Since the 1970s, the many species of birds that hunt insects in flight have seen their populations drop by 80 percent or more, and no one knows why.
The Connecticut Audubon Society recently presented its eighth annual Connecticut State of the Birds report, which this year looks at the alarming condition of the so-called "aerial insectivores," the birds and bats that catch insects in mid-air, as opposed to foraging on the ground or on plants. The report was released at Audubon's Fairfield Center.
"They're disappearing much faster than any of the threatened perching birds," said avian scientist Shannon Kearney-McGee, of the state Department of Energy and Environmental Protection, who co-authored the report with nine other biologists and researchers. "So there is something going on, and this is a Northeast-focused decline."
She said even the chimney swift, which by all accounts was a rugged species that adapted easily to change, has seen its population crash by more than 90 percent since the 1960s.
"A lot of these birds that return in the summer aren't breeding," she said. "And the common nighthawk, we just don't see them anymore here in Connecticut."
Kearney-McGee said even though humans might consider the insect population plentiful, birds likely have a different perspective.
"If they're not the `right' insects, it would be like going to the supermarket and only finding celery," she said, noting that beetles could be lacking in the atmosphere.
She said that scores of scientists throughout the Northeast and eastern Canada are trying to unravel the mystery, but as yet, there is no obvious reason, or group of reasons, for the decline.
The centerpiece of this year's report was the paper, "The Seventh Habitat and The Decline of Our Aerial Insectivores."
The "seventh habitat" refers to our atmospheric layer, which scientists say is home to an unexpectedly large biomass of insects and spiders, animals that use high-altitude air currents to migrate from one place to another. For nearly a century, airplane pilots have anecdotally reported insect strikes above the clouds, and only recently have scientists had proof that there is indeed a sizable population of invertebrates in the sky.
Even troglodytic species, like termites and ants, have been found thousands of feet up.
"The drop in the populations of these aerial insectivores is quite likely an indicator that something is quite amiss in our environment," said Ralph Wood, board chairman of the Connecticut Audubon Society. "As you know, problems with the environment often manifests themselves first with birds."
There is no shortage of ideas as to why these species are crashing and why their numbers are dropping much faster than those of most other birds in the Northeast. Some of these include:
Populations of insects are dropping, too.
Because of global warming, storms are more intense, making migrations treacherous.
Changing conditions in South America, where some of these species overwinter.
A buildup of contaminants in the environment.
Lack of nesting sites.
Non-native and invasive plants don't support the species of insects that these birds like to eat.
"If this entire guild of birds relies on flying insects, and their populations are declining, well, something is rotten in the state of Denmark," said Milan G. Bull, CAS senior director of science and conservation. "There are lot of possibilities, but there seems to be no one answer as to why."
The decline is seen both in birds like the least flycatcher, which darts out from a branch to snare an insect in flight, to the "coursers," like the purple martin, which cruise through the air to catch insects and spiders in the sky. The only common dominator is that they all catch insects in flight.
"The decline is of serious concern to all of us," said Susan K. Whalen. deputy commissioner of the state Department of Energy and Environmental Protection.
"I have 48 gourds, and we had over 150 fledges last year," said Donahue, who attended the report's release at CAS headquarters on Friday.
He said that people can check up on the martins by logging onto his website www.gazebophil.com, which has a view from a camera mounted inside one of the plastic gourds. "The birds arrive with the tax man, and the eggs appear in late April or early May. They fledge in August. I get mail from people all over the world who watch it -- soldiers in Iraq, people in Singapore, Venice, Montana -- even a bank in Rhode Island has it up on a monitor in their lobby."