Habitat and weather are weak correlates of nestling condition and growth rates of four UK farmland passerines

Abstract

Agricultural intensification is believed to have driven declines of farmland bird populations and the invertebrates and weeds on which they feed. We investigated whether habitat and weather, as surrogates for food availability, influenced nestling growth rates and condition of four farmland passerines (Skylark Alauda arvensis , Chaffinch Fringilla coelebs , Linnet Carduelis cannabina and Yellowhammer Emberiza citrinella ). We also tested whether nestling growth rates or condition influenced whether a brood subsequently fledged, starved or was depredated. Linnet nestlings are fed almost exclusively on seeds, and were unaffected by weather. Nestlings of the other species are fed mainly invertebrates and were affected negatively by rain but positively by increasing minimum temperatures and daily hours of sunshine. Condition and growth rates of Linnet nestlings were lower in nests further from oilseed-rape fields, rape seeds being important in the diet of this species. Nestlings of the other three species were unaffected by availability of habitats selected by parents foraging for nestling food. Brood fate was not influenced by growth rates or condition for any species. Most models explained little variation in the response variable. Possible reasons, including the possibility that parents trade off their own survival prospects to ensure reproductive success, are discussed.

Nest and foraging‐site selection in YellowhammersEmberiza citrinella: implications for chick provisioning

“…Where nest failures occurred and the date was unknown, failure was assumed to have occurred at the mid-point between the two final visits to the nest. Where nests were discovered at the chick stage and age was unknown comparisons were made with the feather tract development of chicks of known age (as per Bradbury et al 2003). Nests were checked when chicks were 10 days old to determine fledging success; where a nest contained chicks at 7 days and the nest remained intact but was empty at 10 days (making predation of chicks immediately prior to fledging unlikely), the chicks were deemed to have fledged successfully.…”

“…Nestling © 2010 British Trust for Ornithology, Bird Study, 57, 531-539 mortality in this species has been linked to weather variables such as cold temperatures and increased rainfall that decrease both numbers and activity levels of invertebrates (Bradbury et al 2003, Stoate et al 1998, and a reduction in the growth and body condition of chicks has been linked to the use of pesticides during the breeding season, through a decrease in invertebrate populations (Hart et al 2006, Morris et al . 2005.…”

Effects of breeding habitat and field margins on the reproductive performance of Skylarks (Alauda arvensis) on intensive farmland

“…Yet, the relationship between food availability and nestling condition or survival is not consistently positive, perhaps because factors like accessibility, prey profitability and nutrient composition are not always accounted for. Although some studies found improved nestling weight and survival when food availability around the nest was higher, for example for Yellowhammer Emberiza citrinella (Hart et al 2006), Linnet Carduelis cannabina (Bradbury et al 2003) and Corn Bunting Miliaria calandra (Brickle et al 2000;Boatman et al 2004), other studies could not detect such correlations for Chaffinch Fringilla coelebs (Bradbury et al 2003), Yellowhammer (Bradbury et al 2003) and Yellow Wagtail Motacilla flava (Gilroy et al 2009). For Skylarks, there are indications that nestling condition is significantly affected by the abundance of chick food within 100 m of the nest (Boatman et al 2004).…”

“…A possible explanation is that Skylark parents were able to compensate for a poorer environment by increasing their foraging efforts (Bradbury et al 2003;Gilroy et al 2009). When parents make longer or more frequent foraging flights, this can ultimately lead to reduced condition, elevated mortality rates or a reduced number of breeding attempts per year (Martin 1995;Siriwardena et al 2000).…”

“…A condition-independent indicator of growth (tarsus length) was measured to the nearest 0.1 mm using a pair of callipers. Rainfall and temperature may affect nestling body weight and survival (Donald et al 2001b;Bradbury et al 2003) and were therefore included in the analyses. Meteorological data were obtained from a weather station in the research area (Nieuw Beerta, N53°11.662, E007°8.966), owned by the Dutch Meteorological Institute (KNMI).…”