Our birding trips provide surprises to enjoy and lend credence to discoveries about specific species. A most unusual set of behaviors can be associated with the brown-headed cowbird. The cowbird is thought to have followed bison herds on the Great Plains, taking advantage of insect life flushed out by the bison as they grazed. In today’s “modern world”, cowbirds can be found near cattle herds and horses pursuing a similar meal.
However, most infamously the cowbird engages in the dark art of parasitism. The female can lay an egg a day, usually 40 in a season. In some cases no less than 70 eggs can be laid by a single cowbird. The key to the existence of this species, is the practice of the female to remove an egg from a different species’ nest and lay a cowbird egg in its place. Hugely successful, such eggs have been placed in the nests of over 220 other species, with over 140 of these “host” species raising the cowbird young. Cowbird teens grow rapidly, fledging (being able to fly) in 10 or 11 days
Over the past two months we have been checking nest boxes at Big Hill Springs Provincial Park, learning much about the challenges that tree swallows, mountain bluebirds and house wrens have successfully raising their next generation. After checking the 15 boxes, we take time to bird watch. Spotting two pairs of adult cowbirds, we couldn’t help but wonder if we’d eventually see a young cowbird being raised by some other species.
On July 10th, while checking nest box 11, we saw and photographed a juvenile cowbird nearby. Quite sizable and able to fly, its time as a teen was indeed growing short. As I wandered down to nest boxes 12 through 14, Elaine stayed behind, taking photographs. Well, we were both amazed that an outright act of parasitism had borne fruit in digital form. Nothing short of profound astonishment for us occurred when the “parent” of the teen cowbird was the diminutive least flycatcher. Elaine wondered how a cowbird egg could fit in a flycatcher nest. I thought how valuable it would be for a bird to see its reflection in a pond or puddle and recognize its own species
Upon reflecting on this most unusual moment, I thought of all of the songbirds that would never be born as a consequence of the parasitism. This summer we have seen several incidences of parasitism by cowbirds in a variety of parks. In checking with another avid birder, Calvin, he noted that he sees cowbird babies sitting in the nests of yellow warblers on a regular basis in Carburn Park.
I thought of the advantages for the adult cowbird. No nest has to be built. No time has to be spent on the egg or to feed the rapidly growing cowbird chick. It’s no wonder that 70 eggs could be laid by one female, who could devote her energy to simply finding other nests in which to lay an egg. I guess one could think that even birds carry out adoption services, but without their knowledge. It’s obvious that the female cowbird has the world figure. Simply have another specie’s egg “moove over”.
-Don Cassidy
