Abstract: 1. The niche separation of three species of alcelaphine antelope (wildebeest, topi and hartebeest) with similar body size was compared by measuring bite weight, bite rate, intake rate and selectivity of tame animals in plots containing grass at different growth stages. 2. On growing swards, hartebeest had a smaller bite weight and lower intake rate, and were also less selective of green leaf, than either topi or wildebeest. On senescent swards, hartebeest were more selective of leaf than the other two species. 3. Wildebeest had a faster bite rate than either topi or hartebeest on swards with low biomass and high protein content of green leaf (green flush). Bite weight and intake rate of wildebeest and topi were similar despite the difference in breadth of their incisor rows. 4. Topi were significantly more selective of green leaf than the other two species and were the only species to maintain a rapid bite rate on swards with high green leaf biomass. 5. The feeding experiments did not reveal significant cross-overs between species in the rate of food intake on different grass types, but each species was most proficient either in leaf selection or bite rate when feeding on grass swards in a particular growth stage. We suggest that growth stage is a primary determinant of niche separation. 6. In Serengeti, grazing ungulates which migrate are specialists of the earlier growth stages of grass which tend to be transient, while those that are residential specialize on late growth stages which are more enduring. The mobility of species, and the spatial and temporal dynamics of pastures containing different growth stages of grass, contribute to niche separation.

Abstract: In most cooperatively breeding birds and mammals, reproductive rates are lower for social subordinates than for dominants, and it is common for reproduction in subordinates to be completely suppressed. Early research conducted in captivity showed that losing fights can increase glucocorticoid (GC) secretion, a general response to stress. Because GCs can suppress reproduction, it has been widely argued that chronic stress might underlie reproductive suppression of social subordinates in cooperative breeders. Contradicting this hypothesis, recent studies of cooperative breeders in the wild show that dominant individuals have elevated GCs more often than do subordinates. The findings that elevated GCs can be a consequence of subordination or a cost of dominance complicate the conventional view of social stress, with broad ramifications for the evolution of dominance and reproductive suppression.

Abstract: Mobbing signals advertise the location of a stalking predator to all prey in an area and recruit them into the inspection aggregation. Such behavior usually causes the predator to move to another area. However, mobbing calls could be eavesdropped by other predators. Because the predation cost of mobbing calls is poorly known, we investigated whether the vocalizations of the mobbing pied flycatcher, Ficedula hypoleuca, a small hole nesting passerine, increase the risk of nest predation. We used mobbing calls of pied flycatchers to examine if they could lure predators such as the marten, Martes martes. This predator usually hunts by night and may locate its mobbing prey while resting nearby during the day. Within each of 56 experimental plots, from the top of one nest-box we played back mobbing sounds of pied flycatchers, whereas blank tapes were played from the top of another nest-box. The trials with mobbing calls were carried out before sunset. We put pieces of recently abandoned nests of pied flycatchers and a quail, Coturnix coturnix, egg into each of the nest-boxes. Nest-boxes with playbacks of mobbing calls were depredated by martens significantly more than were nest-boxes with blank tapes. The results of the present study indicate that repeated conspicuous mobbing calls may carry a significant cost for birds during the breeding season.

Abstract: Group foragers may be able to assess patch quality more efficiently by paying attention to the sampling activities of conspecifics foraging in the same patch. In a previous field experiment, we showed that starlings foraging on patches of hidden food could use the successful foraging activities of others to help them assess patch quality. In order to determine whether a starling could also use another individual's lack of foraging success to assess and depart from empty patches more quickly, we carried out two experimental studies which compared the behaviour of captive starlings sampling artificial patches both when alone and when in pairs. Solitary starlings were first trained to assess patch quality in our experimental two-patch system, and were then tested on an empty patch both alone and with two types of partner bird. One partner sampled very few holes and thus provided a low amount of public information; the other sampled numerous holes and thus provided a high amount of public information. In experiment 1, we found no evidence of vicarious sampling. Subjects sampled a similar number of empty holes when alone as when with the low and high information partners; thus they continued to rely on their own personal information to make their patch departure decisions. In experiment 2, we modified the experimental patches, increasing the ease with which a bird could watch another's sampling activities, and increasing the difficulty of acquiring accurate personal sampling information. This time, subjects apparently did use public information, sampling fewer empty holes before departure when with the high-information partner than when with the low-information partner, and sampling fewer holes when with the low-information partner than when alone. We suggest that the degree to which personal and public information are used is likely to depend both on a forager's ability to remember where it has already sampled and on the type of environment in which foraging takes place.

Abstract: Abstract Calls to understand the links between ecology and evolution have been common for decades. Population dynamics, i.e. the demographic changes in populations, arise from life history decisions of individuals and thus are a product of selection, and selection, on the contrary, can be modified by such dynamical properties of the population as density and stability. It follows that generating predictions and testing them correctly requires considering this ecogenetic feedback loop whenever traits have demographic consequences, mediated via density dependence (or frequency dependence). This is not an easy challenge, and arguably theory has advanced at a greater pace than empirical research. However, theory would benefit from more interaction between related fields, as is evident in the many near-synonymous names that the ecogenetic loop has attracted. We also list encouraging examples where empiricists have shown feasible ways of addressing the question, ranging from advanced data analysis to experiments and comparative analyses of phylogenetic data.