The Little Chocolate-breasted Titmouse
BIRDS OF NANTUCKET
by Kenneth Turner Blackshaw

Let's take a flight of fancy - literally. Try to imagine you are a tiny ball of flesh and feathers, one third of an ounce, flying high in the dark sky with hundreds of kindred spirits. You know you are keeping pace with them because your ears pick up their high lisping contact notes. You've been flying for hours buoyed by the dry, cool northwest wind. Flight itself is still new to you since your memories only go back a month or so. The exhilaration you felt when the flight started has been replaced by fatigue. As daylight slowly oozes into the eastern sky, the main thought of your whole flock is about rest and breakfast. Alas, looking down, you only see water - not the familiar water of a Canadian lake but a seemingly unending expanse of wave-tossed sea.

I just gave you a snapshot of the way many Bay-breasted Warblers find their way to Nantucket. The most likely time to see them is from now until the end of September. Getting to know them is a character-building experience for many birders. On page 278 of Roger Tory Peterson's wonderful eastern field guide the heading says "Confusing Fall Warblers." To the right there are pictures of 14 warblers and a kinglet. One of these is the immature Baybreasted Warbler, one of the tiny mites that is winging your way through the darkness.

It was William Bartram, the 18th- century explorer and naturalist, who called these birds "Little Chocolatebreasted Titmice," an excellent name for the spring-plumaged males. His student, the great Alexander Wilson, provided the scientific name,

Dendroica castanea, the chestnutcolored

wood warbler. Both he and Audubon considered this a rare bird, only experiencing it as a migrant in spring and probably losing it in the host of stripy green warblers that came through in the fall.

Most Bay-breasted Warblers nest in the boreal forest. The southern edge of their territory brushes northern New England. Their winter haunts are from Panama down into Peru and Venezuela. When spring calls them north most of them enter the U.S. along the Texas coast and then take an inland route north. Occasionally a few come to Nantucket in May but these birds are way off course.

It was a marvelous treat a few years ago when we had a migration "fall out" of warblers in 'Sconset. I had a brilliant male Bay-breasted Warbler hopping on the ground right next to my feet. Smaller than a sparrow, the spring males are boldly patterned with rich browns, blacks and creams. They sport two white wingbars. Females in spring show a hint of bay color on the flanks but lack the brown and black on the head and throat. Alas in the autumn only the sharp white wingbars remain.

One of the Bay-breast's staple foods in summer is the spruce budworm. The lumber industry doesn't think they eat enough of them so they are attacking budworms with pesticides and also clear-cutting the boreal forests. Between 1979 and 1993 the breeding population of these warblers dropped by 80 percent in New Brunswick. Birds collected right after spraying had a life-threatening brain disorder.

It's hard to know where the tipping point might be for a subtle species like this. Even a simple structure like a TV tower becomes a killing hazard since these tiny birds migrate in the dark.

When you are outside after dark on an evening with northwest breezes listen skyward for the tiny notes of migrating warblers. If you go birding the next morning you will get your chance to pick out a Bay-breast. Another wood warbler, the Blackpoll is almost identical. We used to think that leg color was diagnostic, a Blackpoll's being light and a Bay-breast's dark. Now we know some Blackpolls have dark legs, but their feet are always light.

Lots of luck with that. Many small warblers of this ilk are tossed off as "Baypolls" by frustrated birders. The only other useful mark is that Baybreasts keep a creamy wash on the lower belly and under tail where Blackpolls are white. In George West's illustration, the fall Bay-breast is on the left.

As an aside - collective terms for a group of warblers include a "bouquet," a "fall," a "wrench" and finally my favorite, a "confusion."

Bay-breasted Warblers exit the U.S. the same way they come in, so most of them go west of us. Many of the birds that are fooled by the northwesterly breezes into straggling in our direction are "hatch year" birds making their first migration journey. Sad to say only a few of them are able to make the course correction and get back on track to the southwest. Bay-breasts typically lay five eggs per year to try and make up for their migration risks. The oldest on record is less than five years.

Let's go back to our earlier flight of fancy. You've spent a week on Nantucket, feeding on small insects and bulked up to where 50 percent of your body weight is fat. Now you've moved to the west end of the island, perhaps even to Tuckernuck. You are brimming with energy and fly spiritedly up to join the other mites you hear calling in the dark sky. With luck you'll make it back to the mainland and then join the river of birds south to the Texas coast and finally another thousand miles farther to the tropics

for the winter. Bon voyage! I

George C. West creates illustrations for these articles.

The Maria Mitchell Association sponsors bird walks on Tuesday and Thursday mornings at 6:30 a.m. and Saturday mornings starting at 8 a.m., from the corner of Vestal and Milk Streets. There is a fee for non-members.

To hear about rare birds, or to leave a bird report call the Massachusetts Audubon hot line at 1-781-259-8805.

Find more about Birding Nantucket on the web at http://k-blackshaw.com/ BN/BN.htm