Research · Genes, Not Weather, Drive the Migration Clock of a Long-Distance Songbird

Research · Genes, Not Weather, Drive the Migration Clock of a Long-Distance Songbird

Every autumn, Bobolinks lift off from North American grasslands on a 20,000-kilometre round trip to South American wintering grounds, crossing the Gulf of Mexico and the Caribbean in sustained overwater flights. A new study of a Vermont breeding population now offers one of the most complete answers yet to a long-standing question: how much of that journey is written into a bird's genes, and how much is improvised in response to weather. Between 2008 and 2022, researchers fitted 306 adult Bobolinks with 0.65-gram light-level geolocators, and reconstructed full annual cycles for 29 birds. The verdict: genetics alone explained roughly 22 percent of the variation in fall departure date, with genetically similar birds leaving wintering grounds on similar dates; weather effects, by contrast, were remarkably thin. The study also uncovered consistent sex differences — males departed around day 256 versus day 264 for females — and strong carryover effects across the annual cycle. The conservation warning is sobering: with the population projected to decline by half by 2069, a migration calendar locked in by inheritance may leave Bobolinks unable to keep pace as climate change reshapes the grasslands and stopover habitats they depend on. Vermont farmers have already advanced haying dates by about 10 days, while the birds' nest initiation has not shifted — a widening mismatch with mowing machines.

Sources:

scienmag.com: read report

Journal paper (open access): McGee et al. (2026), Ecology and Evolution 16(9), e74245