Avian Richness in Bellingham, WA

Avian Richness in Bellingham, WA

Adrianne M. Akmajian, Robinson R. Low, Melissa M. Oscarson

 Birds are one of many species vulnerable to increased human population growth and land use. Increasing land use destroys native habitat, which can negatively affect species richness. On the other hand, increased anthropogenic resources can add additional food and habitat for birds and lead to greater species richness in moderately disturbed areas (Lepczyk et al. 2008).

For our group project, we were interested in how urbanization and land use impacts avian richness in Bellingham, WA. Before we could answer that question, we had to learn to identify some birds. We looked up the most common birds sighted in Whatcom County in the month of May using an online, citizen-science database called eBird (ebird.org). This helped us narrow down what birds to expect in the area and what birds to learn. Then, it was time for some serious study. We took a list of over 50 bird species possible and over a three-week period tried to memorize songs, calls, and appearance of each.

A Google Earth view of our study site with land use categories labeled.

After learning as many of the birds as we could, we began our study. To do this study we used a method called a point-count. A point-count works by having an observer stand in one location and record all birds seen or hear in a given area away from the point and in a given amount of time (Ralph et al. 1993; Clergeau et al. 2001). We selected 24-points within a 1-mile area around the WWU campus. We tried to choose points that represented three broad categories of urbanization and land use: green sites that were primarily forested patches, residential sites in neighbors near campus, and high disturbance sites including areas with high traffic use, large areas of impermeable surface such as cement and blacktop, or areas of little to no vegetation. We expected that we would find the most bird species in our green sites and the least in the high disturbance sites, suggesting that the urbanization of Bellingham leads to decline in avian species richness.

We were also interested in how specific parts of the habitat influence species richness. For example, are birds more likely to be in more complex habitats, having large trees and both shrub and groundcover compared to areas with very little vegetation and a large cement parking lot? We had the students in our class help to go out and record both habitat and urbanization variables at each of our 24 sites. These variables included percent canopy, shrub, and ground cover and number of large trees, snags and nurse logs. The urbanization variables assess human use and included percent cement and blacktop and number of houses, buildings, and roads.

We conducted our bird counts over a four-day period from May 18^th to 21^st. At each point, we would spend 5-minutes recording all birds we saw and heard. We used digital recording devices to record bird calls so that we could go back and verify calls we were unsure or identify birds we missed in the field.

Percent cement or blacktop for all 24 sites.
 This variable described 40% of our data!

After the study period, it was time to analyze some data. Between all 24 sites, we identified 34 total bird species! We also found some interesting trends. As predicted, we found the most bird species at green sites compared to the high disturbance sites. We also found that some birds were only found in particular habitats. For example, orange-crowned warblers, Swainson’s thrush, and warbling vireos were only found at green sites. House sparrows and pigeons were common in residential and high disturbance areas, but never seen at green sites. Of all the habitat and urbanization variables we measured, only percent cement and number of large trees (>50 cm diameter) appeared to significantly influence species richness.

Based on our findings, we strongly encourage future city planners to continue to incorporate green areas in Bellingham. In particular, we believe it is important to preserve native and forested patches that are able to sustain the greater number of bird species.

The black-capped chickadee was one of the most
frequently sighted birds in our study and was observed
in all three of the land use categories.

Clergeau, P., J. Jokimaki and J.L. Savard.  2001.  Are urban bird communities influenced by the bird diversity of adjacent landscapes?  Journal of Applied Ecology 38:1122-1134.

Lepczyk, C.A., C.H. Flather, V.C. Radeloff, A.M. Pidgeon, R.B. Hammer and J. Liu.  2008.  Human impacts on regional avian diversity and abundance.  Conservation Biology 22(2):405-416.

Ralph, C.J., G.R. Geupel, P. Pyle, T.E. Martin and D.F. DeSante. 1993. Handbook of Field Methods for Monitoring Landbirds. USDA Forest Service, Pacific Southwest Research Station, Albany, California.USDA-PSW-Gen. Tech. Rept. 141.