While enjoying a late season deer and grouse hunt in the rolling hardwood hills of Aitkin County recently, I watched a flock of Bohemian waxwings descend upon a fruit-filled crabapple tree. It was a delightful sight, these beautiful birds, cousins of the smaller cedar waxwing, busily feeding and calling sweetly to each other.
An irruptive species of bird, it's not uncommon to observe Bohemian waxwings in northern Minnesota during the wintertime. Other species of birds that we sometimes see and usually associate with irruptions in the winter months are pine grosbeaks and common redpolls.
However, up until my encounter with the Bohemian waxwings, I've thus far seen only common birds in the woods and feeders this winter.
The waxwing encounter interested me enough to think about, once again, the phenomenon of irruptions, or, specifically, irruptive species, like the flock of Bohemian waxwings that made short order of the few crabapples left on the tree.
Some people believe that observing large numbers of uncommon birds, or birds not ordinarily seen in any particular geographic area, as a sign of a harsh winter to come.
While it's an intriguing thought that birds have the ability to predict the severity of any given winter, this really is not the case.
Birds that migrate to wintering grounds not usually occupied by them during a normal year are typically birds that are searching for areas that are more favorable. Put another way, food is usually the driving force behind irruptions.
As well, irruptions may also indicate a very successful breeding season; the influx observed could possibly be too many birds for a limited food supply.
Hence, more birds are seen elsewhere as the population disperses.
As already mentioned, the Bohemian waxwing is one species of bird that's often referred to as an irruptive species.
As most people know, we often observe irruptions during the winter months when birds migrate from the north to the south. Aside from the birds already mentioned, other birds most generally associated with winter irruptions in the Northland are pine siskins, purple finches, evening grosbeaks, red crossbills and white-winged crossbills.
Other species that will often shift wintering locales are black-capped chickadees, blue jays, red-breasted nuthatches, varied thrushes and some species of owls.
Owl irruptions, when they occur, always drawing great attention by birders, provide fantastic opportunities to observe high numbers of uncommon species of owls throughout northern Minnesota.
For example, during the winter of 2004-2005, great gray owls, boreal owls and northern hawk owls were extremely abundant across the northern tier of Minnesota north of Bemidji to Roseau and the Big Bog country of Red Lake, to all of northeastern Minnesota.
If I recall correctly, snowy owls were showing up in the northern Red River valley that year as well. It was, without a doubt, a memorable winter for observing owls.
Birds that suddenly move to an area that is outside their normal range, are birds engaged in irruptive behaviors. This behavior is fairly unpredictable, and can occur quickly when a primary food source is unavailable, and a secondary food is scarce or non-existent.
Thus, lucky for most birds, they can easily migrate somewhere near or far to find adequate food supplies.
It is also why fruit-bearing trees and shrubs that retain their fruits in the wintertime are so important to birds and other wildlife.
If not for the crabapple tree, or mountain ash tree, or nannyberry tree or any number of other native and ornamental trees and shrubs, year 'round and irruptive species of birds alike would have a hard time surviving Minnesota winters.
For those people who believe that an irruption is a forewarning of a harsh winter to come, the fact is that once an irruption has been observed, the weather event that might have pushed the birds to move in the first place has already passed.
The opposite can also be true. Sometimes while we enjoy days worth of incredible numbers of American goldfinches or pine siskins at our wintertime birdfeeders, and then the next day they suddenly vanish and don't return, it's tempting to interpret their disappearance as an irruption to another location.
Most likely your birds have simply left on account of a more desirable, natural food source some place else.
For instance, owls that migrate from Canada to spend the winter in Minnesota are seeking a more abundant population of small rodents to prey on.
Lemmings, a common prey species of owls north of the border, undergo frequent upswings and downswings in their numbers. When lemmings reach the low point of the population cycle, this regularly forces owls to migrate southward until adequate numbers of prey are located.
Similarly, songbirds, like the flock of Bohemian waxwings I recently saw, and others, follow the same rules: when the availability of food is diminished because of severe winter or other factors, then these same birds will move until conditions improve for them.
Many of the irruptive species of birds we've come to know and appreciate will readily come to our feeding stations. Other species can be observed in the woods and fields. Fortunately, this puts us in the enriching situation of seeing birds we normally aren't privileged to observe very often 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