An Aerial Survey Technique for the Forest-Dwelling Ecotype of Woodland Caribou, <em>Rangifer tarandus caribou</em>

Abstract

546The forest-dwelling ecotype of Woodland Caribou (Rangifer tarandus caribou) is found at very low densities and is distributed in small herds dispersed over large areas (Courtois et al. 2001). According to systematic surveys carried out during the 1960s and 1970s, the southern limit of distribution is about the 49 th parallel in eastern, and the 50 th parallel in western Quebec (Brassard 1972*). These surveys revealed the presence of six large forest-dwelling herds, each comprising from a few hundred to several thousand animals. Outside these herds, a number of scattered smaller groups were also found, composed of 75 or fewer Caribou. Farther south, Woodland Caribou were limited to two small, isolated herds totalling less than 300 individuals. Accurate and precise population estimates for the forest-dwelling ecotype of Woodland Caribou (Rangifer tarandus caribou) are very difficult to obtain because these Caribou are found at very low densities and in small herds dispersed over large areas.In order to suggest a standardized method, data from aerial surveys conducted in 1991 and 1993 (12 000 km 2 blocks) were used to simulate various survey scenarios. Simulations showed that all the major groups of Caribou would have to be found and counted to obtain a confidence interval of ± 20% (α = 0.10). We tested this technique in a survey carried out in winter 1999 in a 42 539 km 2 study site, opting for a total coverage carried out in two phases. In phase one, we used an airplane, flying northsouth transects spaced 2.1 km apart so as to detect most Caribou track networks. In phase two, a helicopter was used to count and determine the sex and age classes (calves/adults) of Caribou found in phase one. Using 20 radio-collared Caribou, the visibility rate of Caribou groups (phase one) and that of Caribou within the groups (phase two) were estimated at 0.90 and 0.94 respectively for an overall rate of 0.85 (SE = 0.08; α = 0.10). The corrected density was estimated at 1.6 Caribou per 100 km 2 with a 15% confidence interval (α = 0.10). The survey cost approximately $4/km 2 , which is lower than that of two previous surveys ($7/km 2 ). Two main factors contributed to diminish costs: (1) the use of long-range airplanes (5-7 hours flying range) in phase one to minimize travel between the airports and the study site, and (2) the use of helicopters only in phase two for counting and determining the age and sex of the Caribou.Key Words: Woodland Caribou, Rangifer tarandus caribou, accuracy, aerial survey, bias, cost, density, forest-dwelling ecotype, simulation, visibility rate, Quebec.Il est très difficile d'obtenir des estimations de population exactes et précises pour l'écotype forestier du Caribou des bois (Rangifer tarandus caribou) parce qu'on le retrouve en très faibles densités et qu'il est distribué en petites hardes réparties sur de vastes superficies. Les résultats de deux inventaires aériens réalisés en 1991 et 1993 (12 000 km 2 ) ont été utilisés pour simuler divers scénarios d'inventaire afin de suggérer une méthode st...

Forest productivity mitigates human disturbance effects on late-seral prey exposed to apparent competitors and predators

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Comparative woodland caribou population surveys in Slate Islands Provincial Park, Ontario

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