Identifying Nest Predators of American Avocets (Recurvirostra americana) and Black-Necked Stilts (Himantopus mexicanus) in San Francisco Bay, California

Abstract

We evaluated predation on nests and methods to detect predators using a combination of infrared cameras and plasticine eggs at nests of American avocets (Recurvirostra americana) and black- necked stilts (Himantopus mexicanus) in Don Edwards San Francisco Bay National Wildlife Refuge, San Mateo and Santa Clara counties, California. Each technique indicated that predation was prevalent; 59% of monitored nests were depredated. Most identifiable predation (n 5 49) was caused by mammals (71%) and rates of predation were similar on avocets and stilts. Raccoons (Procyon lotor) and striped skunks (Mephitis mephitis) each accounted for 16% of predations, whereas gray foxes (Urocyon cinereoargenteus) and avian predators each accounted for 14%. Mammalian predation was mainly nocturnal (mean time, 0051 h 6 5 h 36 min), whereas most avian predation was in late afternoon (mean time, 1800 h 6 1 h 26 min). Nests with cameras and plasticine eggs were 1.6 times more likel yt o be predated than nests where only cameras were used in monitoring. Cameras were associated with lower abandonment of nests and provided definitive identification of predators.