Age-related differences in diet and foraging behavior of the critically endangered Mariana Crow (<italic>Corvus kubaryi</italic>)
Faegre, Sarah K.
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The Mariana Crow (<italic>Corvus kubaryi</italic>) is a critically endangered, island-endemic corvid whose single remaining population is on the island of Rota, CNMI. Quantitative information on the Mariana Crow's diet is lacking and the effects of age and season on diet and foraging behavior are unknown. Most corvids are social omnivores that typically learn from adults to master complex foraging behaviors. We hypothesized that age-related differences in the diets and foraging behaviors of Mariana Crows would occur due to both a period of physical maturation and steps in learning. This study identified 619 food items taken by 36 wild crows and determined the corresponding foraging strata and substrates for 469 and 363 items respectively. Fourteen percent of food captures were plant-based and 86% were animal prey; 65% of animal prey were insects or their larvae and eggs. The study also identified 209 food items, and their corresponding forest strata and substrates, taken by two captive-reared crows during the first eleven months post-release. Comparisons of the foraging behavior and diets of captive-reared and wild crows indicated that the released crows foraged on all important prey types taken by wild crows; however, several differences in food category proportions were noted. Data from wild crows were analyzed for the effects of age class on two categorical variables: food category and foraging strata, as well as the effects of season on food category. No effect of season was detected; there was, however, a strong association between age class and food category and a moderate association between age class and foraging strata. Two food categories, fruits/seeds/plants and ants/termites/larvae, which were procured and processed with simple behaviors, were taken more frequently by fledglings. Crabs, which were processed using complex behaviors, were captured more frequently by adults. Adults acquired more food items from the ground than other age classes, a result that was driven by their high levels of crab predation. These results highlight vulnerabilities resulting from foraging behavior and may also be useful in assessments of habitat quality and design of diets and enrichment opportunities for captive crows.
- Psychology