USGS Home
Contact USGS
Search USGS

This overutilization of plant resources has led to erosion of thin layers of topsoil needed to sustain plant growth. In areas of heavy grubbing, ponds are formed by the digging action of the geese. The ponds grow in size each year as grubbing continues around their edges.

As the best areas are overgrazed and destroyed, geese move on to graze new areas that are less productive and more prone to destruction. Once the plants are gone, evaporation of soil moisture leads to salinization (salt build-up) of the soil. In some areas, scientists have documented soil salt levels that are 10 times that of seawater. In these areas even the stunted arctic growing willows are killed by the salt and virtually no plants - at least none usable by wildlife - grow.

To find food resources, snow geese families at LaPerouse Bay must now move long distances. Many broods travel more than 30 miles to find suitable grass/sedge sites to feed.

The problem is that in many areas of the arctic, snow goose numbers exceed the ability of the grass/sedge communities to support them. Overgrazing has destroyed extensive areas of the most productive regions of the arctic - the fertile grass/sedge communities that provide food resources that molting adults and growing goslings must have during the short summer brood-rearing period. These same fertile areas are also important to Canada geese, ducks, shorebirds, songbirds, and other wildlife.

This fragile arctic habitat cannot sustain increasing snow goose populations in the long-term. At some point, something will give. Snow geese have adapted to the current situation by expanding nesting and brood rearing in new areas, continuing to contribute to the ever-growing population while destroying more and more habitat in the process.

Aerial view of a goose exclosure erected at LaPerouse Bay in 1982 after snow geese completely eliminated vegetation in the area. Less than five percent regrowth was noted by 1994, which underscores the fragile nature of arctic habitat.

Birds that continue to breed in overgrazed areas have lower productivity and smaller body size. Gosling survival at LaPerouse Bay is 10 percent - only 10 out of every 100 goslings that hatch actually make it to the flight stage.

How can a population continue to grow with a gosling survival rate of 10 percent? Simple. When adults are long-lived, a population can maintain itself or grow even with low recruitment. For example, consider a pair of snow geese which live to be eight years old, the average lifespan of snow geese at LaPerouse Bay. To maintain the population, these geese would need to add only two reproducing birds into the population during their lifetime. Adding four reproducing birds to the population during their lifetime provides a rate of population growth that doubles the population every eight years. Eight years is the average lifespan. Many birds live to be much older.

What will happen if snow goose populations continue to grow? We don't know. Critical and fragile arctic habitats will continue to be destroyed at an accelerated rate as snow goose colonies expand to other marginal habitats. This will impact not only snow geese, but all other species. Eventually, food resources could become so limited that production could not maintain the population. The age structure of the population will continue to shift toward a higher percentage of older birds - a highly unstable situation. The population would likely crash. Loss of hunting opportunity would be tremendous. Recovery of arctic habitats would likely take decades. But we really don't know how long it will take for these areas to recover, if they recover at all.

Composite satellite image of LaPerouse Bay nesting colony area. Blue is water, green is existing vegetation, and orange represents areas that had vegetation in 1973 and had no vegetation in 1993. Scale: the mouth of the bay in the upper portion of the map is about seven miles across. Photo courtesy of the Ontario Ministry of Natural Resources.

Diseases and parasites could run rampant. Renal coccidiosis, caused by a kidney parasite, is present in virtually all of the goslings at LaPerouse Bay, and kills many of them.

Avian cholera, a disease that can kill all waterfowl species, is carried by snow geese. Cholera losses have increased in North America for many years. In recent years, cholera has occurred in snow goose nesting colonies. A major outbreak of cholera in snow geese could kill hundreds of thousands of other birds such as pintail, white-fronted geese, and sandhill cranes. All of these birds and many other species stage together each spring in the Rainwater Basin of Nebraska, a traditional cholera hotspot.