TY - JOUR
T1 - Using re-sighting data to estimate population size of Pink-footed Geese (Anser brachyrhynchus)
AU - Clausen, Kevin Kuhlmann
AU - Balsby, Thorsten Johannes Skovbjerg
AU - Goma, Vianney
AU - Madsen, Jesper
PY - 2019
Y1 - 2019
N2 - In wildlifemanagement, the ability to reliably assess population sizes is a basic prerequisite. When populations are managed specifically to maintain a population target this is even more vital. In this study we apply amark-resight approach using neck-collared geese to develop and present an alternative method to total counts when estimating the population size of Pink-footed Geese (Anser brachyrhynchus). Estimates of population size from the mark-resight approach showed an increasing trend from 31,000 birds in 1991/1992 to 100,700 birds in 2011/2012, and fluctuating numbers around 80,000 in recent years. By exploring the relationship between uncertainty of the population estimate and the monitoring effort, we showed that a minimum of approximately 120 independent flocks greater than 100 birds should be surveyed to derive a ratio estimate of marked to unmarked birdsminimizing uncertainty of the overall population estimate. This threshold was onlymet in the last 6 years of our data series, and therewas therefore a high degree of uncertainty concerning estimates from earlier years. Our analysis revealed that recent mark-resight estimates were in good agreement with the total counts derived from traditional methods, although generally slightly higher. By deriving an independent population estimate, the approach can be used to quality assure the traditional total counts, which may (due to overlooked birds and changing site use) be prone to underestimation of true population size, especially in spatially expanding and widespread populations.
AB - In wildlifemanagement, the ability to reliably assess population sizes is a basic prerequisite. When populations are managed specifically to maintain a population target this is even more vital. In this study we apply amark-resight approach using neck-collared geese to develop and present an alternative method to total counts when estimating the population size of Pink-footed Geese (Anser brachyrhynchus). Estimates of population size from the mark-resight approach showed an increasing trend from 31,000 birds in 1991/1992 to 100,700 birds in 2011/2012, and fluctuating numbers around 80,000 in recent years. By exploring the relationship between uncertainty of the population estimate and the monitoring effort, we showed that a minimum of approximately 120 independent flocks greater than 100 birds should be surveyed to derive a ratio estimate of marked to unmarked birdsminimizing uncertainty of the overall population estimate. This threshold was onlymet in the last 6 years of our data series, and therewas therefore a high degree of uncertainty concerning estimates from earlier years. Our analysis revealed that recent mark-resight estimates were in good agreement with the total counts derived from traditional methods, although generally slightly higher. By deriving an independent population estimate, the approach can be used to quality assure the traditional total counts, which may (due to overlooked birds and changing site use) be prone to underestimation of true population size, especially in spatially expanding and widespread populations.
M3 - Journal article
SN - 0030-5685
VL - 96
SP - 112
EP - 123
JO - Ornis Fennica
JF - Ornis Fennica
IS - 3
ER -