The Tyrant of March

An afternoon walk at Lyons Woods Forest Preserve produced one of these handsome little birds:

Eastern Phoebe (Sayornis phoebe), Illinois Beach State Park, 9/21/2012

This is an Eastern Phoebe (Sayornis phoebe), one of our Tyrant Flycatchers. They're a common breeding bird across most of the eastern US and a large swath of eastern and central Canada as well. They are also quite comfortable around people, routinely nesting under bridges, building eaves, etc. As a result, they've been an important research subject for biologists interested in the evolution of reproductive strategies.

An interesting aspect of phoebe biology is that they often reuse nests -- at least some nests. They are willing to place their nest either on top of a ledge (statant) or affixed to a vertical surface (adherent). Statant nests are sometimes reused, but adherent nests rarely survive the winter and are thus unavailable for reuse. (1) As you might expect, repairing and reusing a nest takes less time than building a new one, and that can be important for reproductive success in many birds -- starting too late can mean less food available for nestlings, and leaves less time available for either a replacement brood or (if lucky) a second brood.

Conrad & Robertson found that among nest builders, the type of nest built didn't affect clutch size or success rates, (1) while Hauber found that nest builders not only initiated their broods later but were less likely to succeed in nesting. (2) Conrad & Robertson also found that younger birds (SY, meaning second year) were less likely to succeed and raised smaller clutches when they did succeed than older birds (3) (ASY, meaning after second year -- aging these guys beyond that is impossible unless they were banded young). I don't know that anyone's examined the issue of the availability of old nests, or whether older birds are more likely to hold territories with old nests, but that does seem like a potential confounding factor here.

Hauber also found another effect of nest type: Brown-headed Cowbirds (Molothrus ater) were more likely to parasitize statant nests than adherent ones. He argued that this shows a preference by the cowbirds for safer nest sites (adherent nests failed more often, frequently from simply falling off!), but I'm not sure how he determined that the cowbirds' ability to detect the nests didn't vary. (4) He didn't find that nest building by the phoebes increased parasitism rates, although that would probably have biased the results the other direction, since adherent nests were never reused.

As a birder, the first Phoebe of the season is a wonderful moment -- it's a reminder of all of those migrants waiting just over the horizon for that first warm night of the season. After that, it's just another phoebe, while you try to find that Acadian or Yellow-bellied Flycatcher. Remembering that every species can be fascinating in it's own right, though, adds a deeper appreciation of the world around us.

(1) Conrad, K. F., & Robertson, R. J. (1993). Clutch size in Eastern Phoebes (Sayornis phoebe). I. The cost of nest building. Canadian journal of zoology,71(5), 1003-1007.

(2) Hauber, M. E. (2002). Is reduced clutch size a cost of parental care in Eastern Phoebes (Sayornis phoebe)?. Behavioral Ecology and Sociobiology, 51(6), 503-509.

(3) Conrad, K. F., & Robertson, R. J. (1993). Clutch size in eastern phoebes (Sayornis phoebe) II: age effects and seasonal variation. Canadian journal of zoology, 71(9), 1738-1742.

(4) Hauber, M. E. (2001). Site selection and repeatability in brown-headed cowbird (Molothrus ater) parasitism of eastern phoebe (Sayornis phoebe) nests.Canadian Journal of Zoology, 79(8), 1518-1523.