Habitat-Specific Population Growth of a Farmland Bird

Abstract

BackgroundTo assess population persistence of species living in heterogeneous landscapes, the effects of habitat on reproduction and survival have to be investigated.Methodology/Principal FindingsWe used a matrix population model to estimate habitat-specific population growth rates for a population of northern wheatears Oenanthe oenanthe breeding in farmland consisting of a mosaic of distinct habitat (land use) types. Based on extensive long-term data on reproduction and survival, habitats characterised by tall field layers (spring- and autumn-sown crop fields, ungrazed grasslands) displayed negative stochastic population growth rates (log λs: −0.332, −0.429, −0.168, respectively), that were markedly lower than growth rates of habitats characterised by permanently short field layers (pastures grazed by cattle or horses, and farmyards, log λs: −0.056, +0.081, −0.059). Although habitats differed with respect to reproductive performance, differences in habitat-specific population growth were largely due to differences in adult and first-year survival rates, as shown by a life table response experiment (LTRE).Conclusions/SignificanceOur results show that estimation of survival rates is important for realistic assessments of habitat quality. Results also indicate that grazed grasslands and farmyards may act as source habitats, whereas crop fields and ungrazed grasslands with tall field layers may act as sink habitats. We suggest that the strong decline of northern wheatears in Swedish farmland may be linked to the corresponding observed loss of high quality breeding habitat, i.e. grazed semi-natural grasslands.

Stage-dependent survival in relation to timing of fledging in a migratory passerine, the Northern Wheatear (Oenanthe oenanthe)

“…This could be especially true for late fledglings: to avoid competition with early fledglings and adults, they may choose to prepare for moult and migration away from the natal site and choose to breed at the novel site the next spring. Fortunately, Northern Wheatears show a very high degree of (natal) fidelity in our (Van Oosten et al 2015) and other study populations, such as in Sweden (Arlt et al 2008), on Fair Isle, UK (Seward et al 2013) and in France (Henry and Ollivier 2015). This is a common pattern in many bird species (Maness and Anderson 2013), and also other factors (covarying with fledging date) could explain the patterns found here.…”

Experimental evidence for an ideal free distribution in a breeding population of a territorial songbird

“…In the Ovenbird, stress levels and sex ratio in nestlings have also been shown to differ between partially harvested and control plots (Leshyk et al 2012). Ultimately, this may reduce male fitness and, thus, population growth rates among habitat types varying in quality (Arlt et al 2008). For these reasons, relatively subtle impacts of human activities on population dynamics deserve careful attention when considering our ever-expanding ecological footprint.…”

Disentangling the effects of date, individual, and territory quality on the seasonal decline in fitness

“…The use of a 2–5 km buffer zone minimized possible biases in recruitment probability due to natal dispersal (see Arlt et al. and Doligez and Pärt for a general discussion). Adults were classified as yearlings or ≥2 yr old, based on plumage characteristics (Pärt ).…”