The Feathers of Winter
For many Nebraska birders, the last big event of the year is the Audubon Christmas Bird Count, which is held annually during the last week of December. It is an occasion to join with friends in a day out to try and see as many species as possible in a single day. More importantly, it produces information that, combined with that from more than fifty thousand other observers, provides a highly documented population sample of early winter birds throughout North America, Latin America, and the Caribbean region. The tradition began in 1900, and as of 2011 there have been 111 national counts. Nebraska counts began in Lincoln and Omaha in 1909. In recent years there have usually been about ten counting locations in Nebraska, with notably long sequences having developed in Lincoln, Omaha, and Scottsbluff and at Lake McConaughy. This last-named location invariably has the highest state count, often tallying about one hundred species, whereas species counts from Lincoln and Omaha are usually in the seventies. Since 1988 the Great Backyard Bird Count has attempted to measure February birds, with an emphasis on species likely to be seen in backyards and near homes. During the 2011 counts in Nebraska, 105 species and over three hundred thousand birds were counted.
Several years ago I decided that I could exploit the Christmas Count’s vast amount of population data to test the idea that moderating winter climates in the Great Plains during the past half century may have resulted in a northward shift of early winter bird populations. I chose about two hundred bird species known to winter in the Great Plains and selected a forty-year period, from 1967–68 to 2006–7, for my study. As I was teaching an ornithology class at Cedar Point in the summer of 2008, I decided to make an analysis of these data a class project. I asked each of my eighteen students to analyze statistically the count data of eleven species, for every state from North Dakota through the Texas Panhandle, over the four decadal intervals.
After all these data had been accumulated, I began to summarize and analyze them (details can be found in Johnsgard and Shane 2009). The broad conclusion of the study was that a large proportion of the more than two hundred species analyzed exhibited a significant northward winter movement in their abundance peaks, which often shifted one state northward and sometimes moved even farther north. These results support the increasingly accepted position that significant climatic warming has been occurring in the Great Plains since at least the 1960s.
It is also of interest to consider the eighteen species of greatest average winter abundance in Nebraska, whose identities and numbers have never before been estimated. It should be remembered that most of the Christmas Counts are centered in cities (the count areas consist of circles fifteen miles in diameter), so the resulting numbers are probably biased toward urban and suburban birds, such as starlings and house sparrows. Some birders also choose to concentrate on watching bird feeders rather than doing outside surveys, which means that typical backyard birds are well represented. Lakes and reservoirs are also attractive counting sites, which results in large numbers of waterfowl and other aquatic birds being counted. Yet, because of the large number of counts and counters, a fair representation survey of a state’s winter bird life is possible.
Typical aquatic birds that appear in the greatest numbers on Nebraska’s Christmas Counts are the common mallard, Canada goose, and common merganser. All are large, cold-tolerant birds that will overwinter wherever open water can be found. The Canada goose has increased markedly in Nebraska over the time period studied, while the mallard has apparently shifted its major early winter population northward into South Dakota. Common mergansers have remained concentrated farther south in Oklahoma; a certainty of open water is necessary for these fish-eating ducks.
Red-winged blackbirds are seed- and grain-eating birds that concentrate in grain fields during fall but gravitate to marshlands during winter. They are one of the most abundant of all North American land birds, with a continental population estimated at more than two hundred million. European starlings are far more city-adapted than red-winged blackbirds, and in many cities they are easily the most common species year-round. In the same manner, the also-introduced house sparrow is most at home in cities but extends into the country around farms and homesteads. Both species are nonmigratory and appear to be in decline, at least in Nebraska.
American tree sparrows are remarkably cold tolerant considering their tiny size, with maximum early winter densities in Kansas. They tend to remain in the country, scratching on the ground for seeds in snow-free sites, but will rarely visit bird feeders. Their continental population has been estimated at about twenty-six million birds.
Horned larks are strictly open-country birds and in Nebraska are likely to be seen in snow-free grain fields, sometimes in large roaming flocks and frequently in the company of Lapland longspurs and snow buntings. None of these relatively abundant species is likely to be seen within the city limits of a town.
American robins are familiar backyard birds during summer, but as cold weather moves into Nebraska they flock up and move variably southward, depending on the intensity of the winter and the availability of fruits, their primary winter diet. The robin is the only species described here that has seemingly shifted its population density south in the past half century. This is probably a statistical anomaly, but wintering robins are highly nomadic, and flocks of as many as ten million birds have been reported in the southeastern states. Their continental population has been estimated as about 320 million.
Judging from the available Christmas Count data, Nebraska may be the best state in which to see Harris’s sparrows during early winter. They migrate south from their arctic nesting areas in central Canada to winter in the central Great Plains, especially eastern Nebraska. They mostly are found in country habitats that offer weedy grasslands, brushlands, or open woodlands. They come to feeders only during times of severe weather, sometimes in the company of white-throated or white-crowed sparrows. American crows may also be found in habitats ranging from open country, which they scavenge widely for food, to fairly heady woods, where they roost, sometimes in very large flocks. In recent decades crows have become increasingly common in towns and cities, where they may look for suet in bird feeders but remain much more wary than woodpeckers or blue jays.
Except for the cedar waxwing, all of the remaining species judged as abundant Nebraska wintering birds are typical bird-feeder species. The cedar waxwing is a berry and fruit eater, especially favoring juniper (red cedar) berries. As such, cedar waxwings inhabit shelterbelts and other places where junipers are present and in towns seek out crab apples or other ornamental fruiting trees. Red cedars are abundant across the Great Plains and largely account for the species’ winter abundance here.
In sequence of their seeming descending winter abundance in Nebraska, the remaining species are northern cardinal, dark-eyed junco, black-capped chickadee, and house finch. Of these, the house finch is a relative newcomer to eastern Nebraska, having invaded the state in the 1960s from the east, although a small population has long been resident in the Panhandle. It quickly became addicted to bird-feeding stations and has gradually tended to displace the more skittish house sparrow in abundance at backyard bird feeders. Northern cardinals have also expanded their range in Nebraska during the past half century, slowly moving farther north as winters have moderated in severity and becoming favorites of people willing to provide them with unlimited black-oil sunflower seeds.
The black-capped chickadee is perhaps the tamest and thus most visually appealing of all the bird-feeder species in Nebraska, although white-breasted and red-breasted nuthatches might win in the tameness category. Dark-eyed juncos are probably the most abundant wintering songbird in Nebraska and the entire Great Plains. Their continental abundance has been estimated at 260 million birds, easily edging out the cardinal’s 100 million, the chickadee’s 34 million, and the house finch’s 21 million.
Over the forty years studied, ten of the eighteen species mentioned have exhibited apparent population increases in the final decade relative to their long-term Nebraska averages, three have apparently been stable, and five have shown apparent declines. Over the same period, twelve of these species have exhibited apparent northward statewide population shifts judging from average state density estimates, one species (the American robin) has seemingly moved south, and six have shown no statewide shifts.
Nebraska data from 2011 for the Great Backyard Bird Count provide a slightly different assessment of winter birds in the state. Based on the number of checklists reporting the species, the ten most commonly encountered birds were (in descending order) American robin, American goldfinch, downy woodpecker, house sparrow, blue jay, house finch, black-capped chickadee, Canada goose, European starling, and mourning dove. Surprisingly, the species seen in largest numbers was the snow goose, which is far from being a “backyard” bird but is often seen flying over towns in enormous flocks. It is a testimony to changing climates that the snow goose, long a symbol of early spring and late fall in the upper Great Plains, is now an abundant winter bird!