Mortality of Wood Warbler Phylloscopus sibilatrix nests in Welsh Oakwoods: Predation rates and the identification of nest predators using miniature nest cameras

Abstract

Capsule Predation was the main cause of nest failure, but predation rates have remained unchanged since the 1980s. Eurasian Jays Garrullus glandarius were the most common predator. Aims To quantify, and compare, nest predation rates for 1982-84 and 2009-11, and to identify predators of Wood Warbler Phylloscopus sibilatrix nests in Welsh oakwoods. Methods During 2009-11, 167WoodWarbler nestsweremonitored and purpose-builtminiature nest cameras deployed at 73 of them.Nest predation rates were compared with 67 nests monitored during 1982-84. Results Of 167 nests monitored from2009 to 2011, 62 failed due to predation (32/73 camera nests, 30/94 non-camera nests), giving an overall Daily Survival Rate (DSR + se) of 0.979 + 0.003. This was not significantly different fromthe rate during 1982-84 (0.967 + 0.006). In 2009-11, the DSR of nests declined temporally during the season at both the egg and chick stages. For chick stage nests, DSR varied annually and nonlinearlywith age of nestlings. Therewas no evidence for an effect of cameras at either stage. Of 32 camera nests lost to predation, the predator was identified from28, resultingin30predatorsbeing identified. Therewas one case ofmultiple predators at a single nest. Themajority of nest predation was carried out by birds (28/30), predominantly Eurasian Jays (18/28), but also Common Buzzards Buteo buteo (5/28), Great Spotted Wood peckers Dendrocoposmajor (3/28) and Eurasian Sparrowhawks Accipiter nisus (2/28). Therewas one predation by both a Eurasian Badger Meles meles and a Red Fox Vulpes vulpes. There were no records of Grey Squirrels Sciurus carolinensis depredating nests. Conclusions Nest predation rates were similar in both periods, suggesting that increased rates of nest predation have not been driving the decline of theWoodWarbler population inWales. Deployment of nest cameras did not affect nest survival rates and were successful in identifying nest predators, the majority of which were avian, especially Eurasian Jays. Knowledge of the identity of nest predators can aid the development of conservation measures. © 2012 British Trust for Ornithology.