Needed: less counting of caribou and more ecology

Abstract

Most aerial surveys designed to estimate numbers of caribou (Rangifer tarandus) lack clear objectives, are inaccurate and imprecise, lack application, and often are doubted by the public. Sources of error in surveys are bias (inaccuracy) and sampling error (imprecision) caused largely by sampling units (strips, secrions of strips, quadrats, or photographs) being inappropriate for highly variable group sizes and distributions. Many visual strip surveys of caribou on calving grounds were inaccurate by 136-374%. Photographic surveys of calving caribou are more accurate but usually have coefficients of variation (CV) of 20-40%, whereas a CV of about 15% is required to detect a 50% change in population size between surveys. Extrapolation of such counts to population size produces unacceptable accuracy and precision. Consequently, no conclusions can be made about changes in population numbers between or among surveys because even large natural fluctuations fall within confidence limits. These problems combined with difficulties of managing caribou populations in remote areas of northern Canada indicate that scarce funds may be better allocated to ecological studies.

Keywords

• caribou
• count
• accuracy
• bias
• census
• precision