Using citizen science to investigate the role of productivity in House Sparrow<i>Passer domesticus</i>population trends

Abstract

Capsule Seasonal variation in garden House Sparrow numbers provides a tool to examine overall annual productivity, measuring the combined success of multiple breeding attempts and post-fledging survival.Aims To develop a metric to use British Trust for Ornithology (BTO) Garden BirdWatch (GBW) data to measure annual productivity in House Sparrows across regions and habitats exhibiting contrasting population trends.Methods We examine variation in annual productivity by quantifying the height of the seasonal peak of garden House Sparrows relative to pre-breeding numbers.We use BTO Nest Record Scheme (NRS) data to explore the demographic drivers of variation in this metric and relate differences to BTO/Joint Nature Conservation Committee/Royal Society for Protection of Birds Breeding Bird Survey regional population trends.Results GBW annual productivity was similar between rural and urban gardens but was lower in the south and the east of Britain (1.32 fledglings per adult), where populations are declining, than in the north and west where populations are stable (1.37 fledglings per adult).Analysis of NRS data showed similar regional variation in clutch and broods sizes. ConclusionThe intensity of effort required to measure breeding success directly through nest monitoring has limited the scale of data collection but these results suggest that Garden BirdWatch (GBW) data can provide a measure of annual productivity across multiple sites.Regional variation in annual productivity (primarily driven by reduced clutch sizes) mirrors population trends, suggesting that reduced breeding success may be influencing House Sparrow population recovery.In recent decades, large changes in the abundance and distribution of many European breeding bird species have been identified (Gregory et al. 2005).Much of our understanding of the extent and drivers of these changes comes from data collected by volunteers through national monitoring schemes (Baillie 2001, Greenwood 2007, Schmeller et al. 2009).While these schemes provide good estimates of many demographic parameters, such as per attempt productivity or annual survival probabilities (Robinson et al. 2004, 2012, Freeman et al. 2007), others are more difficult to estimate.In particular, the relative contribution of variation in the number of breeding attempts initiated per pair and post-fledging survival to population trends remains a key knowledge gap (Bradbury et al. 2000).