Robert M. Gibson

The energetic cost of display in male sage grouse

The energetic expenditure of displaying male sage grouse, Centrocercus urophasianus, was measured for 18 individuals in the field using the doubly labelled water technique. Daily energy expenditure increased significantly with increased display rate, increased time spent on the lek, and decreased ambient temperature. Daily energy expenditure for the most vigorously displaying males was two times higher than for a non-displaying male and four times higher than basal metabolic rate. Estimates of the instantaneous rate of energy expenditure during display ranged from 13·9 to 17·4 times basal metabolic rate. The effort devoted to display differed markedly among males and was correlated with certain other male characteristics. Males that attended leks were in better condition (higher body weight relative to size) than non-attenders, but among lek attenders condition was negatively correlated with increased display effort. Active displayers lost less weight per day and foraged further from the lek than less active males, suggesting that differences in foraging and food intake affect daily energy output. Neither blood parasites nor the potential effects of other diseases as determined by haematocrit levels were associated with display effort.

Sexual Selection in Lekking Sage Grouse: Phenotypic Correlates of Male Mating Success

SummaryMate choice cues in sage grouse were reinvestigated by analyzing relationships between male mating success and a range of suggested cues. Display cues were implicated by significant relationships between mating status (whether or not a male mated) and lek attendance, display rate (corrected for effects of female proximity and time of day) and an acoustic component related to temporal and frequency measure of a whistle emltted during the strut display. Although display rate and the acoustic component were intercorrelated, both exerted significant partial effects on mating success in mutivariate analyses. These display measures also differed significantly between males. In contrast, mating success was not significantly related to measures of territory characteristics, including size and proximity to the lek center, or to body size. These results resolve discrepancies between previous studies and provide a basis for experimental analysis of the role of female choice in this lek system.

How do animals choose their mates

How animals search for and evaluate prospective mates has, until recently, been a neglected aspect of sexual selection. Theory and field data suggest that discrimination varies with the costs and benefits of choice, but a consensus has yet to be reached on the tactics by which prospective mates are evaluated. This intriguing issue may be clarified by new studies that deal explicitly with the process of information acquisition.

Copying and sexual selection

Recent studies of a variety of polygynously mating animals indicate that females do not always choose mates independently, but instead may copy the choices of others. Copying could serve either to increase the accuracy of mate assessment or to reduce its costs. It is also likely to affect the intensity of sexual selection.

Hotspots and the dispersion of leks

Abstract The settlement of promiscuous males on sites where they are most likely to encounter females was examined by computer simulation. The study extended an earlier model of Parker (1978) , which dealt with male settlement on environmentally fixed mating sites, to include populations of mobile females who can mate at any point in their home ranges. Males in the simulations were expected to settle at sites with high levels of female traffic (hotspots) and to correct for the sharing of females between adjacent sites. As a results, males became clustered into fewer and more compact aggregations as female home range size was increased. Increasing female density or allowing males to settle despotically instead of in a free manner had an opposite effect. The same results were found for both bounded and unbounded surfaces, although there was increased aggregation of males at the centre of bounded surfaces as female size was increased. The model may be relevant to the diversity of male dispersions seen in lek and swarm mating animals.

Female choice in sage grouse: the roles of attraction and active comparison

Abstract Previous studies of female choice in sage grouse Centrocercus urophasianus have implicated both the acoustic quality and repetition rate of the stereotyped strut display as putative cues for female choice. Stages in the choice process at which specific components of male courtship display influence female decisions were investigated using field observations of female pre-mating behavior. Females visited a subset of territorial males and then actively chose one of these as a mate. The order in which males were visited suggested that females searched until an acceptable mate was found, rather than employing a “best-of-n” tactic. Numbers of females visiting a male were related to differences in an acoustical component of display (inter-pop interval) whereas the probability that a visiting female mated was related to display rate (Table 3), indicating that initial attraction and active choice are influenced by different components of display. In addition, inter-pop interval and display rate tended to covary inversely (Fig. 1), suggesting that attraction and active choice may impose conflicting selection pressures on display performance.

Mate-choice copying in black grouse.

Recent field studies of lekking birds and mammals have provided evidence that mate selection in these mating systems may be affected partly by females copying the choices of others. Two pieces of e ...

Reversal of a female preference after visual exposure to a predator in the guppy,Poecilia reticulata

To test the hypothesis that female choice has been subject to direct selection by predators, it was investigated whether female guppies would switch their choice of mate from more to less conspicuous males after observing a potential predator. Social and sexual preferences of virgin females for each of two males differing in amount of carotenoid pigmentation (an ornamental trait) were measured both before and after visual exposure to a novel predatory cichlid. Females initially showed strong social and sexual preferences for the brighter of the two males. Preferred males also showed lower levels of fluctuating asymmetry in the area of carotenoid pigmentation and displayed at higher rates. After exposure to the cichlid, almost half of the females became sexually unreceptive, and the remainder showed a nearly unanimous sexual preference for the duller male. Control females that did not see the cichlid continued to prefer the brighter male. These results imply that predators have selected against females that mate with conspicuous males. They also suggest that predators can influence sexual selection on male ornaments proximately through their effects on female choice as well as by imposing mortality on conspicuous males. Both conclusions suggest that indirect selection on female preferences may not play a dominant role in this system.

Dispersion of displaying male sage grouse

SummaryThe distribution of lek sizes was examined in each of three populations of sage grouse in eastern California. Peak seasonal lek sizes collected over a 35 year period were found to covary among the three sites indicating that some global environmental or demographic features modulated male attendance in any given year. Despite these annual variations, the ranks of the three populations with regard to mean lek size remained stable. In all three populations, there was a persistent excess of small and large leks, compared to random settlement on the same number of sites, and a consistency in the ranking by size of particular sites in successive years. The sequential phenology of lek site occupation in each population was correlated with recolonization of habitats surrounding central wintering refuges each spring. Some lek sites utilized for display in early spring were regularly abandoned prior to the onset of mating as more peripheral leks became active. On top of population, site, and seasonal variations in lek size, pronounced daily fluctuations in attendance were common. Multivariate regressions indicated that an average 36% of the daily variation in male numbers was correlated with weather variables, female attendance levels, and prior raptor harassment. Several outcomes of the analyses support the notion that dispersion of males is partly determined by male settlement on current female traffic patterns (hotspot settlement). The analyses also suggest that display is sufficiently costly that variations in male attendance are in part a result of conflicts between strutting and thermoregulatory expenditures.

A re-evaluation of hotspot settlement in lekking sage grouse

Recent analyses of avian leks have come to conflicting conclusions concerning the role of male settlement on female traffic hotspots. This issue was re-examined in the sage grouse,Centrocercus urophasianus, using data on pre-nesting movements of radiotagged females and the dispersion of lekking males collected during a 10-year field study. As expected with hotspot settlement, leks were preferentially located in areas through which females travelled between wintering and nesting ranges before mating. In addition, the distribution of males among leks was related proximately to variation in numbers of females visiting each lek during the mating period and ultimately to numbers that nested within a 2-km radius, within which nesting hens were preferentially attracted. The results show both that hotspot settlement can explain certain coarse scale features of male dispersion, and that female behaviour during different stages of the pre-nesting period may influence particular components of male dispersion to differing extents.