Changing Great Plains Climate and Bird Migrations

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A multitude of snow geese. (Paul A. Johnsgard)

By Paul A. Johnsgard

When I was a youngster in North Dakota during the 1940s and 1950s, the seasons were very obvious and clear-cut to me. For example, I knew that the peak of fall foliage color would occur early in September. Most small birds would be gone by the end of that month, and the major waterfowl migration of ducks and geese would occur in October. By the first of November fall was usually over, and winter snowstorms could strike at any time. Then it would be an infinitely long wait until the spring thaw, and I could not expect to see even early waterfowl migrants, such as snow geese, returning to the prairie marshes of southeastern North Dakota until early April. Sadly, they would stay only a few short weeks before pushing north as rapidly as the melting ice would allow.

After moving to Nebraska in the early 1960s, my seasonal biological calendar for fall and spring had to be reset by several weeks. The fall foliage peak was likely to not occur until about the end of September. The arctic-breeding snow geese would begin appearing in early October, reaching a peak at about the end of that month, or sometimes in early November. That calendar was so reliable that, when I was involved in a NETV documentary in the latter 1980s, I could advise the producer several months in advance that, to catch the main snow goose migration at Squaw Creek National Wildlife Refuge in northwestern Missouri, we would need to reserve an expensive telephoto lens for their movie camera for the third week in October.

During the decades extending from the 1960s through the start of the 21st century, many ecological changes occurred in the northern hemisphere. These were reflected in altered bird migration patterns throughout the central Great Plains, especially as to their timing, magnitude and destinations. During the late 1960s, snow geese gradually began to arrive in Nebraska ever later in the fall, and to build up in even greater numbers. By the late 1970s vast numbers of snow geese would stage briefly at DeSoto National Wildlife Refuge near Blair, Neb., and a few weeks later fly south about 100 miles to the Squaw Creek refuge to remain until freeze-up.

Changes in goose numbers were dramatic. When I first visited Squaw Creek in the early 1960s, snow goose numbers typically peaked there at about 150,000 birds. By 1978 the snow geese at Squaw Creek peaked at 280,000. These numbers reached 350,000 by 1982 and had attained a record high of 600,000 by 1986. Since then the refuge’s peak snow goose numbers have at times reached a million birds.

These increasing goose numbers have been mainly attributed to the increased grain crops available locally to the geese and to the safety from waterfowl hunters provided by a series of strategically placed national wildlife refuges located between North Dakota and the Gulf Coast. Warmer and longer breeding seasons in the arctic have no doubt also benefited snow goose populations across North America. Snow geese have also remained around Squaw Creek progressively later in the fall during the past six decades. Increasing numbers stay there well after freeze-up by moving to nearby deeper and more ice-free waters such as Big Lake and commonly overwintering in the nearby Missouri River valley.

To illustrate changes in migration timing, in 1966 and 1967 snow geese arrived at Squaw Creek during the second and third weeks of September, and their numbers peaked at an average of 165,000 during the last week of October and first week of November. They had nearly all departed by the end of December. By comparison, between 2008 and 2012 maximum numbers ranged from 390,000 to 1,425,000 birds, typically peaking in late November or early December. In 2013 they didn’t arrive until the first week of November. In the past few years snow geese have remained in the general vicinity of Squaw Creek all winter, even though outside the refuge’s boundaries they have been subjected to intense hunting pressures during an extended hunting season that lasts through January.

A similar delayed migration was happening to Canada geese and cackling geese along the Platte River in central Nebraska during these same decades, with their numbers gradually increasing to about one hundred thousand birds overwintering in the Platte Valley by the early 2000s. Smaller numbers of snow geese, Ross’s geese and greater white-fronted geese likewise now sometimes overwinter in the state. Sandhill cranes have overwintered in the central Platte valley in substantial numbers since 2011.

By the early 2000s it was clear to biologists, as had been concluded much earlier by climatologists, that the world was not as it had been and that a long-term climatic warming trend had arrived. An extended nine-year drought and unusually warm summer temperatures brought the news home to Nebraska in 2002. The drought lasted nearly a decade and was followed by a return visit in 2013. While a few Nebraska politicians have professed that the warming trend was only an unavoidable “cyclical” event, rather than an indicator of a long-term climate change resulting largely from human influences, the facts speak to the contrary.

Using the National Audubon Society’s annual Christmas count data obtained from the mid-1960s onward, evidence of a long-term trend toward milder winters is apparent in the Great Plains. In Kansas, Nebraska and even into the Dakotas more water-dependent bird species such as waterfowl and gulls are now regularly present at least until the end of December.

In counts from Lincoln, Neb., the greatest increases in late-December birds over the past half-century have occurred among the Canada goose, mallard and ring-billed gull. Three species of ducks and two species of sandpipers have recently appeared on the Lincoln counts for the first time, and among terrestrial species there have been great increases in the numbers of American robins and red-winged blackbirds.

Other species that usually winter farther south and have increased to a lesser degree are the eastern bluebird, golden-crowned kinglet and yellow-rumped warbler; both the bluebird and kinglet now regularly overwinter locally.

In contrast, some species have gradually declined in the Christmas counts for Lincoln and now tend to concentrate farther to the north and west in Nebraska, or in the Dakotas. These include various boreal forest and arctic-breeding species such as the snow bunting, Lapland longspur, common redpoll and evening grosbeak.

Snow geese. (Paul A. Johnsgard)

In 2008 I decided to try to test the broad-scale influence of this warming trend by analyzing the late-December distributions of migratory birds throughout the Great Plains, using data from the National Audubon Society’s annual Christmas counts. With the help of my ornithology students one recent summer, we determined the mean state -by-state abundances of more than 200 bird species in late December, from North Dakota south through the Texas panhandle. This analysis covered the period from 1968–1969 to 2007–2008, by ten-year intervals.

Determining the five most common species in each of the Great Plains states over each ten-year interval provides a useful overview of major regional population shifts among late fall and early winter birds. In North Dakota the most common bird on Christmas counts for the decade 1968–1977 was the house sparrow; the Canada goose was not among the top five most common species. However, by the decade 1998–2007 the Canada goose was the most common species, followed by the house sparrow; the mallard had by then climbed to fourth place.

In South Dakota the most common bird on Christmas counts for the decade 1968–1977 was the mallard; the house sparrow was second, and the Canada goose was fifth. However, by the decade 1998–2007 the mallard was the most common species, followed by the Canada goose. The house sparrow had by then fallen to fifth place.

In Nebraska the most common bird on Christmas counts for the decade 1968–1977 was the mallard; the house sparrow was third, and the Canada goose was fifth. During the decade 1998–2007, the mallard was still the most common species, followed by the Canada goose; the house sparrow was not then in the top five.

In Kansas and in Oklahoma the most common species reported for the decade 1968–1977 was the red-winged blackbird; it was still in first place for the decade 1998–2007 in both states. In Kansas the greater white-fronted goose had risen to fourth place by the decade 1998–2007, while in Oklahoma the snow goose had reached fifth place.

These relatively few examples clearly point out some of the strong biological effects of very small annual changes in temperature. Over the nearly 11 decades between 1895 and 2008, the average January temperature increased 0.44 degree Fahrenheit per decade in North Dakota (collectively, 4.7 degrees), 0.19 degree in South Dakota, 0.11 degree in Nebraska, 0.10 degree in Kansas and 0.04 degree in Oklahoma (collectively 1.9 degree), showing that regional warming is proceeding most rapidly at northern latitudes. It is likely that life in the Great Plains is destined only to get warmer and drier. Even armadillos, not generally thought to be smarter than our dullest state senators, have gotten the message and increasing numbers have been trudging north into Nebraska.

 

Image Credits: Paul A. Johnsgard

 

References

Paul A. Johnsgard, “A Half Century of Christmas Bird Counts at Lincoln and Scottsbluff, Nebraska,” “Nebraska Bird Review” 66 (1998): 74–84. http://digitalcommons.unl.edu/nebirdrev/38.

Paul A. Johnsgard, “Four Decades of Christmas Bird Counts in the Great Plains: Ornithological Evidence of a Changing Climate” with distribution maps by Tom Shane (2009). http://digitalcommons.unl.edu/biosciornithology/46/.

Paul A. Johnsgard, “Snow Geese of the Great Plains,” Prairie Fire (February 2010): 12–15. http://www.prairiefirenewspaper.com/2010/02/snow-geese-on-the-great-plains.

Paul A. Johnsgard, “Squaw Creek National Wildlife Refuge: Gem of the Missouri Valley,” Prairie Fire (November 2012): 12–13. http://www.prairiefirenewspaper.com/2012/11/squaw-creek-national-wildlife-refuge-gem-of-the-missouri-valley.

Paul A. Johnsgard is a retired University of Nebraska professor who is thinking of moving back to North Dakota to escape the heat.

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