another both PH and ZZ and a third both PH and KS. Two birds sang KS and DC, while two others sang DC only. The overlapping of song groups for the subsequent 3 years are given in Figs . 9, 10 and 11 . Towards the end of the first season an entirely new song pattern, NE, occurred in the centre of the study area and spread to three other birds (Fig. 8) . In the following three seasons this NE song spread through approximately half the study area . The acquisition of NE song was not confined to young birds settling in the area but was also learnt by long established birds whose repertoires had previously been thought to be stabilized. The spread of NE pattern is given in Table III . In the second, third and fourth seasons the main features of the distribution and the overlap of the original song groups remained essentially the same despite the advent of the NE song . There was, however, somewhat more overlapping resulting in 21 known combinations of songs in 1971 to 72, 21 in 1972 to 73 and 19 in 1973 to 74 . At the same time the territorial population increased in 1971 to 72 to 50 pairs and remained at about this level until 1974 . Origin of the Song Groups All the males in the study area in 1970 to 71 are listed in Table II, and those which were survivors from the original liberation are in bold type . It is clear that each song group contained

JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

57

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58

ANIMAL BEHAVIOUR, 26, 1



JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

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60

ANIMAL BEHAVIOUR, 26, 1

Table 1I. Song Groups 1970-71 and Founding Birds Birds

Song pattern groups

song groups showed striking persistence both in space and time. Young birds establishing a new territory or replacing a bird in an old territory

SR VPH -A

Fern d Knob d BR-A -WA

A-RB AWAGA-RY d of YW-A AY-YA

GW-A A-RG RA-Y YR-AG ARY-AR

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H. Gully G-RA AY-GR -AY B-WA

Y-AY

0 0 0

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N77 I°

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0 0 0

DC 0 0 0 0

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0 0 0 0 0

1

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1

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f 71 SE

Fig . 8 . Overlapping distribution of song groups in 1970 to 71 . Each area represents approximately propor-

one or two of the originals together with a number of island-bred birds . The scattered positions of the originals, as observed in 1970, are shown in Fig . 12 . where their locality labels are distinguished by an attached circle . From their known high degree of site fidelity it is likely that these positions are those they took up when they settled to breed after liberation . When the progeny of that first season settled into breeding territories those near each of the founding pairs developed close copies of the founders' rhythmical song patterns . By 1970 to 71 there had developed distinct song groups, each centred on one or two originators . In some places where a group spread to come into contact with a neighbouring group the birds developed both song patterns, and so the overlap of song groups occurred . The discovery of the founding birds in each song group posed the question of whether the song had grown by sons clustering around fathers, or whether the members were of mixed origins . Recruitment of New Birds to Song Groups During the 4 years of the study many birds died and were replaced by young ones, yet the

tionally the number of contiguous males that sang each named song pattern. The small circles represent the single and isolated recordings of NE song in the order which they were heard from 5 February to 29 May 1971 . Pry NE

VPH/PH S NE

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Fig . 9 . Overlapping of song groups in 1971 to 72 .



61

JENKINS : CULTURAL TRANSMISSION OF BIRD SONG I

SR vEH NE SR PH NE

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Fig. 11 . Overlapping of song groups in 1973 to 74 . Fig . 10 . Overlapping of song groups in 1972 to 73 .

usually developed songs that were consistent with the existing song group pattern . In the early stages of colonization the song groups probably grew by accretion as the new birds occupied empty habitat around founders . Later, recruitment was more difficult as birds had either to intercalate themselves between the residents or bond with a recently widowed female . Case histories of these events are given in Figs . 13, 14, 15 and 16 . Only one case was observed of a bird shifting after it had already bred once . This male rebonded about 400 m away from its original territory in the centre of a different song group . It modified its song to match its new set of neighbours and abandoned its other two song patterns .

Development of the `KS' Song Group Two birds, Y-AR and AR-, neighbours between 0 and 200 m on the West Ridge Track, were singing the KS pattern in November 1970 . The older bird, Y-AR, was an original colonizer while the younger bird AR- was Cuvier-bred . Their songs were not identical, Y-AR sang two 'klonk' notes before the 'seet' (KKS) whereas AR- sang only one (KS), but the distinctiveness of the form of the song seemed to justify classifying them into the same song group . The 'seet' note was always of a much higher pitch than the `klonk' notes . If Y-AR originated this song tradition on Cuvier Island (singing KKS) then AR- when it settled alongside copied it imperfectly (singing KS) . However, it is also possible that the originator may have already died by the time

Table III . Changes in the Frequency of NE Songs 1970-74

Season

No. of birds

Song bouts recorded on tape

1970-71 1971-72 1972-73 1973-74

4 14 21 21

5 40 27 31

Song phrases recorded

Days of recording

36 194 233 84

29 35 22 10

Average number of phrases heard per day 12 5. 5 10 . 6 18 .4



62

ANIMAL BEHAVIOUR, 26,

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Fig. 12, The location of the 28 pairs studied in 1970 to 71 . Only males are designated . The attached black circle indicates a survivor from the original liberation .

GAPH NE KK

AR-

K

Fig. 13 . The area of poor habitat claimed by AR-R was previously unoccupied by saddlebacks . This bird initially sang PH song when it first settled alongside GW-A, but developed both KS and NE as it extended its territory and came into contact with other neighbours .

Fig. 14. A-GB claimed a territory by forcing in between established pairs and in doing so developed four of the song patterns sung by its neighbours . However, it never sang either CC or KS songs, both of which song groups ended at this point .

this study began, in which case it could have sung either KS or KKS (Fig . 17) . The next new bird in this song group was YR-AG which started singing in January 1971 using a mixture of KS and KKS phrases with pitch and timing very precisely matching its two neighbours Y-AR and AR- . Eventually YR-AG dropped most of the KKS phrases

and sang almost pure sequences of KS . Further young birds joined the group, RA-W, A-WG and AR-R all singing close copies of the KS of AR- ; a little later RA-G settled alongside R-YA and both sang KKS type . At this point the KS/KKS song group was in a compact area at the head of Pumphouse Valley in the region where West Ridge joined



63

JENKINS : CULTURAL TRANSMISSION OF BIRD SONG RA-G DC

Unb.

Y-AY SE

(H, Gully) ZZ

WG-A zz SE

R-A zz SE

( -AY, zz,SE)

WRW-A

I

I (G- RA,ZZ,SE)

L Fig . 15 . R-YA set up a territory by intercalating between five established birds and sang all the songs of the neighbours and ZZ as well .

Summit Ridge. The area was only a little larger than in the first season but the settlement pattern of the birds was closer, there being seven birds instead of three . The Descending Tone Variant For two seasons, 1970 to 71 and well into 1971 to 72 the high pitched 'seet' ending was invariable . In February 1972, however, a new male, W-AR settled on the southern boundary of the KS song group and started singing a variant KKS in which the final note was lower in tone than the two K notes . This distinctive variant was immediately detectable by ear although the sonagram (Fig . 17), because there are harmonics in the 'seet' note, does not at first appear to indicate a drop in tone . Many counter-singing events were recorded between W-AR using the variant KKS and its northern neighbours singing the older traditional form of KS and KKS, but W-AR never varied its pattern . Further, in February 1974 two males, newly established to the north-east of W-AR, were recorded singing close copies of W-AR's variant song . The final step in the growth and development of this group occurred when -GA many months after settling on the south-west margin of the group, where it had been singing PH and NE songs, unexpectedly developed an incomplete version of KKS in which the S note was left out . That it was a variant KKS was obvious from the timbre and rhythm of delivery . The history of this song group is summarized in Fig . 17 . The PH Song Tradition One of the larger song groups was the PH . From year to year the PH song was acquired by young recruits with no important variations

Fig . 16 . WG-A took over -AY's territory and mate when -AY disappeared after 3 years occupation of the area . WG-A sang very close copies of -AY's songs . R-A did the same thing in a neighbouring territory where it replaced G-RA .

until 1974 when two variants were observed on the fringe of the group, in poor quality habitat . The variations consisted of the elision of certain notes, (Fig . 18) but the identity of the song type was obvious from the rhythm and from counter-singing against nearest PH neighbours. The study ended before it was possible to determine whether these birds founded a new song group . The variants so far discussed may be regarded as arising from errors in imitation, whereas `hybrid' songs, resulted from the incorporation of parts of the songs of two neighbours, into one song . This can likewise provide the basis for a new song tradition . VPH/PH Hybrid Song Male A-Y sang two song patterns VPH/PH and NE . This bird was a most prolific singer and long series of the VPH/PH songs were recorded during two seasons . The song form never varied, being always introduced by 'zeet' notes followed by one VPH phrase and then a series of between 4 and 10 PH phrases (Fig . 4(2)) . The VPH and PH portion were never sung separately . A-Y's territory lay at the head of Pumphouse Valley so that to the south and east PH song was regularly heard ; but A-Y's position also placed it at the upper end of Shooter's Ridge which was wholly occupied to the south-west by birds using VPH and SR . It is probable that A-Y when starting to sing in this position countersung against both these other song groups and combined the VPH and PH into the one performance . The SR pattern was never heard from A-Y . This failure to match all the songs of neighbours is very puzzling and accounts for the discreteness and persistence of the song groups .



ANIMAL BEHAVIOUR,

64

26,

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Fig. 17 . The growth and differentiation of the KS song group . Males ARand Y-AR were singing KS and KKS respectively in 1970 . One or the other, or perhaps a third hypothetical singer, founded the group . Evidence from Hen Island suggests that KS was the likely founding pattern and that KKS was a cultural mutation. In successive years each group grew by addition of further recruits . The dashed lines show the likely sequence of cultural transmission as judged by the geographical location of each bird . The solid arrowed lines indicate survival to 1974 . The first observed cultural mutation was W-AR which spread to WRW-A and an unbanded bird in 1974. The second mutation was GA- . Thus in 1974 the group consisted of four variant sub-groups .

DC/CC Hybrid Song Only the end product of the last mentioned hybrid was known so the steps by which it was reached must remain conjectural, but in this present case several stages of change were observed . Three males along West Ridge AR-, A-GW and IS of YW-A held territories which in part

abutted on each other . AR- sang the DC song very strongly and d of YW-A used only the CC pattern . A-GW, in between, occasionally sang a hybrid of these two songs in which, after a series of DC-type notes, there was appended the second half of a CC phrase (Fig . 19). Later a young male YR-AY intercalated between A-GW and AG- (another CC singer) and developed a



JENKINS : CULTURAL TRANSMISSION OF BIRD SONG 4

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65

was singing to the north of AR-R . It seems that instead of countering the new arrival with its whole song AR-R incorporated a part of it into its existing KS pattern . That it did so at 3 years of age is important, as is also the fact that it had no cause to make this change until the bird to its north GA- itself developed late in life a new song pattern . (GA-, although newly settled in the area, was not a young bird) .

_„

3 2

TOWER C'

Fig . 18 . Hut d sonagram of an incomplete version of PH song, and Tower a' sonagram shows a still further deletion from the PH pattern. Both these new young birds were at the edge of the PH song group in poor habitat .

song which consisted of repeated phrases made up of the end of A-GW's song ; in effect two of the DC notes and the truncated CC . Soon after this bird started to sing A-GW shifted to the other side of its (YR-AY's) territory and started singing CC pattern without the long DC series in front . Some weeks later YR-AY, presumably because it now no longer had any rival singing the original hybrid song, followed A-GW's suit and slowly through a series of stumbling and imperfect versions developed a CC song. Thus in this sequence of events the original hybrid song was abandoned and the two birds involved joined, as it were, the CC song group . It seems likely that if A-GW had not shifted the hybrid song DC/CC would have become established as the nucleus of a new song pattern group . Sonagrams of the songs are set out in Fig . 19 . AR-R/GA Hybrid Song AR-R sang the PH song only when first settling into a territory and later developed KS which it sang quite typically for nearly two seasons. Then towards the end of the 1972 to 73 season AR-R introduced three new notes into its KS song between the introductory 'zeets' and the first KS phrase . This, it will be recalled, is exactly the same location in the song that A-Y included its VPH phrase in what was otherwise a typical PH song . The three new notes in AR-R's song seemed to imitate the incomplete KKS song that the newly established male GA-

`Corrected' Errors in Song Learning Not all variants became fixed . A-GB, when it first settled, sang an incomplete version of the SR song type in which it repeatedly elided the last two notes during the whole of the 1971 to 72 season. The song was without doubt an attempted SR, as the part sung matched precisely the rhythm, note structure and timbre of the birds in the area . By January 1972 A-GB was hesitantly including the terminal two notes but the, timing was not the same as the other SR singers and the numbers of notes in the centre of the phrase was more than those sung by neighbours . However, by November 1972 A-GB had achieved a very precise match between its SR song and those of the older birds . The sequence of events is shown in the sonagrams in Fig . 20 . The other patterns sung by A-GB, (PH, VPH and NE) were all perfected immediately on settling in November 1971 . Many examples of young males singing imperfect versions of well-known songs were recorded . Usually they achieved perfect versions over a period of days or weeks . An example of this process is given in Fig . 21 . Six examples of birds singing seriously disorganized versions of song patterns were recorded . It was obvious what pattern was being attempted but the sounds were so scrambled that it was chiefly from the rhythm that I could classify the attempted song . All the birds involved were young and none of them lasted in the population, so these vocal efforts never initiated a new song tradition . Black-birds (Turdus merula) with very aberrant songs do not succeed in setting up territories either (HallCraggs, personal communication) . Song Patterns on Hen Island In November 1973 I visited Hen Island and recorded M.R.S . songs from 45 different males in the area where the Cuvier colonists were originally trapped . Six of the nine Cuvier Island male rhythmical songs were found still being sung, five of them



66 4 3 2 1

ANIMAL BEHAVIOUR, 26, 1

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Fig . 19. A-GW sang a hybrid song (upper) in which a series of DC phrases preceded the latter half of a CC phrase, but when it shifted to the centre of the CC song group it perfected the CC song (solid arrowed line) and preceded it by only one DC phrase . YR-AY settled alongside A-GW in 1971 and acquired the latter half of its hybrid song (dashed arrowed line) but after A-GW shifted YR-AY itself developed a standard CC song by cultural influence of A-GW's new song (dashed arrowed line) . in closely similar form, on Hen . Further, the same type of minor variability in which note components were repeated, omitted or altered in pitch were found . Three of the Cuvier Island patterns : SE, VPH and CC, were not found on Hen Island, but this may have arisen from inadequacy of sampling . Three other patterns were found which were not known from the Cuvier birds . Thus it seems clear that the birds which colonized Cuvier Island brought with them at least five of the nine song patterns : KS, ZZ, DC, PH and SR . The origin of the NE pattern from Hen Island is not certain .

Father/Son Song Relationship I had shown on Cuvier (i) that song groups existed with one or two of the original colonists in each and, (ii) that there was a strong tendency for new recruits to conform to the group's song pattern, but that (iii) variant forms did occur leading sometimes to the formation of a new song tradition . Consequently, I became very interested to discover whether the growth and persistence of each song tradition was due to the spatial coherence of a group of birds of common ancestry, or alternatively whether young birds moved away from their natal area before



67

JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

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68

ANIMAL BEHAVIOUR, 26,

developing their song patterns . The song groups proved to be so consistent from year to year and so coherent spatially that it seemed probable that the song development of a recruit could be predicted for any given site . To establish parentage of young males setting up territories I made an intensive effort to colourband offspring of already banded breeders . In the 1970 to 71 breeding season eight young of known parentage were banded from four families ; in 1971 to 72 five, distributed over three families and again in 1972 to 73, five distributed over three families, giving a total of 18 birds . Of these 11 birds were observed in subsequent seasons, five being males and six females . For song inheritance purposes, only the five male survivors were of interest. They were

1

Bands A-GB

Date Banded First observed singing November 1970 Nov. 1971 (still alive Feb . 1974) WR-A November 1970 Nov. 1971 (not seen later) WG-A January 1971 May 1973 (still alive Feb . 1974) R-A November 1971 May 1973 (still alive Feb. 1974) YA-Y January 1972 Nov . 1972 (at first site) Feb. 1974 (at new site and alive May 1974) Songs of Males of Known Parentage The details of songs sung by sons as compared to those of their fathers are given in Figs . 22, 23, 24, 25 and 26 . In each case the sons sang only the songs of their immediate territorial neighbours and normally the father was not

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Fig. 22 . Father/son song relationship . Father (AR-) sang DC and KS songs and its son (A-GB) sang SR, VPH, PH and NE songs .



JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

amongst the neighbouring birds . The one exception (YA-Y) Fig . 26 sang its father's song only after shifting its territory back to a position alongside the father. The observations show clearly that irrespective of the parental song young males when settling to breed perpetuate very exactly the existing dialect systems .

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Dispersal of Young Males The natal territory or the actual nest site (marked 0) for each of the five males of known parentage and the sites where they set up their own territories (marked S) are shown in Fig . 27 . Within the limits of the study area each son moved about as far away from its father as

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70

ANIMAL BEHAVIOUR, 26,

was possible, although one did return to its father's vicinity on his second shift. Further, except for this latter bird, each son settled in a song group other than its father's .

1

General Discussion Dialects in the Saddleback A number of authors have reported song dialects (Marler 1952, 1956 ; Thielcke 1961 ;

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71

JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

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Marler & Tamura (1962) found dialect delineation simple because their white-crowned sparrows each sang only one song and this differed slightly but consistently between areas a few kilometres apart. In repertoire species such as the chaffinch (Marler 1952) both the definition



72

ANIMAL BEHAVIOUR, 26, 1

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JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

and delineation of dialects are more difficult . He described a dialect as being `marked by the presence of some distinctive song in the repertoire of most males' . A third type of dialect is reported by Bertram (1970) and Harris & Lemon (1972) in which shared song elements within a population decrease steadily as sampling sites moved further away, until at distances ranging between 15 and 50 km no song components were held in common. Wiley (1971) reporting on the little hermit, a bird in which each individual has only one song, found distinguishable song groups of from two to seven birds within a larger assembly . He does not refer to their groupings as dialects . Grimes (1974) reported a similar kind of song variation on a small scale in the splendid sunbird . Consideration must now be given to what extent the overlapping song groups of saddlebacks fit these various dialectal concepts . For 4 years some individuals sang only one M .R .S . pattern, e .g . PH and CC areas were always quite large and the DC area increased towards the end of the field-work . However, to refer only to their areas as dialects would be a gross oversimplification of the data . Conversely, by strictly following Marler's concept of a dialect (a particular combination of song types), I would have to recognize each of the 24 observed combinations of songs as dialects (Table IV) . In 1970 to 71 (ignoring the incipient NE song) there were 11 such combinations : (SR-VPH), (CC), (CC-PH), (PH), (PH-KS), (KS-DC), (DC), (PH-ZZ), (ZZ), (ZZ-SE) and (SE) ; in 1971 to 72 and 1972 to 73 there were 21 and 19 in 1973 to 1974 . Such a classification seems to achieve little, although with the possible exception of Wiley (1971) the published accounts of dialects were not based on the songs of individually identifiable birds over a period of years . It is quite possible that, say, chaffinch song patterns may prove to be just as complexly distributed and on a much finer scale than hitherto suspected.

73

be possible to reduce the data to a form in which the underlying structure of the distribution of songs shows more clearly . First, the single representatives of song combination numbers 13, 16, 21, (Table IV) were such poor and infrequent singers that they contributed only feebly to the song environment . Secondly, in combination 5 the SR song was rarely used, so that these two birds were effectively part of the much larger PH-NE song group . For the same reason song groups 10 (KS rare) and 12 (CC rare) can be consolidated with the PH-NE group . Thirdly, the VPH/PH song differed only slightly from the standard PH pattern and finally some combinations were ephemeral . Thus there were effectively four large areas in which the predominant songs were (a) PH-NE, (b) CC-NE, (c) DC, (d) SE respectively . Each of these may be regarded as a dialect . A most remarkable aspect of the song groups was their spatial consistency . On only three occasions was a song recorded outside its song group area . Perhaps the most puzzling feature of the song groups is the failure of a neighbouring bird to copy its neighbour at all. At a given point in all the song group distributions a particular song was not imitated by the next bird and consequently the song groups retained their compactness and small size . No explanation can be offered for this limitation of learning, but without this inexplicable discontinuity the song group system would have disappeared and all

Predominant Song Patterns However, the full details of the song group data as presented in Figs . 8, 9, 10, 11, give a more confusing and complex impression of the song environment than that which I got from daily work in the field . Consequently, it should Fig . 26 . Father/son song relationship . The father (AY-) sang CC, PH and NE songs but the son (YA-Y) in its first season sang VPH and in its second season NE and PH when it moved to live alongside its father .

Fig. 27 . Dispersal of young males from natal areas to breeding territories . The circles represent the natal area and the dashed lines indicate where the sons set up territories . All territories (except YA-Y's second shift) were well outside the natal songlgroup .



74

ANIMAL BEHAVIOUR, 26, 1 Table IV. Seasons in which Dialectal Combinations Occurred Seasons Dialectal combinations 1 . VPH 2. * SR-VPH 3 . SR-VPH-NE 4 . SR-VPH-PH-NE 5 . SR-PH-NE 6. VPH/PH-NE 7.* PH 8. PH-NE 9. PH-KS 10. PH-KS-NE 11 . * PH-CC 12. PH-CC-NE 13 . PH-ZZ 14.* CC 15. CC-NE 16. CC-ZZ 17. DC 18. DC-KS 19. DC-KS-SE-ZZ 20. DC-ZZ 21 . DC-SE 22. ZZ 23 . ZZ-SE 24. SE

1970-71

1971-72

1972-73

1973-74

x x x X X

x x x x x x x

x x X X X X

x x x x x x X X X

x x x x x x x x x x x x x x x x x

x x x (x) x X

x x x x x x x x X

x x x

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x x X

x x x

11

21

21

19

NB. (x) This combination in 1973 to 74 was sung by the unbanded replacement of A-Y and was not precisely equivalent to VPH/PH. Entries marked with an asterisk are for 1970-71, i .e . before N.E . song spread through the western part of the island . The following entry shows the eventual and persisting combination including N .E .

patterns would have become general throughout the island. Cultural Transmission of Song Patterns In both the published accounts of family song tradition, Nicolai (1959) and Immelmann (1969), the birds were studied in aviaries . Nicolai crossfostered an 8-day-old bullfinch onto a canary mother . After fledging, the young bullfinch lived in a large aviary with other bullfinches and a male canary whose song it copied precisely . Later its own male offspring copied this song again, and so on, for 4 years . Nicolai considered that the fixation of the canary song in the early weeks of a bullfinch's life to be a case of imprinting and that the learning process was facilitated by an affectional bond between parent and young . Immelmann cross-fostered zebra finches onto Bengalese finch parents and reported that the zebra finches tended strongly to develop the songs of their foster-fathers, especially if fed by them, and despite being reared within earshot of conspecific males . The only published accounts of song behaviour being traced in the field are those of Nice

(1943) for song sparrows and of Kroodsma (1974) for the Bewick wren . Nice had 21 banded sons of banded fathers and two cases of grandsons but she found no male having the song of its father or grandfather . Unfortunately, Nice did not state where in relation to their fathers the sons took up territories . Song-sparrow song is so extremely variable, each male having a distinctive song, that she had no existing dialectal pattern into which the young birds had to become incorporated and consequently she could not predict a new recruit's song development . In the saddleback, I found spatially discrete song groups (Figs . 5, 6, 7) which each contained one or two of the original colonizers, and it seemed likely that the growth of the song groups had occurred by cultural transmission of song patterns from the group founders to subsequent island-bred recruits . This conclusion was reinforced by the discovery that where the groups abutted birds sang both patterns, and it is difficult to see how this could arise under a system of strong genetic control of song patterns .



JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

I could individually recognize virtually the whole population throughout the duration of the study, and consequently the entry of almost all recruits to the song groups was observed . Irrespective of whether the recruits intercalated between established pairs (Figs. 13, 14, 15), or whether they re-bonded with widowed females (Fig. 16), the songs they developed were consonant with the existing dialect system . Again, this only seemed possible if the acquisition of those songs was by cultural rather than genetic mechanisms . Thus there was a strongly developed and highly persistent dialectal system to which new recruits had been shown to conform closely at the time when they mated and set up territories . Although unlikely, it was still possible that song groups had arisen by coherence of a group of related birds whose songs were determined genetically, so the final step in the study was to trace the song development of sons of known fathers . The evidence from the five sons studied established conclusively that they do not derive their song patterns from their fathers either by imitation or by genetic inheritance (Figs . 22, 23, 24, 25, 26) but that they acquire them by cultural transmission from their territorial neighbours . Thus my results for the saddleback father/son relationship are opposite to those of both Nicolai and Immelmann in two important respects : they do not preferentially learn their father's song patterns and they do learn from neighbouring birds with whom they have no affectional bond . Indeed, their relationship with their models is one of competition for territorial space . Immelmann, however, considered that the relationship with a territorial rival was an `emotional' one, although his own work did not include study of birds in the territorial context . I consider important the evidence which indicates that conformity to the song-group pattern was actively maintained. This can be seen in the behaviour of : (i) birds which after setting up a territory shifted to a new song group and at the same time adjusted their song behaviour to match their new surroundings (Fig . 20) ; (ii) those birds which either swiftly or slowly and hesitantly `corrected' their mistakes in imitating their neighbours' songs ; (iii) birds which made slight modifications to long-established song patterns to match songs of newly arrived neighbours ; and (iv) `hybrid' song

75

patterns that simultaneously matched differing songs of different neighbours (Fig . 4(2)) . Song Ontogeny in the Saddleback The male rhythmical songs were heard only from paired territory-holding birds . In the early stages of the colonization of the island these birds were at least yearlings but later they were usually 2-year-olds . During their pre-territorial period they wandered freely about the study area and would have had ample opportunity to hear all the M .R .S . patterns . I consider it likely that during this period they acquired neuronal templates in perfect or semi-perfect form for all these song patterns so that when they set up territories they merely had to select from a range of alternatives the appropriate patterns that matched those of their prospective neighbours . That there is also sometimes a period of `fine tuning' is clear from the evidence of slightly imperfect songs being perfected over a period of time . Thus the sensitive period for song learning . which has been shown to be quite restricted in other species, (Thorpe 1958 ; Marler & Tamura 1934) is indeterminate in the saddleback . Further evidence in this direction comes from the behaviour of those birds which shifted after first becoming territorial and also from those that modified their songs late in life in response to the arrival of a neighbour with a different song . In this last category must be included the gradual but extensive spread of the NE song pattern. Many of the birds which acquired this song did so late in life, some being as much as 3 and 4 years old . The birds were all breeders and long established in their territories so that the length of the sensitive period for song learning in this species does not seem to be related to hormone levels as it does in the chaffinch (Nottebohm 1969) and indeed appears to last throughout its life . The conclusion that saddlebacks acquire their M .R.S . patterns by cultural transmission raises the question of whattpart genetic determination plays in the ontogeny of these songs . Although in my study the evidence clearly establishes that young male saddlebacks do not inherit a genome-dependent template for the development of the details of the M .R .S . patterns, nevertheless there does seem to be a number of underlying features of their loud songs which could be considered to be under more direct genetic control . These include the tonal quality, the pitch, the use of sustained



76

ANIMAL BEHAVIOUR, 26, 1

whistles, the relative rarity of frequency modulation, and a distinctive rhythmical quality, all of which are characteristic features of their songs and may well derive from the underlying genome-determined song template . By contrast, the fine detail of the M .R .S . category, appears to be achieved entirely by cultural transmission . I found no evidence at all that saddlebacks mimicked the songs of other species so the predisposition to learn only the species specific songs which has been observed in other species where song learning is important (Thorpe 1958 ; Immelmann 1969) occurs also in this species . The life-long site attachment behaviour of saddlebacks means that any male recruit must of necessity fit into a very static and continuing pattern of vocal behaviour. Usually this also includes pair-bonding to the already resident female with which the male regularly sings duets . The fact that young birds replacing dead males sang the same songs as the replaced birds suggests that a widowed female may bond preferentially with a new male if it is able to sing the same songs as its predecessor . A wandering unmated male may thus have better chances of finding a mate if it could select from an existing repertoire of song templates matching its prospective neighbours, and hence also those of the predecessor . Significance of Dialects Three ideas about the functions of dialects have been proposed. One possibility is that they have no significance in themselves but that they are merely an epiphenomenon of acquiring a song, but this does not explain why a genetically controlled song strategy should be abandoned during evolution for a learning strategy . Nottebohm (1972) argued the case for the phylogenetic progression from the more primitive genome-dependent strategy to the more open and auditory-dependent vocal ontogenies . Specifically in the saddleback the ephiphenomenon idea is untenable because of the extensive evidence for active maintenance of conformity to the dialect pattern by birds that shifted . A second proposal is that dialects may play a role in an assortative mating system, to restrict the flow of genes across the boundary of two dialect populations and so maintain their adaptations to local habitats (Nottebohm 1970) . Thirdly, Nottebohm (1975) also suggests that regional variations may reflect local adaptations

to the acoustic properties of the habitat . These latter two proposals refer to dialects observed on a large scale and cannot be compared profitably with the Cuvier Island situation . I propose that the dialects in the saddleback ensure outbreeding . The evidence for this is the dispersal behaviour of males of known parentage and subsequent known breeding site . (Fig . 27) . In each case males moved outside their parental dialect area to settle down, and I suggest that they were using the dialects as a reference system to avoid the risk of mating with close blood relatives . That such a mechanism should be necessary may arise from the extremely static nature of the saddleback social organization combined with its relatively long life . If this mechanism is operating as suggested it would be in opposite direction to that proposed by Nottebohm & Selander (1972) for dialects in the chingolo sparrow . However, I can see no reason why both ideas cannot be correct given the different social organization of the two species and the different scale of the two dialectal patterns . Nottebohm (1972) pointed out that the two known examples of filial tradition in song (zebra finches and bullfinches) also have permanent pair-bonds which would increase substantially the risk of excessive inbreeding . He also suggests that mating avoidance between close blood relatives derived from successive broods of permanently paired individuals could be based on shared vocal traditions acquired by father/son transmission . The saddleback pairbond is extremely stable and territorial occupancy is likewise permanent so that risks of inbreeding are considerable . I suggest that the same mating avoidance is achieved here, but by an almost opposite mechanism, that is preferential settlement of males in a dialect other than the parental one followed by acquisition of the local dialect by the recruit . Cultural Mutations The history of the development of the KS song group (Fig . 17) provides detailed field evidence of how the dialects evolved . New song forms have been shown to arise variously by change of pitch of a note, repetition of a note, the elision of notes and the combination of parts of other existing songs . Numerous other examples of such variations were recorded in other song groups . In all cases the nature of the preceding song being imperfectly copied was



JENKINS : CULTURAL TRANSMISSION OF BIRD SONG

well known over a period of years so that the new variant was immediately recogniseable . The appearance of the new form was an abrupt event and the product was quite stable over a period of years . Further, in a number of cases the variant was transmitted accurately in its new form to younger recruits so that a recognizably coherent group of like singers developed. For these reasons I propose to refer to the origin of these new song patterns that persisted in the population in typical form as cultural mutations . The speed with which the song configuration of the population can change and become fixed in new form as a result of cultural mutation greatly exceeds that arising from genetic mutation, and this may be the reason why this process has been selected for in a rapidly evolving group such as the passerines . Nottebohm (1972) discusses the advantages of auditory-dependent strategies of vocal ontogeny . The frequency with which cultural mutations in songs were observed to occur in this species was such as to ensure that song groups could not reach a very large size before undergoing fission into groups with variant songs . The effect of this would be over a period of years to retain a pattern of song group distribution on a rather fine scale . If male recruits do use the dialectal pattern to avoid breeding in their parental areas as proposed, then such a fine scale of dialects would clearly offer a very precise set of reference points to guide their avoidance behaviour. Acknowledgments For their assistance during field research, I thank Mr M . Douglas, A. Mouw, S . Winterbottom and I. McLean. I am especially grateful to C. R . Veitch for advice and assistance with capture and banding of the birds, to the New Zealand Wildlife Service for their help and to Alma and Barry Woolcott for their unfailing hospitality at the Cuvier Lighthouse . The Hauraki Gulf Maritime Park Board kindly gave permission to land and work on the Fauna and Flora Reserve . To my wife who typed the manuscript, and to Dr Fernando Nottebohm and Dr John Krebs both of whom kindly criticized an earlier draft, I express my gratitude . The study was partially supported by grants from the Auckland University Research Committee . REFERENCES Bertram, B . 1970. The vocal behaviour of the Indian hill mynah, Gracula religiosa . Anim. Behav. Mongr., 3,81-192 .

77

Blackburn, A. 1967 . A brief survey of Cuvier Island . Notornis, 14, 3-8 . Busnel, R . G. (ed .) 1963 . Acoustic Behaviour of Animals . Amsterdam : Elsevier . Fleming, C . A . 1964. Wattlebirds . In : A New Dictionary of Birds (Ed . by A . L . Thompson). New York : McGraw-Hill . Gompertz, T . 1961 . The vocabulary of the great tit . Br. Birds, 54, 369-418 . Grimes, L. G . 1974. Dialects and geographical variation in the song of the splendid sunbird, Nectarinia coccinigaster. Ibis, 116, 314-329. Harris, M . A . & Lemon, R . E . 1972. Songs of song sparrows (Melospiza melodia) : individual variation and dialects . Can . J. Zoo! ., 50, 301-309. Immelmann, K. 1969. Song development in the zebra finch and other estrildid finches . In Bird Vocalizations (Ed . by R. A . Hinde) . London : C .U.P. Isaac, D . & Marler, P. 1963 . Ordering of sequences of singing behaviour of mistle thrushes in relationship to timing. Anim. Behav ., 11, 179-188 . Kroodsma, D . E. 1971 . Song variations and singing behaviour in the rufous-sided towhee, Pipilo erythrophthalmus oregonus . Condor, 73, 303-308 . Kroodsma, D . E . 1974. Song learning, dialects and dispersal in the Bewick's Wren . Z. Tierpsychol., 35, 352-380 ., Lemon, R . E. 1966 . Geographic variation in the song of Cardinals . Can . J. Zool., 44, 413-428 . Lemon, R . E . 1967 . The response of Cardinals to songs of different dialects . Anim. Behav., 15, 538-545 . Lemon, R . E. & Harris, M. 1974. The question of dialects in the songs of white-throated sparrows . Can . J. Zoo!., 52, 83-98. Lemon, R . E . & Hertzog, A . 1969 . The vocal behaviour of cardinals and pyrrhuloxias in Texas . Condor, 71, 1-15 . Marler, P . 1952. Variation in the song of the chaffinch Fringilla coelebs . Ibis, 94, 458-472. Marler, P . 1956 . The voice of the Chaffinch and its function as a language . Ibis, 98, 231-261 . Marler, P . & Tamura, M. 1962 . Song `dialects' in three populations of white-crowned sparrows . Condor, 64,368-377 . Marler, P. & Tamura, M. 1964 . Culturally transmitted patterns of vocal behaviour in sparrows . Science, N.Y., 146, 1483-1486. Merton, D. V. 1965 . Transfer of saddlebacks from Hen Island to Middle Chicken Island, January 1964 . Notornis, 12, 213-222 . Mulligan, J. A . 1966. Singing behaviour and its development in the song sparrow, Melospiza melodia. Univ. Calif. Pubis Zool., 81, 1-76 . Nice, M . N. 1943 . Studies in the life history of the song sparrows. The behaviour of the song sparrow and other passerines . Trans. Linn. Soc ., N. Y., 6, 1-324. Nicolai, J . 1959. Familientradition in der Gesangsentwicklung des Gimpels (Pyrrhuia pyrrhula L.) . J. Ornithol ., 100, 39-46 . Nottebohm, F . 1969 . The song of the chingolo, Zonotrichia capensis, in Argentina : description and evaluation of a system of dialects. Condor, 71, 299-315 . Nottebohm, F . 1970 . Ontogeny of bird song . Science, N.Y., 167, 950-956. Nottebohm, F . 1972 . The origins of vocal learning . Am. Nat., 106, 116-140. Nottebohm, F . 1975 . Continental patterns of song variability in Zonotrichia capensis: some possible ecological correlates . Am . Nat., 109, 605-624.



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Nottebohm, F . & Selander, R. K . 1972. Vocal dialects and gene frequencies in the chingolo sparrow (Zonotrichia capensis) . Condor, 74, 137-143 . Oliver, W. R. B . 1945 . New Zealand Birds. Wellington : A . H . & A. W . Reed. Snow, D . W . 1968 . Singing assemblies of little hermits . Living Bird, 7, 47-55 . Thielcke, G . 1961 . Stammesgeschichte and geographische Variation des Gesanges unserer BaumlAufer

(Certhia familiaris L. and Certhia brachydactyla Brehm) . Z. Tierpsychol., 18,188-204 . Thorpe, W . H . 1958 . The learning of song patterns by birds, with especial reference to the song of the chaffinch, Fringilla coelebs. Ibis, 100, 535-570. Wiley, R. H. 1971 . Song groups in a singing assembly of little hermits . Condor, 73, 28-35 . (Received 2 March 1976 ; revised 20 December 1976 ; MS. number : 1512)