Saturday, November 15, 2014

Arctic Warbler (Pylloscopus borealis)

Field marks:  larger than other warblers, long yellow stripe over eye, bill slightly upturned, single wing bar (12 cm.)
极北柳莺 – jí běi liǔ-yīng – ‘extreme north willow warbler’

Most of the birds described here are found in China throughout the year. For most of us in eastern China, the only chance we will get to see this bird is during its lengthy spring and fall migrations along China’s East Coast. During the months of April and May in spring and August and September in fall, there is a very good chance to see this bird darting through the trees of city parks and gardens.

The Arctic warbler undertakes one of the longest migrations of any Asian or European songbird. During the summertime breeding season, this species can only be found in the extreme north of China, in northern Heilongjiang province. Most members of the species breed in Russia in a region approaching the Arctic Circle. This liking for extreme northern latitudes gives the bird its name.

The Arctic Warbler is one member of a large family of warblers, “Acrocephalinae”. China is home to no less than 83 species of warblers. All warblers are small, extremely active insectivores, meaning that they eat no other food besides insects. The limited nature of their diet dictates that these birds must always be in a place where insects are found, thus all warbler species that breed in locations which get too cold to support insect life in winter must fly south to warmer climes. The Arctic Warbler flies as far south as Indonesia and the Philippines to sustain itself in winter.

The Arctic Warbler is part of a sub group of warblers known as “leaf warblers” This group includes all the Asian warblers that are usually seen foraging high in trees for insects. Other species of warblers may choose to hunt on the ground for food or perch along rivers or ponds. All leaf warblers have greenish backs and white under parts with similar markings making identification very difficult. This species can usually be distinguished by its single wing bar, larger size and slightly upturned bill.

During spring and fall migrations, several species of leaf warblers can often been seen together foraging for food among the treetops. All of these species move very quickly while feeding leaping from branch to branch in a state of perpetual motion. Under these conditions it is often impossible to identify which species one is observing. Even seasoned birdwatchers will be unable to make exact warbler identifications on most days.

Photo by Lip Kee

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