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.