Radiant Little Warblers

Spotted one of these today, along with several other members of her family:

Black-and-White Warbler (Mniotilta varia),
Waukegan Beach, Lake Co, IL 5/20/2012

This is a Black-and-White Warbler (Mniotilta varia). They spend a lot of time creeping along branches looking for caterpillar lunches. Since caterpillars are hard to find in the winter around here (not to mention points north of here), they migrate south for the winter, and they're just now on their way back up.

The Wood Warbler family (Parulidae, formally speaking) is a favorite of birders across North America. (They're not found in the Old World, which explains the family's other name, the New World Warblers.) They're colorful and diverse, even traveling in mixed flocks. In some parts of the country, a good day in migration could conceivably include 30 species! Just to illustrate some of the diversity, here's a pretty pair:

Wilson's Warbler (Cardellina pusilla), Seward, AK, 8/3/2012

This one's a Wilson's Warbler (Cardellina pusilla) that I found in Alaska.

And this one's my favorite warbler, a Red-faced Warbler, (Cardellina rubifrons), photographed on the Mogollon Rim in northern Arizona.

Red-faced Warbler, (Cardellina rubifrons),
Coconino NF, Coconino Co, AZ 8/2/2005

The process that forms this sort of diverse group is known as adaptive radiation, and it's usually thought to occur when a new environment opens up, with plenty of ecological opportunities and very few competitors. Rabosky & Lovette tested this idea using wood warblers in North America, and found that rates of speciation were higher early in the radiation, slowing as time went on. (1) This fits the ecological opportunity model, as early speciation events mean that some ecological roles are now filled, and no longer open to be filled by new species.

Price, et al. looked at the timing of this radiation and compared it to Asian warblers in the family Sylviidae as well as to other North American passerines, finding that the Wood Warblers diverged much more recently than other groups, while still finding the same slowing of speciation rates over time. (2) However, they looked at specific locations rather than specific taxonomic groupings, which suggests a possibility of conflating speciation events with range shifts.

I love seeing the first warblers coming back in the spring, like little bits of flame in the trees. Being able to combine fascinating work on evolution with such beauty is a wonderful bonus.

(1) Rabosky, D. L., & Lovette, I. J. (2008). Density-dependent diversification in North American wood warblers. Proceedings of the Royal Society B: Biological Sciences, 275(1649), 2363-2371.

(2) Price, T., Gibbs, H. L., Sousa, L. D., & Richman, A. D. (1998). Different timing of the adaptive radiations of North American and Asian warblers. Proceedings of the Royal Society of London. Series B: Biological Sciences, 265(1409), 1969-1975.