Factors influencing vigilance while feeding in reintroduced California condors (Gymnogyps californianus)

Pressure from potential predators makes vigilance critical for an individual's survival, especially during times of vulnerability. California condors (Gymnogyps californianus), with their heavy bodies and large, broad wings, are slow to take-off. This makes vigilance an essential survival behavior for condors due to their susceptibility when feeding on carcasses. Relatively high overall mortality among reintroduced condors has raised questions regarding the suitability of release candidates. Reduction in this overall mortality is of primary concern to the California Condor Recovery Program. I investigated factors influencing vigilance in 31 reintroduced California condors while feeding on proffered carcasses at a primary release site in Southern California. I measured individual vigilance, via scanning frequency, and a suite of factors previously shown to influence vigilance. I used an information theoretic approach to determine which of a set of explanatory models best fit the variation in anti-predator scanning frequency observed in my data. The best fitting model incorporated the following variables in order of decreasing importance: a negative correlation with the number of individuals at the carcass feeding site, a negative correlation with Julian date, a positive correlation with focal bird age, sex (males were more vigilant than females), and a negative correlation with ambient temperature. Examination of survival behaviors such as vigilance may allow for more rapid identification of problematic behaviors in release candidates, as well as providing insight for aviculturists and field managers regarding foci for future management efforts.