This article first appeared in the February 2005 issue of the
San Antonio Audubon News.
In the course of preparing these articles, it has become apparent that many of our familiar bird Families contain more species native to the New World tropics than occur here. Given the diversity of frugivorous birds in the tropics, when researching this month’s article I was expecting to find mention of a wide array of tropical waxwings. Much to my surprise, there are only three species in this unique Family (Bombycillidae) and all breed exclusively in northern climes.
The Bohemian Waxwing (Bombycilla garrulus) has the widest breeding range, being native to mixed or coniferous woodlands from central Canada and across Alaska and Siberia to Scandinavia. Despite the name, the Japanese Waxwing (B. japonica) breeds only in far eastern Russia, some of the population wintering in Japan. Our own Cedar Waxwing (B. cedorum) [illustration, right] occupies a broad breeding range extending across the southern half of Canada and the northern half of the lower 48 states. In winter, waxwings form large flocks that wander unpredictably seeking fruiting trees and bushes. While the Bohemian Waxwing occurs within the U.S. with fair regularity on the Northern Plains and less often elsewhere, wandering flocks of Cedar Waxwings are a common sight across most of the United States and south to Central America and the Caribbean.
More than 80 percent of the annual food intake of waxwings consists of fruit, the prodigious ability of these birds to gorge upon berries being the stuff of legend. Berries are swallowed whole, the esophagus expanding to allow additional fruit to be stored prior to digestion. Individual berries may pass through the digestive system in twenty minutes or less, the fecal material consisting largely of the undigested seeds. In contrast to such birds as American Robins (Turdus migratorius) which also form wandering winter flocks, waxwings do not commonly take fatty fruits, their digestive system being specialized for the rapid assimilation of simple sugars. Interestingly, although robins and waxwings feed upon many of the same fruits, robins lack the ability to digest sucrose. In captivity, Cedar Waxwings are much better able to maintain weight when fed solely upon berries than are robins, which require a more diverse diet. The different metabolic abilities of these two competing species would seem to indicate a somewhat complimentary division of the food resource.
In the springtime, waxwings frequently feed upon the blossoms of flowering trees, which blossoms may become an important food resource during times when fruit is scarce. At any time of year one may observe these birds fly-catching, especially over water. Waxwings can also take insect prey by gleaning from leaves and branches. Flocks are attracted to insect hatches and outbreaks, both berry crops and insect outbreaks representing locally abundant, ephemeral food resources.
The term waxwing derives from the row of bright red waxy deposits occurring on the tips of the secondary flight feathers of both Bohemian and Cedar Waxwings. It is thought that these drops may function as an indication of fitness during mate selection. These deposits are larger in older birds and pairs of such experienced birds generally raise more young. Breeding begins later in the season than most passerines, courtship displays are subtle and neither do waxwings become aggressively territorial. Nests are generally placed in trees adjacent to open areas, often near water, and clusters of breeding pairs may occur around available fruit supplies.
When foraging for materials with which to construct their cup-shaped nest, waxwings will often steal material from similar nests constructed earlier in the season by other species. Both sexes share in incubation and feeding the young. In addition to insects, the nestlings are fed berries from an early age, a habit often fatal to any cowbird nestlings that may be present.
Although the Japanese Waxwing appears to be suffering the
effects of habitat destruction across its limited breeding range, our own
to be holding their own despite their specialized feeding habits.
In times past,
Cedar Waxwings were a favored target for market gunners, having
a reputation for being both plump and tender, perhaps indicating that
were commonly well fed. In recent decades, Cedar Waxwing populations
possibly due to the widespread introduction of ornamental fruit-bearing
trees and shrubs.
Sources and More Info:
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#257, San Antonio, TX 78209-5710, (210)
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