Behavioral Ecology of the Mariana Crow (Corvus kubaryi): Age-related Foraging, Spatial Behavior, Habitat Selection, and Correlates of First Year Survival

Abstract

There is little information on Mariana Crow foraging, spatial behavior, habitat selection, or the correlates of first year survival, yet these topics of study are critical for management and species recovery. In this work, we demonstrate that adult crows forage more frequently on hermit crabs, which they process using complex behaviors, while fledglings rely more on fruits, and insect larvae, which they procure and process with simple behaviors. Adults acquire more food items from the ground than other ages due to their frequent predation of hermit crabs. We also demonstrate that fledglings have reduced mobility during the first 4-10 weeks post-fledging and that, after controlling for this low post-fledging mobility, sub-adult Mariana Crows range over larger areas than fledglings and family groups. Regardless of age, Mariana Crows have dynamic, shifting home ranges which lack stable boundaries. Mariana crow family groups have core areas that they return to regularly, even as ranges shift. However, we found no evidence of habitat differences in core areas, compared to infrequently used, outer portions of ranges. In our radio-telemetry study of 22 fledglings, only 45% of individuals survived their first year and the majority of deaths were ruled feral cat predations, based on the appearance of the remains. Fledglings with shorter wings had reduced home ranges and daily movements, and lower first year survival. These results highlight vulnerabilities resulting from foraging, spatial behavior, and physical development at fledging. We emphasize the importance of learning in the development of foraging behaviors, the need for habitat-wide predator management to improve first year survival, and need for continued research into the mechanisms leading to poorly developed fledglings with reduced first year survival.