Bias in Canada Goose Population Size Estimates from Sighting Data

An examination of methods to estimate population size in wintering geese

“…In a simple two-sample capture-recapture (LincolnPetersen) study, M equals the number of individuals marked on the first occasion and R is estimated from the ratio of total to marked animals in the sample captured on the second occasion. In typical long-term mark-resight studies, however, marking takes place on multiple occasions, mortality and recruitment occur between marking and resighting, and some individuals are missed during each resighting period, so that M has to be estimated from the resighting histories of marked birds using a Jolly-Seber approach (Sheaffer & Jarvis 1995).…”

“…Two different methods were employed: (a) the 'whole-flock' method, where the total number of birds in a flock was counted and the total number of marked birds in the flock could be assessed with certainty after prolonged watching of the flock; (b) the 'tally' method, where a sample of individual birds within a flock was examined for the presence or absence of markers. In both methods, presence of markers was recorded regardless of whether the marked birds could be individually identified, as recommended by Sheaffer & Jarvis (1995). Inspection of the data revealed no consistent difference between the two methods in estimated proportion of marked birds, and therefore data from both methods were pooled.…”

“…Confidence intervals of the population estimates were calculated following Sheaffer & Jarvis (1995), with the variance of M set to zero because M was considered precisely known.…”

Estimating Animal Abundance: Review III

“…These can be combined together to get estimates of abundance at each time point. Sheaffer and Jarvis (1995) …”

Mark–resight approach as a tool to estimate population size of one of the world's smallest goose populations

“…If these demographic parameters are known, future population size can be precisely predicted, but quantifying them accurately (and keeping them up to date) necessitates detailed knowledge of both reproduction and annual bottlenecks. More recently, the use of mark-resight methods (rising from the umbrella of capture-markrecapture analysis) has become a widespread way to estimate population size in wild populations (Sheaffer & Jarvis 1995, Walsh et al 2010. The main advantage of this approach is that finding every individual becomes unnecessary, but at the same time it relies on important assumptions that are easily violated (closed populations, equal detectability among individuals), and these assumptions, if not treated carefully, might lead to biases in the final result (Kendall 1999, Willson et al 2011.…”