Biology Reference
In-Depth Information
and heavy rains cause your chicks to drown?
Mrs. Kirtland, why not raise them in town?
And what was the fate of those birds that failed to find a home in a young jack pine grove?
Did their offspring survive at all? Skunks and other midsized nest predators do eat Kirtland's
chicks. But did chicks survive better when such top predators as wolves, bears, and pumas
kept the population of skunks, raccoons, and their eggsnatching ilk in check? My field note-
book held more questions than answers.
The singing male above me kept at it. In the heart of his territory were huckleberry bushes,
aromatic sumacs, and sweet ferns (a shrub in the bayberry family), but the tree layer was vir-
tually a pure stand of young jack pines. The pines were hunched and distorted, partly because
they were growing on Grayling sands, an acidic, porous, nutrient-poor soil. The trees were
about eight years old, perfect for this warbler, which builds its cuplike nest on the ground
under the spreading pine boughs. Saplings younger than five years of age offer poor cover,
while the upper branches of jack pines older than twenty years block the sun from reach-
ing the ground. At that age, too, the lower branches of older trees drop off, and overhanging
grasses become shaded out. This exposes the ground nests to predators, which besides skunks
include snakes, thirteen-lined ground squirrels, and blue jays. Kirtland's are also particular
about substrate, the surface on which an organism grows or is attached. Rainwater percol-
ates quickly through Grayling sands, so shielded nests and the surface soil layer stay dry
even after summer cloudbursts. Nestlings left sitting in puddles or on waterlogged soils suf-
fer heavy mortality.
