A Comparison of Methods Used to Obtain Age Ratios of Snow and Canada Geese

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The validity of group counts, cannon-net catches, and hunter-bag checks for estimating productivity of lesser snow geese (Anser caerulesc8f1S caerulescens) and small Canada geese (Branta canademis hutcllinsii-parvipes complex) was studied at Sand Lake National WildJife Refuge during the falls of 1965 and 1966. Age ratios of snow geese obtained from net-trapped samples were signifi­ cantly higher (P < 0.01) than from group counts at the same site. Immature snow geese were shot in a significantly greater (P < 0.01) proportion than they existed in the population as determined by group counts. Cannon-net catches and hunter-bag checks of snow and Canada geese yielded age ratios which were biased because of behavioral characteristics of the geese. Immatures of both species were less wary of trap equipment and immature snow geese were more vulnerable to the gun than adults. It was believed that age ratios from group counts of snow geese were more representative of the population than those from net catches and hunter-bag checks. Sex ratios of net·trapped geese showed a preponder­ ance of males for adult Canada and adult and immature snow geese, whereas females were predominant in the immature SCb'lllent of Canada geese. Hunter selectivity of blue- or white-phase snow geese was not observed at Sand Lake Refuge. Differential vulnerability to hunting between snow and Canada geese resulted from differences in feeding-flight behavior. Knowledge of the proportion of imma­ tures in the population of a species follow­ ing the nesting season is useful in setting annual hunting regulations. At present, goose age-ratio data are gathered primarily on fall migration areas and on wintering grounds. Even though these data are ob­ tained after the hunting regulations for that year have been set, they have value in sub­ sequent years because geese are long-lived birds and do not breed until at least their