Joe, and others:
        Dave Horn's remarks are on the money. One way to get a handle on loss
of habitat for common nighthawks is to look at their history. Audubon [
http://www.abirdshome.com/Audubon/VolI/00067.html ] has an interesting
account, where he writes: "In the Middle States, about the 20th of May,
the Night-Hawk, without much care as to situation, deposits its two,
almost oval, freckled eggs on the bare ground, or on an elevated spot in
the ploughed fields, or even on the naked rock, sometimes in barren or
open places in the skirts of the woods, never entering their depths."
        A generation later during the 1830s, Nuttall mentions the nighthawk's
presence in cities only during fall migration. In 1838 Ohio's first
ornithologist J. P. Kirtland mentions the species, but does not specify
its habitats. By 1882, J. M. Wheaton was to write of this bird in Ohio
that its eggs "are placed on the ground, with this distinction, that the
Nighthawk seeks no shelter, but selects an open field or bare rock. No
nest is constructed." Wheaton goes on to mention that migrating fall
flocks of nighthawks sometimes were seen in the thousands, numbers we do
not see these days.
        A.C. Bent has a valuable essay on this bird (1964)
http://www.birdzilla.com/omnibus.asp?strType=Bent&strTitle=Common+Nighthawk&strURL=common_nighthawk.htm
where he mentions "The nighthawk in increasing numbers is availing
itself of nesting sites provided by the graveled roofs of our cities and
towns. In certain sections of the country this tendency is so marked
that nighthawks are now seldom seen remote from graveled roofs during
the nesting season, according to Lynds Jones (1909)"--the reference is
to "The Birds of Cedar Point", a lengthy treatise by Jones, Ohio's
foremost ornithologist of the day.
        Before the roof-nesting era, this species nested on gravel bars in
lakes and rivers, rock ledges, burned-over lands, and similar barren
spots. Obviously gravel roofs offered a good alternative, as nests on an
elevated platform were less liable to predation. Such roofs still exist
and are still constructed of course, but are going out of fashion these
days.
        If you look at the thousands of years nighthawks must have been coming
to Ohio to breed, only in the last hundred-plus have they relied much on
human structures; this closely parallels the increasing dependence of
other species, like chimney swifts, purple martins, etc., on such
assistance. Over this period, nighthawks' numbers have diminished; they
are on a steady decline in the Breeding Bird Survey, for example.
Probably encouraging the retention or construction of gravel or
"ballast" roofs will help them to some extent, but the increasing
urbanization of American crow and raccoon populations has presented a
new threat to roof nests. Their old natural nest sites are increasingly
disturbed, as well, and we can expect nighthawks to continue to decline
here; they are probably doing so less quickly in Ontario, whence most of
the fall migrants we see probably come.
        For most of us, the best way to see nighthawks in summer is to find an
urban setting (nighthawks are very hard to find out in the countryside
these days outside the migratory periods) which combines large, fairly
low flat-roofed buildings (preferably older/lower-budget ones like
schools, supermarkets, etc., with gravel surfaces) with all-night lights
to attract insects. These lights will make the birds visible as they
dive after prey. Birds will venture into surrounding neighborhoods,
where you can often hear, if not see, them. This time of year, they have
chicks, and are more likely to be seen or at least heard all night long;
at other times they are more crepuscular. They seem to be increasingly
hard to find these days, though, even in promising-looking places.
        In spring, northbound nighthawks move through mostly beginning in early
May, and can be seen sporadically most any time of day high up in small
groups. The real spectacles that remain come in fall, when from
mid-August to early October you can find silent flocks heading south at
low altitudes either side of sundown, especially along insect-rich river
courses, that can number in the hundreds.
        One more thing. In the courtship period of spring, you can experience
the 'booming' sound by going outside just after dark and imitating the
call of nighthawks overhead; they can be induced to dive-bomb you, and
it's a thrill....
Bill Whan
Columbus

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