Communication in prairie grouse

BEHAVIORAL AND NEURAL BIOLOGY 32,

463-486 (1981)

Communication in Prairie Grouse I. Information Content and Intraspecific Functions of Principal Vocalizations DONALD W.

S P A R L I N G 1"2

Department of Biology, University of North Dakota, Grand Forks, North Dakota 58202 Avian vocalizations contain information which can be used by conspecifics to predict subsequent actions of emitters in the process of communication. This study examines information in the calls of greater prairie chickens (Tympanuchus cupido) and sharp-tailed grouse (Pedioecetes phasianellus) by determining when calls are given and their associations with other marker behaviors. Reactions to these calls and their probable functions are determined through playback experiments. Prairie chicken booms contain information about sex, territorial status, mating condition, location, and individual identity of the signaler. They function in long-range advertisement and courtship and thus are similar to songs of passerines. Whoops and stamps are primarily epigamic, cackles are agonistic, and whines denote ambivalent intentions. Sharptail dancing, cork notes and chilks are principally epigamic; whines, cackles and gobbles are agonistic and coos are medium range advertisers. Prairie chicken males responded to playbacks of booms, whoops, whines, and composite calls (a series of sounds made by males when a female visited a display ground). Sharptails significantly reacted to playbacks of coos, chilks, cackles, cork notes, gobbles, and dancing. In general, prairie grouse vocalizations contain similar types of information as the songs of passerines but the information in each call is more discrete. T h e p u r p o s e of this s t u d y is to d e t e r m i n e i n f o r m a t i o n c o n t e n t a n d f u n c t i o n s of p r i m a r y v o c a l i z a t i o n s in g r e a t e r prairie c h i c k e n s (Tympanuchus cupido) a n d s h a r p - t a i l e d g r o u s e (Pedioecetes phasianellus). M a r l e r (1957) r e c o g n i z e d t h a t a v i a n v o c a l i z a t i o n s c o n t a i n specific t y p e s of inf o r m a t i o n w h i c h c a n b e p o t e n t i a l l y t r a n s m i t t e d to c o n s p e c i f i c s . F o r exa m p l e , M a r l e r s t a t e d that s o n g s of m o s t species c o n t a i n i n f o r m a t i o n Present address: Department of Biology, Ball State University, Muncie, Ind. 47306. 2 This and the accompanying paper were part of a dissertation in partial fulfillment of my doctoral degree at the University of North Dakota. Earlier drafts of this dissertation were critiqued by L. Oring, P. Kannowski, R. Seabloom, M. Wali, and G. Halas; L. Oring was major advisor. Financial support was provided by the National Geographic Society, Grand Forks Chapter of the North Dakota Wildlife Federation, Norman Pankratz Conservation Fund and Department of Biology, University of North Dakota. Special thanks to C. Steinhauer, W. D. Svedarsky, and P. Spading for their logistical and moral support. 463 0163-1047/81/080463-24502.00/0 Copyright © 1981 by Academic Press, Inc. All rights of reproduction in any form reserved.

464

DONALD W. SPARLING

concerning sex, individual identity, species, location, marital status, and motivational state of the emitter. Smith (1968) emphasized the relationship between motivational state or message of a signal and its resulting meaning or effect on recipients. As Smith (1970, 1977) demonstrated, messages are relatively consistent through time but meanings vary with context. Morris (1946) and Cherry (1957) distinguished semantics, syntatics, and pragmatics which deal with relations between signals and their referents, each other, and their consequences, respectively. Hailman (1977) elaborated on this trichotomy and provided several examples of its application to optical signals. Although each of these researchers approached the study of animal communication from different perspectives, they all seemed to agree that communication occurs when one organism produces a stimulus with sufficient contextual and structural reliability to enable recipients to predict subsequent actions of the emitter and to act accordingly. Any long-term advantage of such a system such as mate attraction or resource defense can be described as the function of that signal. A study of prairie chicken and sharptail communication is valuable for several reasons. First, most studies on avian vocal communication have been on passerines and relatively few experiments have dealt with nonpasserines, including galliforms. Displays of prairie grouse have been described by Hamerstrom and Hamerstrom (1960), Lumsden (1965), and Hjorth (1970), but only Kermott and Oring (1975) quantified sharptail responses to playback experiments. The only other experimental studies of grouse communication were on blue grouse (Dendragapus obscurus) (Falls & McNicholl, 1979) and hazel grouse (Tetrastes or Bonasa bonasia) (Bergmann, Klaus, Muller, & Weisner, 1974). Second, prairie chickens and sharptails are closely related, probably congeneric species (Short, 1967) with similar ecological requirements and mating behaviors (i.e., highly developed polygyny or promiscuity and communal displaying by males). A comparative study of communication can help determine how species respond to such conditions. Finally, the two species are sympatric over much of their range and hybridize wherever sympatry occurs (Johnsgard & Wood, 1968). In these areas communication appears to be very important in maintaining hybridization at a low level. Responses to conspecific playbacks can be compared to interspecific responses to the same calls (Sparling, 1981, accompanying paper). METHODS

Observations Observations were made from blinds located on display ground peripheries through the 1975-1978 mating seasons. All display grounds in 1975-1977 were located in northwestern Minnesota but one sharptail ground in eastern North Dakota (ca. 80 km west of the study area) was

INFORMATION IN PRAIRIE GROUSE CALLS

465

studied in 1978. Two or three focal display grounds were visited on a rotating basis so that prairie chicken, sharptail, and mixed grounds could be observed. Each ground was visited one to three times per week. Display grounds held 5-25 prairie chickens and/or 4-30 sharptails each year. Observation methods included 5-min activity samples of focal animals (Altmann, 1975) collected every 20 rain throughout the 1975 and 1976 seasons and 15- to 60-rain samples collected in 1977. Focal animals were sampled so as to maximize the number of individuals recorded in a day. A few individuals may have had proportionately more samples across a season. These birds usually held central territories and had significantly higher mating success. Fifteen different prairie chicken and 18 sharptail behaviors were identified and recorded during these periods.

Playback Experiments Sounds used for playbacks were recorded with a Uher 4000 ReportL tape recorder at 19 cm/sec and Uher 516 directional and Sennheiser 804 ultra-unidirectional microphones. Playback amplitudes were standardized at 95 dbA, slow needle response, with a General Radio 1595A sound level meter held 1 m from a speaker. They were played with a Uher tape recorder through Nagra DH speaker-amplifiers. Two speakers were usually used on different parts of a display ground to reduce risk of habituation. Experiments consisted of three 3-rain contiguous periods of preplayback, playback, and postplayback. All behaviors of a subject male were recorded during these periods. Because several vocalizations were tested, playback order was randomized for each male and at least 10 min separated successive trials. Possible habituation during a series of playbacks was checked by replaying a call that had elicited obvious responses from a subject; there were no noticeable differences between first and second responses in any of these checks. Playbacks were conducted when males were quiet and females were absent. Prairie chicken playbacks included booms, stamps, whoops, cackles, whines, and composite sounds. Sharptail sounds included coos, gobbles, cackles, two types of dancing (with 5 and 20 chilks/min, respectively), whines, chilks, cork notes, and composite calling (see Hjorth, 1970, and Sparling, 1979a, for descriptions and sonograms of these calls). Composite calling in each species included epigamic sounds made on a display ground when females were present. They consisted of a continuous string of booms, whoops, whines, and cackles from prairie chickens; and dancing, cork notes, and chilks from sharptails. Six prairie chickens were individually banded, two were the only prairie chickens on a mixed ground, and the rest (zero to five depending on test) had distinctive markings (see Hamerstrom & Hamerstrom, 1973,

466

DONALD W. SPARLING

for examples of these marks) and stable territories. Nine sharptails were banded, one limped, and the rest (zero to eight) had distinctive markings and stable territories. There was little possibility that one or two birds may have been tested twice with the same call.

Data Analysis To help determine relationships among vocalizations and other behaviors, all prairie chicken and sharptail behaviors were entered into transition matrices in which preceeding acts were recorded by rows and following acts by columns. Each species' matrix was correlated by columns. In all, 12,363 prairie chicken and 7255 sharptail acts were entered into the matrices. Resulting correlation matrices were then subjected to cluster analysis using the unweighted pair-group arithmetic averaging procedure (UPGMA, Sneath& Sokal, 1973). This method is based on linking variables (in this case, behaviors) that share the greatest similarities (i.e., are highly correlated). Similarities are measured as cophenetic values, a multivariate analog of correlation coefficients. New variables are added to existing clusters based on the average similarities between the new variable and existing members of the cluster. Once all behaviors have been linked a pictoral representation or dendrogram is created that shows relationships among behaviors. In effect, similarities decrease as behaviors are linked from right to left. True relationships among many highly correlated variables can be distorted due to constraints imposed by a two-dimensional dendrogram. For example, if behaviors 1, 2, and 3 were equally similar to 4 but differed among themselves, a three-dimensional figure would be needed to adequately show relationships among these behaviors. This distortion increases from right to left on the dendrograms. Cophenetic correlation values (Sheath & Sokal, 1973), which are formed by correlating the original correlation matrix with the matrix of cophenetic values, estimate this distortion; high values (arbitrarily > .80) indicate low distortion. Further discussions of cluster analysis in ethological research are in Morgan, Simpson, Hanby, and Hall-Craggs (1976), Aspey and Blankenship (1977), and de Ghett (1978). To evaluate the effects of playback experiments, responses of subject males were compared to behavioral indices (Table 1) similar in concept to that developed by Emlen (1972) for indigo buntings (Passerina cyanea). Indices for each grouse species were computed from mean activity rates taken from all of the 5-min samples. A score of " 0 " for an activity index category meant that the bird gave less than half the mean number of acts during that period. A score of " 1 " represented between 0.5 and 1.5 times the mean and " 2 " meant that more than 1.5 times the mean number of acts were given. Theoretically, each bird could score a maximum of 14 points for a period but maxima were not obtained because

INFORMATION IN PRAIRIE GROUSE CALLS

467

TABLE 1 Behavioral Indices Used in Evaluating Prairie Grouse Responses to Playback Experiments Score

Prairie chicken

Sharptail

Rate of booms" (per min) 0<~N~<2.0 2.0 ~< N ~ < 6.3 N>6.3

Rate of coos (per min) 0~3.7

2

Rate of whines (per rain) 0~ 12.5

Rate of gobbles (per min) 0~ 3.0

0

0~
1

0.6 < N ~ <

2

N > 1.7

0 1 2

Minimum distance from speaker (m) Distance t> 10 Distance >I l0 3 > distance ~< 10 3 > distance < l0 3 ~< distance 3 <~ distance

0 1 2

No alert responses Semialert posture Upright alert

0 1

2 0 1

Agonistic behavior* (acts/rain) O<~N<~0.5

1.7

0.5 < N ~ <

1.6

N > 1.6

Alertness No alert response Semialert posture Upright alert

Orientation toward speaker No apparent orientation No apparent orientation Looks toward speaker Looks toward speaker Approaches speaker Approaches speaker Courtship No courtship behavior N > 5 stamping bouts/rain Frequent whoops and stamping

behavior No courtship behavior N > 3 dances/rain Frequent dances plus chilks or cork notes

Booms, whines, gobbles, and coos are specific for a species, the other criteria are for both species. b Agonistic behavior is the total of face offs, stand offs, fights, forward rushes, and running parallels. s o m e b e h a v i o r a l c a t e g o r i e s s e l d o m o c c u r r e d together. B e h a v i o r a l scores w e r e t e s t e d a m o n g p e r i o d s of e a c h call with F r i e d m a n t w o - w a y a n d K r u s k a l - W a l l i s o n e - w a y a n a l y s e s of v a r i a n c e u n d e r the null h y p o t h e s i s that there were n o differences in scores a m o n g periods. The K r u s k a l - W a l l i s test is less a p p r o p r i a t e t h a n the F r i e d m a n test for r e l a t e d s a m p l e s (Siegel, 1956) b u t w a s u s u a l l y a c o n s e r v a t i v e c h e c k o n statistical significance. T o help d i s t i n g u i s h specific r e s p o n s e s to p l a y b a c k s a n d to f u r t h e r d i s c r i m i n a t e p e r i o d s , d i s c r i m i n a n t f u n c t i o n a n a l y s i s (Nie, Hull, J e n k i n s ,

468

DONALD W. SPARLING

Steinbrenner, & Bent, 1975) was employed with all behaviors serving as predictors. The first step in discriminant analysis is a stepwise procedure which selectively adds independent variables (behaviors) to a discriminant model based on a decreasing ability to separate periods. At each step an F test tests if a significant additional separation of periods has occurred. Also given is a value for Wilk's h, an inverse measure of group discrimination. The lower the value of Wilk's h, the greater is the resolution of groups. After stepwise analysis is completed and all significant independent variables have been added, discriminant analysis enters a classification stage. In this process data are restructured into discriminant functions. Each case is assigned coefficients on each of the significant functions. These coefficients are comparable to "loadings" in factor analysis. Mean values of these coefficients for each dependent variable (period) constitute group centroids. Canonical discriminant function coefficients are computed for the independent variables and can be compared to group centroids. If centroids and canonical coefficients have similar values on the discriminant functions, they can be interpreted as being related to each other. In this study, such a relationship is viewed as a response to a particular experimental period. Finally, the SPSS version of discriminant analysis presents a summary table showing the number of existing cases which were correctly or incorrectly classified with the discriminant model (a correctly classified case is one whose predicted and actual period were the same). These tables are omitted in this paper, however, to conserve space. Data did not always fit a multivariate normal distribution which is an assumption of discriminant analysis, and results should be interpreted cautiously. Only those tests which found at least one significant independent variable, generated a significant discriminant function, and significantly separated playback periods from one of the Other two periods are considered in this study. Further discussion of discriminant function analysis is in Pimentel and Frey (1978) and Sparling and Williams (1978). RESULTS Contextual Occurrence

Types of information present in a signal and its probable function(s) can be determined by identifying when it occurs and which birds are most apt to give it. The occurrence of a signal can be compared to the daily and seasonal patterns of a species' activities and to occurrence of prespecified "marker" or functionally unambiguous behaviors. In prairie grouse (i.e., prairie chickens and sharptails collectively), for example, daily occurrence of vocalizations can be compared to general levels of male activity. Early mornings (arrival to a ½ hr after arrival) were characterized by high levels of epigamic behaviors, greatest probability of

INFORMATION IN PRAIRIE GROUSE CALLS

469

visitation by females, and reaffirmation of territories. Midmornings were distinguished by decreases in courtship and slight increases in agonistic behavior associated with territorial maintenance. Activity during late morning (starting a ½ hr before departure of males) was greatly reduced and consisted primarily of feeding, preening, and some low-level territorial maintenance. Seasonal occurrence of vocalizations can be compared to three arbitrary divisions characterized by territory establishment (Weeks 1-4 of mating seasons), peak periods of female visitations (Weeks 5-11) and postmating (Weeks 12-13+). Marker behaviors in prairie grouse included agonistic overt fighting, face offs, running parallels and stand offs; epigamic dancing, stamping and flutter jumps; and comfort behaviors (see Hjorth, 1970, for descriptions of these behaviors). Comfort behaviors (e.g. preening, feeding) were essentially noncommunicatory activities and should not correlate with any vocalization. Daily rates of prairie chicken behaviors collected through the mating season (Table 2) indicated that whoops, flutter jumps, stamps, and booms were epigamic. These behaviors occurred far more frequently when hens were present and in early morning periods when hens were most likely to visit than at other times. Forward rushes were frequently directed at females as they entered a male's territory, and at other intruders, as indicated by their rises during hen visitations and in early morning, respectively. Overt fighting was common when females were present but other forms of ritualized agonistic behavior such as face offs, whines, and cackles replaced fighting during the rest of the day. Seasonal rates of prairie chicken behaviors (Fig. 1) support interpretations of daily activity rates. Whoops and stamps were most frequent during Weeks 5 and 7 when many females visited the display grounds. Whines were common throughout the mating season but tended to decrease slightly when females were present. Booms were relatively constant throughout the season but increased during peaks of hen visitations. Cackles varied unpredictably through the season. As was expected, behaviors which occurred together were also closely linked in cluster analysis (Fig; 2). The top cluster (face off to cackle) was composed of agonistic displays. The next cluster (forward to run parallel) contained a closely associated group of behaviors which occurred in epigamic contexts (forward rush to whoop) and two agonistic behaviors which were only loosely associated with the principal cluster. Walk, alert, and comfort were maintenance or alarm behaviors and were not associated with any communicatory display. Whines and booms were not associated with any cluster, probably due to their ubiquitous occurrence. Booms, however, significantly correlated with whoops (r(14) = .946, p < .01) and stamps (r(14) = .503, p < .05) and were directly involved in epigamic contexts. Whines did not correlate with any other behavior and more intensive examination was necessary

X SE J? SE .~ SE X SE

0.19 0.06 0.18 0.07 0.25 0.04 0.11 0.05

0.69 0.16 0.18 0.07 0.22 0.41 0.03 0.02

Forward rush 11.83 0.88 8.21 0.88 2.69 0.31 0.91 0.30

Boom** 11.29 1.25 5.84 0.97 1.07 0.22 0.33 0.17

Stamp** 5.96 1.75 1.44 0.49 0.32 0.09 0.04 0.03

Whoop** 8.83 2.13 14.57 2.60 9.11 1.23 2.44 1.00

Whine** 2.06 0.61 2.56 0.47 1.03 0.21 0.36 0.16

Cackle* 1.02 0.32 0.85 0.24 0.11 0.04 0.01 0.01

Flutter jump**

1.54 0.95 0.07 0.04 0.10 0.03 0.01 0.01

Fight

0.00 0.00 0.22 0.11 1.13 0.11 1.53 0.18

Comfort**

.05.

** p < .01 for interperiod comparisons, one-way analysis of variance;

* p <

df = 3, 272 for all tests.

a Samples from this period were recorded when conspecific hens were present on a lek. They occurred at the same time of day as early morning periods. b Sample sizes (N) refer to number of samples taken.

Hen visiting" (N = 21)b Early morning (N = 18) Midmorning (N = 102) Late morning (N = 35)

Face off

Acts per minute

TABLE 2 Rates of Common Prairie Chicken Behaviors when Hens Are Present and through Mornings

Z

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f~

~7

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4~

INFORMATION IN PRAIRIE GROUSE CALLS

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471

1.8 B 1.2

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9

2.11.4-

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I

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1

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12 10 12 21 15 14 17 3 7 16

Fl6. 1. Mean display rates (acts/rain) by prairie chicken males (A-E) for most commonly occurring behaviors and number of females visiting booming grounds (F) by week during the 1976 mating season. Data come from 5-rain focal animal sampling periods and are very similar to other years of the study. Sample size (N) is the number of samples collected. (A) Whoops, (B) stamps, (C) whines, (D) booms, (E) cackles, (F) number of hens visiting by week. Note scale differences when comparing rates.

to determine similarities among contexts containing this vocalization (see below). Daily rates of sharptail behaviors (Table 3) indicated that forward rushes, dancing, chilks, and cork notes occurred most frequently when hens were present or likely to visit. Cackles also occurred most often when hens were present but increased from early to midmorning if females were not present while the other displays steadily decreased through the morning. Coos were greatest in mid- and early mornings when no females were present. The remaining behaviors did not vary significantly through mornings. Weekly peaks of sharptail dancing, chilks, and cork notes coincided with major hen visitation periods (Fig. 3). Cackles were infrequent relative to some of the other behaviors and were most common in the middle of the mating season. Whines and coos were given more frequently than cackles but followed similar patterns. Gobbles peaked in

472

DONALD W. SPARLING

Face Off ~ " Fight Stared

Off

Cockle Forword

Value 0.95 0.93 0.78 02T 0.91

Forward Rush 0.97 I ~ itilmli dump

.... I

Run Parallel Walk

0.39 0.94

Alert

0.86

C,omfor t

I

0.95 099 0.81

Whine

O.I 5 -O.I

I

Boom -0.03

I

0.12

I

0,27

r

0.4.2

i

0.57

I

0.72

0.87

I

I.O0

Cophenetic Value FIG. 2.

Cluster of prairie chicken activities. Cophenetic correlation = .86.

early season when overt aggression was greatest and declined through the remainder of the season. Cluster analysis of sharptail behaviors resulted in five loosely associated groups (Fig. 4). The first two groups (face off to run parallel and stand off to cackle) were composed of agonistic behaviors. The third cluster (forward rush to cork) was composed of behaviors that were primarily involved in epigamic contexts. The principal courtship displays--chilks, cork notes, and dancing--were closely linked in this cluster. The fourth cluster (forward to comfort) were principally maintenance behaviors while the last group was formed by loosely associated gobbles and coos. Coos were probably associated with agonistic behaviors for they correlated significantly with run parallel (r(17) = .485, p < .05) and gobbles (r(17) = .597, p < .05). These marginally significant correlations might be spurious, however, because of the many individual correlations in these analyses.

Prairie Chicken Playbacks Prairie chickens responded significantly to booms, whoops, composite calling, and marginally to whines (Table 4). In each case playback periods (period 2) had mean scores higher than those of either pre- (period 1) or postplayback (period 3). Composite calling may have elicited the strongest responses because differences among mean scores of playback and other periods were greatest for this recording. Detailed responses of prairie chickens are in Fig. 5 and Table 5. Booms elicited weak responses because most activities except alert decreased

3( SE X SE X SE X SE

1.43 0.68 3.98 0.98 1.38 0.27 1.67 0.52

Gobbles

1.05 0.17 0.46 0.12 0.59 0.08 0.58 0.12

Face off 0.29 0.09 0.21 0.07 0,15 0.04 0.05 0.03

Forward rush* 1.78 0.79 3.74 1.04 2.62 0.49 1.21 0.36

Coo* 4.33 0.53 1.18 0.51 0.21 0.06 0.10 0.05

Dancing** 13.52 2.59 1.19 0.44 0.23 0.10 0.04 0.04

Chilk** 9.29 1.46 1.20 0.67 0.37 0.16 0.00 0.00

Cork notes** 1.30 0.43 0.89 0.50 0.68 0.22 0.66 0.35

Whines

0.43 0,14 0.0! 0.01 0.11 0.04 0.06 0.03

Cackles**

0.19 0.11 0.21 0.09 0.07 0.03 0.06 0.03

Fight

0.24 0.09 2.30 0.77 2.90 0.50 3.72 1.00

Comfort**

.05.

** p < .01 for interperiod comparisons, one-way analysis of variance,

* p <

df = 3, 179 for all tests.

a Samples from this period were recorded when conspecific hens were present on a lek. They occurred at the same time of day as early morning periods. b Samples sizes (N) refer to number of samples taken,

Hen visiting" (N = 24)b Early morning (N = 25) Midmorning (N = 90) Late morning (N = 44)

Context

Acts per minute

TABLE 3 Rates of Common Sharptail Behaviors when Hens Are Present and through Mornings

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DONALD W. SPARLING A

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G

H

7.2- - 1 2 4.82.4-

I II 1

5

10

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I II

I I

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N

4 3 3

8 14 8 12 3 13 1020 15 3

F]c. 3. Mean display rates (acts/min) by sharptail males (A-G) for most commonly occurring behaviors and number of females visiting dancing grounds (H) by week during the 1976 mating season. Data come from 5-rain focal animal sampling periods and are very similar to other years of the study. (A) chilks, (B) dance, (C) cackles, (D) cork notes, (E) whines, (F) coos, (G) gobbles, (H) number of hens visiting by week. Sample size (N) is the number of samples collected. Note scale differences when comparing rates.

b e t w e e n periods 1 and 2. Stepwise discriminant analysis selected alert, cackles, w h o o p s , and fight as behaviors important in discriminating periods. P r e p l a y b a c k was separated f r o m p l a y b a c k primarily by having f e w e r cackles and m o r e whoops. Success of discriminant analysis classification was low with 17% of the cases in periods 1 and 2 misclassified as belonging to the opposite period and 37% o f the cases in periods l and 3 similarly switched• A high degree of misclassifications b e t w e e n pre- and p o s t p l a y b a c k periods indicated that birds quickly reverted to their initial activities after playbacks• In contrast, good discrimination o f periods 1 and 3 would suggest that p l a y b a c k effects were longer lasting.

475

I N F O R M A T I O N IN P R A I R I E G R O U S E CALLS

F(~ce Oil

J - F

I :

Run Parallel

027

Stand Off

093

Fight

099

Whine

086

Cackle

002

Forward Rush

046

Flutter Jump

0.70

Dance

O91

Chilk

099

Cork

-OOt

Forw~lrd

l -0.03

0.12

FxG. 4.

o.~'7

0.42

0.ST

Cophenetic Value

Value 076

088

Walk

0.96

Alert

0.95

Cluck

0.65

Comfort

021

Gobble

059

Coo

0)2

O,B7

Cluster analysis of sharptail activities. Cophenetic correlation = .87.

Playbacks of whines elicited additional whines and alert responses during playback and booms in postplayback. No significant discriminant functions were extracted for this call but stepwise analysis suggested that whines, booms, whoops, face offs, and fights were useful in discriminating periods. Composite sounds elicited booms, whoops, stamps, and alert responses but discriminant analysis only selected approach and alert behaviors. Preplayback periods had fewer alert and approach responses than playback periods. No cases in periods 1 and 2 were switched but 31% of the cases between periods I and 3 and 25% of those between periods 2 and 3 were interchanged. Thus birds appeared to alter their behaviors during playback but reverted to their original activities during postplayback. Responses to playbacks of whoops included increased whines and alert behaviors; birds appeared to decrease booming during postplaybacks. Although no significant discriminant functions were extracted for this call, five behaviors may be indicative of additional responses (see Table

5).

Sharptail Playbacks Significant differences in sharptail responses were elicited by coos, cackles, gobbles, chilks, cork notes, and low-chilk dancing (Table 4). In

476

DONALD W. SPARLING TABLE 4 Mean Behavioral Index Scores of Male Prairie Grouse Responses to Conspecific Playbacks Dur

Post

X,2"

Call

N

Pre

Boom Whine Composite

13 8 8

A. Responses of prairie chickens 2.46 2.92 2.08 26.79 2.12 3.50 2.62 6.63 1.12 5.00 3.00 10.19

p

Ha

p

.001 .05 .005

20.64 2.72 9.98

.001 n.s. 0.01 n.s.

Stamps

6

2.33

2.67

2.17

1.08

n.s.

.25

Cackle Whoop

8 6

2.75 1.00

3.62 3.50

3.12 1.50

3.05 8.00

n.s. .06

.00 5.62

.05

Coo Cackle Chilk Cork notes

18 9 10 6

2.17 2.44 2.30 1.67

B. Responses of sharptails 4.11 2.11 12.11 2,11 1.44 6.78 3.69 1.90 8.75 4.50 2.50 8.08

.01 .05 .02 .03

12.15 7.58 7.01 6.79

.01 .02 .05 .05

Composite Gobble

9 10

1.55 1.70

n.s. .01

4.25 7.79

n.s.

n.s.

3.78 4.70

2.22 3.10

4.22 12.60

.05 n.s.

Whine Dance

9 11

1.33 4.36

2.55 5.83

1.55 3.91

2.67 6.04

n.s. .05

1.73 7.60

.O5 n.s.

Dance-chilk

12

3.58

4.42

3.25

2.17

n.s.

5.67

X 2 = Friedman two-way ANOVA statistic, df = N - 1 for each test. H = Kruskall-Wallis one-way ANOVA statistic; df = N - 1 for each test.

55(c°~po~iN=8 'e' t~ ~

1.5

4,5

a

Responses

b

Responses

FIG. 5. Detailed responses of prairie chicken males to playbacks of conspecific sounds. Values include means (center bar) and one standard error. In each group the first line represents preplayback, the second--playback, and the third--postplayback.

477

INFORMATION IN PRAIRIE GROUSE CALLS

TABLE 5 Results of Stepwise Discriminant Analysis on Significant Prairie Chicken Playback Experiments

Playback Composite Booms

Whoops b

Whines b

Step 1 2 1 2 3 4 1 2 3 4 5 1 2 3 4

Variable entered Alert Approach Alert Cackle Whoop Fight Alert Fight Booms Face off Whine Whine Booms Whoop Face off

Wilk's k

df

p

Separates periods"

.638 .431 .722 .617 .567 .529 .796 .723 .636 .562 .493 .751 .649 .585 .499

2,21 2,21 2,36 2,36 2,36 2,36 2,15 2,15 2,15 2,15 2,15 2,21 2,21 2,21 2,21

.009 .002 .002 .001 .001 .002 .09t .156 .171 .190 .204 209 .196 .099 .096

1-2,3 1,2-3 1,3-2 1-2,3 1-2,3 1-2,3 1,3-2 1,2-3 1,2-3 1,2-3 1,3-2 1,3-2 1,2-3 1,2-3 1,2-3

Period separation is based on comparing standardized canonical discriminant function coefficients and group centroids; commas link similar periods and hyphens separate unlike periods. b Analyses of whoop and whine playbacks failed to extract significant discriminant functions.

comparison to other periods, playback sessions had the highest mean scores in every case except cackles. Gobbles and cork notes appeared to elicit stronger responses compared to the other calls. Detailed responses of sharptails to conspecific playbacks are shown in Fig. 6 and Table 6. Playbacks of coos significantly increased the rate of cooing and gobbling and slightly depressed chilks and face offs. Of the variables selected by discriminant analysis, fewer alert responses and coos and more stand offs and comfort behaviors occurred in period 1 than in period 2. Eight percent of the cases in periods 1 and 2 were cross-classified as were 25% of the cases between periods 1 and 3. Chilks increased coos and alert behaviors and decreased chilks during playback periods. Discriminant analysis selected alert, chilks, cork notes, and comfort behaviors as being important. Preplayback periods were most clearly separated from playback sessions by having fewer alert behaviors and more chilks. Fifteen percent of the cases in periods 1 and 2 were switched as were 15% between 1 and 3 and 5% between 2 and 3. Thus playbacks of chilks may have a lingering effect on sharptail activities. Playbacks of cackles decreased most activities except alert. With discriminant analysis alert, cackles and fights were important in group sep-

478

D O N A L D W. S P A R L I N G

6.5

Cork Note,

N=6

4,e

2.5 2,i l~t

Chill N=IO

hO~

Cockle, N=9

o

,3

~ ,s

~

0.5

t

-

,5

8

®

,,'?

o

Responses

o

o =: ,j

"7

=

<

~,

Y.

Responses

a~ 25

it~ t~ ~..... ,hFewc.,.N=.

o C

o

~

Responses

F I G . 6. Detailed responses of sharptail males to playbacks of conspecific sounds. Lines as in F i g . 5.

aration. Playback periods had the highest level of alert behaviors and cackles and the lowest level of fights. Only 5% of the cases in periods 1 and 2 were interchanged but 45% of the cases between 1 and 3 were switched. Apparently the overt effects of cackle playbacks were of brief duration. Responses to cork notes included elevated rates of coos, gobbles, and alert behaviors. Alert, comfort, stand off, approach, gobble, and fight were also found to be significant in discriminant analyses with periods 1 and 2 separated primarily by alert and comfort behaviors. No cases between preplayback and playback were interchanged but 14% of the cases between periods 1 and 3 and 2 and 3 were cross-classified. In at least some cases, therefore, playbacks of cork notes appeared to alter the behavior of males even during postplayback.

479

INFORMATION IN PRAIRIE GROUSE CALLS TABLE 6 Results of Stepwise Discriminant Analysis on Significant Sharptail Playback Experiments

Playback Coo

Chilk

Cackle

Cork notes

Gobbles

Low-chilk dancing

High-chilk dancing

Step

Variable entered

Wilk's k

df

1 2 3 4 1 2 3 4 1 2 3 1 2 3 4 5 6 1 2 3 1 2 3 4 1 2 3 4 5 6 7

Alert Comfort Stand off Coo Alert Chilk Cork notes Comfort Alert Cackle Fight Alert Comfort Stand off Approach Gobble Fight Approach Cackle Alert Alert Comfort Whine Stand off Alert Stand off Cork notes Comfort Gobble Fight Dance

.810 .712 .643 .582 .443 .380 .337 .292 .603 .535 .458 .496 .272 .200 .155 .118 .099 .738 .480 .356 .789 .612 .517 .427 .859 .666 .546 .477 .416 .373 .338

2,51 2,51 2,51 2,51 2,27 2,27 2,27 2,27 2,30 2,30 2,30 2,18 2,18 2,18 2,18 2,18 2,18 2,24 2,24 2,24 2,30 2,30 2,30 2,30 2,30 2,30 2,30 2,30 2,30 2,30 2,30

p .005 .002 .001 .001 .000 b .000 .000 .000 .001 .001 .001 .002 .000 .000 .000 .000 .000 .026 .002 .001 .029 .006 .004 .002 .002 .018 .007 .007 .006 .008 .003

Sparates periods ° 1-2,3 1,3-2 1-2,3 1-2,3 1-2-3 1-3 1-2-3 l-3 1,3-2 1,3-2 1-2,3 1-2 1-2 1,2-3 1,2-3 1,2-3 1-2-3 1,3-2 1-2,3 1-2,3 1,3-2 1,3-2 1-2,3 1,3-2 1,3-2 1,3-2 1,3-2 1,3-2 1,2-3 1,2-3 1,3-2

Period separation is based on comparisons between standardized canonical discriminant function coefficients and group centroids; commas link similar periods and hyphens separate unlike periods. b A significance value of .000 means that the significance level was smaller than the limits of the program.

Principal responses to playbacks of gobbles included gobbles and coos. Playback periods were distinguished from preplaybacks in discriminant analysis by having more alert and approach responses and fewer cackles. Periods 1 and 2 were correctly distinguished 95% of the time and periods 1 and 3 89%. Thus the effects of gobbles may also be long lasting. Dancing sounds consisted of loud foot stamping that is homologous to prairie chicken stamping and tail rattling produced by modified lateral

480

D O N A L D W. S P A R L I N G

rectrices (Lumsden, 1965). Dancing was frequently accompanied by chilks and cork notes. Responses to low chilk playbacks included increases in gobbles and alert behaviors. Alert, comfort, whine and stand off were also selected by discriminant analysis as being important in distinguishing periods. Fewer stand offs and comfort behaviors and more alert behaviors occurred in playback than in preplayback periods. No cases in periods 1 and 2 were switched but 23 and 14% of the cases in comparisons between periods 1 and 3 and 2 and 3, respectively, were interchanged. Any effects produced by these playbacks appeared to be temporary. Discriminant analysis also found that dancing with a high rate of chilks elicited significant responses from sharptails. Of the behaviors found to be important by discriminant analysis, dance, cork notes, stand offs, and comfort behaviors were most useful in distinguishing periods 1 and 2. Eighty-six percent of the cases compared in these periods were correctly grouped. DISCUSSION

Table 7 summarizes the major types of information present in prairie grouse vocalizations. TABLE 7 I n f o r m a t i o n C o n t e n t of Principal Prairie Grouse Vocalizations or Sounds

Call

Boom Stamping Whoops Whines Cackles Composite

Individual identity

+ + +

Sex

ReproducTerritory tive p o s s e s s i o n A g g r e s s i o n condition L o c a t i o n

A. Prairie c h i c k e n v o c a l i z a t i o n s° + + + + + + + + + + + + + + + + + + + + + + + + ? + + + + ? + + + + + + + + +

+ + + + + + + + + + +

Possible danger

+

B. Sharp-tailed grouse v o c a l i z a t i o n s Coos Gobbles Chilks Cork notes Dancing Whines Cackles Composite

+ + + + + +

+ +

+ + + + + + + + + ? ?

+ + + + + + + + + + + + + + +

+ + + + + + + + + + + + + + +

+ + + + + + + + + +

+ + + + + + + + + + + + +

a Plus signs indicate relative a m o u n t of predictability in a vocalization for c o n v e y i n g information c o n t e n t ; + = s o m e w h a t predictable; + + = substantial predictability p r e s e n t ; + + + = highly predictable. All v o c a l i z a t i o n s provided some predictability of location.

INFORMATION IN PRAIRIE GROUSE CALLS

481

Information Content and Functions of Prairie Chicken Sounds Booms and associated visual displays (e.g., forward posture and pinnae elevation) convey a broad range of information by virtue of their widespread occurrence. "Listless tooting" (Hjorth, 1970) is a highly variable form of booming which is given by males in the center of their territories. This display denotes a low likelihood of attacking and its variable structure may characterize individuals. "Booming parallel" (Hjorth, 1970) is given near territorial borders and indicates a higher likelihood of attacking. Highly stereotyped booming occurs when hens are present and clearly conveys courtship intentions. Booms can also travel for more than 3 km under favorable conditions (Hamerstrom & Hamerstrom, 1960) and have low frequencies which help pinpoint display grounds or specific males. Principle functions of booms include attracting birds to display grounds via long-range advertisement and to particular territories. Advertisement would attract females and may discourage other males from approaching. However, on very small display grounds attraction of other males may be desirable if a combination of signals from several males acted as a beacon in guiding hens. Males are encouraged to advertise by whooping and when they hear booms as in the playback experiments. Humans can frequently determine the relative size of a lek from the amount of booming that occurs and prairie chickens may also. Booms also function in territorial maintenance and as tonic signals (Schleidt, 1973). Territorial maintenance is supported by the change in cackles and fights during boom playbacks. As tonic signal booms can maintain status quo among males and reduce overt aggression. Individual variation in listless tooting would be helpful in this respect if it distinguishes neighbors from strangers. Because playbacks of stereotyped booms slightly inhibited most activities and had no appreciable effects on a lone male (Hamerstrom & Hamerstrom, 1960), it is unlikely that these booms play a direct and immediate role in intermale communication. Rather, the present evidence strongly supports the tonic signal and mate attraction hypotheses. Stamping is closely associated with epigamic booming displays and probably attracts females or induces copulatory behavior. Whoops occur almost exclusively during courtship, are only given by males, and can be heard for 1-2 km. Contextual evidence shows that their principle function is mate attraction. Changes in overt fighting and face offs in playback experiments also demonstrate that the call is slightly aggressive. Hamerstrom and Hamerstrom (1960) played whoops to a lone male and found that it boomed and flutter jumped and they suggested that the vocalization was aggressive. Prairie chicken whines and cackles convey some ambivalence in different contexts including intense aggressive encounters, when a possible

482

DONALD W. SPARLING

predator such as a raptor is observed, or during flutter jumps when a new bird arrives on a display ground. However, the specific meanings of these vocalizations vary with the situation. Whines of alerted birds and playbacks of whines are usually followed by contagious, reciprocal whines from others; vigorous cacklers in territorial disputes appear more likely to attack than silent birds; and loud calls may increase a male's conspicuousness during flutter jumping. In general, cackles are more aggressive than whines. Functions of these calls include territorial defense, alerting others to danger, and attracting a female's attention. Composite sounds initially elicited alert responses but later increased epigamic displays such as booms, whoops, and stamps. They were also very effective in attracting males to display grounds after flushing or walking off and have been used to lure males for trapping (Silvey & Robel, 1967). This combination of sounds may serve as a Gestalt of an active group of prairie chicken males and probably signals that a female is present. Hearing these sounds, males are attracted and begin to court.

Information Context and Functions of Sharptail Sounds Coos are most common when pressures such as territorial intruders and females are absent. The calls are most often given by males in the center of their territories and slightly more by peripheral than by central males. Coos can carry over I km under good conditions. Some aggressive information is also present in the call and accompanying forward posture. One of the most important functions of coos is as a tonic signal. By serving as frequent reminders or "place holders," coos help maintain territories and minimize overt aggression. Males responded aggressively to playbacks of coos by cooing and gobbling. Coos may also advertise a sharptail display ground's location but are probably less effective in this than chilks (L. W. Oring, personal communication). These functions, with the exception of tonic signals, are supported by Lumsden (1965), Hjorth (1970), and Kermott and Oring (1975). Central males tend to gobble more frequently than peripheral ones and males are as likely to call from territorial peripheries as from their centers. Gobbles may be individually characteristic (Kermott & Oring, 1975; Sparling, 1979a). Aggressive females gobble at other hens on display grounds (H. G. Lumsden, 1965, personal observation). Therefore, gobbles denote aggressiveness, individual identity, and perhaps social status but not sex or reproductive condition. The most apparent functions of gobbles among males is territorial establishment and maintenance. This is supported by the early peak and subsequent decline of gobbles during the mating season and by the increased coos and gobbles during playback experiments. Gobbling by females deter others from mating until gobblers have chosen their mate. Hjorth (1970), who did not observe sharptails during the period of territory establishment, concluded that this signal was a low-priority activity

INFORMATION IN PRAIRIE GROUSE CALLS

483

but Lumsden (1965) and Kermott and Oring (1975) identified gobbles as highly aggressive. Gobbles and coos elicit similar responses and share similar functions. Based on contextual evidence, however, gobbles are more aggressive than coos. This premise was supported by Kermott and Oring (1975) who stated that coos were primarily involved in advertisement and that gobbles were the principle vocalizations denoting aggression. Dancing, chilks, and cork notes are highly associated with each other and with periods of female visitations. They are also only given by males. Chilks may be heard by humans for more than 2 km under favorable conditions. These sounds are primarily epigamic. Chilks may function as long- and medium-range advertisers while cork notes and dancing are probably limited to short-range stimulation of females. In addition, dancing and chilks are occasionally directed toward other males and function in territorial defense. Lumsden (1965) cited both aggressive and epigamic functions for all three displays, Hjorth (1970) emphasized that chilks and cork notes were "intensely aggressive," and Kermott and Oring (1975) described chilks and cork notes as epigamic displays that were ritualized from aggressive acts. Playbacks of chilks and cork notes further established the aggressive nature of these calls as sharptails responded to both by cooing and gobbling. Dancing with few chilks also elicited aggressive responses, probably because this form of dancing most commonly occurs in agonistic displays between males. Kermott and Oring (1975) consistently elicited dancing with playbacks of dancing but this response was not observed during low-chilk playbacks in my study. However, dancing was important in separating periods in experiments with high-chilk dancing. Kermott and Oring (1975) did not state if chilks were present in their tests but I tried five different levels of chilks in dancing playbacks without consistently eliciting dancing from males. Under natural conditions dancing is obviously contagious among males (Hjorth, 1970; Lumsden 1965). Future research may determine if dancing is significant in intermale communication. Whines and cackles in sharptails are most frequent during very close, intensely aggressive encounters and only occasionally occur when potential predators are observed. Thus they are clearly aggressive. Because whines did not elicit significant responses from sharptail males and responses to cackles appeared weak, one might conclude that neither call was very important in intermale communication. However, of all the calls tested, cackles and whines were most out of context. The calls may evoke very different responses when played from a speaker than when coming from a nearby male. Crouching was often observed during these playbacks and may be an appropriate response to loud, intensely aggressive signals with no recognizable source.

484

DONALD W. SPARLING

Interspecific Comparisons Because prairie chickens and sharptails are closely related species, they might be expected to have homologous vocalizations. Hjorth (1970) identified booms and coos, whoops and chilks, and whine-cackles as homologous. He did not clearly distinguish between whines and cackles within a species but the two calls are distinct in number of notes per bout, note duration, and internote interval (Sparling, 1979a). Thus the two species share four pairs of structurally homologous yet functionally different vocalizations. A comparison of these homologous calls provides some insight on the two species' social behavior. Booms contain all of the information normally assigned to bird song (e.g., Marler, 1957) but coos apparently are not involved in mate attraction or long-distance advertisement. Whoops and chilks have similar epigamic functions but chilks are probably more aggressive than whoops. While whines and cackles are associated with ambivalence in prairie chickens, they are clearly aggressive in sharptails. Sharptails responded more vigorously to conspecific vocalizations than did prairie chickens. For example, sharptail responses to coos, chilks, gobbles, and cork notes were more obvious than prairie chicken responses to booms, whoops, and whines. The reasons for this difference are not clear but may be related to species-specific differences in intraspecific aggressiveness. Ammann (1957) stated that sharptails were more aggressive than prairie chickens and were more likely to usurp prairie chicken display grounds than the reverse. Although I did not find obvious differences in interspecific aggressiveness, sharptail males spent a greater proportion of time in face offs and other aggressive activities than prairie chickens. In addition, more of the sharptail's vocal repertoire has aggressive functions. The reasons for this difference in intraspecific aggression between greater prairie chickens and sharp-tailed grouse are unknown. At present there is no reason to believe that intraspecific competition, which is often cited as a cause of aggression, is any greater for sharptails. An answer may be related to interspecific competition, as sharptails are sympatric with more confamilials than are prairie chickens (see Sparling, accompanying paper). Information content in prairie grouse vocalizations is similar to that found in other avian species. For example, prairie chicken booms contain information about species and individual identity, sex, location, and motivational status of the emitter. Perhaps the major difference between the primary vocalizations of grouse and song in most passerines is that prairie grouse vocalizations tend to have relatively discrete units of information. This appears to be particularly true for sharptails. Further study may reveal other similarities between prairie grouse vocalizations and song such as vocal learning (Sparling, 1979b), dialects, and geographical variation.

INFORMATION IN PRAIRIE GROUSE CALLS

485

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Smith, W. J. (1970). Displays and message assortment in Sayornis species. Behaviour, 37, 85-112. Smith, W. J. (1977). The Behavior of Communicating. Cambridge, Mass: Harvard Univ. Press. Sneath, P. H. A., & Sokal, R. R. (1973). Numerical Taxonomy. San Francisco: Freeman. Spading, D. W. (1979a). Reproductive Isolating Mechanisms and Communication in Greater Prairie Chickens (Tympanuchus cupido) and Sharp-Tailed Grouse (Pedioecetes phasianellus). Ph.D. Dissertation, University of North Dakota, Grand Forks. Spading, D. W. (1979b). Evidence for vocal learning in prairie grouse. Wilson Bulletin, 91, 618-621. Spading, D. W. (1981). Communication in prairie grouse. II. Ethological isolating mechanisms. Behavioral and Neural Biology, 32, 487-503. Spading, D. W., & Williams, J. D. (1978). Multivariate analysis of avian vocalizations. Journal of Theoretical Biology, 74, 83-107.