A few weeks ago, I received an an email from a local resident, one that had been addressed to many other recipients on the local community email list. I do not recall the exact title of the email, but it was something similar to “A Magnificent Visitation.” Attached to the email was a brief video depicting a flock of several hundred birds flying in coordinated patterns over the desert. The grace and wonder of birds in flight cannot be denied. I am sure that the sender of that email had nothing but good intentions. People liked the video. One neighbor even chimed in with comments referring to her happiness at seeing so many of these same birds at her feeders.
I was alarmed when I saw the video. I immediately recognized the birds in flight as a flock of brown-headed cowbirds. This was a larger flock of that species than I had ever seen in the valley. NOT good! Allow me to explain:
Brown-headed cowbirds are nest parasites (also known as “brood parasites”). They do not build nests nor do they incubate eggs or raise their own young. Those favors come from other birds, a list that tops over 220 species, including a wide variety of our songbirds. Female cowbirds are experts at finding the nests of other birds. They quickly lay their eggs during brief times when the host birds leave their nests to feed or seek water. Most birds do not recognize the alien egg, and proceed to incubate it as their own. When the egg hatches, a tiny, blind, featherless cowbird emerges to shove any remaining eggs or previously hatched young out of the nest. It remains there alone, to be fed and fledged by its unwitting foster parents, be they sparrows, warblers, vireos, or other species like the dazzling lazuli bunting pictured above.
The original niche that nature had carved out for brown-headed cowbirds in the area we now know as the United States was that of a prairie grassland bird that was closely associated with herds of roaming bison. The bison broke up the soil with their heavy hooves as they moved, exposing a banquet of food for ground-foraging cowbirds. There were other races of cowbirds in a few other locations, such as the inter-montane grasslands of central British Columbia. However, I do not believe that brown-headed cowbirds are native to southern Arizona. They are a relatively recent introduced species, likely first appearing here when they followed large herds of cattle that were driven into the region in the 1800s by Euro-American settlers.
The story of these birds does not sound so bad until one realizes some important aspects of their ecology coupled with the plight of our declining songbirds. Brown-headed cowbirds are flying egg factories. A single female cowbird can lay up to three dozen eggs in three dozen songbird nests every year. Considering that an average songbird nest would normally raise three or more young birds, that adds up to over 100 songbirds destroyed by each female cowbird every year.
North America’s songbirds have been rapidly declining in recent decades due to a variety of factors, all caused directly or indirectly by the activities of mankind. Here in southeastern Arizona, cowbirds are impacting our dwindling bird populations seriously. Like tumbleweed, buffle grass, or other non-native species, they are capable of wreaking havoc on ecosystems like this one that they are not endemic to. As a native species, the brown-headed cowbird is protected under the Migratory Bird Treaty Act… but native to where? What ecoregions?
I won’t tell my readers how I react to the presence of cowbirds here on our property, but I’d bet some of you can guess. All life is deeply beautiful and all life should be respected and revered. As I grow older, I embrace such tenets more and more deeply, but there are times when one must act to protect certain things. I never kill rattlesnakes, for example, even the ones that commonly sleep under our ramada, but when mice get into the engine compartments of our vehicles, decisive action is essential. Brown-headed cowbirds? Never welcome here.
