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.
The 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.
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.
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.
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