Brewer’s Blackbirds, Our Other Blackbird
by Ro Wauer
Blackbirds are some of our most abundant birds this time of year. It is next to impossible to ignore our resident blackbirds, both in town and about our fields and pastures. Huge flocks of redwings, cowbirds and grackles, either in species-specific flocks or in mixed flocks, can often seen wheeling about on their way to or about feeding sites or en route to overnight roosting sites. Oftentimes, European starlings are added to the mixture. A drive into the countryside can easily turn up all of these ground-feeding blackbirds, sometimes so numerous that can blacken the ground or, in flight, look like a dark cloud.
But there is yet another blackbird that is with us during the winter months that we often ignore because of so many look-alike others. This other blackbird is the Brewer's blackbird that is with us only from mid-October to late April. And yet it is fairly common in some localities. Small flocks of Brewer's often can be found along the edge of highways throughout South Texas. They walk about searching for seeds and tiny insects, spiders, and such. Very rarely do they associate with other species, although isolated flocks do frequent feedlots that attract large numbers of blackbirds.
Brewer's blackbirds can easily be identified by both their appearance and behavior. They are slightly larger than redwings, and considerably smaller than grackles. They are most like the common grackle, principally because the adults of both species possess pale yellowish eyes. But the tails of these two species are very different, long and keel-shaped on common grackles, but long and straight on Brewer's blackbirds. Plus, Brewer's habit of walking about includes an obvious head jerk with each step. This behavior can be recognized even at a distance.
Although wintering Brewer's blackbirds can usually be found throughout Texas, except in the high mountains, all leave the state in spring. The exception is a lone nesting record in Jeff Davis County in 2000. Breeding birds can be found throughout most of the other western states from northern Arizona to northern Canada. Nesting birds utilize various habitat types from sagebrush in the Great Basin to streamsides in all the western states. Even then, unlike most other birds that flock in winter but nest alone, Brewer's are colonial nesters. Dozens of nests are often built close to others within preferred localities. And the breeding birds even feed together in flocks. This gregarious behavior allows inexperienced birds to learn about food sources from more-successful foragers. And such behavior also provides them greater protection from predators.
Another characteristic of breeding Brewer's blackbirds is that some flocks practice polygamy, where one male mates with more than one female while each female mates with only one male. The logic of this behavior, according to ornithologist Paul Ehrlich and colleagues, discussed in The Birder's Handbook, is that "when males hold territories that vary greatly in the quality of resources...Females will tend to choose superior males - by interference those that have high-quality territories. When those males already have mates, females have a choice. They can either select a male that holds an inferior territory, or they can become the second mate of one of the superior males." Such behavior is most likely to provide for greater success in reproduction.
Bird behavior can vary considerably in all of the species that we see in our yards or elsewhere in the vicinity. It not only makes birds even more fascinating, but makes one wonder what other characteristics they possess that we have yet to learn about.