Study system
This study was carried out in eight of the island populations in a
metapopulation of house sparrows inhabiting eighteen islands in northern
Norway (66°N 13°E; see map in
Baalsrud et
al. 2014). The high recapture rates (~74%) in these
eight study populations, combined with extensive sampling effort, allows
close monitoring of the life-histories of most of the individuals
inhabiting these islands. Each time a bird was handled, as nestling,
fledged juvenile or adult, we took a blood sample for genetic analyses.
A pedigree based on 605 highly polymorphic and independent single
nucleotide polymorphisms (SNPs; Niskanen et al. 2020) was
generated and then used for estimating the number of recruits produced
per individual. We used specific data sets for the different analyses,
but in general this metapopulation has been monitored continuously since
1993. However, systematic SNP genotyping of all adults started in 1998
in some islands and in 2003 for others. Therefore, the maximum possible
time period of data included in these analyses differed between
populations (Table S1).