Latitudinal differences in life-history traits and parental care in northern and southern temperate zone House Wrens

Abstract

South temperate songbirds differ from northtemperate species in life-history traits, having greater adultsurvival, smaller clutch size, longer developmental periodsand extended parental care. Due to its broad distribution,the House Wren, Troglodytes aedon, is an excellent modelto evaluate selective pressures that may influence themaintenance of present clutch size. Here we report data onlife-history traits and parental care of socially monogamousHouse Wrens from a north temperate and a south temperatepopulation. Southern House Wrens exhibited smallerclutch sizes and longer developmental periods thanNorthern House Wrens; however, we did not find significantdifferences in adult survival probability betweenpopulations, contrary to a critical prediction of the cost ofreproduction hypothesis. Our data did not support the hypothesisthat smaller clutches are the consequence ofgreater food limitation in the south. Southern wrens havegreater adult body mass but smaller territories; southernnestlings reached a greater proportion of adult body mass6?7 days before fledgling, and provisioning rates to thenest per nestling were greater in the south. We did not findsupport for the hypothesis that reduced clutch size is aconsequence of limited parental activity at the nest assouthern wrens did not reduce parental care during theincubation and nestling stage. Our data better supports theoffspring quality hypothesis; southern wrens invest moreper nestling than northern wrens as provisioning rates pernestling were significantly higher and developmental periodslonger in the south. Published results from TropicalHouse Wrens suggest that neither food limitation nor nestpredation can explain reduced clutches in Central America.We suggest that south temperate and tropical wrens maydiffer in parental investment strategies as tropical wrensseem to invest even less per nestling than north temperatewrens