Two populations of Barbados Zenaida dove (Zenaida aurita) have in previous work been found to use two radically different modes of feeding competition. The St. James (StJ) population is territorial; it competes aggressively with conspecifics but scramble competes with heterospecifics. The Deep Water Harbour (DWH) population forages nonaggressively in large homospecfic flocks. Earlier studies linking these social differences with differences in individual and social learning suggest that Z. aurita is ideal for testing predictions from Brown's (1964) theory of economic defendability. Firstly, the hypothesis that resource defence will increase as the spatial clumping and temporal predictability of a resource increases was tested at 6 sites at DWH with a randomized complete block design. Secondly, spatial distribution of food was manipulated at both DWH and StJ in an attempt to alter the mode of foraging competition at DWH from scramble to interference, and to elicit group-feeding in the otherwise territorial StJ doves. As predicted, rates of aggression per intruder were highest for those sites at DWH receiving a spatially clumped and temporally predictable food source. Unlike those at DWH, doves from StJ did not modify their mode of foraging competition in response to variations in spatial distribution, but rather as a consequence of increased resource density. Interference competition appears to be the default strategy for Zenaida doves, with birds switching to scramble competition when a threshold of resource density is reached, only to revert back to aggressive defence when the spatial clumping and temporal predictability of food increases.

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Previous work on feral pigeons (Columba livia) and zenaida doves (Zenaida aurita) suggests that both individual and social learning varies with type of competition: rapid non-aggressive feeding is associated with rapid individual learning as well as rapid social learning from the tutor types a bird usually feeds with in the field. Comparative learning tests, however, may be influenced by intervening variables like neophobia and tameness: tests are always run on captive animals by human experimenters using novel stimuli. / This thesis compares pigeons to territorial and group-feeding zenaida doves on their response to novel stimuli in the field and in captivity, in the presence or absence of humans. In single cages, tameness and neophobia co-vary with learning: pigeons are more rapid than doves at learning, at interacting with a novel apparatus and at feeding in the absence of the human; territorial zenaida doves are slower than group-feeding doves on all three tests. Multiple regressions show that neophobia and tameness explain an important part of the variance in learning. These results are confirmed by a re-analysis of data previously obtained on finches (Whittle, 1996), where neophobia predicts individual learning which in turn predicts social learning. / In the field, however, neophobia has opposite effects: territorial zenaida doves now show the smallest effect of novel stimuli on feeding latency. Experiments that test evolutionary predictions about learning using captive animals are thus open to questions of internal and external validity: when we measure comparative performance on a captive learning test, is it really learning we are measuring and does it mirror, as it should, adjustment to environmental novelty in the field?

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