Effects Of Nest Predation On A South Temperate House Wren Population

Nest predation can have several effects on breeding birds. It reduces breeding success but also, it can strongly affect parental investment and reproductive decisions. Here we tested the extent of effects of nest predation on south temperate house wrens Troglodytes aedon bonariae by comparing the nesting success and breeding decisions of pairs breeding in plots that differed in nesting failure rates. During 2007 and 2008 breeding seasons we monitored nests built in nest boxes with a 27 mm entrance hole in a plot (E1) and with a 54 mm entrance hole in another plot (E2). At the end of the 2008 breeding season we reduced entrance holes of nest boxes at E2 to 27 mm. During 2007 and 2008 breeding seasons, nest failures were higher at E2 than E1 (70.6% and 25.8% respectively). Clutch sizes, brood sizes and number of fledgling produced per nest were smaller in E2 than in E1. However, females at E2 laid bigger eggs. Hatching success was lower at E2 than at E1, but fledgling success was similar between sites. Females nesting at E2 performed less frequently a second brood than those at E1. We did not detect differences between sites in individual breeding dispersal, mate change, apparent adult survival and offspring survival and recruitment. As a consequence of a reduced clutch size, higher hatching failures and lower frequency of double broods, individuals nesting at E2 had a lower annual productivity than those at E1. No differences in nest failure frequency and productivity were found between sites during the 2009 and 2010 breeding seasons. Our results provide experimental evidence of the existence of reproductive costs beyond nest loss associated with nesting in areas with high risk of nest predation in house wrens.