Let's Talk About Birds: Blackpoll Warblers


8/17/2016

Gold Medal Migration!

The fall migration of Blackpoll Warblers from across their continent-wide (Alaska to Nova Scotia) boreal breeding grounds to their tropical wintering grounds in South America was something of a mystery for a long time.  Bird watchers rarely if ever reported seeing Blackpolls south of the Virginias.  Were they simply being overlooked because the male Blackpoll’s fall plumage—much different than its very distinctive, chickadee-like breeding plumage—could be easily confused with other species?

 

Piecing the puzzle together from hundreds of pieces of information, ornithologist, Ian C. T. Nisbet, offered a surprising hypothesis some fifty years ago.  He proposed that Blackpoll Warblers, after reaching the coast somewhere between New England and the Mid-Atlantic States, deliberately flew out over the Atlantic Ocean, perhaps to take advantage of northeasterly trade winds that could make a nonstop flight to the West Indies and beyond possible.

 

In support of his theory were observations by bird banders that Blackpoll Warblers tended to carry much larger fat deposits in fall than other migratory warblers.  Captures of roly-poly Blackpolls wrapped in a thick, blubber-like fat layer, and weighing twice their usual lean body mass of just twelve grams, were not unusual.  Skeptics cast doubts, though, citing obvious disadvantages to a small bird undertaking such a potentially hazardous migration.  Now, thanks to technological advances, the Blackpoll Warbler’s Olympian feat of trans-oceanic fall migration is neither a mystery nor a controversy: it is a scientific certainty!

 

A team of scientists, one of whom refers to their study subjects as “little meatballs with wings,” recently employed geolocators to track the migrations of Blackpoll Warblers from breeding grounds in Vermont and Nova Scotia to South America, and back again.  They outfitted three dozen Blackpolls with very small light-sensitive data loggers programmed to continually record light levels wherever the birds were.  The data could later be used to identify sunrise and sunset times and day lengths, variables which could, in turn, reveal where on earth the birds were each day.  But, there was a catch:  the researchers had to catch the same birds again the following year!

 

The team managed to relocate, recapture, and retrieve geolocators from five of their warblers, and statistical analysis of the light level data encoded in them illuminated once and for all the amazing trans-oceanic fall migration long ago hypothesized for the species.  In two to three days of non-stop flight each of the five warblers traversed between 1300-1800 miles of the open ocean.  All of them then stopped for up to two weeks in the West Indies before making another 500-mile flight across the Caribbean Sea to final wintering destinations in northern South America.  Clearly, if there were a songbird Olympics, Blackpoll Warblers would win a gold medal in the migration marathon! 

 

Anybody who would like the chance to see some Blackpoll Warblers, can join me for a fall warbler watching tour to the Laurel Highlands on September 17-18.  For details and to register, go to:  https://www.aviary.org/special-events/bird-banding-warbler-watching, or contact Audrey Beichner (412-258-9463; Audrey.Beichner@aviary.org).