Condor’s Top Cited, #6: 100 Years of Change in Glaucous-winged Gull Populations

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Image credit: L.K. Blight

Our series highlighting top papers of 2014 and 2015 continues this week with a study from The Condor: Ornithological ApplicationsA century of change in Glaucous-winged Gull (Larus glaucescens) populations in a dynamic coastal environment by L.K. Blight, M.C. Drever, and P. Arcese.

When ecologists track changes in wildlife populations, the question of what’s “normal” for those populations is important to consider, but this can be hard to determine over a short period of time. With this in mind, Blight and her colleagues assembled a very long-term data set to see how Glaucous-winged Gull populations fluctuated over many years. The harvesting of eggs had seriously depleted gull numbers before being banned by the Migratory Bird Treaty of 1916, but in the decades following the treaty, the population was able to recover, increasingly rapidly over the following seventy years. In the 1980s, however, greater numbers of Bald Eagles (a gull predator) and the decreasing abundance of fish in the area caused gull populations to drop again, ultimately decreasing to about 50% of peak levels by 2010.

Because gulls sit in the middle of the food chain and will eat almost anything, they can be an important indicator of what’s going on in the broader ecosystem. This study highlights the value of long-term retrospectives for providing unique perspectives on causes of population change and indicates the need to exercise caution in assuming that historical data represent “pristine” conditions by virtue of their age alone.

Read the full paper at http://www.aoucospubs.org/doi/full/10.1650/CONDOR-14-113.1.

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