Just as Cliff Swallows adjusted to the push of humans (and
their structures) across North America, so did Barn Swallows (Hirundo rustica). This species,
virtually worldwide in distribution, has been known to be associated with
humans for over 2,000 years in Europe. But it may have had a limited breeding
range in North America, thought to be primarily in the mouths of caves.
Needless to say, these were very limited nesting habitats.
Nowadays, however, Barn Swallows nest throughout southern
Canada and the United States, excepting the southwestern deserts and peninsular
Florida. They are so successful because they nest on just about any structure
provided by humans—houses, barns, overpasses, bridges, even small culverts.
Drive across country, and there will be Barn Swallows nesting under just about
every bridge you cross. But look for them in vain on natural substrates!
Like Cliff Swallows, Barn Swallows utilize mud for the
foundation of their nest, and they gather it in the same way from the water's
edge, although singly rather than in groups. The mud walls are usually about an
inch thick. Rather than retort-shaped, their nest is cup-shaped, so the young
spend their time looking out at a broader world, although still constricted by
the ceiling of their nest site.
Some people think having Barn Swallows nest on their house
brings good luck. Others are turned off by the mess they make. The parents
collect fecal sacs from the nest for the first 12 days after the eggs hatch,
but after that the young just stick their rear end over the edge and let fly.
That's a lot of incremental excrement in the subsequent 8 days before they
fledge.
With clutch sizes averaging around five eggs, the nest of a
Barn Swallow fills up fairly rapidly with growing young, so the young need to
leave the nest as soon as they can fly. The adults "park" them on
nearby tree branches or fence wires and feed them for up to a week more. Then
they are on their own.
Barn Swallows have been much studied in Europe, especially
their mating behavior and sexual selection. Birds of both sexes with longer and
more symmetrical tails have greater reproductive success, parental effort, annual
survival, ability to withstand parasites, immunocompetence, and other measures
of fitness. Thus an individual has a fairly good chance of judging the true
quality of a prospective mate.
So Barn Swallows nested in caves, and Cliff Swallows nest on
barns. Care to guess where Cave Swallows nest?
Dennis Paulson
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