disappearing thunderbirds

This is the time of year when I should have enjoyed many mild evenings on my patio, counting scores of swooping, acrobatic Common Nighthawks (Chordeiles minor) in the growing dusk as they migrated to their South American wintering grounds.  As a kid, I could rely on early autumn's twilight skies being filled with a steady stream of hundreds of nighthawks.  Now I feel fortunate to count 25 in an entire season. Although nighthawks are still fairly common breeding birds in the sandy forests of northern Michigan, they are becoming rarer in southern parts of the state, especially in urban areas. This situation is echoed across much of the Upper Midwest and northeastern U.S.  This past year, I served on a committee which reviewed state threatened and endangered species, and I recommended that Common Nighthawk be placed on the Special Concern list. Although "special concern" status offers no legal protection, it is a call to vigilance.

Nighthawks are birds of myths and misconceptions.  Most people only see nighthawks on migration.  Being crepuscular, they are primarily out and about at dawn and dusk.  Not only are they inactive during the day, but their cryptic coloration blends in seamlessly with leaves and branches, rendering them virtually imperceptible in a woodland's mottled sunlight.  I recall nighthawks abruptly appearing at a local baseball diamond's stadium lights as darkness fell. They would flick into sight, snatching bugs in their huge, yawning mouths, and just as quickly disappear.  Startled observers didn't know what to make of this strange creature. 

The struggle to make sense of these mysterious birds is reflected in some of the more common colloquial names. "Nighthawk" itself indicates that they were at one time mistakenly thought to be raptors; there was once a bounty on nighthawks, which supposedly ate young poultry. "Bullbat" was coined by those who erroneously thought nighthawks were large bats. Nighthawks belong to the family Caprimulgiformes, often known as "goatsuckers" because of the persistent myth that they nursed at the teats of goats with their wide mouths (which are actually designed to efficiently catch large moths).

The decrease in nighthawk numbers is primarily due to habitat loss.  As birds that favor nesting in forest openings, nighthawks suffer from deforestation, as well as a reduction in openings  due to fire supression (one old nickname, "burnt-land bird," indicates their preference for recently burned-over areas).  Surprisingly, habitat loss in cities may be a critical factor.  There are fewer buildings with gravel rooftops, which are favored urban nesting spots.  These days, most flat-topped roofs are tarred or rubberized. The surface gets too hot for the incubating birds, burning their feet and cooking their eggs. Against a dark background, their eggs (and the nighthawks themselves) are easily seen by aerial predators.  Finally, Ring-billed Gulls (Larus delawarensis) have moved into urban areas and also like to nest on flat rooftops, displacing the nighthawks.  Tertiary causes of nighthawk population declines include being hit by cars as they forage along roadsides, and the sharp increase in pesticide spraying the last few decades. Perhaps even the decline in silkmoths in the eastern U.S. is playing a role.

Nighthawks survived generations of being misunderstood. Now we comprehend their relationship to other birds, their ecological role, and their needs.  When do we begin to understand how to counter their declines so future generations can ponder this curious and enigmatic bird?

To me, there is something incredibly sad about seeing just a lone nighthawk, or perhaps merely a few, in the falling twilight of a late summer evening.  True, it is still beautiful to watch as each individual traces a graceful arc in the sky as it wings its way south.  But nighthawks belong in large autumn flocks, each bird part of a sweeping, looping ballet performing against the backdrop of a deepening ultramarine sky.

Further information

How much should we be concerned about nighthawk population declines? 

• Listed as Special Concern in New York. The original New York state breeding bird atlas found concentrations of nighthawks in all major cities; current atlas data (2000-2002) found none in these areas. 
• Designated as a high priority candidate for listing as a species at risk in Canada.
• In Ontario, declines appear to be accelerating; atlas trends comparing distributions of first (1981-1985) and second (2001 to present) atlases shows severe declines.
• Fall migration in Ohio greatly diminished since 1993; largest flights 200-500 birds with most reports of fewer than 50 daily compared to historical daily counts of >3000 daily, according to The Birds of Ohio.
• Listed as threatened in New Hampshire, where numbers are down precipitously from historical levels.
• Listed as Special Concern in Indiana, and endangered in Connecticut.

Resources:

• Brauning, D. W., M. C. Brittingham, D. A. Gross, R. C. Leberman, T. L. Master, and R. S. Mulvihill. 1994. Pennsylvania breeding birds of special concern: a listing rationale and status update. Jrl. Pennsylvania Aca. Sci. 68:3-28.

• [COSEWIC] Committee on the Status of Endangered Wildlife in Canada. 2004. The COSEWIC candidate list, December 8, 2004. COSEWIC web site

• Gorn, L. 2003. Common Nighthawks. New York State Breeding Bird Atlas Newsletter 7:4.

Comments

[TroutGrrrl]

I was fortunate enough to enjoy a couple nighthawks a little bit early tonight, before it was too dark to see them without streetlights. I don't think I've ever seen them in as much daylight...

[Pamela Martin]

We have seen a few small groups passing over Thomasburg in the last few weeks, largest maybe 8 or so birds--much larger have been seen in the past. Interesting about the loss of urban habitat--growing up in Toronto in the 60's and 70's, the nighthawk was a very familiar bird to me: a constant in the summer evening sky.

The nighthawk was a species of much concern and discussion among atlassers during the recent data collection for the Ontario Breeding Bird Atlas (2005 is was our final year of five for this go round)--hard to find breeding birds at the best of times, given their habits, etc. (I found none), but now probably hard to find because their numbers are down.

I was also interested to read of their shady reputation (though perhaps I should have guessed it from the appellation "goat sucker")--they've always been a favourite of mine.

[Tom Andersen]

About 20 years ago I interviewed Bob Arbib, who lived in the town I was covering as a reporter and who, I think, was just retiring as editor of American Birds. One of the things he told me was that there used to be nighthawks nesting on the roofs in Mamaroneck, New York, where he lived, and in other nearby towns, such as Greenwich and Stamford, Connecticut. If I asked why they were no longer there, I don't remember the answer, but it was interesting to read your explanation about gravel versus tar roofs.

I used to go to the local ballfield in late August and early September, toss a tennis ball into the air, and watch the nighthawks swoop towards it to see if it was a moth. This fall was the first time since the late 1980s that I saw not a single nighthawk in migration.

[Cindy M.]

I tend to agree with your 'declining silkmoth theory'- and it's not just silkmoths that are in decline, at least in my area, all species are down. Gypsy moth spraying has put a huge dent in the local moth population. (Don't even get me going on chemicals)
For many years we enjoyed the booming of Common Nighthawks over area lakes as we fished- this year we've seen very few of them, and their migratory numbers are way down. I too find it incredibly sad.

[john farrell]

I grew up in Bridgeport Ct. Not much of a place for nature. But On spring nights I was amazed by the virtual roar of nighthawks as they plunged above the rooftops of our three story houses and industrial city double deckers. There were gravel roofed factories all around that neighborhood and I never imagined that such a magnificent bird might nest on one. That was in the fifties I don't believe I've seen one since. But now I live in the burbs.
I remember my first whistling duel with a mocking bird and my surprise that barn swallows consider our garage a fourstar accomodation. And there's a catbird that comes around every year and seems to have gotten used to me. Then there are the wild turkeys. I've noticed that since the toms have chased more than a few residents, more cats seem to be on the prowl. Two birds came after me on my front porch but thought the better or it when I reverted to Killer ape mode and went after them. It was fun and all the kids in the neighborhood think I'm nuts but the toms left me alone. Oh, yeah, gulls. Today in a squall there were flocks of them camped on ocean facing lawns hunkering in the wind and favenously feeding on worms driven to the surface by the sudden torrents of rain.
I'm surprised they don't go after monarch butterflies which seem to migrate over our pretty much deserted beach to feed on goldenrod and milkweed.

[Nuthatch]

The gulls (or any birds) don't eat Monarchs because they are mildly poisonous and taste lousy due to the larvae feeding on milkweed.