Ten years of Winter Backyard Bird Surveys show patterns
By Patricia Thompson, WDFW Wildlife Biologist

Puget Sound distribution of brown creeper (Certhia americana)

Thanks to hundreds of volunteers collecting data for WDFW’s Winter Backyard Bird Surveys from 1993 through 2002, and some rigorous data analysis, we are able to start seeing some patterns in bird populations in Washington.

We are able to detect changes in abundance or the relative number of birds in a species (see “Top Ten” table), and distribution or where the species are found in Washington (see “Most Widespread” table).

We would like to use these data to identify landscape features, for example housing density or tree height, that affect the number of birds, the species of birds (species diversity) and how the birds use these landscapes.

The fact that most of our volunteers were in the Puget Sound area is both good and bad. It’s good because we have a lot of data from a concentrated area. But it’s bad because we need more data from the east side of the Cascades in order to come to any statewide conclusions.

Total Averaged Pine siskin (Carduelis pinus) Count Per Year

Total Averaged Anna’s hummingbird (Calypte anna) Count Per Year

“Most Widespread” (Distribution)

We have two very good examples of how the surveys can show changes in abundance in Washington backyards. One is the Pine siskin (Carduelis pinus) which is an irruptive species, or one that moves its wintering areas and shows up in large numbers at times.

From the graph at right, you can see that 1995 was an irruptive year for pine siskins, and 2001 was a lesser irruption. This does not mean that there are more pine siskins overall, or a larger population, but that they are concentrated in different areas.

Another example of a trend that we saw was in the Anna’s hummingbird (Calypte anna). Many of you have said that you are seeing more and more Anna’s hummingbirds over-wintering in Washington. The proof is in the data shown in the graph here.

Above is an example of a distribution map using the brown creeper (Certhia americana) in the Puget Sound area where we have a large amount of data. Brown creepers generally prefer mature, coniferous forests or mixed coniferous/deciduous forests, but we have them all over the urban environments. They are also found in drier eastern Washington but we do not have enough data from that region to be conclusive on the distribution.

Now that the data are validated and summarized we can move on to statistical evaluation to see if the trends we see are significant. Then we can look at the different habitat features and possibly tell which ones affect bird populations and species distribution.

We feel these surveys can tell us much about general trends so we hope to resume data collection in the near future using the vast wealth of volunteer energy in Washington state.

Click on graphs for larger image