Hatch date influences pre-fledging survival of temperate-nesting Canada geese

Abstract

Among the numerous demographic parameters that influence population size, unbiased estimates of pre-fledging survival remain difficult to obtain for precocial birds. In this study, we used capture-mark-recapture modeling to estimate pre-fledging survival in a population of temperate-nesting Canada geese Branta canadensis maxima that has undergone an exponential increase over the last two decades. We examined whether pre-fledging survival was affected by relative hatch date, initial brood size, mother age, and weather conditions at hatching. Between 2005 and 2014, 8679 goslings were marked with web-tags at hatching at two adjacent sites. A total of 3922 of these birds were initially recaptured and banded before fledging while 338 were recaptured and banded in subsequent years as after-hatching year birds. Multistate models with joint live and dead encounters were used to estimate pre-fledging survival and evaluate the effects of rearing sites, gosling characteristics, and weather conditions at hatching. Pre-fledging survival of Canada geese varied between 0.45 (95% CI: 0.41-0.50) and 0.75 (0.62-0.84) among years and sites with an overall mean of 0.62 (0.54-0.68). Survival rates were lower for late hatched birds and tended to increase with initial brood size and mother age. Weather conditions at hatching did not affect pre-fledging survival. Significant effect of hatch date on pre-fledging survival has often been described in geese nesting in highly seasonal environments (e.g. the arctic) but our findings of such a relationship in temperate-nesting Canada geese indicate that a selection pressure on the timing of breeding can also occur at more stable temperate latitudes.