The Great Backyard Bird Count is an annual four-day event that engages bird watchers of all ages in counting birds to create a real-time snapshot of where the birds are across the continent. Anyone can participate, from beginning bird watchers to experts. It takes as little as 15 minutes on one day, or you can count for as long as you like each day of the event. It's free, fun, and easy-and it helps the birds."

Personal tools

Snow Depth Survey

In 2001, Great Backyard Bird Count (GBBC) participants went out in force with binoculars--and rulers. In addition to recording the bird species they saw, they measured the snow, submitting some 52,000 reports of snow depth from across the United States and Canada. Researchers at the Lab of Ornithology then used this unprecedented wealth of data to create a snapshot of bird distribution and snow cover.




View Results for 2001


View Results for 2002


View Results for 2003


Patterns from 2001 GBBC data

Snow cover and bird distribution

Within the subregion designated by heavy orange lines on the map, we examined whether various bird species were less commonly reported from areas with increasing snow depth. We found a striking pattern for American Robins and Red-winged Blackbirds: participants were most likely to report these species from locales with little or no snow cover.

The case of the American Robin

The graph below shows that participants had the highest probability of finding American Robins in areas without snow. That probability dropped dramatically in areas with even just a few centimeters of snow cover. This result did not simply reflect greater snowfall at locations farther north. Some regions had unusually low snow cover and unexpectedly high numbers of robins. These data suggest that American Robins may be avoiding snow, a pattern revealed by GBBC data from previous years as well.

        Robin Snow Depth Graph

Do Other Species Avoid Snow Too?

Red-winged Blackbirds showed a pattern similar to that found for American Robins. Other species such as Northern Flickers and White-throated Sparrows showed a less pronounced pattern but also were less likely to be found in areas with lots of snow. By submitting your GBBC data this year, you can help us confirm whether these and other species are responding to snow or some other factor.

Why Might Some Species Avoid Snow?

Heavy snowfall may force ground-feeding birds to move in search of food. American Robins and Red-winged Blackbirds forage on the ground to some extent. However, not all ground-feeders show the expected pattern of snow avoidance. For example, there was no clear pattern for Dark-eyed Juncos, which feed primarily on the ground. Besides snow, other factors influencing a species’ distribution include weather, diet, and the species’ normal range and altitudinal limits.

Junco Snow Depth Graph

What do the snow depth patterns mean? Does snow cover determine the distribution of birds?

Data from the 2001 GBBC have revealed some interesting patterns, but we need data from additional years to determine whether birds really do shift locations in response to snow, rather than some other factor. For example, House Finches and House Sparrows were most likely to be found in areas with the least snow, but the same pattern might result if some other factor, such as winter temperatures, determined the birds’ distribution. The graph below shows a very gradual decline in encounters with House Finches as snow depth increases. This is not the pattern expected if the birds are moving in response to food supplies covered by snow (namely, a sharp decline between no snow cover and a few centimeters, deep enough to cover the ground).

    Finch Snow Depth Graph

We need your help in the 2006 Great Backyard Bird Count.

Will snow accumulations during the 2006 GBBC differ from those in previous years? Help contribute your data to this year's map. Will American Robins, Red-winged Blackbirds, White-throated Sparrows, and Northern Flickers shift their ranges this winter to coincide with areas with the least snow? Or will this year reveal different patterns, indicating that some other factor besides snow is more important in determining the distribution of these and other birds? Participate this year and help answer these questions!