Earlier this summer I received correspondence from readers who had observed fewer numbers of swallows in their neighborhoods.

Marcy Gagne, in western Maine, wrote, “Last year, our neighbor mentioned the absence of the barn swallows, with only about seven pair coming back to his barn, for the first time in over twenty-five years. Nobody thought much of it, off year perhaps … but this year there are only two. And … the swallows who usually swoop down to retrieve the feathers our chickens and ducks lose, are nowhere to be found.”

Marcy questioned whether the spraying for West Nile virus (in states other than Maine) could be having an indirect affect on swallow populations by reducing their source of food. At the same time, she acknowledged that other factors may be playing a part.

“So … things change … patterns change. There are a lot of variables in a bird’s life … but I wonder if something more serious is taking effect here.”

Good question. Judy Markowsky, director of Maine Audubon’s Fields Pond Nature Center, concludes this may be a possible scenario, but isn’t possible to confirm without hard, widespread data.

But it is this initial “anecdotal” (informal observation) data that has, in the past, given impetus to serious, widespread investigation.

Meanwhile, the observations still trickle in.

Bob Myers – otherwise known as “Birdman Bob” -does a short segment about birds and birdwatching on radio station 89.9 FM WERU in Blue Hill (102.9 FM in Bangor). He also has been receiving reports of fewer swallows, and turned to Bill Townsend for help in addressing this issue.

Townsend is a former park ranger and birding trip leader, as well as a high school science teacher. He publishes a newsletter about natural history in Maine called “The Guillemont,” which is now in its 33rd year of publication. He is currently working as a naturalist aboard a cruise boat.

“Swallows are probably more than a little lower in numbers,” Townsend said. “They will abandon some nest sites if the nearby habitat changes and the population of flying bugs isn’t as easily found as previously. Tree swallows are susceptible to parasites if their nest boxes (or natural holes) aren’t cleaned out.

“The mild winters of the past 10 years (last winter was just barely up to average, remember – even though it seemed to be a bad winter) have allowed a number of eggs of parasites to survive through to spring. If we slip into a period of colder winters it might make a difference in the nesting success locally,” he added.

Townsend himself has also noticed a lack of cliff swallows nesting in traditional sites around Bar Harbor.

The cold wet spring could also have had an effect, according to Jerry Longcore.

Longcore, a University of Maine wildlife ecology associate and leader of the Patuxent Wildlife Research Center in Maryland, said that cold, rainy weather can dampen flying insect populations that swallows depend upon. In addition, he added that unusually warm weather – such as we have been experiencing in Maine -will cause high mortality in nestlings.

And there could be a more ominous reason for their apparent reduction in numbers.

“Things may be affecting them on their wintering grounds [of Central and South America]- something may be going on there. It could be that just a lot fewer came back [to their breeding grounds], but we have no way of knowing this,” he added.

West Nile Virus could have a direct effect on bird populations, as evidenced by the media coverage of affected crows, ravens, and blue jays. But they’re not the only ones; according to the USGS National Wildlife Health Center, more than 150 species of birds are known to have been afflicted with this disease.

There are myriad reasons for bird population declines, both local and otherwise. Trained scientists can only do so much; this is where everybody’s observations are invaluable. The Cornell Lab of Ornithology recognizes this; it has a number of “citizen science” projects for people to contribute to. Visit the Lab at www.http://birds.cornell.edu/ to learn more.

Are you noticing fewer swallow populations in your neck of the woods? I’d like to hear from you.

Chris Corio, a volunteer at Fields Pond Nature Center in Holden, can be reached at fieldspond@juno.com