Abstract: We investigated the foraging producer-scrounger system of a captive flock of feral pigeons (Columba livia) by monitoring the number of food patches each individual produced. In one experiment, three different patch types were tested on the whole flock while, in a second, flock composition was varied for one patch type. In all cases we found non-uniform distributions of the number of patches produced per individual, which suggests the existence of producer and scrounger roles. This result could not be explained by either dominance or variability in individual learning ability. Individuals switched roles in response to changes both in food patch type and flock composition. These results are discussed in light of the skill pool hypothesis, which suggests that, in a group, different foraging specialists will profit by parasitizing each other's food discoveries.

Abstract: INTRODUCTION Africa is the earth's second largest continent, comprising 20% of its surface. Largely tropical, Africa extends as well into temperate zones to 37 N and 35 S. Eastern and southern Africa display steep elevation gradients due to the prevalence there of volcanic orogeny and rifting (29). Local landscapes are distinguished by substantial geological heterogeneity, dissected land forms, and resultant steep gradients of precipitation and vegetation. The consequent pronounced fragnientation of habitats and sharp juxtaposition of distinct vegetation types, combined with climatic oscillations in geological time, contributed to major adaptive radiations of the mammalian fauna (102, 120). Early zoological expeditions recorded that habitat fragmentation and wide spatial variation of animal densities and diversities were distinctive features of African ecosystems (92, 138, 162, 226). Those early records provided the bases of natural history information on animal distributions, habitat preferences, feeding habits, and general ecology; scientific research followed only much later (201). Modem scientific study of African savanna-grassland mammals began in the 1950s (23, 24, 107, 108, 148, 149, 197,203, 204, 210,230), long after the distributions and densities of the major game animals had been affected by growing human populations, colonial land and hunting policies, and virulent exotic diseases that affected the animals both directly and indirectly (57). The mammalian fauna has been increasingly isolated and fragmented within game reserves of varying size, habitat diversity, and animal species diversity; the ability to sustain it in the absence of active management is increasingly questioned (112, 187). For species with population sizes greater than 100 individuals, game reserve area (A) and faunal ...

Abstract: Sixteen Quarter Horses were randomly divided into two groups after sorting by age and sex. After a 10-day preconditioning period, each animal was scored for emotionality and trainability. Each group then completed a series of learning tasks in a modified T-maze for 20 consecutive days. Group P/D was initially tested on a simple place-learning task, while Group D/P was trained in a visual discrimination task. The groups were tested alternately on the two tasks with 10-day extinction periods between each task. Upon reaching a criterion of 11 of 12 correct responses (the last 8 responses consecutive), a horse was retired for the day. If this criterion was not attained, the horse completed 20 trials. Learning occurred at a faster rate on the discrimination tasks compared to the gradual learning curves observed on place tasks. Animals learned more rapidly and reached higher levels of performance as the series of tasks progressed. Trainability and emotionality scores tended to predict the final level of learning achieved. Correlations of performance ranks within emotionality and training groups were higher between tasks of the same type than between the different tasks. Rank correlations between odd and even days on each task indicated that the within-group rankings were more consistent on the discrimination task than on the place task.