Food, audience and sex effects on pinyon jay (Gymnorhinus cyanocephalus) communication.

Pinyon jays (Gymnorhinus cyanocephalus) have a complex social system that may require a complex communication system. They need to interact with multiple flock members, and they form life-long pair-bonds. We researched whether pinyon jays would selectively vocalize depending on the presence or absence of food and certain flock members. We recorded the vocalizations of nine pinyon jays (four pair-bonds and one single male) in response to different audience types. The calls of the test bird were recorded after it was given either an empty food cup or one containing 50 pinyon pine (Pinus edulis) seeds, and the bird was in the presence of one of the following audience types: (1) two males and two females including subject's mate; (2) two males and two females excluding subject's mate; (3) four males excluding mate; (4) three females excluding mate; and (5) no audience. Birds gave fewer calls when there was food. When alone, birds called in a manner that may maximize long-distance transmission. Trends indicate that birds call differently to their mate. A sex effect was also found in that males and females called in a distinct manner, possibly reflecting differences in dominance status. Overall, birds responded to the presence or absence of an audience.

Sociality and social learning in two species of corvids: the pinyon jay (Gymnorhinus cyanocephalus) and the Clark's nutcracker (Nucifraga columbiana).

The hypothesis that social learning is an adaptive specialization for social living predicts that social species should learn better socially than they do individually, but that nonsocial species should not exhibit a similar enhancement of performance under social learning conditions. The authors compared individual and social learning abilities in 2 corvid species: the highly social pinyon jay (Gymnorhinus cyanocephalus) and the less social Clark's nutcracker (Nucifraga columbiana). The birds were tested on 2 different tasks under individual and social learning conditions. Half learned a motor task individually and a discrimination task socially; the other half learned the motor task socially and the discrimination task individually. Pinyon jays learned faster socially than they did individually, but nutcrackers performed equally well under both learning conditions. Results support the hypothesis that social learning is an adaptive specialization for social living in pinyon jays.

Differences in hippocampal volume among food storing corvids.

The hippocampal complex (hippocampus and parahippocampalis) is known to play a role in spatial memory in birds and is known to be larger in food-storing versus non-storing birds. In the present study, we investigated the relative volume of the hippocampal complex in four food-storing corvids: gray-breasted jays (Aphelocoma ultramarina), scrub jays (Aphelocoma coerulescens), pinyon jays (Gymnorhinus cyanocephalus), and Clark's nutcrackers (Nucifraga columbiana). The results show that Clark's nutcrackers have a larger hippocampal complex, relative to both body and total brain size, than the other three species. Clark's nutcrackers rely more extensively on stored food in the wild than the other three species. Clark's nutcrackers also perform better during cache recovery and operant tests of spatial memory than scrub jays. Thus, greater hippocampal volume is associated with better performance in laboratory tests of spatial memory and with stronger dependence on food stores in the wild.

Performance of four seed-caching corvid species in operant tests of nonspatial and spatial memory.

The performance of 4 seed-caching corvid species was tested using 2 different operant nonmatching tasks. These species differ in their dependence on stored food, and differences in spatial memory tests have been correlated with better performance by the more cache-dependent species. Acquisition and retention of a color non-matching-to-sample task was tested in Experiment 1. Acquisition of the color task was not correlated with cache dependence, and no differences between species in performance during memory testing were found. Acquisition and retention of an operant spatial non-matching-to-sample task was tested in Experiment 2. Species differences in the spatial task were found for acquisition and during retention testing. The influence of natural history on the evolution of memory is discussed.

Performance of four seed-caching corvid species in the radial-arm maze analog.

Four seed-caching corvid species were tested in an open-room analog of the radial-arm maze. During Experiment 1, the species more dependent on stored food. Clark's nutcrackers (Nucifraga columbiana) and pinyon jays (Gymnorhinus cyanocephalus), acquired the task more quickly and to higher accuracy levels than either scrub jays (Aphelocoma coerulescens) or Mexican jays (A. ultramarina). During Experiment 2, performance after retention intervals was tested. When intervals of 30-210 min were tested in ascending order, species differences observed during acquisition were again obtained. However, when intervals of 5-300 min were tested in random order, the species differed only at shorter intervals. During Experiment 3, only nutcrackers gave any indication of performing above chance after a 24-hr retention intervals. Results support the hypothesis of species differences in spatial information processing that correlate with dependence on stored food.

Effects of response strategy and retention interval on performance of Clark's nutcrackers in a radial maze analogue.

Two groups of Clark's nutcrackers (Nucifraga columbiana) were trained to use either a stay or shift response strategy in a radial maze analogue. Each trial had a preretention stage, a retention interval, and a postretention test. In Experiment 1, acquisition with a 5-min retention interval was studied. Response strategy did not affect the rate at which the task was learned. Performance following longer retention intervals was tested in Experiments 2-4. Changes in retention intervals were presented in trial blocks of increasing duration in Experiment 2 and were randomly presented between trials in Experiment 3. Experiment 4 extended the retention interval to 24 hr. No difference in performance was found between the 2 groups in any of these experiments. These results suggest a flexible relationship between spatial memory and response requirement in food-hoarding birds for at least 1 spatial memory task.

Investigations of density interactions among breeding birds in ponderosa pine forests: correlative and experimental evidence.

We assessed the importance of interspecific competition among insectivorous birds breeding in northcentral Arizona's ponderosa pine forests. We examined density interactions among species using two analytic approaches; correlative and experimental. The correlative approach examined patterns of change in breeding densities over four years at the community level and within two foraging guilds; picker-gleaners and aerial feeders. The relationships between morphological and behavioral similarity with pairwise density interactions were also assessed. Our experimental approach involved placement of nest boxes on two treatment plots to increase breeding densities of secondary cavity nesting birds that were in foraging guilds with open nesting insectivores.We found little evidence of interspecific competition. Patterns of density fluctuations indicated large positive covariances among species at both the community level and within guilds. Pairwise density interactions were independent of morphological or behavioral similarity. Nest boxes significantly increased breeding densities of the secondary cavity nesters. However, these increases did not induce reprocal density changes in the open nesting species. Interspecific competition for food during the breeding season appears to be unimportant in ponderosa pine bird communities.