Study population and life-history data collection
We systematically monitored and collected life-history data from a free-living, nest-box population of house sparrows (Passer domesticus ) on Lundy Island (51°10’N, 4°40’W), 19 km off the coast of Devon, United Kingdom, starting in the year 2000 though genetic data from as early as 1990 were also available, and used for pedigree construction (see below). Annually, we monitored all nest boxes on the island, and tagged >99% of the population with uniquely numbered metal rings from the British Trust for Ornithology and a unique combination of three colour rings, either as nestlings for birds in nest boxes, or during their first winter for birds fledged from wild nests. We were thus able to obtain the hatch year and age of virtually all individuals to the precision of one year, and the exact hatch dates for birds hatched in nest boxes. Due to the geographical isolation of Lundy Island, immigration and emigration is almost absent (four suspected immigrants in 2000 - 2011, and three confirmed emigrants up to 2015; Schroeder et al., 2015). We collected survival data through biannual surveys where we recorded the presence/absence of each bird, with annual re-sighting probability between 91-96% (Schroeder et al., 2015). Except for those with an explicit death record, birds that were not sighted for two years consecutively since their last sighting were assumed dead, and the year when they were last seen was assumed as the death year, allowing us to calculate lifespan for each individual.
We repeatedly collected blood samples from individuals, typically at two days of age, 12 days of age, and at most subsequent captures after fledging. Blood samples were stored in 96% ethanol at room temperature until DNA extraction using the ammonium acetate method following Richardson et al. (2001), and subsequently stored at -20°C until analysis. We then assigned genetic parentage using up to 23 house sparrow microsatellite markers from Dawson et al. (2012) for sparrows hatched in 1990 – 2019. Using the software CERVUS 3.0 we assigned the genetic parents to >99% recruits with 95% confidence (Kalinowski et al., 2007; Schroeder et al., 2015), totalling 10,731 birds in the pedigree used in this work. From this pedigree, we calculated annual reproductive success (ARS) for each bird as the annual number of genetic recruits, i.e. offspring that reproduced and appeared in the pedigree as dams or sires themselves. We also calculated lifetime reproductive success (LRS) as the sum of ARS across the lifespan of each individual.