Characteristics of Common Raven (Corvus corax) Predation on Sandhill Crane (Grus canadensis) EGGS

Abstract

Abstract Common Ravens (Corvus corax) are considered an important predator of Sandhill Crane (Grus canadensis) eggs, but direct observations of predation events are rare. We observed 25 events of Common Ravens at or near artificial nests with infertile crane eggs; 15 of those events resulted in predation. Reconnaissance time averaged 1.8 ± 3.0 min, egg handling averaged 5.8 ± 3.9 min, and total time to reconnoiter, approach, and consume or remove eggs from a nest averaged 8.4 ± 5.7 min. Ravens consumed 67% of the eggs at the nest and cached the other 33%. To eat an egg, ravens always punched a hole in the surface, but hole sizes and shapes differed. To cache eggs, ravens carried eggs away intact, leaving no evidence in the nest, and concealed them 5.5 to 180 m from the nest. The rapidity of some raven depredation events indicates a high potential for success of taking crane eggs from an active but unattended nests. Given the diverse patterns of eggshell remains and ravens' ability to carry whole eggs, dis...