Tree swallows are being used to investigate how climate change promotes early breeding, as they have been found to advance egg-laying by between 5-9 days over the last 32 years.
Alaska is warming up at twice the rate of its parent nation, so the swallows there were investigated alongside local temperature, wind measurements and precipitation. With the life-style of swallows, the distribution of their aerial insect prey should be expected to be heavily influenced any breeding success.
Tachycineta bicolor and the rest of its genus live in North America, alongside other swallow species. The tree swallow migrates from Central America to the north in Spring and nests in cavities, unlike the mud-builders such as the barn swallow. Fairbanks, Alaska was the focus of the study for 16 years, where there was a significant decrease in average times between lay and hatch dates. This, of course, would have influenced the expected advances of both lay and hatch dates!
In fact, the dates of egg-laying were found to be changing very rapidly. Temperature was not the only or primary driver of change, with windiness and precipitation more important. The wind force proved to be the only trending driver over time. Wind has declined during May in Fairbanks over 36 years, but of course this could be correlated with both temperature and precipitation, especially in microclimates. The weather conditions that immediately precede laying have a strong effect on the start of laying.
We must also take into account evidence from California that tree swallows feed their young less when “windiness”(average daily wind speed) is at high levels. Prey organisms will be even more affected by the 3 conditions measured here. Climate change affects all factors within a community and has special effects on each member of the food chains. An aerial predator and an aerial prey show here that wind displaces temperature as the main factor that we can discern. The effects of climate change are obviously complex and unique to a species, unlike some studies that have previously simply looked at a single aspect of change.
Rachel Irons and her co-authors from the University of Colorado, Boulder, the Alaska Songbird Institute and the Alaska Department of Fish and Game, Threatened, Endangered and Diversity Program produced their ground-breaking paper yesterday in the Proceedings of the Royal Society B .