“A Year of Birding in Bloedel” is a column that runs every Friday in the Bainbridge Islander. The project is planned to continue in 52 parts through 2014 to help readers find and identify birds in the island’s garden sanctuary. Beginning with this entry on the bald eagle, each column will also be published here on the Bainbridge Conversation blog each Friday.
The author, Ted Anderson, is a retired professor of biology, having taught at McKendree University (Ill.) for 32 years and for the University of Michigan’s summer biological station for 20 years, where he frequently taught the biology of birds.
Anderson is also the author of “Biology of the Ubiquitous House Sparrow, from Genes to Populations” (2006), and “The Life of David Lack, Father of Evolutionary Ecology” (2013). Ted and his wife Carol have been members of Bloedel Reserve for 7 years. They live in Kingston.
My wife and I took advantage of a sunny Wednesday morning last week to enjoy a leisurely stroll through the Bloedel Reserve. The most conspicuous bird species, besides the many ducks and geese, was the Dark-eyed Junco (Junco hyemalis). We observed several individuals foraging on or near the paths as we walked, and the rather metallic and desultory trill, all at one pitch, that constitutes the male’s song at several places in the reserve.
The Dark-eyed Junco occurs throughout North America, and like many such species, it shows considerable variation across this extensive range. In the Pacific Northwest, where the species is a year-round resident, male juncos have a black hood that covers the head and chest, a brownish back, rufous flanks, gray rump and tail, and white underparts as well a white beak and white outer tail feathers. In females the hood is dark gray rather than black.
In eastern North America juncos are migratory, breeding primarily in Canada and the northernmost states, and spending their winters in central and southern states. There the species is uniformly slate-colored except for the white underparts, beak and outer tail feathers. Audubon referred to the species as the “Snow-bird,” and many Easterners still call it the snowbird.
The Dark-eyed Junco has been a research subject in many ecological, behavioral and physiological studies. Arguably the most groundbreaking such study was published by the Canadian physiologist William Rowan in 1925. Rowan kept juncos in outdoor aviaries in Alberta throughout the winter with nighttime temperatures dropping to as low as minus 50 degrees. He artificially increased the day length in one cage with two 50-watt light bulbs, while the second cage served as a control on natural day lengths. In a few weeks the juncos in the cage with increased day length began preparations for breeding in the dead of winter, while those in the other cage did not.
Rowan suggested that day length, or photoperiod, was the environmental cue that triggered the timing of migration and reproduction in the species. Many follow-up studies on numerous species of birds confirmed this conclusion and demonstrated the existence of an internal biological clock (circadian rhythm) in birds and most other organisms, including humans. Studies on birds identified the role of melatonin in the regulation of the circadian rhythm, a fact that has led to the use of melatonin to alleviate the effects of jet-lag in humans.
