SURVIVAL, MOVEMENTS, AND HARVEST OF EASTERN PRAIRIE POPULATION CANADA GEESE

Abstract

Abstract: The Eastern Prairie Population (EPP) of Canada geese (Branta canadensis interior) nests in the Hudson Bay lowlands of Manitoba and migrates through south-central Manitoba, western Minnesota, and Iowa, with a wintering terminus primarily in Missouri, Arkansas, and southern Illinois. The southern range of the EPP historically extended through Arkansas and along coastal southwestern Louisiana and Texas. However, during the 1950s and 1960s a progressive northern shift in wintering distribution occurred as numbers of geese wintering in Louisiana and Arkansas declined while numbers wintering in Missouri increased. Continued temporal and geographic shifts in fall and winter distributions were suspected during the 1980s when numbers of wintering Canada geese increased in Minnesota and declined in Missouri. However, concurrent increases in numbers of Mississippi Valley Population (MVP; B. c. interior) and Mississippi Flyway Giant Population (MFGP; B. c. maxima) Canada geese in portions of the winter range shared with EPP geese confounded interpretations of winter population and harvest surveys. During 1984-93, researchers conducted a cooperative banding and observation effort to improve information on survival rates, harvest rates, and winter distributions of EPP Canada geese. Consistent harvest regulations within 3-year periods during 1984-93, combined with extensive observations of marked geese, allowed for an integrative analysis of survival and movements of this population relative to changes in harvest pressure. We used observations, recaptures, and hunter recoveries of marked geese to provide information on survival, harvest, and movements of the EPP that is needed for long-term management of this population.

Annual survival rates of neck-banded adult geese averaged (x ± SE) 0.707 ± 0.019 during 1984-86, 0.651 ± 0.022 during 1987-89 when harvest seasons were restricted, and 0.595 ± 0.028 during 1990-93 when harvest seasons were liberalized. Annual survival rates for neck-banded adults were lower versus leg-banded adults during 1987-89 and 1990-93 (P ≤ 0.05). Mean survival of neck-banded adults during the harvest seasons in 1987-89 was lower than the mean rate in the harvest seasons of 1984-86, primarily due to a low survival estimate in 1989. Survival averaged 0.918 ± 0.0129 during the 1987 and 1988 harvest seasons but declined to 0.665 ± 0.051 during 1989. Restrictions in harvest correlated with a decrease in direct recovery rates and an increase in survival rates of neck-banded adults during the 1987 and 1988 harvest seasons, but not in 1989. Higher recovery rates in 1989-92 suggested that increased harvest mortality contributed to lower survival of adult geese. However, mortality rates during the 1989-92 harvest seasons increased at a greater proportion than increases in direct recovery rates, suggesting that factors other than harvest could have significantly impacted fall mortality rates of adult geese.

Estimated within-year probabilities of movement, along with population size estimates, suggested there was a northern shift in fall distributions of EPP Canada geese and delayed migrations during the late 1980s. Probabilities of southward movement for geese in the northern regions of the Flyway declined significantly during October and November when season lengths and quotas were reduced during 1987-89. While restrictions in harvest in 1987-89 corresponded with delays in fall movements, subsequent increases in harvest pressure in 1990-92 did not promote southward movement of geese in early fall. Geese that survived the harvest season in 1990-92 had lower rates of movement during October and early November than did geese that survived the harvest seasons in 1985-86. The gradual shift in the estimated timing of north-south movement, for birds known to have survived the harvest season, suggests mortality rates were higher for geese that moved south early in the fall in 1990-92. However, the lack of information on reporting rates and crippling loss for Canada geese prevented direct estimation of the proportion of fall mortality attributable to harvest.

Our study demonstrated that a variety of factors can interact to affect the distribution of Canada geese and complicate approaches to population management. Information from marked geese is a critical tool for monitoring changes in survival and harvest rates of Canada goose populations, especially in light of recent changes in winter distributions and resultant mixing of populations. Data for EPP Canada geese indicated that neck-banded geese had lower survival and higher recovery rates than did leg-banded geese. If harvest was the major source of mortality for EPP geese, our results suggested that actual reporting rates for Canada geese were lower than rates estimated for mallards (Anas platyrhynchos). In contrast, if harvest was not the major source of mortality for geese, then managers need to consider nonharvest mortality rates when determining optimal harvest rates for sustainable populations of Canada geese. In light of recent changes in band inscriptions designed to increase reporting rates, we recommend that managers limit the use of neck bands and that monitoring programs for Canada geese be designed to minimize potential biases due to colored auxiliary markers and differential reporting rates. We also recommend that band reporting rates be evaluated for goose populations across North America. Information on temporal and spatial differences in reporting rates would improve management efforts for EPP Canada geese by allowing a better understanding of the relative impacts of harvest and nonharvest mortality rates.