Geography Reference
In-Depth Information
one seeks nests, then a thrush—be it an American robin; European blackbird;
i eldfare; or song, Swainson's, or wood thrush—is the ideal subject.
It is easy to i nd nests when we form a “search image” for them. Training
brains to i lter out the typical jumble of shrubbery, leaves, and shadows to
focus on the out-of-place clump, errant tuft of moss, and shady tree cavity, my
team found more than sixteen hundred nests of forty species. We found nests
of ducks and hummingbirds; nests of warblers and woodpeckers; and nests
on the ground, behind walls, and well into the canopy. But half of all the nests
we found were located around eye level in native understory shrubs. Their
architects were American robins and Swainson's thrushes, both of which
build similar, open-cup nests. Swainson's thrushes mostly built their palm-
sized cup in a shady crotch of salmonberry. Robins were less choosy, placing
their larger domiciles on nearly any suitable surface, natural or manufactured,
including the garage rafters right above my mother-in-law's clean car. Thrushes
construct their nests to blend into the background, which in Seattle means
siding them with fresh, emerald moss. The moss often trails below the nest,
like a Sasquatch's ratty beard, to disguise the stark outline. The other construc-
tion materials belie their builder's identity. Robins plaster a grass lining together
with mud, but Swainson's thrushes forego mud and line the nest with a deli-
cate bed of translucent leaf skeletons.
Despite their similar nesting habits, in terms of productivity, robins and
Swainson's thrushes are quite distinct. Although twice the heft of a female
Swainson's thrush, a mother robin lays fewer eggs. A typical clutch of her bright
blue eggs numbers three, whereas the paler Swainson's eggs are nearly always
laid in sets of four. Half of all Swainson's nests we found l edged young, but
only 40 percent of robins' nests did so. Squirrels, jays, or hawks preyed on
most of those that failed. A few were destroyed by storms or abandoned by
parents that nested too close to trails frequented by humans. Nests that suc-
cessfully l edged young birds rarely contained dud eggs or starving young,
something not uncommon in other urban locales, and therefore typically
