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Aerial Sightability and Classification of Grizzly Bears at Moth Aggregation Sites in the Absaroka Mountains, Wyoming

Aerial Sightability and Classification of Grizzly Bears at Moth Aggregation Sites in the Absaroka Mountains, Wyoming

In 1991-92, we simultaneously observed grizzly bears (Ursus arctos horribilis) from the ground and air at moth aggregation sites east of Yellowstone National Park, Wyoming, to determine the ability of aerial observers to sight and classify bears. The Interagency Grizzly Bear Study Team (IGBST) uses aerial surveys to count and monitor the reproductive success of unduplicated females with cubs (0.5-year olds) in the Greater Yellowstone Ecosystem (GYE). Much of their effort is focused in alpine talus areas because females with cubs congregate there to forage on army cutworm moths (Euxoa auxiliaris). Aerial observers sighted 92% (49/53) of all bears, 85% (22/26) of independent bears, and all (n = 10) family groups present during 6 surveys, but they misclassified 3 of 5 subadults as lone adults, 1 of 7 lone adults as a subadult, and a female with 3 yearlings as 4 lone adults. Further, aerial observers sighted 89% of all bears (n = 55) and 79% of independent bears (n = 28) that used moth sites on the days that surveys were conducted. Classification of family groups and lone bears did not significantly differ between ground and aerial counts, but further stratification of lone bears indicated significant (P = 0.03) under-representation of subadults and over-representation of lone adults from the air. Low sightability of subadults (56%) and misclassification of family groups also contributed to these errors. Aerial observers sighted and accurately classified all 5 adult females with cubs present during the aerial surveys, and no yearlings were misclassified as cubs. However, using other data collected from the ground, we found that aerial observers sighted only 82% of all females with cubs because 2 of 11 family groups observed to use study sites were not present during aerial surveys. Nevertheless, aerial sightability and classification of females with cubs and estimates of litter size at moth sites seemed reliable.

  • Author(s) Sean L. O'Brien and Frederick G. Lindzey
  • Volume 10
  • Issue
  • Pages 427-435
  • Publication Date 1 January 1998
  • DOI
  • File Size 334.01 KB
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