Implications of Spring Water Levels on the Production of American White Pelicans Nesting at Marsh Lake, Minnesota

摘要

Weinvestigated the relationship between spring water levels and production of American white pelicans (Pelecanus erythrorhynchos) nesting colonially at Marsh Lake in southwest Minnesota during 2003-2012. We obtained estimates of pelican nest and chick numbers from aerial photographs to determine population levels. We used historical streamflow data to characterize April water conditions, a period when nest-site selection typically occurs. Pelicans used 4 islands and 1 peninsula for nesting, ranging from relatively high-elevation sites connected to or near the mainland to more distant low-elevation sites in the middle of the lake. The number and proportion of nests on high-elevation sites are positively related to discharge in the Upper Minnesota River during April. In years when high water inundates low-elevation sites during pelican nest-site selection, pelican nests were located on the high-elevation locations near or connected to the mainland. Over 90% of the variation in the number of nests on high-elevation sites is related to the mean daily discharge in the Upper Minnesota River during April. In addition, the proportion of nests on high-elevation sites also increases as mean daily discharge during April increases. However, chick production was negatively related to discharge during April. More than 84% of the variation in the number of near-fledged chicks produced per nest was related to mean daily discharge during April. Although high-elevation sites in close proximity to the mainland offered nesting pelicans refuge from high water levels, they also expose American white pelican nests to greater predator risk. Nest camera monitoring indicated that high-elevation sites exhibited significantly higher predator activity than low-elevation sites, and experienced lower nest success (i.e., probability that at least 1 egg from the nest hatched). Proposed changes in the management of Marsh Lake call for the installation of a water control structure at the Marsh Lake dam that will allow for active management of lake levels. Our study provides managers with models for predicting impacts of water levels on American white pelican production. (C) 2015 The Wildlife Society.