The park’s common loon (Gavia immer) population is one of the most southerly breeding populations in North America. The majority of Wyoming’s population of breeding common loons occurs in Yellowstone. The common loon is listed as a Species of Special Concern in Wyoming because of its limited range, small population, sensitivity to human disturbance, and loss of breeding habitat outside of Yellowstone. Wyoming’s breeding loon population is isolated from populations to the north by more than 200 miles, limiting immigration from other populations. Since the mid-2000s, Wyoming’s population has declined by 42%. Yellowstone’s loon population has declined since surveys began in 1989. However, detailed data from a study initiated in 2012 indicate that the number of loons present in the park can vary widely from year to year. Continuing research will try to analyze any trends in productivity, nesting success, and number of breeding pairs to attempt to determine why some years are more productive than others.
Number in Yellowstone
In 2016, park biologists checked at least 18 lakes for loon activity. Yellowstone Lake had two loon territories. Fourteen of the lakes were occupied by at least one loon, with a total estimate of 31 adult loons. Nine loonlets fledged during 2016.
In the western United States, common loons breed in Idaho, Montana, Washington, and Wyoming. The total western US breeding population is estimated at 90 territorial pairs. Wyoming’s breeding population is isolated and totals approximately 16 territorial pairs including 11 in Yellowstone. Western populations of breeding common loons are known to overwinter from Washington south to California. Spring and fall migrants in Wyoming represent breeding populations from Saskatchewan that overwinter around Mexico’s Baja California peninsula.
There are several threats to Wyoming’s loon populations. Direct human disturbance to shoreline nests and chicks lowers survival rates, as do the loss of breeding habitats and water level fluctuations (e.g., erratic spring flooding). Contaminants like lead (from sinkers) and mercury, in combination with hazards on wintering grounds (e.g., marine oil spills and fishing nets) challenge loon reproduction and survival even further.
Fish are the primary prey of loons. As part of a multi-park study on mercury concentration in fish, fish from various lakes where loons nest were screened for mercury. Fish were sampled from Beula, Grebe, Yellowstone, and Lewis Lakes. Fish from Beula, Grebe, and Yellowstone lakes exceeded the threshold at which fish-eating birds may be affected by mercury toxicity. Fish from Lewis did not exceed that threshold although they still contained mercury.
Loons are long-lived; they have relatively low chick production and a poor ability to colonize new breeding areas. Given the very small size and isolation of Wyoming’s breeding loon population, it is at a particularly high risk of local extinction.
Songbirds and Woodpeckers
Passerine and near passerine species comprise the majority of bird species in Yellowstone.
Annual Bird Program Reports. National Park Service, Yellowstone National Park. https://www.nps.gov/yell/nature/birdreports.htm
Mcintyre, Judith W., Jack F. Barr, David C. Evers, and James D. Paruk. Common loon. The birds of North America Online. https://birdsna.org/Species-Account/bna/species/comloo/introduction
Last updated: July 17, 2018