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Thursday, April 18, 2013

An Endangered Bird - The Golden-cheeked Warbler

Tweeh-tweeh-tweeh-TWEE-sy! Can you hear it? Early March marks the return of the Golden-cheeked Warbler to the Texas Hill Country. This beautiful neotropical warbler spends its winters in the forests of Central America and its summers in fewer than 40 counties in south Central Texas. Sadly, this unique bird is one of over 200 species of migratory birds whose survival is threatened by the destruction of native habitat - in both its winter and summer ranges - due to agriculture and development. 

The Golden-cheeked Warbler (formerly Dendroica chrysoparia now Setophaga chrysoparia) is a 4 to 5 inch-long songbird with dark gray upperparts and white underparts with thick black streaks on its sides. Its head has a black cap and throat, bright yellow ‘cheeks’, and a dark eye-line. Dark wings with two white wingbars complete the brightly colored male, while the female is duller with olive-green upperparts, a streaked cap, and a generally white throat. 

This warbler is totally dependent on mixed woodlands of oak and stands of old-growth Ashe Juniper (colloquially called ‘cedars’) for nesting habitat, just like those found in the ravines and canyons that surround our neighborhoods on the western side of Austin. This unique habitat provides the warbler with long strips of peeling bark from the mature Ashe Juniper trees, and they use them, along with spider webs, to construct their nests. An insect-eating bird, Golden-cheeked warbler forage through the leaves and bark of oaks and other trees, gleaning them of a multitude of caterpillars, spiders, beetles, and other small insects. 

Golden-cheeked Warblers arrive at their breeding grounds by mid-March, returning largely to the same areas each year and nesting from April to May. Females lay 3-4 eggs during the nesting season, with the young fledgling birds leaving the nest only 8 or 9 days after hatching, staying in the vicinity of their caring parents. Of the nearly 360 bird species that breed in Texas, the Golden-cheeked Warbler is the only one that nests exclusively in Texas, so each one is a native Texan! 

The major environmental threat to the warbler is native habitat destruction and fragmentation, with the most significant factor being the widespread removal of Ashe junipers in the south central region of Texas. Over the twenty year span between the early 1970s and 1990s, coincident with urbanization removing 50% of suitable habitat, the warbler’s population declined dramatically from over 15,000 birds to less than 5,000, prompting it to be listed as an endangered species in 1990 by the U.S. Fish and Wildlife Service. 

What can we do to help preserve this unique Texas species for future generations? Buy shade-grown coffee, which reinforces better agricultural practices that protect habitat in the warbler’s wintering range. Here at home, support the Balcones Canyonlands Preserve System (BCP), which contains the greatest amount of prime warbler habitat in large, undisturbed tracts. Take a guided hike on one of the BCP tracts offered by trained volunteers with the City of Austin’s Wildland Conservation Division to learn more about this unique bird. And respect the fact that from March 1 to July 31 the much of the BCP is closed for the Golden-cheeked Warbler breeding season, and citizens must obtain a permit for limited access during this time. 

Most of all, consider it good fortune if you see a Golden-cheeked Warbler, a rare native denizen of the Texas Hill Country, and think twice before cutting down those life-sustaining Ashe junipers! 

In the spring of 2009, city biologists began banding Golden-cheeked Warblers on the BCP. Since then, over 350 birds have been banded from an overall estimated population of about 1000 pairs across all BCP tracts. By banding the birds, individuals can be re-sighted and provide information regarding the number and size of territories, as well as loyalty to specific territories. When in hand, biologists can determine the approximate age of the birds, and begin to understand how age affects habitat choice, mating and nesting success, migratory return rates, and overall survival rates.