| dc.description.abstract | The American white pelican (Pelecanus erythrorhynchos) is a prominent breeding bird in Minnesota, but little information has been available on their production, population dynamics, growth and development, or demographic characteristics. I examined life-history traits of American white pelicans nesting colonially at Marsh Lake, Lac qui Parle Wildlife Management Area, Minnesota. Marsh Lake is an impounded river floodplain lake on the Upper Minnesota River that holds the largest American white pelican breeding colony in Minnesota (and one of the largest American white pelican breeding colonies in North America).
An analysis of colony population levels and spring streamflow data indicated that more than 84% of the variation in the number of near-fledged chicks produced per nest was related to mean daily discharge during April. In years when high water floods preferred low-elevation nesting habitat on islands in the middle of the lake, American white pelicans are forced to establish nests on high-elevation sites that are closer to the mainland. The proximity to the mainland leaves the high-elevation sites accessible to mainland mammalian predators, and production rates decline.
An examination of size at hatch and growth of American white pelican chicks showed little variation in initial size and growth rates between years. However, substantial variation in initial size and growth rates were detected within season depending on the timing of hatch. Initial mass did not vary throughout the nesting season, but initial tarsus and wing length were shorter in chicks hatched later in the season. However, growth rates for mass, tarsus, and wing were faster for late-hatched chicks, potentially allowing late-hatched chicks to fledge at an earlier age.
An analysis of demographic characteristics of American white pelicans nesting at Marsh Lake indicated timing of nest initiation was not related to age or body condition of adults.
However, nests were initiated earlier on the preferred nesting island at Marsh Lake. Although some individuals may nest at an earlier age, the estimated age of maturation for American white pelicans nesting at Marsh Lake suggests they are unlikely to begin nesting until they are at least five years old. | en_US |
