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McKearnan, J.E. 1997. Colonial waterbird population analysis project, Phase I. Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resources. 56+ pp.


Since the 1970's, the Minnesota Department of Natural Resources has collected population data for seventeen species of colonial waterbirds. Because of the enormity of the task not all colony sites are visited every year. Many observers and census methods have been used to collect data. The objectives of this project were to compare Minnesota's program with that of other states and to assess the utility of the data for determining population trends. Phone and mail surveys of personnel of other states responsible for the monitoring of colonial waterbirds were conducted to see how other states census colonial waterbirds and how they analyze their data. Most states census only a few species of colonial waterbirds, though, some do census most of all species on a regular basis. Most states analyze data by comparing total populations; few states have used variables that affect census numbers. Three methods of trend analysis were examined using three species (Double-crested cormorants, common terns, and great egrets) in Minnesota's database. The first method, a comparison of total population counts between two years, can be useful if all colonies are counted for all years, but its accuracy can be affected by random annual fluctuations in population numbers if only a few years are censused. The second method, simple regression analysis, can only be used if most of the colonies are censused for several years during a time period. This method does not control for variables affecting population counts. The third method, a more sophisticated population trajectory method used to analyze North American Breeding Bird Survey data, can be used with data where not all colonies have been censused every year and it can control for such factors, e.g., observer effects, that affect population counts. The results for the third method are preliminary, but do show promise for producing accurate population trajectories using Minnesota's data. More analyses need to be conducted to adjust the method for the peculiarities of colonial waterbird population dynamics and Minnesota's database.

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