REPRODUCTIVE SUCCESS OF COMMON RAVENS INFLUENCES NEST PREDATION RATES OF THEIR PREY: IMPLICATIONS FOR EGG-OILING TECHNIQUES.
Brianne E. Brussee; U.S. Geological Survey; 800 Business Park Dr. Suite D, Dixon, CA, 95818; (530) 669-5071; bbrussee@usgs.gov; Peter S. Coates
Increased abundance and distribution of Common Ravens (Corvus corax) across western North America is a likely characteristic of the Anthropocene, and effective measures are often needed to minimize raven impacts on sensitive prey species. We designed a 6-year study using remote videography on nests of ravens and their prey (black-crowned night-herons, Nycticorax nycticorax) on Alcatraz Island. Our goals were to: 1) document effects of oiling raven eggs, a technique designed to kill eggs, on raven reproduction; and 2) estimate subsequent impacts of reduced raven hatching success on night heron nest and chick survival. Results from Bayesian multinomial logistic exposure models revealed that daily predation rates on night-heron nests and chicks were the highest during years when ravens nested successfully. Daily predation rates on night heron nests and chicks decreased during years with raven egg-oiling, and the lowest daily predation rates for nests occurred during years when ravens did not naturally nest on the island. Survival of night heron eggs and chicks was also highest during years when ravens were present but not nesting on Alcatraz. Our results suggest that egg-oiling can be a viable localized method to reduce raven recruitment and may aid in the conservation of sensitive avian species.
Ecology and Conservation of Birds I