Andy, sounds like you had a great coastal road trip. Concerning your comment

> I thought it interesting we neither saw nor heard any Red-breasted
> Nuthatches, Pine Siskins or American Goldfinches on this trip, not to
> mention Red Crossbill. Scarcity of Red-breasted Nuthatches, Pine Siskins,
> and Red Crossbills on the outer coast this winter seems to be our
> experience
> on the several trips we've taken out there.

Your observations concerning low numbers of certain songbird in coastal
areas is noteworthy. Siskins, crossbills, and other nomadic seed eating
finches come and go, presumably following conifers seed crops. However,
there are a number of birds that occur in coastal conifer forests, but are
found at substantively lower densities than in dryer habitats in the Puget
Trough. These include the Olive-sided Flycatcher, Western Wood Pewee,
Red-breasted Nuthatch, Cassin's Vireo, Red-eyed Vireo, Yellow-rumped
Warbler, Townsend's Warbler, and Bullock's Oriole. The shrub communities
associated with wet conifer forests are also characterized by low densities
of many species including Bushtits, Willow Flycatchers, Black-capped
Chickadees, Bewick's Wrens, MacGillivray's Warbler, Yellow Warbler, and
Spotted Towhee.
I suspect that the low densities or absences can be attributed to
a number of factors. Perhaps most importantly are the persistent fog, rain,
and cool temperatures that often occur during the breeding season.
Presumably these conditions can reduce the amount and activity of insects
available for insectivorous birds, and place thermal stress on young broods.
Tree species composition, and high cover of conifers is also
probably a factor. The high tannin content of western red cedar may
suppress insect biomass, limiting insectivorous birds such as warblers and
flycatchers. Chemical induced insect suppression by conifers has been
suspected in other areas, such as the pine forests of the southern United
States, where the high resin content of the trees apparently eliminates many
insects as food for birds. Old growth western red cedars are characterized
by relatively low amounts of foliar biomass, which reduces the amount of
cover for songbirds or platform nesting species such as Murrelets. Cedar
foliage also possesses an unusual geometric shape of its leaflets which may
effect the ability of birds to exploit arthropods. The shrub layer of salal
and evergreen huckleberry may further contribute to paucity of birds, as
their tough, leathery foliage may inhibit arthropod production. And finally,
the rot characteristics of red cedar may make it difficult for the smaller
cavity nesters to excavate holes through the hard sapwood.
One of the few bird that increase in density in cedar stands
compared to the adjacent hemlock/spruce stands is the Orange-crowned
Warbler, which appears to forage locally in the deciduous broad-leaved
understory species such as evergreen huckleberry, salmonberry, and cascara.
The absence of birds in these wet forests is noteworthy, as research
on birds in Southern Cascades of Washington revealed an opposite trend; wet
stands tended to possess higher species diversity then dry forests. The
seemingly contradictory pattern between the two areas may be explained by
far wetter conditions that are experienced on the Olympic Peninsula then
even the wettest stands in the Cascades.
It should be noted however, that in coastal riparian habitats avian
diversity and abundance can be much, much higher. Riparian vegetation
surrounding coastal estuaries, lakes and rivers all have higher diversity.
The large freshwater area on the east edge of Lake Quinault is a good
example. Over the years it has produced green heron, common loon, trumpeter
swans, marbled murrelets, Caspian tern, large flocks band-tailed pigeon,
merlin, red-eyed vireo, and even a vagrant northern parula warbler. In
fact, my single highest morning count on the Olympic Peninsula comes from
this paradise.

Fred Sharpe
UC Davis
fsharpe at sfu.ca