Tuesday, November 27, 2007
Raccoon Biological History
The raccoon has had a tremendous reversal of fortune in the last 70 years both in terms of numbers and distribution.
By the late 1980s, the number of raccoons in the U.S. was estimated to be 15 to 20 times greater than the number that existed during the 1930s.
This reversal of fortune is partly due to the widespread regrowth of forests and revegetation of riparian areas, partly due to the rise of suburbia where they do so well, partly due to a decline in trapping and hunting, partly due to raccoons spreading out into new areas with the arrival of human-based food and denning structures (especially in the Plains states), and partly due to the stocking of raccoon in areas as far flung as California and Alaska (where islands were stocked with raccoons from Indiana).
Raccoons are not native to most of Canada, and in fact some tribes in northern Canada still do not have a name for the raccoon.
There are now raccoon populations in Germany (introduced in 1934) and they are spreading into France and the Netherlands. In 1936, raccoons were released into the former Soviet Union, and commercial trapping began in 1954. By 1964 the number had risen to over 40,000, but due to deep loose snow (which makes winter foraging very difficult) the raccoon seems to only thrive in the Caucus region and Byelorussia.
Most of a raccoon's diet is fruits, berries, nuts and seeds, and they strongly prefer to den near water (average distance 200-400 feet) which is why berry-rich and nut-rich hedgerows near water, corn and soy fields are the most likely location to find them.
In the spring, diet may be supplemented with birds eggs and hatchlings, and in the fall wounded wildlife may also be an important food source. In late fall acorns are important, and in the summer insects. Crustaceans are preferred all the time. Frogs are rarely eaten as they are hard to catch.
Raccoon population densities are extremely variable and depend almost entirely on food. Densities range from a low of 1-3 per square kilometer for North Dakota and Manitoba to 4-14 per square kilometer in Texas chaparral, to 15-20 in the tidewater and marshy areas of Virginia.
Numbers as high as 30 per square kilometer are reported in some swamps and waterfowl areas (where eggs, nestlings and wounded birds are important food supplements), and on the Swan Lake National Wildlife Refuge in Missouri (a marsh), 100 raccoons were removed from a 102 acre tract -- a density level of 250 per square kilometer.
Raccoon home ranges also depend on food density. A typical range is 100 to 250 acres, but they may be as small as five acres to as much as 12,000 acres depending on food availability. Male raccoons always have much larger ranges than females, and almost always leave the area they are born in.
Canine distemper and rabies appear to be the major population control agents for raccoons, with distemper capable of wiping out a raccoon population in an area.
The spread of rabies was greatly accelerated northward in the eastern U.S. in the 1970s due to several thousand raccoons from Florida being used to restock depleted hunting club lands in North Carolina, Virginia, and West Virginia.
Raccoons often move their young from tree dens to ground dens in the spring, when they are 45-65 days old, perhaps so they will not fall out, and perhaps to encourage them to start foraging on their own.