Heterogeneity in body condition, survival, and seasonal origins among lesser snow and Ross's geese

Abstract

Individual heterogeneity in fitness within a population is well established and provides the required variability for natural selection to take place. Yet, in the case of overabundant midcontinent lesser snow (Anser caerulescens caerulescens) and Ross's geese (A. rossii), individual variation in regards to harvest effects on population growth has largely not been considered when evaluating management actions to reduce population size. In this dissertation, I first examined heterogeneity in body condition among hunter harvested individuals and the general population of midcontinent lesser snow and Ross's geese during the spring Light Goose Conservation Order in 2015 and 2016 across Arkansas, Missouri, Nebraska, and South Dakota. I found a body condition bias in decoy harvested geese, such that individuals removed by hunters were in lower body condition (less lipid content) relative to the general population. This finding suggests that disproportionate removal of lower conditioned individuals is a feature of the currently observed compensatory nature of harvest among midcontinent light geese. I also explored methods to estimate the magnitude of individual variation in survival rates of adult lesser snow geese using mark-recovery data via a Bayesian state-space model. I identified limitations to estimating heterogeneous survival rates using mark-recovery data alone and suggest future simulations to explore alternative methodological approaches. Finally, I evaluated differences in spring body condition among individuals using different wintering habitats through stable isotope analysis. I found that individuals overwintering in coastal marsh habitats had lower lipid reserves relative to those individuals overwintering in rice-based agricultural landscapes, suggesting a carry-over effect from winter habitat use that may influence harvest susceptibility or other fitness parameters. In conclusion, continued research to identify the amount of individual variation in survival parameters of cohort specific geese can further elucidate the role of heterogeneity on the Light Goose Conservation Order attempts to reduce population size.