Ethology 103,1032-1041 (1997) 0 1997 Blackwell Wissenschafts-Verlag, Berlin ISSN 0179-1613

Department o f Biological and Environmental Science, Universig ofbvaskyla, hvaskyl~ and Department ofZoology, Uppsulu Universig, Uppsula

Responses of Male and Female Black Grouse to Male Vocal Display

MATTI HOVI, RAUNO V. ALATALO, MATTI HALONEN & ARNE LUNDBERG

HOVI, M., ALATALO, R. V., HALONEN, M. & LUNDBERG, A. 1997: Responses of male and female black grouse to male vocal display. Ethology 103, 1032-1041.

Abstract

The evolution of leks may be explaned by several hypotheses. The ‘female preference’ hypothesis, which states that females favour males that have aggregated, has recently gained some empirical support. Low-quality, unattractive males may, however, settle near attractive males, as predicted by the ‘hotshot’ hypothesis. We tested whether black grouse Tetmo t e h x females use auditory cues to find the preferred leks, and whether males respond to vocal display emitted on leks. We conducted a playback experiment with male vocal display (rookooing) on leks, where the visiting females and displaying males were counted. The number of males tended to increase more on playback leks. Specifically, the number of 1-year-old males was greater on playback sites than on control sites. Also, the number of females, in relation to the lek size before the start of the experiment tended to increase. In addition, we used aviary playback trials to test whether females distinguish between single-male and multi- male displays. In a choice test, females showed greater preference for the ‘multi-male’ tape. The tendency for increased male numbers on playback leks resulted from increased visits of young, mobile males which were attracted to leks that they perceived to be large. This suggests a ‘hotshot’-type mechanism in the settlement of young males. Because females also responded to the supplemented auditory advertisement, or directly to the increased number of males, the ‘female preference’ hypothesis IS also supported. Females may, at least in part, base their decision of which lek to visit on auditory cues, but visual contact to males may be also needed.

Corresponding author: Matti HOW, Department of Biological and Environmental Science, University of Jyvaskyla, Box 35, SF40351 Jyvaskyla, Finland.

Introduction

The origin of lek mating systems has received much attention and a number of hypotheses have been formulated to explain their evolution (HOGLUND & ALATALO 1995). These can be divided into two categories according to whether active female mating preference plays a role or not. Explanations using female preference assume that females, for whatever reasons, prefer clusters of males over solitary males (QUELLER 1987) or, larger clusters over smaller clusters (BRADBURY 1981; GIBSON et al. 1990). This preference has to be strong enough to yield an average benefit for males to form clusters. Correlations between lek size and male mating frequency (ALATALO et al. 1992; HOGLUND et al. 1993) have been taken as evidence for the preference hypothesis. A similar pattern may arise if females passively move towards the strongest stimuli of male display (OTTE 1974), even though this mechanism is unlikely to be the only factor behind the evolution of leks

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Responses of Black Grouse to Vocal Display 1033

(BRADBURY 1981; DRONEY 1994). For passive auditory attraction (or signalling hypoth- esis) (OmE 1974) to hold, males should, on average, increase their mating success by joining an aggregation of other males and thus increasing the auditory range (drawing area; BRADBURY 1981). However, the addition of sound output (number of displaying males) does not increase drawing area (and visiting females) in the same proportion. Doubling the number of males would not double the number of visiting females. Therefore, clustering would not be advantageous for an average male.

It has been suggested that black grouse Tetra0 t e h x females prefer mating on larger leks (KRUIJT et al. 1972; ALATALO et al. 1992). Active preference for large lek size implies that females are able to choose between leks to some extent. Given that two or more leks are usually available within a female’s home range, she can make her choice by visiting several leks before the mating decision. Visits to more than one lek occur commonly in many avian species (e.g. black grouse, KOIVISTO 1965; some of the manakins, LILL 1976; THERY 1992; ruff Philomachuspugnax, LANK & SMITH 1987; great snipe Galhago media, HOGLUND & ROBERTSON 1790a; and Lawe’s parotia Parotia lawesiz, PRUETI-JONES & PRUE’IT-JONES 1990). Alternatively, females may not need to visit leks if they can distinguish between small and large leks on the basis of male vocal display. Female responses to the vocal display of lekking males has rarely been tested in birds. GIBSON (1989) found that, on a within-lek scale, sage grouse Centrocercus urophasianus females were attracted to territories supplemented with playback. In several studies of anurans, females preferred loud calls (WHITNEY & KREBS 1975; FELLERS 1979; HOGLUND & ROB-

ERTSON 1988). However, it has rarely been tested whether females discriminate among leks or choruses according to the perceived auditory stimulus. Only in a katydid grasshopper (Orthoptera; Conocephalus nigmpleumm) has it been shown that females prefer multi-male song over single-male song (MORRIS et al. 1978). The ability to assess lek size from the sounds generated by calling males should be beneficial for females if it reduces search costs, or if it helps to get information on the mating options available. This ability could exist in species where the radius of the drawing area (BRADBURY 1981) is greater than the distance between adjacent leks. Under these circumstances, it would be beneficial for males to join clusters, not in order to increase the drawing area but to make the aggregation sound more attractive.

We conducted two experiments with black grouse to test responses of females to male long-distance vocal display. The specific aim was to test whether females prefer to visit leks that are artificially made ‘noisy’. Black grouse males advertise their presence at leks with loud ‘rookoo’ calls, which can be heard 2-3 km away in calm conditions. Calls also include distinct ‘hissing’ and ‘cackling’ sounds, which can only be heard at shorter range (for a description of different calls, see KOIVISTO 1965). During the mating period in late Apr. and early May, males start displaying well before sunrise. Females could, in principle, use the sound as a cue when searching for leks. Because they preferentially visit larger leks (ALATALO et al. 1992), an ability to discriminate between small and large leks by sound is to be expected.

We also investigated the response of males to increased display. The ‘hotshot’ hypoth- esis for the evolution of leks (ARAK 1983; BEEHLER & FOSTER 1988; HOGLUND & ROBERTSON 1990b) proposes that unattractive males should settle near attractive ‘hot shots’ because of the chances of parasitizing their mating success. In principle, males could

1034 M. HOVI, R. V. AIATALO, M. HALONEN & A. ISJNDBERG

use auditory cues to locate the attractive males, or alternatively be attracted to large leks themselves. We therefore tested whether males are attracted to leks that are artificially made to sound large.

Methods

The Playback Experiment in the Field

The playback experiment aimed to make a small lek sound like a large onc. It was performed on leks on frozen lakes during 1994 and 1995 at Petajavesi and Konnevesi, Central Finland. Beforc the mating seasons, i.e. before the first female visits, we selected adjacent leks, with similar number of males, and formed pairs of leks for the experiment. One lek from each pair was randomly assigned as the ‘treatment’, with the other as the ‘control’. In both years, we observed four different lek pairs, giving eight leks with the playback treatment, and eight as controls. The distance between playback and control varied from 2 to 11 km (x = 6.6 h). Because of the apparent dependence between treatments and controls, we used paired test in the analysis. All t-values in the results refer to the Wilcoxon’s paired test. Between years, there was no difference in the number of males warm- Whitney U = 25.0, n, = 8, nz = 8, ns) or in the rate of female visits (U = 27.5, ns).

The playback treatment consisted of eight different 1-min endless tapes (one for each site) compiled from vocalizations of four different males recorded on a bog lek in Petajavesi in 1987-88. The playback was tested before the start of the experiment, and it could easily be heard by a human from a distance of 1 km on frozen lakes. This is not much less than the sound generated by displaying males. We used Blaupunkt (Blaupunkt-Werke GmbH, Hildesheim, Germany) and Philips (Philips Electronics, Eindhoven, Netherlands) cassette players and two 40 W loudspeakers erected side by side on each lake shore. The distance between the displaying males and the loudspeakers depended on the size of the lake, and ranged between 300 and 600 m. The tapes were played every morning, starting on 30 Apr., 1994, and on 28-29 Apr., 1995. Me stopped the experiment on 3-5 May, 1994, when the ice broke up, and on 7-9 May, 1995.

The playbacks were started evety morning between 03.30 and 04.00 hours and played for at least 2 h. Within each lek pair, treatment and control leks were observed on alternate mornings. We observed the leks from tents on the lake shore, and counted the numbers of displaying males and recorded every arrival and departure of visiting females. We included occasional visiting young males in the male count if they landed on the same lake within sight of the lek. On one pair of leks, yearlings could not be separated from adults owing to the great distance from the shore. Females were regarded as visiting the lek if they landed on the ice or in adjacent trees, or if they flew over the arena. We tested the responses both by including and excluding the first morning after the onset of the experiment, to assess whether the birds might react with a time delay, and whether the effect of the treatment might reduce over time.

Experimental Playback Trials in the Aviary

Captive black grouse had been housed in Konnevesi Research Station since 1992, when six females were hatched and hand-raised in captivity. Another six females were trapped in Suomussalmi and brought to the Station in Dec., 1993. Outside the study periods (Apr.-May), each female was kept in her solitary indoor box and fed with oats, birch twigs and berries. In 1994, playback trials were started on 26 Apr. and stopped on 10 May, and in 1995 ran between 19 April. and 5 May. This is the period when females are receptive in the field, and we assumed a similar schedule in captivity because light-dark cycles in their wintering room closely followed the natural rhythm.

The tapes used in the trials were either compiled from four original tapes containing single-male vocalization, ‘rookooing’ (‘multi-male tapes’, as above) or used as such (‘single-male tapes’). The endless 1 -min tapes were replaced daily, so that the identity of the rookooing males changed, or so that a different part of the tape of a given male was used. As a result, both tape types were different for every trial. On the single-male tapes, there were 12-19 phrases per minute @ = 14.2), and on the multi-male tapes there were 9-16 phrases per minute per male (x= 13.8, duration of each phrase ranged typically from 2.5 to 2.9 s; KRUIJT & IF. VOS 1988). Because there were more males, the rookooing on the multi-male tape sounded more continuous, while there were distinct pauses on the single-male tape. The recording and output levels of the two different tapes were kept similar

In the trials, each female was introduced into a 1 x 1 m outdoor pen made of mesh wire, with opaque plastic canvas fences between the pens preventing visual contact with other females. Each morning, two Sony

Responses of Black Grouse to Vocal Display 1035

cassette players (for single-male and multi-male tapes) were placed 15 m from a pen, one to the left and the other to the right side of a focal female (only one or two females were tested per morning). The loudspeakers were reversed after each trial to eliminate any absolute site effects. After starting the tapes, we waited for 15 min before observations to minimize the effect of our disturbance near the pens and then watched at a distance of 30m from the nearest pen from a hide that was easy to enter without disturbing the birds. The birds were observed from a hide situated 30 m away from the nearest pens, which was easy to enter without disturbing the birds. M. HOW recorded phonotactic response of each focal female over a 30-min period with 1-min intervals. He judged whether the female was in the lefdright one-third of the pen, or in the middle. The sum of positions during the trial was taken as the preference score for each playback. Most females were tested twice or more (X = 4.5 and 1.9 times in 1994 and 1995) in order to decrease the variation caused by changes in motivational levcl. All probability values are two-tailed.

Results

The Field Experiment

There were no differences in male or female numbers present (averaged across the study period) between playback and control lakes (males: X & SD = 3.6 2.0 and 3.9 k 2.8, tY15.0, n = 8 ; females: Xk SD=2.1 f 2.2 and 1.6 1.4, t=8.0, n = 7 (one tie), ns). Despite our efforts at matching playback and control leks in terms of male numbers, control leks were significantly larger than playbacks just before the start of the experiment @ = 4.3 vs. 2.9 males, t = 0.0, n = 8, p < 0.05). The change in male numbers (adults and yearlings pooled) from the pre-treatment situation to the mean of the exper- imental mornings was positive (+0.7) on playbacks, and negative (-0.4) on controls, but the difference was not statistically significant (t = 7.0, n = 8, ns). The number of first year males (separated from adults on seven lek pairs) during the treatment was significantly higher on playbacks compared with controls (t = 2.0, n = 7, p < 0.01, Fig. 1). This result

10 I n . -

8 -

6 -

4 - 0

n

P/- 0% I

0 2 4 10

Control F&. 1: Number of yearling (open circles) and all male black grouse (filled circles) in pairs of control and playback leks. The values are means across the whole study period. The chagonal line indicates

no difference

1036

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0 0 0

M. How, R. V. ALATAIO, M. HALONEN & A. LUNDBERG

3 ,

0 8 0 0

I n i t i a l lek s i z e F&. 2: The rate of female black grouse visits to control (open circles) and playback leks (filled circles) in relation to dfferent lek sizes. The rate is averaged across the study period. Initial lek size refers

to the number of males before the start of the experiment

could arise if small leks consisted mainly of yearlings, but there was no correlation between the original number of all males and yearlings during the treatment (rs = -0.01, n = 14, ns). Thus, there was no need to adjust the number of yearlings to the original lek size.

There was a significant positive correlation between the original number of males and the number of visiting females, averaged across the treatment period (r, = 0.61, n = 16, p < 0.05). In fact, there was a strong a priori assumption of greater numbers of females visiting larger leks (ALATALO et al. 1992). We therefore removed the effect of original lek size on female visiting probability by dividing the number of visiting females by the number of males before the experiment. This measure allowed us to estimate the relative attractiveness of the playback and control leks. There was a tendency for females to visit playback leks relatively more often than controls (t 1 6.0, n = 8, p < 0.05, Fig. 2).

Finally, we re-analysed the results by omitting the counts of the first morning after the start of the experiment. This was done because there might be a time lag in the response of birds. Alternatively, if the grouse responded strongly in the beginning but ignored the tapes afterwards, the real effects would be over-emphasized in the above results. The results after omitting the first motning differed from those with the first morning included in that the change in total male numbers was significant (t = 5.0, n = 8, p < 0.05), but the number of female visits was not significantly different (t = 10.0, ns). However, the number of females per male was significantly higher in the playback than in the control group (t = 5.0, n = 8, p < 0.05). The difference between playback and control in the number of yearling males remained (t = 2.0, n = 7 , p < 0.05).

Responses of Black Grouse to Vocal Display

The Aviary Experiment

1037

The black grouse females captured as fd-grown did not differ from those raised in captivity in the proportional preference for the multi-male tape (Mann-Whitney U = 15.5, n, = 6, n2 = 6, ns). In consequence, in the following tests we used all females as a pooled data set. The preferences of each female from both years were combined to give a reasonable estimate of their preference. Ten captive females expressed an overall preference score of at least 10 (minutes on each side of the pen). Two females gave markedly lower scores (5.2 and 2.0), that is, they spent almost all of their time in the middle of the pen. Because of their apparently low motivation to mate, they were omitted. Of the 10 females, eight showed preference for the multi-male tape, whereas two apparently preferred the single-male tape (Wilcoxon’s t = 10.0, n = 10, p < 0.05, Fig. 3). Of the two females that deviated from the general pattern, one was very consistent in her choice, while the other showed only slight preference for the single-male tape (Fig. 3).

Discussion

The increase in male numbers and the hgher number of yearlings on playback leks suggest that yearling males tended to visit these more often than control sites, where the number of males seemed to decrease. It is possible that some of the extra males observed at playback leks were attracted at the expense of the control sites. The pairwise design of the experiment may effectively reveal differences, and this appears to strengthen our interpretation, because the birds may have had the choice between playback and control. Young males are known to show less dtsplay site tenacity than older males (DE VOS 1777; ALATALO et al. 1992). Thus, it seems that the artificially increased auditory display attracted

16

12

8

%4 4

0

a, & 0 V (II

a, V C a, & a, a, L4 n4

Individual females

Fig. 3: The preferences shown by 10 captive female black grouse to single-male (open bars) and four- male tapes (filled bars). Preference for each tape was measured as the number of positions on each side of a pen during a 30-min period, with scans taken at 1-min intervals. The scores are the means

of several trials per female

1038 M. HOW, R. V. ATATALO, M. HALONEN & A . LUNDBERG

young males. Game theory models of ideal free distribution with unequal competitors (SUTHERLAND & PARKER 1985; PARKER & SUTHERLAND 1986) predict that young males should settle on small leks, where the pressure of competition is lowest. In support of this, ALATALO et al. (1992) demonstrated that young males preferentially settled on leks with small number of adult males. However, the results of the current study are not necessarily incompatible with those of ALATALO et al. (1992). In this study, all leks were small, consisting of only a few males, and the site tenacity may be lower on small leks, especially for yearling males. The optimal lek size for young males may not be the smallest, as small leks are often despotized by one dominant male (see H O ~ I et al. 1995, 1996), but rather of intermediate size, which here were mimicked by the playback treatment. Indeed, an earlier study suggested that the intermediate-sized leks might offer the highest prob- abilities for young males to mate (ALATALO et al. 1992).

This finding appears to resemble the mechanism of male aggregation assumed in the hotshot hypothesis for lek evolution. In this study, instead of gathering around certain attractive individuals in order to parasitize their mating success ( A U K 1983, 1988; BEEHLER & FOSTER 1988), the mobile males were attracted by artificial male display, perhaps indicative of large lek. In fact, if poor quality males were attracted by a large lek, this could indicate that they did so to utilize the preference of females for mating on larger leks. The number of female visits was related to the original lek size, but also increased in response to the playback. The reason why mobile males visited leks which were perceived to be large might be a greater probabdity of meeting females, even though their actual chances of mating there would be relatively low. Spatial spillover of mating success might be the only chance for a low-quality-male to obtain matings (RINTAMIXI et al. 1995).

Females seemed to join leks supplemented with playback more often than controls. Black grouse females may visit several leks during the mating season, especially if the leks are close to each other (KOIVISTO 1965). As predicted, females could be attracted by increasing the perceived number of displaying males, and there was no time lag in their response. An alternative explanation is that females were attracted to the increased number of males, and not dtrectly by the playback. Both sexes of black grouse show strong breeding site fidelity after their first breeding attempt (WILLEBRAND 1988). Therefore, a significant difference in the number of females could have been produced by yearling females responding to the playback. The occurrence of young males suggests that there were also young females in the population, assuming that there was no sex-biased mortality among the yearlings. To our knowledge, older females rarely, if ever, visit more than one lek (ALATALO, unpublished data).

The results from our aviary experiment suggest that when given a chance to select between two adjacent displays, possibly perceived as a small lek, and a solitary male situated close to each other, females, in general, appeared to favour the former. The difference between solitary males and leks of a few males is perhaps even more profound than on our tapes. Solitary males display discontinuously, whereas in our experiment, the playback consisted of a more continuous display of one male drawn from a lek. This result implies that, in nature, females can effectively discriminate against solitary displaying males with the help of auditory cues. It is notable, however, that one female orientated herself consistently towards the single-male tape.

Earlier studies indicate that almost all copulations in black grouse take place on lek

Responses of Black Grouse to Vocal Display 1039

territories (KOIVISTO 1965; DE VOS 1983; KRUIJT & DE VOS 1988; ALATALO et al. 1996; but see HJORTH 1970), whereas matings off-lek are more common in some other species (LANK & SMITH 1987; PRUETT-JONES 1988). Our result allows the interpretation that females can choose leks instead of solitary males when offered simultaneously, and thus save time and energy. The ability to distinguish between single-male and multi-male displays is thus potentially advantageous for females. However, we did not test whether they can discriminate between different-sized multi-male displays, and thus reduce the search time needed to find the lek with the best mating options and reduce the time needed for searching. In the sage grouse C: tlrophasiantls, however, travelling to leks did not increase the energy expenditure appreciably compared with foraging trips, and mobility did not significantly increase the risk of predation (GIBSON & BACHMAN 1992). Therefore, costs of sampling between leks may be low and consequently, there may have been little selection for accurate discrimination.

Demonstration of mating preferences is often difficult and demands large sample sizes, if the population is polymorphic in respect to what individuals prefer (see also FISKE et a1.1994). Estimating the proportions of different ‘preference phenotypes’ is an even more tedous job. To obtain statistical support, one should test each female repeatedly before she can be assigned a ‘preference’. If females are tested as a population and a null hypothesis cannot be rejected, one cannot be sure about preferences of individuals. Our results from the captive birds suggested that females might differ in what they favour. If each female is assumed to have mated where they seemed to show most preference (too few copulations were observed for tests), the four-male-lek would have resulted in eight matings (two per average male) and the solitary male would have achieved two matings. Thus, the preference for the multi-male tape was too weak to benefit males that clustered. Females should have favoured multi-male and single-male tapes with a ratio of more than 4:l. Earlier experiments indicated that female preferences have a role in lek evolution in this species: once on a lek, females disproportionally prefer central over peripheral males (HOVI et al. 1994). However, even if preferences exist also between leks, females obviously do not use solely auditory cues when selecting where to go.

To conclude, females were able to discriminate between vocal displays of leks vs. solitary males in controlled aviary condtions. Vocal display may have a role in attracting females to leks, either directly or indirectly via increased number of males. The fact that young males gathered at leks where male vocalizations were supplemented suggests that a mechanism similar to the ‘hotshot’ model might be operating, except that young mobile males were attracted to the leks perceived as large instead of attractive top males (ARAI< 1983; BEEHLER & FOSTER 1988).

Acknowledgements

M. EINBORK, S. JOKINEN, T. KESKINEN and J. KILPIMAA helped in conducting the field experiment. L. IJAS, A. KOLJONEN, P. T. RINTAMAKI and P. VAIKEAJARVI assisted in founding the aviary stock. At the Konnevesi Research Station we were helped by the staff, particularly R. LATVANEN and J. RAATII.AINEN. The manuscript was criticized and commented by H. HOI, S. PARRI, P. T. RINTAMAKI and K. VIIPALE. We were financially supported by the Academy of Finland (R. V. ALATALO & M. HOW), University of Jyvaskyla (M. HALONF.N), and Swedish NSRC (A. LENDBERG).

1040 M. H o w , R. V. ALATALO, M. HALONEN & A. LUNDBERG

Literature Cited

ALATALO, R. V., BuRKE,T., DUNN, J., H A N O ~ E , O., HOGLUND, J., LUNDBERG, A,, MOSS, R. & RINTAMAKI, P. T. 1996: Paternity, copulation disturbance and female choice in lekking black grouse. Anim. Behav. 52, 861-873.

__ , HOGLUND, J., LUNDBERG, A. & SUTHERLAND, W. J . 1992: Evolution of black grouse leks: female preferences benefit males in large leks. Behav. Ecol. 3, 53-59.

ARAti, A. 1983: Male-male competition and mate choice in anuran amphibians. In: Mate Choice (BATESON, P., ed.). Cambridge Univ. Press, Cambridge. pp. 181-210.

__ 1988: Female mate selection in the natterjack toad: active choice or passive attraction? Behav. Ecol. Sociobiol. 22, 317-327.

BEEHLER, B. M. & FOSTER, M. S. 1988: Hotshots, hotspots, and female preferences in the organization of lck mating systems. Am. Nat. 131,203-219.

BRADBURY, J. W. 1981: The evolution of leks. In: Natural Selection and Social Behaviour (ALEXANDER, R. D. &TINKLE, D. W., eds). Chiron Press, New York. pp. 138-169.

__ 1983 Social behaviour of black grouse: an observational and experimental field study. Ardea 71, 1-103. DRONEY, D. C. 1994: Tests of hypotheses for lek formation in a Hawaiian Drosophila. Anim. Behav. 47, 351-

FELLERS, G. M. 1979: Mate selection in the gray treefrog, Hy/a versicolor. Copeia 1979, 286-290. FISKE, P., K k d S , J. A. & SETHER, S. A. 1994: Correlates of male maung success in the lekking great snipe

GIBSON, R. M. 1989: Field playback of male display attracts females in lek breeding sage grouse. Behav. Ecol.

__ , BACHMAN, G. C. 1992: The costs of female choice in a lekking bird. Behav. Ecol. 3,300-309. __ , TAYLOR, C. E. &JEFFERSON, D. R. 1990 Lek formation by female choice: a simulation study. Behav.

HJORTH, I. 1970 Reproductive behaviour in Tetraonidae. Viltrevy 7, 1 8 6 5 9 6 . HOGLUND, J. & ALATALO, R. V. 1995: Leks. Princeton Univ. Press, Princeton. _- & ROBERTSON, J. G. M. 1988: Chorusing behaviour, a density-dependent alternative mating strategy in

-_ & -- 1990a: Spacing of leks in relation to female home ranges, habitat requirements and male

__ & -- 1990b: Female preferences, male decision rules and the evolution of leks in the great snipe

__ , MONTGOMERIE, R. & WIDEMO, F. 1993: Costs and consequences of variation in the size of ruff leks.

H o w , M., ALATALO, R. V., HOGLUND, J., LLINDBERG, A. & RINTAMAKI, P. T. 1994: Lek centre attracts black

361.

(Gallinago media): results from a four-year study. Behav. Ecol. 5, 210-218.

Sociobiol. 24, 4 3 9 4 4 3 .

Ecol. 1, 3 6 4 2 .

male common toads (Bufo bufo). Ethology 79, 3 2 6 3 3 2 .

attractiveness in the great snipe (Gallinago media). Behav. Ecol. Sociobiol. 26, 173-180.

(Gallinago media). Anim. Behav. 40, 15-22.

Behav. Ecol. Sociobiol. 32, 31-39.

grouse females. Proc. R. Soc. Lond. B. 258, 303-305.

competition? Behav. Ecol. Sociobiol. 37, 283-288.

grouse. Behaviour 133, 561-578. KOIVISTO, I. 1965: Behaviour of the black grouse, Lymms t e t t i x (L.), during the spring display. Finn. Game Res.

26, 5-60. KRCIJT, J. P. & DE VOS, G. J. 1988: Individual variation in reproducuve success in male black grouse, Tetrao

tetrixL. In: Reproductive Success (CIJJTTON-BROCK, T. H., ed.). Chicago Univ. Press, Chicago. pp. 279- 290.

__ , __ & SIIKAMAKI, P. 1995: Black grouse leks on ice: female mate sampling by incitation of male

-- , _- & RINTAMAKI, P. T. 1996: Habitat differences and variabibty in the lek mating system of black

__ , -_ & BOSSEMA, I. 1972 The arena system of the black grouse. Proc. Int. Om. Congr. 15 ,399423. LANK, D. B. & SMITH, C. M. 1987: Conditional lekking in the ruff (Phi lomach~~pugn~) . Behav. Ecol. Sociobioi.

LILL, A. 1976: Lek hehaviour in the golden-headed manakin, P$ra eythrocephala in Trinidad (west Indies). Z.

MORRIS, G. K., KEm, G. E. & FULLARD, J. H. 1978: Phonotactic preferences of female meadow katydids

OPE, D. 1974 Effects and functions in the evolution of signaling systems. Ann. Rev. Ecol. Syst. 5, 3 8 5 4 1 7 . PARKER, G. A. & SUTHERLAND, W. J. 1986: Ideal free distributions when individuals differ in competitive

20,137-145.

Tierpsychol. Suppl. 18, 1-84.

(Orthoptera: Tettigoniidae: Conocephalus nigropleumm). Can. J . 2001. 56, 1479-1 487.

ability: phenotype-limited ideal-free models. Anim. Behav. 34, 1222-1 242.

Responses of Black Grouse to Vocal Display 1041

PRW~T-JONES, S. G. 1988: Lekking vs. solitary display: temporal variations in dispersion in the buff-breasted

__ & PRUETT-JONES, M. A. 1990 Sexual selection through female choice in Lawe’s parotia, a lek mating bird

QUELLER, D. C. 1987: The evolution of leks through female choice. Anim. Behav. 35,1424-1432. RINTAMAKI, P. T., AIATALO, R. V., HOGLUND, J. & LUNDBERG, A. 1995: Male territoriality and female choice

on black grouse leks. Anim. Behav. 49, 759-767. SUTHERLAND, W. J. & PARKER, G. A. 1985 Distribution of unequal competitors. In: Behavioural Ecology:

Ecological Consequences of Adaptive Behaviour (SIBLY, R. M. & SMITH, R. H., eds). Blackwell, Oxford. pp. 255-274.

THBRY, M. 1992: The evolution of leks through female choice: differential clustering and space utilization in six sympauic rnanakins. Behav. Ecol. Sociobiol. 30, 227-237.

DE VOS, G. J. 1979: Adaptedness of arena behaviour in black grouse (I’efrao fetrix) and other grouse species petraonidae). Behaviour 68,277-314.

WHITNEY, C. L. & KREBs, J. R. 1975: Mate selection in pacific treefrogs. Nature 255, 325-326. WILLEBRAND, T. 1988: Demography and ecology of a black grouse (fitruo tetr ix L.) population. PhD thesis,

sandpiper. Anim. Behav. 36, 1740-1 752.

of paradise. Evolution 44, 486-501.

Uppsala Univ., Uppsala.

Received: December 13, 1996

Acc@d.AprillO, 1997 (W’ Wcklerj