ON THE WING

Breeding, migration seasons mixing

Posted Aug. 12, 2011, at 2:19 p.m.

The waxing month of August heralds many changes in bird populations. Shorebird migration is in full swing, having started back in July, and there are reports of gathering songbirds and appearances of warblers not normally seen in certain areas during the breeding season.

For other birds the breeding season is still happening. American goldfinches are one of our latest breeders — egg-laying commences in late June and July and can continue into August. The start of nest-building seems to coincide with the flowering of important food plants, especially thistle, a favorite.

They’ve been making themselves very obvious lately. It seems as if every section of sky contains one or more of the bright yellow males performing their circling flights. First, I’ll hear their signature “perchickoree, perchickoree” call which is also whimsically interpreted as “potatochip, potatochip.” Upon looking up, I’ll see one or more of the birds making wide circles in an undulating motion. The finch will flap a few times, fold its wings in close to its body, dip down, then flap again. Its upward swing is punctuated by its flight call, seeming to add a special emphasis to it.

In reading up on this finch I was interested to learn of its dual nature. They are very gregarious during winter but tend to be more territorial during the breeding season, with aggressive interactions taking place between them. However, they have been known to nest loosely in “colonies” and apparently have a complex hierarchy in which dominant and submissive birds engage in much ritualistic behavior.

I had the opportunity to observe some interesting behavior between two male goldfinches recently. They did not appear to be acting aggressively toward each other — in fact, they seemed to be foraging together. One of the males would cling to the stem of a Queen Anne’s lace, while the other alighted on a thistle nearby and, if one moved along, so would the other. The only thing approaching discord occurred when one of the males attempted to land on the same thistle head as the other. The perched bird raised its head and beak as if to say, “Find your own, buddy,” and that was enough to settle things.

Male goldfinches are very involved in the rearing of their young; they feed their mates for several days after the young hatch and may assume full care of the brood if the female leaves to start another clutch. Much of their behavior during this time has been studied, and what is occurring is obvious to a trained observer. For example, a male returning to the nest with food will circle overhead until the female calls, teeteeteeteetee, upon which the male will drop down to feed her.

As with many small songbirds, goldfinch nests can become parasitized by the brown-headed cowbird. The two birds’ nesting periods don’t usually overlap, but it has been documented. However, this oft-successful reproductive strategy of the cowbird backfires because of the simple fact of diet.

Goldfinches are adapted to a diet composed mostly of seeds. Even the young are fed regurgitated, partially digested seeds. So while the goldfinch can satisfy its protein requirements on a purely granivorous diet, cowbirds, which are more insectivorous, apparently cannot. They may “hatch successfully, [but] their growth is retarded and almost all die before they can leave the nest,” according to the “Birds of North America” species account.

I was tickled to read in “Stokes Guide to Bird Behavior” that once goldfinch young leave the nest, they are conspicuous as they follow their parents. They can be identified easily by their “chipee, chipee” calls, which are unlike an adult’s calls. Stokes goes on to say that the calls of goldfinch fledglings “mark the end of the breeding season and the imminence of fall colors and cooler weather.”

But summer is not over, not yet, despite the change in avian rhythms and tempos.

This week’s column is dedicated to Judy Kellogg Markowsky, who suggested me to the editor when the idea for a birding column was first pitched to the paper 11 years ago. I had done some writing previously for the Fields Pond Audubon Center newsletter and Judy nudged me in this direction. Thank you, Judy. Your knowledge and passion about birds and nature were an inspiration.

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