By Michelle Werts

I am fascinated by annual migrations.

I find it remarkable that so many creatures around the world are able to make the same trek season after season, year after year, when most humans these days have trouble navigating without their smart phones or GPS units. However, the mind-blowing regularity of some species’ habits may also be their downfall.

Wood thrush
Wood thrush. Credit: Bill Lynch (Billtacular)/Flickr

Dr. Bridget Stutchbury, professor of biology at York University, and colleagues just published a study in the journal PLoS One that details the migratory patterns of individual songbirds. Strutchbury attached penny-sized geolocators to wood thrushes to track their long-distance migrations from Pennsylvania to Costa Rica and Belize and back again. The results of the study revealed that while departure dates in the fall for Central America varied, the individual birds would depart for North America each spring within the same three-day window. En masse, spring migration departures occurred over a month period, but Stutchbury’s research reveal that each individual wood thrush adhere to a punctual departure date each spring, which has interesting implications.

As stated in the report, “The high repeatability in spring departure date suggests a stronger influence of endogenous schedules than local environmental conditions.” Basically, no matter what the external circumstances, the studied wood thrushes were following an internal clock that told them when to leave each spring. The consequence of such a rigid schedule is that as climate changes, the birds’ food sources will begin peaking at different times — regardless of whether or not the birds have arrived to consume them. A 2010 study (by Both C, Van Turnhout CAM, Bijlsma RG, Siepel H, Van Strien AJ, et al.) in Proceedings of the Royal Society B-Biological Sciences revealed that such a “mismatch between timing of food requirements and food availability” “may have become a major cause for population declines in long-distance migrants in highly seasonal habitats.”

So while an individual bird’s punctuality is both awe-inspiring and impressive, it may not be so good in the long run for its health and survival.