Dispersal and survival of snow geese.
Preliminary studies have demonstrated that reproductive success of lesser snow geese dispersing from degraded areas increases significantly above the declining levels experienced by birds remaining in degraded areas. This dispersal involves both birds nesting in degraded areas but rearing their broods in more intact areas as well as those individuals that have begun both nesting and rearing broods in less degraded areas. The latter group are generally young females who will continue nesting in the new areas. This pattern of dispersal has two important consequences for overall Mid-Continent population dynamics: a) the potential for density-dependent reduction in population growth rate is thwarted and b) the cycle of goose population growth and habitat degradation extends geographically with existing snow goose colonies acting as epicenters for a spreading trophic cascade.
To monitor this and incorporate these movement patterns into our population projection model, we need precise estimates of dispersal from large colonies. New mark and recapture (and resight) models will enable us to estimate dispersal. We will be able to obtain precise estimates of dispersal from the La Pérouse Bay colony by adding to and capitalizing on our existing database. Fine tuning the models with that data, we hope to obtain reasonable estimates of dispersal from other colonies using smaller and shorter-term databases. Because we are interested in estimating dispersal both by females that only move for brood rearing and by those that have begun nesting in new areas, some of our resighting observations will be made at the newer colonies during the nesting period.
An additional benefit will accrue from these dispersal studies. Detailed analyses of the birth and death rates of snow geese using the initial version of our population projection model have shown that the factor that influences population growth the most is annual adult survival. Even minor changes in this rate, perhaps caused by changes in harvest rate or even disease, could greatly alter population dynamics of snow geese in the region. In view of this, continued monitoring of annual survival rates using the recapture and recovery of banded birds remains a component of our research program. Building on the extensive La Pérouse Bay database, we will be able to detect even small changes.
- revised 10/11/97 -