The cover story of our August 2015 issue, by author and photographer Mac Stone, describes what we’re learning about golden Prothonotary Warbler. Long-term studies of the warbler in Virginia, Illinois, and other states have revealed much about the species. Here are three amazing facts scientists have learned and a description of a citizen-science project you can take part in:
Instead of nesting wherever they can find a spot, adults use their experience from past breeding seasons to decide where to nest. Jeffrey Hoover of the Illinois Natural History Survey, who studies a breeding population in southern Illinois, found that when adults successfully produce two broods at a nesting site, they are highly likely to return to the same place to breed the next year. When they don’t have a successful nest, they tend to look for a different site to try.
The behavior known as conspecific brood parasitism, in which females lay eggs in nests of other members of their species, occurs in more than 200 species worldwide but is rare in songbirds. It was discovered in a wood-warbler only a few years ago, when researchers at two locations in Virginia realized that Prothonotaries were dumping eggs in other Prothonotaries’ nests. According to authors Catherine Morton and Anna Tucker, more than 23 percent of clutches at one site (PDF) and more than 33 percent at the other (PDF) contained at least one chick that was not related to the resident female.
With age comes experience
After analyzing more than 18 years of data from Virginia, biologist Lesley Bulluck of Virginia Commonwealth University and her colleagues noticed that older female Prothonotaries are more likely to produce two broods, and therefore twice as many young, in years with warmer springs. Females that are at least three years old tend to arrive in breeding areas sooner, they say, and likely take advantage of earlier peaks in caterpillar abundance in warm years. The study shows that birds in a single population can respond to changing temperatures differently depending on their age.
Stone also writes about research on Prothonotary populations at Francis Beidler Forest in Harleyville, South Carolina. In 2008, biologists at Beidler began banding Prothonotary Warblers and asking visitors to help them keep track of the birds. The goal of the work, known as Project PROTHO, is to learn more about the birds’ territory sizes and the microhabitats they use. Banding continued until 2011, stopped for a few years, and was resumed in 2014.
If you visit Beidler, stop at the visitor center and ask for a brochure about the project. Then, if you spot a banded warbler on the property, take note of its band colors and their arrangement, and look for the numbered aluminum medallions along the boardwalk to record the bird’s location.
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