Population Changes of Double-Crested Cormorants (Phalacrocorax auritus) on Four Islands in the Beaver Archipelago and Assessment of Aerial Photogrpahy as a Means of Monitoring Nesting Population Size
Western, Jessica L.
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Since the mid-1970's, the double-crested cormorant population in many areas has been steadily increasing. Often, this increase in cormorant numbers has been blamed for a decrease in sport and commercial fish populations. Because of a recent decrease noted in several fish populations in the Beaver Archipelago, including smallmouth bass, brown bullheads, and rock bass, a five-year study has been undertaken in order to better understand the double-crested cormorant and its relationship with these fish populations. This study looked specifically at the change in the cormorant population on the individual islands of Pismire, Hat, Gull, and Grape since 1997. There were two main goals in this study: documenting and accounting for any changes in the nesting population of cormorants on Grape Island, and assessing aerial photography as a means of counting the number of nesting cormorants. By combining ground counts from 2002 with those from previous years, it was found that there has been a decrease in the nesting cormorant populations on most islands. It was also discovered that the most likely reason for the desertion of the Grape colony was repeated harassment by coyotes crossing onto Grape from Hog Island. Counts taken from aerial photographs were found to differ significantly from counts taken on the ground, however, with some improvements, it is believed that aerial photographs could still be an important tool in the monitoring of nesting cormorant populations.
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