This past winter (2000-2001) the Cornell Laboratory of Ornithology received many calls from feeder watchers who were concerned about the low numbers of birds at their feeders.  The consensus of these calls was that the numbers and kinds of birds that showed up at  feeders was unusually low compared to previous winters. These concerns were also voiced in the general press and in publications for bird watchers. Black-capped Chickadees and American Tree Sparrows were among the species reported as being in lower abundance. 

Most of the calls we received were from the northeastern U.S. and adjacent Canada. However, from these anecdotal reports we could not tell how widespread the declines were. Were these just local declines at individual feeders or had the abundance of some feeder birds shown more widespread declines?

To answer this question, we examined Project FeederWatch data already received online from this winter. In order to be as rigorous as possible in our analyses, we established the following "rules":

Rule #1: In order for a decline to be considered potentially real, we had to show that this past winter's (2000-2001) abundance was lower than it had been in the previous several years. Because even Black-capped Chickadees migrate in some winters, lower numbers this year than one single previous year may only indicate normal variation in wintering range between winters.

Rule #2: In order for a decline to be considered potentially real, we had to show that the decline also occurred in the middle of winter, when temperatures are often at their coldest and birds are most likely to utilize feeders, and not just at the beginning of winter (when the reports of low abundance were most numerous).

Rule #3: We could only use data from FeederWatchers who had reported observations each winter since 1997-98. We compared these observers' reports from the 2000-2001 winter with the abundances that these FeederWatchers recorded in each of three previous winters. This eliminates the possibility that as new FeederWatchers began the project, they systematically reported from sites with fewer birds (compared to long-time FeederWatchers). We don't think that this was likely, but we wanted to be as conservative as possible in our analyses

The species that we examined were Black-capped Chickadee, American Tree Sparrow, White-throated Sparrow, and Dark-eyed Junco. Unfortunately, the effort required to process data from each of these species meant that we could not examine more species at this time.

We found that Black-capped Chickadees were indeed in lower-than-normal numbers, but the declines were far from uniform throughout the northeastern U.S. and adjacent Canada. The largest declines were from southern Maine through Vermont and New Hampshire, in parts of eastern-most Ontario, and in a region along the New York - Pennsylvania border. (This is demonstrated by the bright red-colored areas in the map below.) 

Notably, the large region of lower abundance (bright red areas) seen in late fall/early winter (November and December map on left) had shrunk by mid winter (January and February map on right). This suggests that chickadees were present, but simply were not coming to feeders, in early winter.

On the maps above, the red colors demonstrate areas in which FeederWatchers reported fewer Black-capped Chickadees this winter than in the previous winters.

Legend: The red color indicates a decrease in abundance this year relative to a previous year. The blue color indicates increases in abundance. The brighter colors indicate a relatively large change (+/- 2 birds difference) has occurred and the gray color indicates regions with little or no change in abundance (+/- half a bird difference).

Our conclusion: The data do not show a general decline in abundance of either of a single species across a wide region, or across several species in a single area. Instead, most of the changes (chickadees being the exception) appear to be explained by birds shifting their wintering ranges this year compared to previous years. For example, American Tree Sparrow were seen in banner numbers in the region around the junction of  Lake Huron and Lake Erie. Likewise, Dark-eyed Juncos appear to have wintered farther north than has been typical throughout eastern North America.

The Black-capped Chickadees, in contrast, were probably present in many (but not all) areas in early winter, but simply not utilizing feeders.

To see maps that show these results, follow the links below. Please note that these are relatively large images (0.3MB) and may be slow to download for some people. The images that we have available are:

Black-capped Chickadees: 6 maps comparing this winter's abundance with abundances in 3 previous winters, and both for early and mid-winter.

American Tree Sparrow: 6 maps.

White-throated Sparrow: 6 maps.

Dark-eyed Junco: 6 maps.

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