View articles by date | ON SCIENCE Home Page | View articles by topic

The problem of exploding deer populations has no attractive solutions

Few residents of Missouri or Illinois have prospered more in the 20th Century than have our deer. Early in the 20th century white-tailed deer were rare in the midwest. Uncontrolled hunting had reduced their numbers to about 500,000 nationwide, and some states had no deer at all.

In order to protect the remaining deer, laws were past in the 1920s and 30s to restrict hunting, particularly of does (females). This course of action seemed sensible, but ignored a fundamental fact about deer: Deer reproduce quickly. A doe matures at 2 or 3 years, and then typically gives birth to twins each year for 10 or more years.

Any student of biology could have predicted what would happen, what would HAVE to happen, if hunting were severely restricted. Since Malthus and Darwin, biologists have recognized that populations that grow unchecked do not increase in a linear fashion, but exponentially. That is to say, the population does not increase the same amount each year, but rather grows by ever-greater amounts as the babies have babies, like compound interest. A deer herd that has plenty to eat and is not hunted by humans or other predators will double in size every three years!

With the restrictions on hunting, deer populations indeed began to grow. Numbers of white-tailed deer rebounded slowly at first, then more and more quickly. In the last few decades deer numbers have literally exploded, and now exceed 30 million nationwide. There are more deer today in Missouri (an estimated 900,000) and Illinois (an estimated 750,000) than at any time in our nation's history.

Much of the growth in the national deer population has occurred near urban areas. Deer have adapted well to encroaching suburbia, for two reasons:

1. Growth of suburbs. Paradoxically, land development tends to improve deer food supplies. Because the reproduction and survival of deer depend directly upon the quality of the food available to them, the improved food has led to more deer. Deer browse on leaves, and require large quantities of new growth with high nutritional content to maintain normal reproduction. Deer populations forty years ago rarely grew large for the simple reason that most of the trees in an undisturbed forest are old, and only the undergrowth provides suitable food. It is because land development usually involves clearing land that urban development leads to increased deer food supplies. There are far fewer trees, but the trees are new growth, and very munchable. So are garden shrubs. Deer eat very, very well in surburbia. Many residential areas are reporting as many as 200 deer per square mile, three times what a forest will support.

2. Restriction of hunting. Nobody wants someone shooting at deer near their kids. Not surprising, then, much of the area in which deer populations are growing most rapidly has been declared off limits to hunters. Removing their only significant predator - hunters - allows deer populations in suburban areas to grow unchecked.

Anyone who lives in the western parts of Saint Louis County, or anywhere else in the suburbs surrounding St. Louis, knows the result of providing ample food and no hunting: lots of deer.

What should we do to respond to this plague of deer? You can't just "remove" the deer to some forest far from St. Louis, like they are trying to do in Town and Country at a cost of $360 per deer. Why doesn't this humane approach work? Other St. Louis deer from surrounding areas just take their place! Imagine trying to empty people from a prime section of Busch Stadium by physically removing individuals one at a time. You would never get anywhere, because other people would just crowd in. For every deer removed from Town and Country, there are two eager to get in and have a good meal.

There are only two real options for slowing the growth of local deer populations: decrease the birth rate or increase the death rate.

Decreasing the birth rate is certainly the most ethically palatable approach. However, deer birth control has proven impractical. Every female deer must be captured for the first dose, and redarted for each subsequent booster shot. Only in very small isolated populations is this practical. Nor is there any effective oral contraceptive for deer.

This leaves increasing the death rate. On more remote forest land, many states have opted to extend the hunting season, increase the bag limit to four or more animals, and encourage the shooting of antlerless females. In the suburbs, the only approach that has had any success is to thin out the local herds each year with professional sharpshooters or bowhunters. The meat from such culling is usually donated to charity.

No one wants to kill Bambi, but Bambi starving to death is every bit as unpleasant an option, and if the Missouri and Illinois deer herd continues to grow, that is what is going to happen. The deer populations will continue to increase until something limits their growth. At the turn of the century the "something" was limited food (there were few suburbs then) and efficient predators (there was unlimited hunting then). If predators (hunters) don't limit today's deer populations, then the populations will continue to grow until lack of food does.

Number of White-tailed Deer per Thousand Humans (source: Insurance Information Institute, State Wildlife Agencies, US Census Bureau)

Miss 657
W Va 500
Mont 436
Wisc 346
S Car 285
Vt 283
Maine 268
La 236
Texas 234
Minn 219
SD 219
Mich 193
Ky 187
Tenn 184
Kan 181
MO 175
Va 161
Neb 158
Ga 154
NC 143
Iowa 126
PA 17
NH 72
Ill 65
Fla 58
NY 55
Md 47
Del 45
Ohio 44
NJ 23
Conn 23
Mass 12
TI 12

ADAM NOTE: The reason NY and NJ come out so low is that both states have large urban city populations. The suburbs of NY and NJ are among the most deer-dense in the nation.

© Txtwriter Inc.

Txtwriter Home Page | BACKGROUNDERS | ON SCIENCE | Text Books | Book Reviews
This website is the copyright ©1998-2013 of Txtwriter Inc. All rights reserved.