Data from: Rapid adaptive phenotypic change following colonization of a newly restored habitat

Real-time observation of adaptive evolution in the wild is rare and
limited to cases of marked, often anthropogenic, environmental change.
Here we present the case of a small population of reed warblers
(Acrocephalus scirpaceus) over a period of 19 years (1996–2014) after
colonizing a restored wetland habitat in Malta. Our data show a population
decrease in body mass, following a trajectory consistent with a population
ascending an adaptive peak, a so-called Ornstein–Uhlenbeck process. We
corroborate these findings with genetic and ecological data, revealing
that individual survival is correlated with body mass, and more than half
of the variation in mean population fitness is explained by variation in
body mass. Despite a small effective population size, an adaptive response
has taken place within a decade. A founder event from a large, genetically
variable source population to the southern range margin of the reed
warbler distribution likely facilitated this process.