October's here, leaves are changing colors and many of the birds we've enjoyed watching and listening to all summer long have either left Northern Minnesota or are about to. Although bitter-sweet, we all know that they'll be back next spring.
I'm still hearing the soft warbled notes and calls of eastern bluebirds. These charming birds are among the most favorite birds to many people, including yours truly. And, though nesting season has been over with for weeks now, bluebirds are still present and are migrating southward in both small and large flocks. If you listen or watch closely, you'll still see bluebirds from time to time - but not for much longer.
After broods are raised by resident pairs, most of the offspring disperse from the immediate breeding territory of their parents. Although not very far, and according to the literature, young bluebirds typically disperse less than a mile from their parental territories.
This "natal dispersal" is common in many species of animals. Ruffed grouse, for example, are well known for their "fall dispersals" when young birds begin leaving natal areas in search for their own potential territories. This is also the time of year when it's common to encounter young grouse in unusual places, such as backyards or other open areas.
Young grouse, perhaps because of their inexperience and unfamiliarity with areas they've dispersed to, are often vulnerable to predation, and it's no different with young bluebirds. Dispersal to areas outside their parents' breeding territories is always new and strange to young birds. That said, dispersal is beneficial as well.
Moving to new areas, away from parental territories and nest-mates, reduces the chances of inbreeding. Dispersal can also provide young bluebirds their first glimpse at potential breeding territories of their own - places they might return to the following spring. Additionally, dispersal puts young birds into association with other young birds from non-related broods.
Thus, potential mates can sometimes be encountered during these natal dispersals.
The groups of bluebirds that we observe in September and October can range from small to large flocks comprised of all young birds from many different broods, to smaller flocks of family groups, to small and large flocks of mixed young birds and family groups. As found in the literature, these flocks can number from as high as 100 birds to as few as one breeding pair and their last brood. The groups of warbling bluebirds that I've been seeing lately usually number no more than a dozen birds.
During a moment of relaxation on my deck during one Saturday afternoon in mid-September, I happened to notice one such flock of bluebirds flying through my backyard. Numbering at less than a dozen birds, the bluebirds, which I assumed to be juveniles, followed each other from tree to tree. I frequently observed some of these birds displace one another from various perches as they restlessly flew and chased one another. Sometimes attempts were made by young males of the flock to mate with non-receptive females.
The young bluebirds seemed to behave as adult birds behave in the springtime after having arrived at their breeding territories. I witnessed a couple of the backyard bluebirds inspecting the cavities of two of my artificial nest boxes. And another bird actually carried bits of dry grass in its beak. If I hadn't known better, I would have thought it was the beginning of nesting season again.
As with most, if not all, migrating birds, the changing levels of hormones, which are triggered by the changing amount of daylight, are thought to be the driving forces behind the urge to migrate in the first place. While weather plays a critical role in the timing of migration too, such as sudden winter-like events in early fall that can "push" migrating birds southward as they search for more abundant food sources, it's the amount of daylight, or photoperiod as it's also called, that triggers hormonal change and subsequent migratory behaviors.
Eastern bluebirds, as are other species of bluebirds, are considered to be insectivorous birds. Anyone familiar with bluebirds knows that they are experts at capturing insects, even capturing them "flycatcher-like" in mid-air. But come fall, as migration commences, and especially as the autumn progresses and becomes colder, the availability of fruit is essential to bluebird survival.
During this time of year I have watched flocks of migrating bluebirds feeding on the leftover fruits of cherry trees, as well as on nannyberry, dogwood, grape, sumac and hawthorn. These fruit-eating bluebirds never seem to loiter within these and other fruit bearing trees and shrubs for long; they seem to feed-on-the-fly, so to speak, traveling together in a wave of sorts as they quickly forage and move on.
Like so many other species of migrating birds do in the fall, bluebirds often appear to be in a hurry wherever they go - a sense of urgency, if you will, seems to overpower their willingness to stay in any particular place for long. Maybe this is the reason why bluebirds often go unnoticed by many people; autumn bluebirds are always on the move.
Summer's gone, autumn's here, and the beloved bluebird is migrating to warmer climes. Indeed, we'll have to endure another long winter here in the Northland before we become reacquainted with the eastern bluebird once again. In the meantime, we still might have a few more opportunities to see and hear bluebirds as we get out and enjoy the great outdoors.
Blane Klemek is the Bemidji area assistant wildlife manager, DNR Division of Fish & Wildlife. He can be reached at firstname.lastname@example.org