Common Nighthawks: Two Strikes and a Temporal Mismatch
Story by Bryan Pfeiffer
On a warm August evening at Boston’s Fenway
Park, everything had fallen into place by the
fifth inning: The Red Sox were beating the
Angels 6-0. My pals and I in right field were
enjoying two of baseball’s four food groups
– beer and peanuts. And a half-dozen common
nighthawks were feeding on big white moths
high above the outfield grass.
It was a fitting display for an odd bird with
a dubious relationship to people.
But first, a dubious name: the common
nighthawk – hardly common anymore – is
not purely a nighttime hunter and is not at
all a hawk; rather, it’s a member of the family
Caprimulgidae, which translates from the Latin
to mean goat-milker. Nighthawks and their
relatives (including the whip-poor-will) yawn
wide-open mouths to inhale insects on the
wing or, as the legend goes, to suck milk from
the udders of goats.
Nighthawks nest in prairies and grasslands, coastal sand
dunes, forest clearings (including burns and clearcuts in mixed
or coniferous woods), rocky outcrops, and even on flat rooftops.
In quieter cities and towns across the county, our summertime
dawn and dusk choruses once featured the buzzy peent calls of
nighthawks foraging for insects attracted to street (or stadium)
But no more. During the past 30 years or so, nighthawks have
vanished from most northeastern communities. The cause is not
clear. It may be due in part to the use of new rubberized roofing
materials which lack the gravel that once served as nighthawk
camouflage and probably kept eggs from rolling around.
Or perhaps the decline of nighthawks signals something
more troubling in our skies. Biologists and birdwatchers are
now documenting population declines among a number of
other North American birds that hunt insects on the wing,
including whip-poor-wills, swifts, swallows, and flycatchers – a
suite we call aerial insectivores.
In the search for a cause, it’s reasonable to investigate the
common denominator: airborne insects, which we humans
have been attacking with pesticides for more than half a century. Even so, not all aerial insectivores are declining; some are
doing fine. The other complication is that we know relatively
little about the status of insect populations. We’ve been counting
birds for more than a century, but are only now beginning to
understand insect abundance and population trends.
Another theory involves what conservationists call temporal
mismatch. Migratory birds generally synchronize their breeding
with peak food abundance or availability, but as the planet
BIRDS in focus
warms, some insect species now reach peak abundance earlier
in the season. So it’s possible that nighthawks, wintering in
South America, don’t get the memo and are failing to adapt to
global warming at the same rate that their prey are responding.
A lot of this remains speculative, and our search for a
cause of aerial insectivore decline is complicated by the usual
threats: habitat loss (here and in the tropics), pollution, industrial agriculture, housing development, and invasive species.
It does appear that the aerial insectivores that migrate farthest
– particularly common nighthawks, which make one of the
longest migrations of our land birds – fare worse than those
that migrate shorter distances. It could be that the demands of
a big migration compound the other threats. It’s difficult to say,
though, because we know so little about what happens to these
birds once they leave us in the fall.
But we can still watch common nighthawks on their journey
south. From mid-August through mid-September here in the
Northeast, nighthawks migrate in plain view, sometimes in
big numbers. Look for them moving in the late afternoon or
evening along river valleys or lake shores. Decades ago, particularly in the Midwest, birders could sometimes see nighthawks
in migration by the thousands, but here in the Northeast, we’re
more likely to count dozens or, on a good evening, a hundred or
so. It’s not a bad way to pass the time during the waning days of
summer – especially if your favorite baseball team is no longer
in the pennant race.
Bryan Pfeiffer is an author, wildlife photographer, guide, and consulting naturalist who
specializes in birds and insects. He lives in Montpelier, Vermont.