People in Glass Houses Should Draw Their Shades
People in Glass Houses Should Draw Their Shades.-In a recent issue of the Condor (1945:mj) there is a posthumous field note by George Willett, wherein he comments on the large number of Russet-backed Thrushes (Hylocichla ustulata &data) killed by flying against windows. He titles the article with a query-“Does the Russet-backed Thrush Have Defective Eyesight?” The explanation of fatality incidence, it seems to me, lies not in defective eyesight but rather in habits of tunnel flight and inexperience with passages to light that are blocked to flight by window glass.
It is well known that this species migrates in the lowlands, frequenting en route its typical association--the woodlands of moist ground and streamside. Its use of environments of human culture, the heavy verdure of gardens and yards, is less well known and is here indicated by the fatalities. In my twenty-five years of residence in Pasadena, California, the spring influx of Russet-backs has been clearly but briefly noted. The overwintering Hermits leave the dooryards in April; suddenly, of a later morning, thrushes posses the shaded thickets again ; the migrating Russet-backs abound for a few days and are gone.
This spring, when the Russet-backs stopped by, well-rotted compost-like wood-soil was being dug from a pit and spread as a, dressing beneath shrubbery. Each barrow load dumped was promptly searched over by one or more thrushes that stayed about. ‘The birds alternated between the pit and the dumpings as I drove them from first one and the other. Some of the time they fitted low into the neighbor’s yard and back. Never in all this driving about did the migrants go up in the trees as do the wintering Hermits when disturbed, never except when cornered by buildings.
This low flight through the understory of plantings is characteristic within the native habitat which locally consists of riparian woodland and farther north of other moist sylvan growths. This shadowy humid world of rich soil and rapidly decaying ground litter has climate, flora and fauna unique to itself. The Russet-backed Thrush has here its niche. Even in migration underplanted trees, moist soil, dense humid shade, a,nd compost are irresistible. It is in this gallery habit rather than in defective eyesight that I readily see the cause of the high fatality. Willett recorded during the migrating season. Shooting through the underforest the newly arrived traveler follows an aisleway leading out to light. When too late the aisle is recognized as a direct view through a house and not a direct flight path, there remains but a slight clatter and a small limp body to record an error of ecology.
The Chat and the Yellow-billed Cuckoo affect the same natural habitat as the Russet-backed Thrush and fly through the same galleries and tunnelways. All three migrate, yet only the thrush becomes a significant casualty about human dwellings. This seems to be explained by the thrush’s acceptance of sylvan bosky haunts besides the riparian. The other two stick to the willows an&brambles. -ROLAND CASE Ross, Los Angeles City Schools, California, December 17, 1945.
