Territorial Basking Counts to Estimate Alligator Populations

Counts of territorial basking American alligators (Alligator mtssissippiensis) employing the Petersen Index principle of mark and wcapture were tested on four national wildlife refuges from 1969 to 1971. Individual alligators were marked on their basking sites by animal length, site description, vehicle odometer reading, and flagging tape without the necessity of physically trapping, marking, or recapturing specimens. Some alligators were painted to ascertain stability of basking territories, to serve as a known population, and as another way to estimate the sample population. Counts were conducted during the first 7 to 10 days of the first sustained spring wann front. The high recovery rate of marked alligators will achieve precision within 20 percent of the mean estimate (95 percent confidence) when 30 or more alligators are counted in the sample area. Accurate estimates can also be made of size (age) classes. Failure of an observer to see alligators, a small population in a sample unit, and recognition of the proper warm front are the main problems that may be encountered in using this counting technique. The American alligator has been classified by the U. S. Bureau of Sport Fisheries and Wildlife (1968) as an endangered species. The inclusion of the alligator in the Bureau's Redbook has stimulated pressures for more effective regulatory legislation, has intensified research projects, and has promoted management actions. Excessive and illegal harvests, accompanied by loss of habitat, have been blamed for the reduction of wild populations. Only on intensively protected and managed areas, such as state and federal wildlife refuges, have wild populations been maintained in substantial numbers. In addition to their obvious commercial values, alligators have values ranging from an essential part of many ecosystems to a nuisance in conflict with management of other wildlife species. Population information is essential to determine the current status for the Redbook, for the management of alligators in critical ecosystems, and to support appropriate legislative actions. Chabreck (1967) described a number of techniques used to inventory alligators. The methods included night counting, call and nest counts, and the mark-recapture of tagged animals. The objective of the present study was to develop an inexpensive inventory procedure that would yield a fairly precise and reasonably accurate estimate of a sample population in a variety of habitats. BASKING TERRITORIALITY AS A BASIS FOR CENSUSING ALLIGATORS A number of techniques have been developed to inventory wildlife species that depend upon stability of territories as the basis to identify and enumerate individuals, pairs, or groups of animals. Territory mapping of bobwhite quail (Colinus virginianus) is described by Mosby and Overton (1950) and Rosene (1957); roadside census of small birds, by Howell (1951); cottontail rabbits ( Sylvilagus floridanus ), by Kline ( 1965 ); and red-winged blackbirds ( Agelaills phoeniceus ), by Hewitt ( 1967 ); calls of mourning doves ( Zenaidura macroura), by McClure (1939) and calls of American woodcock ( Philohela minor ), by Kozicky et al. ( 1954 ); drumming of ruffed grouse ( Bonasa umbellus ), by Dorney et al. ( 1958 ); and analytical