Kelly, J. P., Etienne, K. L., Roth, J. E.
An investigation of nest predation and associated foraging behaviors by resident Common Ravens (Corvus corax) indicated that occupation of heronries, predation of Great Egret (Ardea alba) nests, duration of patrol flights, landing rates, and number of interactions with ardeids varied with the productivity of resident ravens. Annual increases in raven predatory behaviors were consistent with increases in foraging experience for a few to several years after ravens became resident at colony sites. However, overall nest predation did not increase at three sites from 1999–2004, and at one of these sites, predation did not differ from levels measured before ravens were resident, suggesting that ravens may have interfered with the nest predatory activities of other species. Ravens at one colony site obtained most or all of their energy needs from the heronry. Predation of Great Egret nestlings was most likely 14–29 days after first hatch, when parental attendance begins to decline. Regional monitoring of heronries in the San Francisco Bay area, California, indicated highly variable rates of nest predation by Common Ravens and a low overall presence of ravens, even though ravens occurred throughout the region. Implications for conservation include the potential value of manipulating raven reproduction to limit nest predation, exclusion of other nest predators by resident ravens, annual increases in nest predatory behaviors, and the importance of regional monitoring to substantiate concerns about raven predation.
Kelly, J. P., K. L. Etienne, and J. E. Roth. 2005. Factors influencing nest predatory behaviors of Common Ravens in heronries. Condor 107: 402-415.