Crescent Warbler
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Crescent
Warbler, Geothlypis
crescens L 10-15 cm, WS 18-20 cm, Family: Parulidae
IUCN Conservation Status: Least concern (LC)
Description:
Small,
active songbird with round body, large head, and long tail. Full-bodied and
chunky for a warbler. Yellow-green overall, with olive upperparts and yellow
undersides, with gray head. Males have a black throat and lores and a distinct,
white, crescent-shaped band across breast. Females paler overall with a less distinct
breast patch and lacking the black throat. Both sexes have obvious white eye-ring.
Pinkish legs long, more obvious than in other native warblers; bill pinkish,
heavy.
Voice:
Song
is a slow, burry warble, usually descending in pitch. Song usually three to five
syllables, lasting one to two seconds, often written as Cheery-churry-chore.
Song is slower and deeper than other native warblers. The most common call is a
short, metallic tsik.
Range and Habitat:
Summer
range encompasses most of Novasola, excluding the interior steppe, but more
common in higher elevations and wetter climates. Migrates to spend winter in southern
California and Mexico. Can be found in most wooded ecosystem types like conifer,
deciduous, and mixed forests, shrublands, and wetlands, but are usually found only
in areas with dense understory vegetation or shrub layer. Associated with
secondary growth or disturbed areas within forests and riparian thickets.
Discussion:
Not to be confused with the Crescent-chested Warbler of Mexico, the Crescent Warbler is likewise named
for their obvious breast band, but Crescent Warblers can still pose a challenge
for identification, as their small size and habitat preferences make them difficult
to observe. However, Crescents are notably slow-moving and heavy for a warbler,
as is their song, which is often the best feature to use to distinguish them.
Crescent
Warblers forage deep within dense cover and eat mostly insects and other
invertebrates which they pick from foliage or the ground. Their preferred food
sources include caterpillars, ants, moths, beetles, flies, and bees. They have
been observed on rare occasions eating berries. Often they skulk within thickets
of willow, alder, rhododendron, manzanita, ceanothus, and raspberry, but will
at times forage higher, into the subcanopy, especially in dogwood and young
Coopers-fir and spruce.
Like
most native warblers, Crescents winter off the island in California, Arizona,
and Mexico, but they breed on Novasola, arriving in mid-to-late May and leaving
in mid-August. When males arrive in the spring, they establish territories,
which they do mostly through song. Crescent Warblers may sing from exposed
perches or from under dense cover, but it is much more common to hear them than
to see them, as even when exposed their coloration, though bright, easily
camouflages them. Multiple neighboring males will sing over one another, making
shrub thickets seem to echo with song. Crescent Warblers form monogamous pairs
during breeding. Females build nests, usually near the ground in areas of dense,
in not seemingly impenetrable, vegetation, often in the crook of forking stems,
and both parents will incubate eggs and feed chicks. They are very secretive
when near the nest, and this makes finding Crescent Warbler nests extremely
difficult.
Closely
related to the MacGillivray’s Warbler and Mourning Warbler from mainland North
America, the three species form an interesting phenomenon, similar to a “ring
species” phenomenon, where connected populations may form hybrids with each other while the
two end species are too distantly related to hybridize. In this case, Crescent
Warblers can hybridize with MacGillivray’s Warblers, and MacGillivray’s can
hybridize with Mourning Warblers, but Mourning and Crescent Warblers cannot form
hybrids, even though some Crescent Warblers breed outside Novasola in Canada
where their ranges overlap with both other species. This has become a recent
topic of much research and debate over what constitutes a “species”.
Like
most endemic warblers on Novasola, few writings or references to the Crescent
Warbler exist before Reichwald’s descriptions for the Novasola Research Corps.
Since then the Crescent has remained somewhat mysterious, despite its abundance;
an infrequently studied common warbler. In recent years however there has been a
marked uptick in Crescent Warbler research, especially genetic studies. Their
habitat preferences and stealthy nesting habits are likely to blame for the
gaps in knowledge.
“An
upside to this area is the abundance of birdlife. Perhaps of most interest to
me are the many warblers I have observed and heard during this hike, of at
least three varieties, all of which yellow. Having not yet gotten a good look
at any, I have relied so far only on song to differentiate them. I don’t know
whether this area is particularly dense with warblers when compared to other
stretches of the Fastwaters, as it seems, but I am hopeful I should get the
chance to study them in great detail.” – Expedition log, May 29, 1902
“Similar
in habit and in habitat, the Crescent Warbler may to the amateur eye be easily
confused with that of the Black-eared Warbler. The male plumage of each species
is sufficiently distinct alone, but this may be difficult to observe while
under cover. Should the bird’s calls not give the identity away, look to form.
Where the Back-eared Warbler is small, quick, and bouncy, the Crescent Warbler is
corpulent, slow, and methodical.” – Manual to Novasolan Birds, 1914
“It
is the that [Crescent Warbler’s] song which shall always give me reason for
pause. Not for some love of the warbled tune or for a particular interest in
the bird itself, but for what I know that song to be exhibitive of: difficult
country. It took only a short time for me, and the rest of the Corps likewise, to
understand that should we hear a chorus of Crescent Warblers we could reasonably
and reliably expect to be met with dense foliage and shrubbery to impede our
forward progress. Indeed, the more warblers we heard the thicker we would
expect the country to be with briars and thickets and green, such that instead
of continuing to push our way painfully through overgrown and unforgiving
lands, we would guide ourselves and determine our path of travel by the absence
of such song.” – Native Birds of Novasola, 1912