Jackson Bloch’s Yellow Warblers

“Birding isn’t as romantic as people think,” Jackson told me after we had been standing in the same spot for half an hour, searching for yellow warblers through the thick trees and undergrowth.

Studying birds certainly takes a lot of practice and concentration, and half of the times Jackson pointed out a bird to me I saw movement and nothing else. “You can’t focus too much on one area, or you’ll miss larger movement,” he said, following the birds with his binoculars. Jackson performs this vigil up to four times a day, starting in the early morning, in his search for yellow warbler nests. He is on the lookout for female warblers carrying twigs and other debris in their bills to build their nests. Jackson has their nest-building schedule down to the minute, but has only found four nests so far. Most of the female warblers that he observes have been stuffing themselves with insects, not building nests, while the rust-streaked males have either been chasing females or warding off other males, called “mate guarding.” Finding the yellow warbler nests is key to Jackson’s research, hence his dedication to observing the birds for hours on end in the field.


Jackson observing Yellow Warblers off of the Eagle Nest trail on Kent Island

Jackson’s project builds off of a study of an entirely different species, the fabulously named Superb Fairy-wren, which is subject to parasitism from Horsfield’s Bronze Cuckoos. The Cuckoos will lay an egg in the Fairywren nest, and the mother Fairywren will treat the egg as her own, expending energy and food that would otherwise go to her chicks. The study suggests that Fairywrens have a natural ability to detect the Cuckoo intruders. The mother encodes a “password” call in her song while she is incubating her eggs, and once they hatch, the baby Fairywrens repeat the call when they beg for food. The mother can therefore identify the intruder Cuckoo, which imitates the password imperfectly. Amazingly, the chicks can learn the password before they hatch, as their mother’s song permeates the thin walls of the egg.

A female Yellow Warbler carrying nest material (Photo by Jackson Bloch)

A female Yellow Warbler carrying nest material
(Photo by Jackson Bloch)

Jackson is investigating whether yellow warblers use the same “password” method to defend against parasitism from Brown-headed Cowbirds (another spectacularly named species), which intrude into the warbler nest like Cuckoos. Yellow warblers have never been studied for a password call, so Jackson’s project will expand past research to other species. While there are no Brown-headed Cowbirds on Kent Island, the password call may be a species-wide behavior. Once he finds more nests, Jackson will plant recorders in them, and using a computer program, will see if the sonograms of the incubation calls and the chicks’ begging calls match. He needs at least 10-12 nests to conduct his study, and Jackson said that only finding four so far has been frustrating.

I’m learning that science involves a lot of standing around and not seeing much, but all of the researchers here agree that the payoff is worth the tedium. If he finds positive results, Jackson will confirm that multiple species can detect parasites by teaching their young a secret password, a fascinating conclusion. Even if his results are negative, Jackson said that his ability to find his study subjects, especially through listening, has “increased dramatically.” Observing Jackson observe the birds was a valuable exercise in patience, one of the many valuable lessons that I am learning from my scientist friends.

Listen to the Yellow Warbler call:


Jackson told me that using your ears is actually more important than using your eyes to locate birds. The yellow warblers have a clear, loud song and are relatively easy to pinpoint, but it can still be difficult to pick out the warbler song among the many birdcalls on Kent Island. Before I became attuned to the warbler call, I had trouble hearing it through the background noise of the annoying starling screech and the constant cries of gulls.


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