Six count circles have been set up in various locations in the salt marshes of the Plum Island Ecosystem in Rowley and Newbury. Three 10 minute point counts have been carried out between June 1st and the first week of July at each circle. Counts are spaced out so that they are at least a week apart and all six circles are sampled on the same day. The counting period runs from 5 AM through 10 AM.
Initially two observers counted simultaneously and recorded their observations independently. Since 2008, we have adopted the double observer protocol recommended by Nichols, et al. (2000) in order to estimate detection probabilities. If only one observer was available, detection probabilities have been estimated through distance sampling.
To carry out a count, observers enter the circle and proceed to the center, marked with a short pvc pipe. One person serves as the primary observer and the other the recorder and secondary observer. After waiting a minute, the primary observer identifies to species all birds observed visually or detected by songs or calls within a 10 minute count period. The secondary observer records those observations and adds any additional ones that the primary observer missed. Observers distinguish between three distances, 0-50m, 50-100m and >100m (the latter outside the circle). The edge of the circle is marked at various points with stakes to serve as a guide for distance or the distance is estimated using rangefinder binoculars. The two observers switch roles at the next site.
Nichols, J.D., J.E. Hines, J.R. Sauer, F.W. Fallon, J.E. Fallon, and P.C. Heglund. A double-observer approach for estimating detection probabilities and abundance from point counts. Auk 117: 393-408
AOS for codes in data refers to the American Ornithologists' Society (AOS) taxonomy and nomenclature, http://birdpop.org/AlphaCodes.htm.