[Tweeters] Nighthawks as bioindicators
fsharpe at sfu.ca
fsharpe at sfu.ca
Fri Jul 1 14:05:01 PDT 2005
I too have been impressed by the number of common nighthawks in the lowlands
and montane areas of the SE Olympic Peninsula. I counted seven territorial
birds between two sites along the South Fork of the Skokomish on 28 June.
Extensive outcrops of basalt provide some natural nest sites for the
species. However, logging practices on private timber lands appear to be
primary factor favoring this ground nesting species.
Nighthawks are particularly fond of the gravel substrates found on
yarding platforms and abandoned or lightly traveled logging roads. However,
tight rotation forestry practices using feller-buncher technologies can also
result in extensive areas of non or poorly vegetated soils. On many logging
units, I estimate that over 50% of the land surface exhibits tractor tread
marks and disrupted soil horizons. Consequently, bare exposed patches of
soil are common, and the effect of heavy machinery also can reduce the
deciduous shrub component (formerly present as understory or edge
vegetation). Subsequent mechanical brushing or spraying further reduces
deciduous shrubs during the sapling conifer stage.
Nighthawks appear to be benefiting from these forestry practices. I
am concerned, however, that many other species of birds are not fairing so
well with these forestry techniques. This includes most birds that utilize
structurally complex older forests, in addition to cup nesting birds that
utilize deciduous thickets. In addition, water birds may also be negatively
affected by these forest practices. There is evidence that the mobilization
of fine sediments can substantively increase on steep slopes when soil
horizons, root networks, and vegetation cover are disrupted by heavy
machinery. Hood Canal, an imperiled marine embayment, receives the runoff
from many rivers in the SE Olympics.
Two years ago while sampling birds in an intensively harvested area
above the Middle Fork of the Satsop River (2,600 feet), we awoke to a
sunrise where for 15 minutes, we detected zero species of birds. It had an
eerie felling of Rachael Carsons silent spring. It was probably no
coincidence that the first bird detected was a common nighthawk. After
three hours of hiking, a respectable list of 20 bird species was obtained.
However, the total number of individuals was low. To be sure, this was a
mid-elevation site, above range of most lowland birds. However, it gave me
pause to wonder.
When conducted with care, forest practices, including clearcutting,
can provide habitat for many birds and other wildlife. The apparent
increase in nighthawks may reflect a healthy landscape. As Mary Hrudkaj
points out, nighthawks also benefit from a diverse habitat mosaic, as this
provides high insect biomass. However, I am concerned that the increase in
nighthawks may also reflect widespread forestry practices that produce
extensive barren areas and a reduction in early sucessional deciduous
vegetation. Consequently Waynes thoughts on censusing nighthawks is a good
one, for this species can provide insight on changing land use practices.
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