Estimating Sighting Proportions of American Alligators During Night-light and Aerial Helicopter Surveys

Wildlife Outstanding Technical Paper

We used mark-resight methods to estimate sighting proportions of American alligators (Alligator mississippiensis) during night-light and aerial helicopter surveys. Alligators ≥122 cm were captured during 5- to 12-day periods on Orange Lake and Lake Woodruff National Wildlife Refuge, Florida, and marked with paint on the dorsal neck area. Replicate helicopter surveys were subsequently flown on each area to record marked and unmarked individuals. Population estimates were calculated and compared with night-light and aerial counts of alligators ≥122 cm. Estimated mean proportion of alligators ≥122 cm sighted during May-June night-light surveys was 0.189 for Orange Lake and 0.090 for Lake Woodruff NWR. Mean sighting proportions during May aerial surveys were 0.106 for Orange Lake and 0.172 for Lake Woodruff NWR. Night-light and aerial alligator counts can be corrected for visibility bias to estimate population size, but sighting proportions may vary depending on habitat type, environmental conditions, and season.

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20108