BIRDS DO IT!
How can I talk about spring when its 100 degrees in the valley? It’s because I have the opportunity for frequent visits to a mountain meadow at 8400 feet where spring is still happening in mid-June. Just this week the serviceberries and chokecherries were in full bloom covering the hillsides and roadsides with a white mantle. The aspen leaves may have turned dark, summer, green but the oaks haven’t—still showing the light sea green of new growth.
Wildlife watchers have been observing young great-horned owls down in the valley for many months but mountain birds are just now getting around to it. Over several weeks, I’ve seen relatively elusive birds such as green-tailed towhees and MacGillivray’s warblers singing from exposed perches. They were difficult to see this week. There is little need for them to announce their presence as nesting has begun.
Several of our nest boxes attract tree swallows, violet-green swallows, mountain bluebirds and house wrens. The tree swallows, in fact, were really going at it this week.
They were flying in and out of nest boxes and, yes, copulating. Over and over again.
Encounters were brief—but frequent. We watched this pair on our seed feeders complete the act ten or more times over the course of a few minutes—immodestly in full view of a flock of pine siskins and Cassin’s finches.
Tree swallows spend much of their days airborne, but not so much as the white-throated swift which can be seen copulating in mid-air near cliff faces in locations such as the Colorado National Monument. I recall the first time I saw a pair of swifts seem to collide and then tumble earthward before resuming their flights. Recounting this to a friend, his comment was, “well, that behavior gives new meaning to the concept of performance anxiety!”
Tree swallows spend their winters in Southern Mexico although some populations can be found in Southern Arizona, Southern California and the Gulf Coast. They are a common summer resident in Colorado mountain meadows where they co-exist with violet-green swallows and mountain bluebirds—all of which may share the same next boxes. Here, a female mountain bluebird surveys the meadow from the box she and her mate selected last week.
Nesting behavior raises a lot of questions that are still being studied. Some mountain bluebirds have already nested at lower elevations. Why do some nest so much later and higher? What was the pair in this nest box doing a month ago when their cousins were nesting in the valley? Why do so many birds fly north to breed when very closely related species, with whom they spend most of the year, do not?
Studies have shown that tropical birds tend to have very low nest success (often <20%) because of the high rate of predation. Adult birds, however, tend to be long-lived and usually lay only two or three eggs so they can try again when the nest, eggs, or fledglings are lost. In contrast, most birds nesting in North America have larger clutch sizes—even to five or six. Apparently, the idea is both to overwhelm the system and to take advantage of everything else that is growing all of a sudden. Here, everything occurs at once. The flowers bloom. The insects hatch. All the eggs are laid. That’s why June in a mountain meadow is so fascinating for its remarkable fecundity. Insects abound. Butterflies flit in mating pairs. The birds are calling, chasing each other, and mating. Too soon, it is all over. Better go out and take a look before you have to wait until next year. (This post provided by Nic Korte, Grand Valley Audubon Society. Send questions/comments to firstname.lastname@example.org]To learn more and to participate in the activities of Grand Valley Audubon, please see our website at audubongv.org and “like” us on Facebook!]