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Upper Midwest Environmental Sciences Center

Method Development for Determining Causes, Timing, and Magnitude of Mortality of Common Loon Chicks in Northern Wisconsin

Study Area: Iron, Forest, Vilas, and Oneida County, WisconsinRecent research in northern Wisconsin found that common loon (Gavia immer) productivity was lower on lakes where chicks had elevated blood mercury levels. However, these results are confounded with other ecological variables. Biologists need a knowledge of mortality factors to discern the effects of mercury exposure, prey abundance, and predator relationships on loon productivity.

Traditional observation studies have provided limited information on loon chick productivity and have been ineffective in identifying the specific causes and timing of mortality.

Recent advances in implant techniques and transmitter miniaturization now provide a promising alternative.


Common loon chick and transmitterWe developed and evaluated a radio attachment technique for loon chicks and followed the fates of individual chicks during the summers of 1997 and 1998.

To accomplish this, we developed methods to collect loon eggs, to hold adults on nests while eggs were artificially incubated, to incubate and hatch eggs, implant radio transmitters, and release chicks back to nest.

Adult common loon returns to nest containing recently added radiomarked chick


Information on behavior, growth and development, energy expenditure, and survival were collected for both radio-marked chicks and nest mates that did not have transmitters. The marking technique proved successful and we identified several sources of loon chick mortality.

Contributing causes of mortality included attack by intruding adult loons, bald eagles, aquatic predators (e.g., large fish), and disease. This project provides new methodology that may be used to fill a critical information need in our understanding of common loon chick mortality and may have application to a host of bird species.

This project will be completed by October 2001.

Prinicpal Investigator: Kevin Kenow

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