 Even Cowbirds Get The Blues. If I didn’t know anything about grasslands before, I do now. My four day indoctrination into grassland attributes began on Thursday when I joined an elementary school class on a field trip to the Walker Valley. We gathered in a field under a dead but still shady pine tree with 24 students, several assistants, and two teachers. Then we turned our eyes and ears to the land around us. An adult assistant stood to read to the class from a pamphlet. As she read, one Western Meadowlark picked at a pile of horse poop while another poured out a melodious song perched on a power pole. Surely the Meadowlark must be the grassland habitats most worthy bird icon I thought to myself while silently answering questions the assistants tossed to the students. “Where would a grassland bird hide?” ‘In its feathers!’ I shouted in my mind and pictured a hawk-threatened Meadowlark crouched in the open with its bright yellow front pressed hard to the ground so that its neatly camouflaged head, back, and tail hid it from harm. Then, still listening as the assistant read and asked questions, I caught sight of a female Cowbird some distance away riding on the haunches of a horse. Like a coin stuck in a pay telephone I heard a ‘clink, clink’ in my head. No, it wasn’t due to heatstroke. It was the sound of a crystal clear idea dropping into its rightful place in my train of thought. The icon bird of the grasslands isn’t the Meadowlark – it is the Brown-headed Cowbird. Who can say where and how an organism begins adapting, but somewhere back in the mists of time a bird species must have begun hanging around a herd of grassland-loving bison. Here the bird(s) would have found ample food scared up by the large beasts as they moved around. And ample food on the bison’s fur coats, which would have hosted invertebrate parasites and attracted swarms of flies. The bulky bison would provide plenty of food and shelter. It was a mobile habitat that suited the proto-Cowbirds well. However, there was a problem, in order to follow constantly moving herds of bison it would be impossible to stop and nest. It is very likely that proto-Cowbirds were once nest builders. And as traditional nesting separated them from the host bison herds, it was necessary to evolve a solution. How could nest building, and raising young, be accomplished in a habitat where constant movement is the norm? If the mists of time were to part for a moment we might glimpse the first female Cowbird laying an egg in the nest of a host bird. Would the Cowbird feel conflict between an urgent need to keep up with the bison herd and an equally strong urge to nest? Perhaps she would attempt to build a nest then abandon her effort and fly after the herd. If she had already mated then she could only do what any desperate mother might; seek a foster parent. And so it would happen - the first Cowbird egg appearing in a Savannah Sparrow nest. A remarkable adaptation solution brought about by one bird’s dependence on a grasslands dependent mammal. But, as we know the bison herds were doomed. When the first settlers moved west the bison herds which still numbered in the hundreds of thousands were soon all but destroyed. Luckily for the Cowbirds the settlers brought herds of domestic horses and cattle to replace the extirpated bison herds. And Cowbirds, being so adaptable probably didn’t spend a lot of time weeping over the bison but simply flew to the next biggest thing standing in a field. Not only did the settlers supply host beasts for the Cowbirds, they also cut down forests and turned once endless tracts of bush into prairie. The prairies where then populated with domestic animals and as a result the Cowbird spread to heretofore unsuitable habitats. This brings us back to the present day with the elementary school class, and attendant adults, standing in an open pasture. The topic was grasslands and just behind the gathered group sat the most adaptable bird to ever tread these open places – the Brown-headed Cowbird. When there was a lull in the reading I stepped up to one of the assistants and shared my Cowbird epiphany. “Bad bird!” she said. “No,” I continued. “I can’t think of a bird more affected by grasslands…” “Bad bird!” she intoned and took a step backward. I could see that championing the Cowbird as the icon of the grasslands would be impossible. In the 3 days following my expedition into Walker Valley I spent time in two other extensive grassland areas and there I encountered many birds that call this often arid and hostile environment home. But none, not even the ubiquitous Vesper Sparrow or Long-billed Curlew have modified their lifestyle as much as the Cowbird in order to stay in this habitat. To e-mail Tom CLICK HERE To look at previous column CLICK HERE |
