by Carl Strang
The blackbird family is an interesting study in mating systems. The red-winged blackbird has the typical songbird pattern of separate nesting territories established by the males, who then attract one or more mates (depending on the quality of the male and of his territory), each of whom produces a clutch of eggs.
The common grackle has what I call the Singles Bar mating system. I have observed this casually in past years. This year I decided to focus a little more closely. The first grackles arriving from the south all appeared to be males. Very quickly their numbers rose enough that they began to gather in treetops and display.
Compare the above photo to the one below.
In the first photo, the birds are focused mainly on me. In the second, the one in the middle is displaying, fanning his wings while he calls. Notice how the others all are turning to watch him. The wires above the red cedars along the east boundary of Mayslake Forest Preserve provided another display area. I will be interested in seeing if those cedars become the location of a nesting colony later in the season.
Grackles are not as fiercely territorial as their red-winged blackbird relatives. Often they nest in colonies. These display groups draw in females, and the females select their mates. I had hoped to observe this in action, but apparently it has progressed more rapidly than I expected, for already these singles bars appear to have evaporated and I am seeing pairs of grackles flying around together. Next year I’ll hope to try again. I had expected a more prolonged sorting out, with many females present at once. Instead I now suspect that the females joined the males singly rather than in groups, and fairly quickly settled on their mates. Later I plan to feature a third blackbird mating system, that of the cowbird.