by Paul  Green, Director of Citizen Science, National Audubon Society
Photo credits at end

A preliminary descriptive analysis of this year's Great Backyard Bird Count (GBBC) results reveals changes in the patterns of bird distribution and numbers as we would expect with changing climate and weather conditions between years. In February 2006 participants reported distribution patterns of note for American Robins and northern seedeaters, and various reactions to food availability in northern Canada. GBBCers reported a more northerly distribution for a broad suite of species following a period of above-average temperatures.

Weather Summary

The United States had its warmest January on record, with an average temperature of 39.5 degrees Fahrenheit, which was 8.5 degrees (4.7 degrees Celsius) warmer than the average for 1986-2006. The jet stream remained unusually far to the north during January, trapping cold air in Canada and Alaska. None of the lower 48 states experienced below-average temperatures, and each state was warmer than the long-term average.

NOAA reports that 15 states in the Northern Plains, Great Lakes, and Midwest had record high temperatures for the month, with an additional 26 states having temperatures much above average. More than 74 percent of the United States was classified as "much above normal." Some regions, such as the northern and central plains, that normally  have some of the most severe winter temperatures, had temperatures more than 10 degrees Fahrenheit above their January average. January was warmer than December by 6.1 degrees on average, the reverse of typical years in which January would be 2.4 degrees colder than December.

North of the jet stream, however, temperatures were much lower than average. Fairbanks, Alaska, reached a minimum temperatures of minus 51 degrees Fahrenheit on January 27, with a high of only minus 40 degrees for that day.

Southern Insect-eaters

Some species that might be able to take advantage of warmer temperatures showed predictable results in 2006. Insectivores, such as most swallow and warbler species, move south and out of the United States and Canada to track available food. Those that are more catholic in their diet may linger farther north. The Tree Swallow, which can eat berries during the winter when insects are scarce, is the most northerly of the wintering swallows. Much is made of its ability to digest bayberry (Myrica spp.) berries, with their waxy coating, and winter distribution of Tree Swallows increasingly reflects the distribution of species of bayberry.

The Tree Swallow has broadened its distribution from 11 states in 2001 to 20 states in 2006. Adjusted GBBC figures showed an increase of 43 percent in the number of checklists reporting the species since 2005 to 642, and the number of birds reported up by 134 percent to 25,795. The number of birds reported from those checklists increased from 4,000 in 2000 to 25,795 in 2006.

Orange-crowned and Pine Warblers show similar patterns. Orange-crowned Warbler occured in five new states and provinces for GBBC in 2006, namely New Mexico, British Columbia, Washington, New Jersey and Nova Scotia. The number of checklists reporting Orange-crowned Warblers was up by 55 percent, and the numbers up 98 percent, with participants often reporting these birds were at suet and nectar feeders.

Orange-crowned Warblers often feed by probing, and in winter can often be seen feeding on the ground for insects, as well as taking vegetable food. Their ability to survive on vegetable food, and their change in feeding location from tree to ground, may enable them to winter father north than most warblers. As a result, they may be well placed to take advantage of warmer northern winter temperatures to increase in numbers and distribution.

Like the Orange-crowned Warbler, the Pine Warbler was reported by an increasing number of checklists when compared with 2005, a 12 percent increase to 2,344, and the number of birds reported increased by 74 percent to 6,283. Pine Warblers were reported in Missouri, Indiana, Michigan, Nova Scotia, and Prince Edward Island in 2006. An ability to feed on seeds of pine species during the winter would help this species benefit from warming temperatures.

American Robins--Flocks as Loud as Jets

Compared with 2005, the number of checklists reporting American Robin decreased by around 6 percent, while the number of birds reported from those checklists increased by 57 percent. A large part of this increase was accounted for in the Yakima region of Washington State, which appears to result from at least two possible causes.

Robins returned to the southern interior of British Columbia by early February, about a month earlier than normal. Then, with falling temperatures in the entire region during the GBBC weekend, it is possible that the birds retreated south and to the relative warmth of eastern Washington, while birds from farther east also moved to Yakima when the cold weather hit. Since Yakima is a cetner for growing apples and graps, the area has a lot of cold-weather food for robins.

The 2005 Yakima figure of 150 American Robins from 8 checklists soard to 45,285 birds from 31 checklists. Across the state of Washington, robins reported through GBBC checklists increase from 2,895 to 85,065, and checklists containing American Robin increased from 403 to 840, accounting for a large part of the overall increase. Eyewitness accounts from Yakima suggest the robins created a phenomenal spectacle.

During the count, temperatures were down to minus 10 degrees Fahrenheit in eastern Washington and minus 30 degrees in Central British Columbia. Robin Conway, one of our two Washington regional reviewers, reports that every three or four years, when big pockets of very cold air settle in, the robins make a pit stop to avoid the coldest air nd settle in to feed on unpicked apples,  Russian Olive, and crabapples.

The largest flocks estimated this year were around 40,000 in the Moxee area, where in 2002 residents reported flocks of up to 250,000 in that same area--all roosting in small riparian groves. The noise was reported by one person as sounding like four or five big jet engines in need of lubrication because they screeched so much.

Large increases in robin counts occurred acros the continent, including British Columbia, Oregon, and Idaho, and in the east in New Jersey, Maryland, North Carolina, Kentucky, Florida, and Tennessee. States showing decreased robin counts included Texas (down 70 percent), Louisiana (down 76 percent), Mississippi (down 55 percent), and Georgia (down 25 percent). It is possible that warmer weather led American Robins to winter farther to the north, although other factors may also be involved.

Creepers Crept Up

A suite of other species showed increases over 2005. For example, Brown Creeper, a bird about which relatively little is known, has shown a remarkable increase. The adjusted number of checklists with Brown Creeper reported is up by 57 percent to 2,523, with a 53 percent increase in the number of birds. Warmer temperatures over the winter would probably lead to decreased mortality for many species, which could help account for larger numbers of many of the smaller-bodied species, Brown Creeper included.

Irruptions and non-irruptions for seedeaters

Common Redpoll, as an irruptive species, is always a candidate for investigaton in GBBC, normally alternating the years they come south in large numbers, and years when they do not. Animated maps in the GBBC map room for this species blink like a light! While the literature talks of reliable two-year cycles, GBBC data indicate that there is some complexity in the figures. The year of 2005 was the second "on" year, about 90 percent as strong as 2004 across the continent. In 2002, Common Redpolls showed different patterns in east and west: they streamed south along the Rockies but not in the east. Now, in 2006, a strong southward movement occurred in the East, but not in the West.

Overall, numbers of Common Redpolls were down to about half in 2006. Adjusted checklist numbers were down to 58 percent of 2005 levels, and the number of birds was at 49 percent of 2005 levels. But it's the pattern that is more intereting. The articulation point occurs around North Dakota. In North Dakota, adjusted numbers from 2004-2006 were 2,002, 2,549, and zero. Farther east, in Quebec for example, the figures for 2004-2006 were 3,297, 2549, and 4,980. So we see a clear east-west divide, birds coming south in the east but not in the west.

One report from Dick Cannings in Canada indicates that the spruce cone crop in northern British Columbia and the southern Yukon is "monumental," with huge numbers of Common Redpolls, White-winged Crossbills, and Pine Grosbeaks everywhere. In southern British Columbia the seed crop is poor, and birders report "the worst year in memory" for winter forest finches with not even Red Crossbills appearing in any numbers. The pattern we observe could therefore be the result of redpolls remaining to the north in western Canada where few people took part ini GBBC.

Snow Buntings mirrored Common Redpolls in some respects. The number of checklists reporting them was down 22 percent and numbers down 48 percent. The distribution showed birds coming south in the East but staying north in the West, perhaps reflecting poor seed availability in the northeast of Canada. Snow Buntings were seen most frequently and in the greatest numbers from Minnesota and Ontario to all points west, as well as Alaska and Alberta.

The Pine Siskin is another seedeating species whose populations move around the continent in winter, locating the best food sources. Pine Siskin checklists and numbers were down by 35 percent, but the distribution varied greatly. Once again, numbers in the East were high. In Ontario there was a three-fold increase in the number of checklists reporting the species and a five-fold increase in the number of birds reported.

Meanwhile, in western states and provinces, such as Oregon, Washington, Idaho, and California, numbers of checklists reporting the Pine Siskin, and the number of individual birds reported, were down to around one-fifth or less of 2005 levels. The British Columbia coast usually has the highest concentration of wintering Pine Siskins on the continent, and in 2006 there were almost none. Victoria reported 68 siskins during the Christmas Bird Count when, in a good year, they may have 10,000. Good food farther north is probably the answer to what we see happening with Pine Siskins this winter.

Owl Oscillations

Just as 2005 was a spectacular year for Great Gray Owls, this year was remarkable for their absence. The adjusted number of birds was down to nine percent of the 2005 figure, and the number of checklists reporting the species was down to three percent of last year's figure.

Minnesota, for example, reported 344 Great Gray Owls on 68 checklists in 2005, and just one bird on one checklist in 2006. Food supplies of small mammals were probably plentiful this year in the northern areas where there are fewer GBBC observers.

In contrast, Snowy Owls came south in record numbers during this GBBC, with 182 reported. Three of the to ten reporting locations for this species were in Washington State, with 35 reports--compared with zero reports of this species in 2003, 2004, and 2005. For more on the Snowy Owl story, read "Record Counts of Snowy Owls."

Crow Family Troubles?

Two members of the crow family show a decreasing trend. Whereas the adjusted number of checklists for American Crow was around the same when compared with 2005, the number of birds reported was 35 percent to 204,440 birds.

People who find roosts of gregarious species, such as the American Crow, can skew numbers easily, but this decrease was a general one across the continent. In addition, Yellow-billed Magpie, restricted to a small area, 500 miles by 150 miles, in California, was reported on 135 checklists in 2005, with 1,835 individual birds counted. In 2006, the number of checklists reporting the species was down 10 percent to 122, and the number of birds reported was down 45 percent to 994.

Continued Expansions

The GBBC also provided updates on species showing an increase in their ranges. Eurasian Collared-Doves appeared as escaped birds in Florida in the 1980s, and they have been expanding their range on the continent ever since. This year, Eurasian Collared-Doves were reported in three new regions for the GBBC: Ontario, Saskatchewan, and Nevada. Red-bellied Woodpecker, pushing north in previous years, now appears to be moving west with records for Colorado and the Texas Panhandle.

Flights of the Cranes

The map of Sandhill Crane distribution from GBBC results is always one of the most interesting and most easily translated. Straight lines pointing at stop-over sites and breeding grounds from wintering grounds show clearly the pattern of migration of various wintering crane populations. Or not. What is interesting is that in cold years, the Sandhill Cranes are still on their wintering grounds, or just beginning their migration at the time GBBC is held. Take a look at the animated map, paying close attention to 2003 for the Florida population, 2002 and 2003 for the Texas and Arizona populations, and 2001 for the California populaton.

Nebraska's Platte River is a staging ground for migrating Sandhill Cranes. In 2006, as in 2005, significant numbers of birds were counted there: 2,751 from 4 checklists this year. In those slower years of 2002 and 2003, the counts were from 1 checklist with 4 birds, and 2 checklists with 111 birds. Likewise, in those colder years of 2001 and 2002, New Mexico produced large counts of birds not yet migrating. In other words, the birds had left early in 2006.

Sandhill Cranes streaming up from Florida through Tennessee produced a count of 5,256 individual birds on 25 checklists in 2006, while in 2003 there were only 191 birds on 7 checklists, since the birds had not moved that far north in mid-February. In 2003 the Sandhill Cranes has reached Georgia but not Tennessee. We can even see the fine difference between 2005 and 2006. In 2005 the birds had reach Georgia in numbers but fewer had reached Tennessee. In 206, the situation was reversed. The story is the same on the West coast. In 2003, no birds had reached Oregon at the time of the GBBC, whereas in 2006, 16 checklists reported 351 birds.

The GBBC maps provide a very graphic representation of the effects of climate on the migration timing of Sandhill Cranes, and also of their migration routes toward their dispersed breeding grounds in the northern parts of the continent. The maps represent a startling illustration of what we can achieve with thousands of sets of eyes and ears focused on birds during the GBBC period.

We are always interested in hearing from you about what you observe from an analysis of the results. Send email to citizenscience@audubon.org. We invite you to explore more trends on your own in the "GBBC results" section.

Photo credits
Orange-crowned Warbler, Simon Tan, Texas
Pine Warbler, Errol Taskin, Louisiana
American Robin, Anne Middleton
Brown Creeper, Donna Bingham, New Jersey
Pine Siskins, Perry Greico
Snowy Owl, Kim L. Graham, Ontario
Yellow-billed Magpie, Tiny Gehrke, California
Eurasian Collared-Dove, Vicki Lackey, Texas
Sandhill Crane, Darrell Leidigh, Florida