Maintenance of livestock farming may buffer population decline of the Barn SwallowHirundo rustica

Abstract

SummaryPopulations of farmland and long-distance migratory birds have suffered steep, often dramatic, declines in the last few decades. The Barn Swallow Hirundo rustica is a small migratory farmland bird that breeds synanthropically in farms, particularly where livestock is reared. Populations of this species have suffered marked declines in different parts of its European breeding range. Here, we first report a dramatic decline of 8.4% per year of the number of breeding pairs and the extinction of 19.6% of the colonies in three agricultural areas in Northern Italy, which differ in general ecological conditions. This decline was estimated on a very large sample of 190 randomly chosen farms where breeding pairs were censused both in 2001 and 2010, and occurred at different rates in the three study areas. Barn Swallows declined most (9.3% per year) in an intensively cultivated area where colonies are widespread, and least (1.3% per year) in a hilly area with a comparatively small density of colonies. Variation in livestock farming significantly influenced population dynamics. Specifically, cessation of livestock farming at a given farm between the two census years resulted in a significantly steeper decline in the number of breeding pairs compared to farms where livestock farming was maintained. Our findings highlight the fact that European populations of Barn Swallows breeding in intensively cultivated agro-ecosystems may become significantly depleted in the next decades, and indicate that maintenance of livestock farming may contribute to buffering the population decline of this species.

Lifetime reproductive success, selection on lifespan, and multiple sexual ornaments in male European barn swallows

“…In addition, males do not apparently fertilize females breeding in other colonies, at least in our study area (see Ambrosini et al. for a description of the study area). However, since natal dispersal is high (Balbontín et al.…”

“…The colonies were chosen to represent very small (3–6 breeding pairs), medium (12–19 breeding pairs), or large‐sized (22–26 breeding pairs) according to recent large‐scale censuses (Ambrosini et al. ). In all study years, we captured and individually marked with numbered metal and plastic colour rings all the adults breeding in the focal colonies.…”

Population and Colony-Level Determinants of Tertiary Sex Ratio in the Declining Barn Swallow

“…The first main novel findings of this study of a markedly declining population [29], [31] of barn swallows were that TSR was consistently male-biased among yearlings as well as older individuals, did not change between age classes and was homogeneous among colonies. Second, temporal variation in TSR of yearlings at the time of their recruitment as sexually mature individuals was negatively related to annual survival of adults, which we considered as a proxy for ecological conditions experienced by our population during the annual cycle.…”

“…Barn swallows in northern Italy have suffered a sharp population decline (4–9% per year) during the last decades [29], [31].…”

“…In this 16-years study of a declining population [29]–[31] of the socially monogamous, colonial, long-distance migratory barn swallow ( Hirundo rustica ) we first analyze how TSR changes according to age, by comparing 1-year old individuals (‘yearlings’) at sexual maturation to older individuals. Second, we test whether TSR of yearlings at the time of recruitment depends on harshness of ecological conditions experienced during their first year of life.…”