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    Channel Islands

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Orange-crowned Warbler

Brad Sillasen
 

Scientific Name
Oreothlypis celata sordida

Introduction
This endemic subspecies of orange-crowned warbler is a small, comparatively drab warbler of shrubs and low vegetation that is found on all of the Channel Islands. It is different than other orange-crowned warbler subspecies owing to its shorter tail, longer broader bill, and darker plumage.

Quick and Cool Facts

  • The orange-crowned warbler is divided into four subspecies that differ in plumage color, size, and molt patterns. The Channel Islands subspecies is the darkest green and is found only on the Channel Islands and locally along the coast of southern California and northern Baja California.
  • Observant birders discover this cryptic warbler breeding in oak woodlands and giant coreopsis thickets across the islands, sometimes in astonishingly high densities.
  • Typically, the orange-crowned Warbler is a ground nester, but the Channel Islands subspecies has adapted to select higher nesting sites in oak trees, giant coreopsis and lemonade bushes.
  • Orange-crowned warblers are known for belting out a high-pitched trill, but males on the Channel Islands have a much more variable, melodic song than is typical of the species.
  • Owing to the Channel Islands subspecies lack of a need to migrate long distances after breeding through unfamiliar terrain, (30 miles to the mainland) it has a have a much higher probability of surviving from one breeding season to the next than highly migratory populations.
  • Only 45% of Alaska warblers lived one year, contrasted to 75% that lived to one year on Catalina Island.

Appearance
Generally, the orange-crowned warbler is a small warbler with olive-green upper parts and faintly streaked, yellow under parts. Head has inconspicuous orange crown, broken eye-ring, and faint eye-line. Sexes are similar. What best distinguishes the Channel Islands sub-species is given by the original describer of the subspecies, C. H. Townsend (1890): "Adult male: Entire plumage decidedly darker than H. celata lutescens. Feet and bill larger; wings slightly shorter. There is an appearance of grayness about the upper plumage, owing to a leaden tinge on ends of feathers. Throat and under parts slightly streaked."

Range
Research focused on orange-crowned warblers shows that the species as a whole is widely distributed, but the Channel Islands subspecies, is largely relegated to the Channel Islands because of intensive development on the nearby mainland. These warblers are one of many island endemics that have made the Channel Islands famous for their unique flora and fauna.

Two of the largest islands – Catalina and Santa Cruz – are where long-term study sites have been established to follow the breeding activities of but the Channel Islands subspecies. The islands are in close proximity and are alike with respect to topography, habitat, and many other features. However, they differ in two key aspects: their predator community and the amount of rainfall they receive It is not known exactly where individuals that breed on the Channel Islands go after their February-June breeding season, but most leave the islands to spend their "winters" (July-January) on the coast of southern California and northern Baja.

Habitat
Gilbert et al. (2010) report that orange-crowned warblers on the Channel Islands prefer humid and shaded sites on slopes, in canyons gullies and sea-cliffs in chaparral, Torrey pine, coastal bluff and coastal sage scrub vegetation types.On Santa Rosa Island, orange-crowned warblers preferred coastal sage scrub, grassland and chaparral and avoided closed-cone pine and oak woodland.

Feeding
Most warblers, including but the Channel Islands subspecies, exhibit migratory tendencies, taking advantage of the spring flush of insects in temperate zones, gleaning insects off leaves. Their diet includes insects and spiders, but it also includes seeds and fruit. Orange-crowned warblers rely on insects like caterpillars to feed their young. Astudy by the Catalina Conservancy, shows that but the Channel Islands subspecies consumes lesser quantities of fruit and nectar.

Reproduction
Like many members of its genus, orange-crowned warblers are ground nesters with cup style nests. However, but the Channel Islands subspecies frequently nest off the ground ad well, mostly in oak trees, lemonade berry bushes, and giant coreopsis plants. The islands where off-ground nesting occurs are generally free from visually-oriented nest predators like jays, and these nests tend to have higher success than ones on the ground, which are more susceptible to snake and mammal predation.

Average clutch sizes around 3 to 6 are typical. The orange-crowned warblers incubate their eggs for approximately 12 days. Once the eggs hatch, both the male and the female provide parental care to the offspring. They provision food in the nest for 11 days (nestling stage) and out of the nest for upwards of 2 months (fledgling stage) while the young grow and develop the necessary skills to fly and find food on their own. If at some point a predator finds the nest and eats the eggs/nestlings, the pair will usually start over again and build a brand new nest, hoping for better luck the next time.

Conservation Status
The orange-crowned warbler, Vermivora celata, are a species of Least Concern by the IUCN Redlist. This species has an extremely large range, and hence does not approach the thresholds for "Vulnerable" under the range size criterion The population trend appears to be increasing, and the population size is extremely large, For these reasons the species is evaluated as "Least Concern."


Additional Information

Did You Know?

Santa Barbara Island live-forever                 timhaufphotography.com

The Channel Islands are often called the "North American Galapagos" because they are home to over 150 endemic or unique species.