What a difference a year can make. If you recall, April 2007 in the northland was very mild; ice-out and leaf-out was early. In fact, by the first week of May most of the quaking aspen and cottonwood were entirely leafed out, oaks were well on their way, and chokecherry trees were blooming everywhere. It was an early spring in northern Minnesota to be sure.
But April 2008 was a very different story. The month toyed with springtime conditions and then did an abrupt about face. At the time, around mid-April, just before the second blast of snow and Arctic air, some neo-tropical migrants were just beginning to trickle into the region. I remember waking up on one promising April day to the pleasant calling of a phoebe perched outside my bedroom window. Other notable early April arrivals that I noticed included common snipe, tree swallows and American woodcock.
At last, it would seem, spring is finally here. The wood and chorus frogs, which had begun vocalizing but then stopped because of cold, snow and ice, are now hard at it once again, day and night. And now some species of warblers are arriving, namely the yellow-rumped warbler, but I've also seen and heard ruby-crowned kinglets, Swainson's thrushes, yellow-bellied sapsuckers, yellow-shafted flickers and belted kingfishers. Still, one of my favorites, the eastern bluebird, has been glaringly absent. Where are they?
It was not until the first weekend in May that I recorded my first bluebird sighting. I usually notice bluebirds a month earlier. And while none of my old boxes have been occupied as of yet, I observed a pair sitting on top of one of the five new boxes that I just installed alongside a neighbor's pasture. Nevertheless, for insect eating birds like bluebirds, phoebes, tree swallows and warblers, this spring has been a tough one.
People from around the state have been reporting finding dead tree swallows and bluebirds inside bird houses. Because of our bizarre April weather and relatively cool start in May, insects have not been emerging as they normally do by this time of year. Thus, birds that subsist on mostly invertebrates have had a difficult time maintaining body weight. If fat reserves are depleted and adequate forage unavailable, birds can and do starve to death.
The good news is that the overall population of birds such as bluebirds will probably not be impacted. Rest assured, the reproductive potential of bluebirds and other neo-tropical migrants is, by and large, high. And should normal spring-like Aprils return in the coming years, bluebird and tree swallow populations will weather this out just fine.
Regarding the delightful bluebird, few birds have received as much attention as them. The male's musical song, blue plumage and rusty red breast, not to mention both sexes' parental devotion to their young and their acceptance of artificial nesting boxes, make them a favorite of bird enthusiasts' young and old alike.
Eastern bluebirds are cavity nesting songbirds. In other words, bluebirds nest inside holes in trees that are most often the result of hardworking woodpeckers. Simply put, bluebirds do not have the ability to excavate their own tree holes, and so, they have to rely on woodpeckers for cavity construction, or they'll seek out naturally occurring cavities in trees for nest sites.
Bluebirds belong to the same family that robins and thrushes are members of. Though not commonly observed on the ground like robins and thrushes, bluebirds are most often seen perching on fences, posts, power lines, or on conspicuous branches where they ambush insects from. And like all members of the family, bluebirds feed primarily on insects, but will forage on berries if insects are scarce. This occurs frequently when migrating birds arrive at their northern breeding grounds and cold weather sets in. When this happens, insects are inactive and difficult to locate. Fruit-bearing trees and shrubs that have kept their fruits throughout the winter become a highly important food source.
Eastern bluebirds receive much competition for nest sites from other cavity nesters such as non-native house sparrows and European starlings. These aggressive species will often out-compete eastern bluebirds and, in some cases, are physically driven out from nest sites or even killed.
Habitat loss has most affected bluebird distribution and abundance. But thanks to conservation-minded individuals, groups and wildlife agencies, bluebird populations are not nearly as troubled as they once were. Throughout the United States where prime bluebird habitat exists, countless numbers of ambitious projects have been implemented to assist in the bluebird's recovery. Miles of "bluebird trails" with erected bluebird houses along their routes have been established.
As already mentioned, bluebirds begin showing up here in northern Minnesota in early April. They prefer open areas with short or sparse grass free of underbrush for potential nest sites. Prime locations tend to be rural, mowed or grazed areas, prairies and near road right-of-ways.
Perhaps this year's bluebird and tree swallow nesting season won't be as successful here in our region of Minnesota. But who is to say for sure? Last month undoubtedly tested the limits of some animals and, sadly for them, over the very edge of existence. Indeed, Nature, never known to run on humankind's clock, ticks only to rhythms of mystery and chance 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