Migration season is always a birder’s paradise as species
that aren’t usually found in Iowa can be seen passing through. August through
October are typically peak migration months.
Warblers are one such group of birds that are fun to watch.
During fall migration many warblers have their winter coats instead of their
bright breeding plumage which can make it an extra challenge to identify the
different species. Though they sing less because they aren’t searching for a
mate, listening for their short vocalizations is still one of the best ways to
help identify warblers. This is especially useful if you want to identify the
species as they migrate during the night. Most warblers migrate, or at least start
their migration, during the night. They will “drop-out” during the day and use
that time to refuel for the next flight.
In addition to the 10 species of warblers that breed in
Iowa, there are also 16 that pass through Iowa during migration. Two of these
species—the bay breasted warbler and the Canada Warbler—are Species of Greatest
Conservation Need (SGCN) meaning these species have a low or declining
population.
Canada Warbler
The Canada warbler (Cardellina canadensis) nests in the northern United States and in Canada and spends
winter in northwestern South America. It is one of the earlier migrants and may
spend only two months at its breeding location. Unlike many warbler species, the
Canada warbler does not have a noticeable difference in its breeding and
non-breeding plumage. It is sometimes called the “necklace warbler” because of
the band of dark streaks across its chest. Both sexes have the necklace,
although the male’s may be slightly darker and more conspicuous. The chest,
throat, and belly are yellow and the back is grey. They also have white
eyerings or spectacles.
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Bay Breasted Warbler
The bay breasted warbler (Setophaga castanea) breeds in the northern United States and Canada
and spends winter in northwestern South America. It is one of the later
migratory species and may linger quite late into fall. In summer, the male is
known for having a blackface, chestnut head, and reddish-brown on the flanks.
The female has a more muted version of the male’s plumage. During the fall
migration, the bird is in its non-breeding plumage and becomes a greenish
“confusing fall warbler.” In order to identify it look for light streaking on
the back, thick wing bars, dark colored legs and feet and the reddish wash that
some birds keep from breeding season.
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So,
if you’re looking for a challenge this fall, grab your binoculars and head out
for some warbler watching.
The Wildlife Diversity Program has a poster
of all the Iowa warblers for $10, which you can order by calling 515-725-8200
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