Bison Birds

The American Bison was historically called buffalo. That is a misnomer, as buffalo are actually old world species, but when European explorers first arrived to North America and encountered these huge animals, they named them something that they were familiar with.

 Bison once roamed in the millions, mostly across the wide open plains of middle and western North America. There is some historical record of them even in extreme southwestern Ontario, in the vicinity of what is now the Windsor area, as there were hundreds of hectares of tallgrass prairie before settlement. But that is the topic for another post.

Bison were well adapted to the cold, fierce winters of the mid-western part of the continent. Their winter coats were densely hairy, as this image shows, with the front end of the animal being the most densely hairy.

This was incredibly useful when facing the wind, which they typically did, to withstand the cold.

After the winter weather, they lost much of the dense hair towards the back of their bodies as shown next. Even so, the front end of the animal still retained a lot of dense hair. 

 Bison were always known to roam widely. The huge herds would have a home range of hundreds of thousands of square kilometres or more of open grassland. This next photo shows a single bull bison on a huge grassland at Grasslands National Park in extreme southern Saskatchewan. At the time I took this photo, in July, the bulls are usually well away from the cows and calves.

 It was said by early explorers that bison always moved into the wind as they were foraging, especially during the more inclement weather. This resulted in their long-range movements, and was advantageous in that a large herd of bison, numbering in the thousands, would eat off much of the short-grass prairie, but by keeping on the move, they would find new grasslands and give the areas they moved from, a chance to regenerate in time for a following season. Sometimes they would feed intensively on areas that had burned off via a prairie fire, and was regenerating with lots of tender fresh, green fodder.

Tallgrass Prairie National Preserve, OK

And that brings us to the Bison bird.

Most birds build their own nest, lay their eggs in it and raise their young.  This next photo shows a typical eastern grassland type bird nest. It is that of a Song Sparrow, and at the time of taking this photograph, it did not have a cowbird egg in it.

 But the Bison bird is a species that depends on following Bison, for the insects they disturb by their hooves during their movements as well as the seeds they break off of the grasses they are moving through. So the birds must follow the movements of these herds of Bison, and don't stay in one place for several weeks while they build a nest, lay eggs and feed the young to the point of the next generation being able to fend for themselves. No, these Bison Birds adapted so as to lay their eggs in the nests of other birds, with the new host raising the young of the Bison bird.

As time went on, Bison herds diminished considerably, and were at great risk due to the loss of foraging and roaming habitat due to settlement as well as the slaughter of millions of animals for their hides, or just for what was considered 'sport'. Large areas of the Bison's former habitat was turned into grazing lands for other animals, such as beef cattle. Probably the most best known breed at one point was the Texas Longhorn, but other breeds were eventually added. Hence the likely reason for the current name of this bird species. Texas Longhorns were aptly named, and came in various colours. They were the new grazer of the mid-western part of North America, some roaming free and others on large fenced grazing lands.

I'm sure that most readers will have caught on quite early in this post that the bird species I am referring to is none other than the Brown-headed Cowbird. 

male

female

 It is the only North American bird species that demonstrates this 'parasitic' behaviour, much to the dismay of some bird enthusiasts. I admit that I have had mixed feelings over the years, especially when I see a cowbird egg in the nest of a more 'desirable' species such as a Yellow Warbler, Prothontary Warbler, Wood Thrush, or some other species. All three of the aforementioned species have been, or are, considered a Species At Risk. 

Yellow Warbler

Not quite sure if this next image showing the young bird being fed is a cowbird or a young Yellow Warbler. It has some characteristics of being a cowbird, but would be easier to tell a few days after this photo was taken.

  Cowbirds are certainly not at any level of risk. In fact they often can be seen in huge flocks.

 

Presumably when these Bison birds were more or less confined to the wide open spaces of the mid-west, they had fewer potential host species to choose from. But as the eastern forests were cut down and opened up to a more agricultural landscape, these Bison birds adapted and became widespread throughout the east. In fact the cowbird is known to parasitize more than 220 species of birds in this way! As a result of the loss of forests, cowbirds became the dreaded edge species as they would regularly venture into a forest for 100-200 metres, and interior forest bird species nesting within that zone were heavily parasitized. Some ornithologists consider interior forest to be a minimum of 100 metres from any edge, whereas other specialists consider interior forest to be at least 200 metres from an open edge. Currently most forests in southwestern Ontario have been reduced to the extent that there is very little good quality interior forest to prevent cowbirds from entering and impacting the interior breeding bird species. Wood Thrush, now a Species At Risk, is usually an interior forest species, but sometimes can be found near the edges especially when proper interior forest is diminishing.

 This next photo shows an adult cowbird visiting the nest of a Yellow-breasted Chat, an extremely rare breeding bird in Ontario. 

I took this photo in about 1980. This was the first confirmed nesting of the Yellow-breasted Chat at Rondeau, and one of the few in all of Ontario. It was well away from any real forest edge, although a severe windstorm had caused a lot of blow-down which resulted in some shrubby habitat dominated by raspberry. It was great habitat for chats, but cowbirds also made it into the area. Fortunately the young chats in the nest were well along in their development so that if a cowbird laid an egg, it would not hatch before the chats would likely have fledged.

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