For much of the latter twentieth century, and especially during the past few decades, the Great Plains has experienced a warming trend that is part of a global phenomenon. The year 2014 had the highest annual average global temperature (58.24° Fahrenheit) of any year since such records began over 130 years ago. Previous heat records were broken in 2010 and 2005. The last time the Earth’s record for annual cold temperatures occurred, it was more than a century ago, in 1911.
With regard to birds, the side effects of global warming include changes in their breeding phenology or fecundity, in the composition and structure of their breeding and wintering habitats, or their migration timing, routes, and staging areas. Accelerating global climatic changes have already had many evident effects on birds. These include a poleward shift in avian wintering ranges, northward movements in the breeding ranges of some North American birds. Various other biological influences on birds and other wildlife have been reported. Less obvious indirect effects of climate change on a species might result from climate-based influences on regional parasites, diseases, competitors, and predators.
Other more dramatic effects of global warming, such as changes in the frequencies of severe rainstorms, hurricanes, and other climatic disasters, may have massive short-term consequences on local or regional populations. During 2010, over three million acres of land were affected by wildfires in the US, and in Nebraska some 270,000 acres of forest lands were lost to fires during the extreme drought of 2012.
In North America the average spring arrival times of many short-distance migrants breeding in the Northeast occurred an average of nearly two weeks earlier during the second half of the twentieth century than the first half. Over a sixty-three-year period of the twentieth century, at least twenty-seven migratory species exhibited altered spring arrival dates in southern Manitoba, with fifteen of the species arriving significantly earlier as the century progressed. Another Canadian study found that both spring and fall migration patterns of passerines at Long Point, Ontario, were affected by global warming during the period 1975–2000.
The National Audubon Society recently reported in a major study the effects of climate change on 588 species of North American birds, using data from three decades of Christmas Bird Count data and Breeding Bird surveys. More than half of the species studied will probably be adversely affected by climate change, with 188 species judged likely to lose more than 50 percent of their current climatic range by 2080. The other 126 “climate-endangered” species are likely to lose more than half of their current range by 2050.
I recently analyzed forty-seven years (1967–2014) of Audubon Christmas Bird Counts (CBC), evidence for population changes and shifts in late December ranges of nearly 150 species of birds in the Great Plains region. My analysis included all of the forty annual CBC surveys from the 1967–68 to the 2006–07 counts, plus the results of the most recent 2013–14 CBC. I quantitatively described the early winter abundance for 147 of the most commonly encountered regional species, illustrating their temporal changes in geographic distributions and relative abundance between 1967 and 2014.
Over this forty-seven-year period, there has been a progressive winter warming trend regionally, and associated ecological changes, influencing the early winter regional abundance and geographic distributions of many birds. The great majority of these changes have involved northward shifts in early winter distributions. Over this approximate half-century interval, at least six species (Canada goose, mallard, black-capped chickadee, American goldfinch, and house finch) have shifted their areas of greatest early winter abundance two states northward, and the centers of maximum abundance of at least ten other species have shifted northward by at least one state. Milder and less stressful early winter temperatures, with associated extended periods of ice-free water and greater access to snow-free foraging sites, are probably responsible. These recent population shifts have been most evident in the northern half of the region, where increases in mean January temperatures have been greatest. Nearly all of these population and distributional changes can be attributed to recent climate changes in the Great Plains.
As some examples of poleward shifts in breeding ranges in the Great Plains, northern cardinals have increasingly moved north to become permanent residents of eastern South Dakota and southeastern North Dakota during the past century and have nested west to Bismarck. Although still quite rare in winter, the red-bellied woodpecker also is moving slowly north into both eastern South Dakota and southern North Dakota along riparian woodlands. Northern mockingbirds now breed regularly in southern Nebraska and have occasionally nested in South Dakota. Scissor-tailed flycatchers have begun nesting in southern Nebraska with some regularity. The great-tailed grackle has rapidly expanded its distribution substantially northward in the Great Plains from southern Texas over the past half-century. It began nesting in Oklahoma by 1959, Kansas by 1969, Nebraska by 1977, and South Dakota by the late 1990s. It has also been seen in North Dakota, but nesting in the state has apparently not yet been reported. The white-winged dove had been reported at least nine times in North Dakota by 2008, and the tropically oriented Inca dove is now a regular in Oklahoma, has wandered north to North Dakota and Montana, and has even wintered in Nebraska.
Many migratory bird species have moved their wintering regions farther north in the Great Plains during the past forty years, as lengths of the frost-free season have increased noticeably. The white-winged dove, Savannah sparrow, lark bunting, and fish crow have all begun wintering as far north as Kansas. Snow geese and Ross’s geese have shifted from wintering on the Gulf Coast of Texas to refuges as far north as northern Missouri and Kansas, while Canada geese are also commonly wintering in northern Kansas and Nebraska, and locally to the Dakotas.
In Nebraska and Kansas many water-dependent species are now wintering commonly on ice-free rivers and impoundments. The largest recent Christmas Count changes around Lincoln have occurred among Canada geese, increasing from less than one thousand in 1991 to about twelve thousand birds in 2013. Many of the rapidly increasing species have benefited from increasingly later fall freeze-up and earlier spring thawing. Since 1998, three species of duck and three sandpipers, as well as the western grebe and marsh wren, have all appeared on Lincoln Christmas Counts for the first time. Similar trends have occurred in western Nebraska. Species that markedly increased in Scottsbluff’s Christmas Counts during the second half of the twentieth century include the Canada goose, American wigeon, blue jay, and American crow, all of which have probably responded to the region’s long-term warming trend.
Among terrestrial species, very large increases have occurred in Lincoln’s counts of the American robin, dark-eyed junco, and red-winged blackbird. Other species that have increased to a lesser degree on Lincoln’s Christmas Counts and that perhaps now winter in Nebraska in increasing numbers are the eastern bluebird, golden-crowned kinglet, and yellow-rumped warbler. Some boreal species that have declined significantly on recent Lincoln counts and perhaps now regularly winter still farther north are the Bohemian waxwing, common redpoll, evening grosbeak, and red crossbill.
There is a notable shift of relative abundance in the northern Plains states, from predominantly small, cold-adapted passerines such as snow bunting, Harris’s sparrow, Bohemian waxwing, and horned lark to increasingly water-dependent birds such as mallard and Canada goose. The snow goose and greater white-fronted goose have also increased relatively, especially in the central Plains states of Kansas and Oklahoma. Although not entirely water-dependent, the red-winged blackbird is certainly closely associated with wetlands, and its numbers have greatly increased over the past four decades as the ice-free season has increased, a trend that is especially evident in the Texas panhandle.
More significant to humans than changes in avian migration patterns and breeding times is the role that global warming is having on both human- and avian-borne diseases. The 1999 invasion of West Nile virus in the US is an example of a previously tropical disease that in recent years has moved into temperate-climate regions and has caused great mortality both to birds and humans in the US and Europe. Another potential example is highly pathogenic avian influenza (HPAI, strain H5N1), a mosquito-borne disease that originated in the Old World subtropics. By 2008 the virus had been found in some North American wild birds. If mutations occur that make this lethal virus easily transmittable to humans, it could produce far more devastating consequences than has West Nile virus.
In spite of the popular positions against global warming espoused by some persons for political or religious reasons, it is now far too late to argue about whether global warming is occurring and if humans have caused it; that horse left the barn long ago. The winter conditions typical of the early to mid-1900s in the northern Plains are history. The only question now is what can be done to limit the release of greenhouse gases into the atmosphere before there is a veritable worldwide stampede of undesirable and eventually cataclysmic ecological effects.
Johnsgard, Paul A. and T. Shane. Four Decades of Christmas Bird Counts in the Great Plains: Ornithological Evidence of a Changing Climate. University of Nebraska Digital Commons, 2009. http://digitalcommons.unl.edu/biosciornithology/46/.
Johnsgard, Paul A. Global Warming and Population Responses among Great Plains Birds. University of Nebraska Digital Commons, 2015. http://digitalcommons.unl.edu/zeabook/. Print edition also available: http://www.lulu.com/spotlight/unllib. See this reference for additional citations of studies mentioned above.