Nest concealment but not nest size affects nest predation probability in a South American Grass Wren population

JEFFERIES, MARÍA MILAGROS; LLAMBÍAS, PAULO EMILIO

Congreso; North American Ornithological Congress; 2020

Nest depredation is the prime cause of nest failure in passerines. To contribute towards ascertaining how predators shape avian life histories, we evaluated the effects of vegetation cover and nest size over nest depredation probability in a Grass Wren (Cistothorus platensis) population at the Central Andes of Argentina. The Grass Wren is a small insectivorous territorial passerine that builds domed nests well concealed among vegetation. To analyze if visual exposure of nests increases nest depredation, we measured nest vegetation structure at two scales from the nest: micro (0.5m) and meso-site (1m, 3m, 5m and 10m). To assess if predation risk increases with nest size, we evaluated if nest volume was correlated with nest depredation probability. Over 9 breeding seasons, we measured vegetation structure at 304 nest sites and calculated the volume of 236 nests. Nest depredation was affected by vegetation structure at both micro and meso-site scale. Nest survival was higher for nests built on sites with taller grasses at 0.5m and at 5m from the nest. Additionally, nest depredation was lower for those nests located in Pampas Grasses Cortaderia selloana with greater vegetation concealment and placed at further distance from the plant edge. In contrast, nest depredation probability was not affected by nest volume. Our results suggest that nest concealment and location are more important in determining nest depredation than nest size.