Howdy, friends. This week your fearless host is going to another weekend bluegrass festival, so I thought we would talk about a bird that makes Appalachia its home during part of the year.  Entirely by chance, I happened to pick a species whose males are a brilliant blue.   I hope I’m not posting this from a muddy field as happened over Memorial Day, I guess we will see how packing goes.  

This week’s bird is the cerulean warbler.  It is notable for two reasons: its striking sexual dichromatism and the length of its yearly migration. It breeds and summers in deciduous hardwood forests in the east and Midwest of the US, and migrates through Mexico and Central America before settling down for the winter on the eastern slopes of the Andes in South America.  There it prefers subtropical forests in Venezuela, Colombia, Ecuador and Peru, with what looks like a little bit of encroachment into Bolivia.  In both locations, it prefers mature, unbroken forest, ideally near a body of water.  

This warbler forages for insects in the mid to upper canopy, hopping from branch to branch and snagging insects or their larvae.  It is known to catch some of its food on the wing, but hopping around from branch to branch is apparently a more efficient use of its time and energy in most cases.  Foraging is segregated by height.  Males forage higher up and females take the lower strata.  The cerulean warbler will forage with mixed flocks of other species of birds, all of which will choose their own section of canopy and stick to it, preventing the flock from competing with each other for food.  

During the breeding season, cerulean warblers are monogamous and very territorial and aggressive toward other warblers of the same sex.  They will use songs to mark their territory, but are not above physical altercations.  Female warblers are known to attack the nests of rivals and destroy their eggs.   Both members of the pair choose a nesting site and work together to build it.  Should the nest fail for any reason, the couple will try again.  An interesting thing that I learned about these further attempts is that the pair will preserve the spider and caterpillar silk which they use to bind the nest together and reuse it in their new attempt.  Such construction materials or at least suitable examples might be too hard to come by to bother leaving the silk with the failed nest.  

The female broods over the eggs alone, the male works to feed the female and the chicks.  The chicks will hatch in about a week and a half, and fledge about 10-12 days later.  They are capable of fending for themselves after about another two weeks.  Cerulean warbler chicks fall victim to a variety of predators, especially chipmunks and blue jays.  Nature, as always, is as cute as it is brutal.  The pair will occasionally fall prey to brood parasitism, unwittingly raising the young of the brown-headed cowbird. In an effort to conceal the location of the nest, the female “bungee jumps” when exiting.  She will leave the nest with wings folded and fall several feet before beginning flight.  

The cerulean warbler is rated as “near threatened” but the IUCN. Habitat fragmentation due to farming, specifically replacing large mature trees with cash crops, has reduced the available land it can use and left it especially vulnerable to brood parasitism, which is harder to pull off in a dense forest.

Be good to yourselves and others, PT. Have a good weekend.

Links: https://tinyurl.com/4amkwv8k, https://tinyurl.com/2zfuux8y, https://tinyurl.com/msb8kd5m, https://tinyurl.com/24ntzhyf, https://tinyurl.com/2z3vt7cp