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Examine a thousand quail from hunters' bags, and you'll find that about 80% of them are birds of the year. Think it over. From one October to another, eight out of 10 quail are disappearing, to be replaced by next spring's hatch.
This yearly surplus is where we get our game crop and the predators get their kill. In taking it, neither we nor they are destroying anything that would survive without us.
Wildlife-population fluctuations have had more attention than most people realize. In one major job Paul L. Errington has done field research for more than 25 years in Wisconsin and Iowa. His early work on quail uncovered relationships that apply generally in wild communities.
Especially meaningful was his discovery that the number of birds a given area could winter was definitely limited and surprisingly consistent from one year to the next. It didn't seem to matter how many there were in the fall; by spring, the birds were whittled down to a "carrying capacity" level which was a characteristic of the particular area. And it happened whether enemies were plentiful or not. Quail that had what they needed in food and cover enjoyed relative security. Less lucky birds, skimping along in "slum" situations, took big losses from predators and other hardships.
I once asked Errington something I'd been thinking about. "Why don't mink clean the muskrats out of a marsh? It looks to me as though they could work through the houses and kill them at will."
Paul didn't go for that. "Not at all. A muskrat on his home grounds and in good health can avoid a mink. Sometimes we get big concentrations of rats when conditions are favorable for a couple of seasons, and populations may be cut down to size by a disease we've been studying. Usually the first indication of disease is that the mink are killing a lot more rats."
WHEN PREDATORS ARE UNDERTAKERS
The disease-predation hookup is real, but no biologist would expect predators to kill only diseased animals. The flesh-feeders have a heyday on the occasion of such creature calamities as food failure, bad weather, changing water levels, drought, overcrowding, and other emergency conditions. Such hardships, in effect, lower the supporting capacity of the range, and the predator is more of an undertaker than anything else.
As many a field man has seen, conditions on the land are the key to production. In a good piece of range, a fairly high density of animals can live in reasonable safety; but in another area, the same number would be top-heavy, and part of them would go the way of all surpluses. There may be little security of any kind in a really poor range where the game-prey animal is just hanging on. Often enough that's where someone will try to stock coop-reared pheasants, and we'll have another demand for fox control.
There are all sorts of local conditions, and you can find a sample to prove nearly anything?if you want to. Consider what might be done with a situation encountered by David A. Arnold in his fox project for the Michigan Game Division.