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Summer has come to the river and its valleys, bringing a cavalcade of change to the animal world. Today, my thermometer registered 113° F. I don’t leave southern Arizona during the summer like so many people do every year. This is my favorite season here, because so much happens in the natural world during the fierce heat of summer…
Mike and Mavis have successfully raised their seventh brood here on our land. This year, four new ravens have fledged and left the nest. Here are two of them. Note the pinkish-white bordering around their beaks and their pink mouths. As they mature, the pinkish color on their beaks disappears, and the inside of their mouths turns black.Several weeks ago, the velvet mesquite trees erupted with fresh blossoms. These are the precursors to an abundance of bean pods that provide one of the most crucially important food sources for the valley’s wildlife.A closer look at the flowers of a velvet mesquite tree. These blossoms perfume the air with a sweet, heady fragrance.A queen butterfly alights to drink from the wet mud surrounding our watering hole. This insect is often mistaken for its well-known cousin, the monarch.The back side of a male Gould’s turkey in full display. These birds – and their tails – are huge! The white tips on the tail feathers are one of the field marks that distinguish this race of wild turkeys from their eastern relatives. Part of the display involves dragging the wing tips on the ground, an action that creates a loud rasping sound, meant to intimidate rival males.A male summer tanager comes to feed from a block of suet. This is America’s only all-red bird, a living statement of resplendent color and grace. Their future in this valley is being threatened by large numbers of brown-headed cowbirds.This male black-headed grosbeak has been sending his voice through the bosque every morning, a series of loud, robin-like notes.Few of our western birds are more strikingly colored than the western tanager. A different race of this species stays here in the valley floor to breed every summer. Most western tanagers utilize very different breeding habitats – namely, conifer forests at higher elevations.A male blue grosbeak that visits daily for water. Blue is one of the rarest of colors among Earth’s terrestrial vertebrate animals.A new beaver dam graces the flow of the San Pedro River. Dams like this permit substantially more water to infiltrate the ground below their surfaces, recharging the shallow aquifers that give life to the river’s riparian forests of cottonwoods and willow trees. There were five more dams below this one. I cannot think of a single mammalian species that is more beneficial to the river and its forests than beavers are.I awoke one morning to find this characteristic fresh imprint at the foot of my entry steps. A rattlesnake had curled up there the night prior, leaving its signature circular mark. No other Arizona snakes rest in such a circular position. For reference, the grizzly track cast in concrete is six inches in width. Grizzlies were once common along this river until they were wiped out by Spanish and American settlers.A black-tailed jackrabbit resting in the shade of a mesquite trunk on a toasty summer day. When the heat cranks up, animal behavior changes. This hare let me approach within four feet, something it would not have allowed on a cooler day. The name “jackrabbit” is a misnomer, as these creatures are hares, not rabbits. Until I came to live in southeastern Arizona, I would not have believed that there could be pink snakes native to our country. This coachwhip snake appeared on a hot afternoon, five feet of blazing bubblegum pinkness! Coachwhip snakes are expert climbers. Kathleen and I looked out a window one day to see this tail protruding from an active Gila woodpecker nest. Fortunately, the snake did not wipe out the entire brood – it consumed one or two nestlings and moved on. A gopher snake encountered on a sandy bank of the San Pedro River. These snakes attain lengths of seven feet or more and are often mistaken for rattlesnakes. They are among the most effective rodent controllers we have. Favored food items include mice, rats, and gophers.A diamondback rattlesnake slithers through the mesquite bosque, traveling in a manner common among rattlesnakes, using caterpillar motion. When snakes crawl in this fashion, their bodies remain almost straight rather than sinuously curved. We never kill these animals. They have a right to live here, no less than we do. When summer comes, we are always on guard, watching closely where we place every footstep, especially after dark.Beavers add a special touch of beauty to the river, creating ponds that mirror their surroundings and provide needed habitat for a long list of other creatures.
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.
