(3) Demographic modeling
A traditional SFS-based model recovers a bottleneck in population size, as expected: the estimated effective population size during the bottleneck is ~16,000 individuals (1% of the ancestral population size). However, our demographic model suggests that the current population size of North American starlings is nearly identical to its pre-bottleneck size (Supplementary Information). In fact, every run of the model finds that starlings’ current effective population size (1.6 million individuals) is considerably higher than the estimated Ne of the founding population. This model suggests that starlings experienced rapid population growth after the initial founder effect, which may contribute to the overall lack of evidence for inbreeding. We do detect very low levels of inbreeding within some populations (Table 1, highest FIS = 0.082 in Washington). Taken together, these models do not suggest a classical founder effect, whereby effective population size remains very low for many generations post-bottleneck.