During a leisurely stroll in the backyard one recent afternoon, I noticed a flock of bluebirds flying just above the tree tops. Numbering at about a dozen or so and flying in a southerly direction, the bluebirds were calling softly their telltale bluebird warble. In fact, it was their calls that alerted me of their presence in the first place.
After bluebird broods are raised by their attentive parents, most of the offspring disperse from the immediate breeding territory. 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 autumn 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 and necessary to bluebirds, including most other species of wildlife.
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 nonrelated broods.
Thus, potential mates can sometimes be encountered during these natal dispersals. The groups of bluebirds that we observe in late summer and early fall 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.
While weather plays a critical role in the timing of migration, 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 changes that in turn elicits migratory behaviors.
Eastern bluebirds are mostly 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 and later 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, as they seem to feed-on-the-fly while traveling together in blue waves of wings 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 during the autumn months because bluebirds are always on the move.
Our Minnesota summer is almost gone. In fact, meteorological fall is already here and our beloved bluebirds are preparing to migrate once again to warmer climates. Indeed, we’ll have to endure another long winter here in the Northland before becoming reacquainted with the eastern bluebird, but for now we still have several more opportunities to observe beautiful bluebirds as we get out and enjoy the great outdoors.