Lek attendance surveys were analyzed to gain a better understanding of the life history of greater sage-grouse (Centrocercus urophasianus) on lands administered by the bureau of Land Management's Cody Field Office (northern Bighorn Basin, WY). The frequency distributions of sampled high observations were analyzed relative to the range of days in the lek attendance season from 1958 through 2005. The mean frequency distributions for male and female high observations were considered lek attendance peaks. The female peak had a mean high observation frequency around April 9 and the male peak had a mean high observation frequency around April 13. These peaks were significantly separated (P<0.0001). Computation of a 95 percent confidence interval suggests the male peak may be between 2.83 and 5.07 days later than the female peak. These local results are relatively early in the lek attendance period when compared to other observations in Wyoming and suggest that after the female peak attendance, a peak in male attendance closely follows. Local identification of peak attendance periods may help improve local nesting, fledging, and brood-rearing period inference. Existing life history information, combined with local peak female attendance data, suggests that peak nest initiation for the Bighorn Basin may begin April 12, peak incubation may begin April 21, and peak fledging/brood-rearing activity may begin May 16. Improved inference may also lead to improved decisions regarding habitat management and conservation.