Nature or Nurture?
VOLUME 17, NUMBER 4, SPRING 2003 PDF
is a quarterly publication of the S.C. Sea Grant Consortium—a university-based
network supporting research, education, and outreach to conserve coastal
resources and enhance economic opportunity for the people of South Carolina. To subscribe, email your name and address to Annette Dunmeyer.
Director: M. Richard DeVoe
Director of Communications: Linda
Art Director: Patty
Contributing Writer: Susan
Nature or Nurture?
John H. Tibbetts
happens if we let wildlife go wild?
Alicia Kelly was
napping on her den couch in suburban Charleston one afternoon last October.
Her three-month-old daughter, Patricia, was sitting awake, propped up
and protected in the space between Kelly’s prone body and the couch’s
“I was sound
asleep, lying on my side, baby in front of me,” says Kelly. “Then
I felt something land on me. I thought it was my dog’s front legs,
like she does when she wants me to get up. But I looked and thought, that’s
not Serena. It was a deer; I saw the rack on him. Your mind cannot process
that. He was right there, and he just stared at me, and I stared at him.
I think he was as stunned as I was. I’m sure it was just a few seconds,
but it felt like minutes. Then my baby screamed and that brought me into
reality and I screamed too.”
Panicking, the white-tailed
deer leaped away and ran down a hallway, crashing into walls. “He
didn’t stop after that,” says Kelly. “He ran all over the
house,” looking for an escape route. Kelly grabbed her daughter and
started for the back door.
“Then I saw
him come down the hallway. The deer was heading for the back door too.
He lowered his rack, and just bam! He hit that glass, but he didn’t
Kelly fled the house,
and Charleston County deputies arrived and sedated the seven-point buck.
Because the deer suffered internal injuries, a veterinarian later put
the animal to sleep.
When the deer initially
approached the Kelly home, he probably glimpsed himself in the glass back
door. “It was mating season, and he saw another male deer in reflection,”
says Diane Duss, supervisor of animal control for Charleston County Sheriff
Department. Responding to a competitor, he butted the door. When the lock
and doorframe gave way, the buck skidded across the den rug to the couch
and, rearing, threw his forelegs on Kelly. The glass door rebounded against
the wall and closed behind the buck, cutting off his only escape route.
A bewildered deer
rampaging through a suburban house is a rare occurrence, but it’s
just one example of increasing conflicts between people and wildlife around
the country. Each year, more Americans complain about wild animals that
have lost deep-country habitat and now search for food and shelter in
cities and suburbs.
Many metro areas
have planted trees and protected open spaces, creating habitat for wild
creatures. Homeowners have built ponds and planted flower gardens that
attract wildlife, and they have left out pet food and uncovered garbage
containers. Some creatures have come to depend on us for handouts, adapting
so successfully to human-made environments that they are no longer truly
wild. In the parlance of wildlife biologists, these creatures are called
“subsidized species,” and their populations are growing much
faster than our understanding of them.
Some common nuisance
animals include opossum, crow, rat, squirrel, fox, muskrat, and skunk.
Non-native birds such as house sparrows, street pigeons (also known as
rock doves), and starlings prosper in huge numbers in every major city
in the nation, regardless of climate. “Some species are enormously
successful because they travel around on our coattails,” says Stephen
R. Palumbi, Stanford University biologist. “They tend to be species
that take advantage of the disruptions we cause.”
tolerating a broad range of environmental conditions, thrive in urban
centers. Opportunistic species can transfer from one kind of prey or nesting
site to another if they have to. And some creatures prefer “edges”—they’re
drawn to places like transitions between forests and meadows or subdivisions.
Omnivores, which eat almost anything, adjust particularly well to cities.
Certain species—the super-adapters—have most or all of these
“There are only
three choices a critter has to make (when faced with a human-dominated
environment), and those are to adapt, move, or die,” says Clark E.
Adams, a Texas A&M urban wildlife researcher. “And those that
are adapting cause us big problems.”
The coyote, once
unknown in the eastern United States, is one of the super-adapters, prowling
from the tip of Florida to Alaska, finding habitat in major metros, college
campuses, and golf courses. This omnivorous animal “will go to our
garbage cans or our pets for its food source,” says Adams.
Packs of “coydogs”—coyotes
interbred with dogs—have migrated from suburban Westchester County
to the Bronx’s abandoned lots and even Manhattan’s Central Park.
In ranching areas, coyotes kill thousands of head of livestock, causing
$13.6 million annually in damages.
South Carolina had
no coyotes in 1978; today the animals are ubiquitous, taking up residence
in every county. “I’ve seen coyotes in just about every town
in the South Carolina lowcountry,” says Christian Agnew, a biologist
and part-owner of Wildlife Solutions, Inc., an animal-control enterprise.
A rabid coyote bit Agnew on Sullivan’s Island in November 2000. “The
coyote had to cross the bridge, because coyotes don’t swim for the
heck of it.”
Instead of migrating
north to breed in the Arctic, large numbers of Canada geese now summer
in the United States, dropping excrement mounds that foul golf courses,
parks, and public beaches. Just 20 geese can leave a ton of feces each
in attics and eating out of garbage cans, not only carry rabies but also
roundworm, which can infect humans and cause blindness; there is no known
cure. In places where raccoons proliferate, they can degrade water quality.
As humans alter wildlife
habitats, large predators are also changing their habits. Alligators routinely
show up in southeastern back yards and swimming pools. Hardy and adaptable,
alligators can live and breed in drainage ditches if driven out of their
habitat. Alligator populations—about 100,000 alligators in South
Carolina and an estimated one million gators in Florida—have grown
rapidly, as have alligator attacks. American saltwater crocodiles have
found homes in the cooling canals of Florida’s nuclear power plants.
Bears, it turns out,
have a taste for pet rabbits, goats, and llamas. Two years ago, bears
in New Jersey went on a rampage, killing livestock and pets and breaking
into homes and cars. In South Carolina, bears have wandered out of wildlife
refuges and been hit by cars.
Having grown accustomed
to people in some western communities, mountain lions stroll fearlessly
through back yards and urban paths in the noonday sun. Mountain lions—also
known as cougars, pumas, and panthers—have altered their diet to
raid Alpo and Purina meals. Their populations and attacks are sharply
on the rise. Various mountain-lion subspecies once ranged throughout the
United States, but until recently they have been relegated to western
states and a narrow range in South Florida.
The most dangerous
and expensive fur-bearing animal is one of the mildest-mannered—Bambi.
Deer, in fact, is the number-one vertebrate pest in the United States,
according to the Jack H. Berryman Institute at Utah State University.
At least three-quarters
of a million vehicles collide with white-tailed and mule deer annually
in the United States, injuring about 29,000 people and killing another
200. That makes deer deadlier than sharks, alligators, bears, and rattlesnakes
Wealthy suburbs and
resort communities are ideal habitat for deer, which prefer forested places
with small clearings and low-lying vegetation in early stages of growth.
Applying copious doses of water and fertilizer on their lush gardens,
prosperous suburbanites create tasty treats for deer safe from hunters
exiled to distant forests. “Many of these places have wonderful deer
habitat, but there is nothing but Cadillacs to kill them,” says Jay
Butfiloski, furbearer project biologist with the South Carolina Department
of Natural Resources (DNR). Some homeowners have installed eight-foot
fences to keep out animals they call “rats with hooves.”
Deer menace forest
ecology and wildlife habitat in dozens of states throughout the eastern
third of United States. When deer populations explode, they often strip
woods of native vegetation and eliminate niches for other species. Deer
eat wildflowers, small bushes, and seedlings, displacing smaller animals
from their habitat. “Deer have a huge, huge impact on all the little
components of a forest,” says Steward Pickett, senior scientist at
the Institute of Ecosystem Studies, based in Millbrook, New York.
most large predators and creating edge habitat between forests and lawns,
Americans have created ideal conditions for deer. “It’s a simple
fact that deer do not have the predators they use to have—the red
wolf, the eastern cougar, and the Florida panther,” says Larry Richardson,
wildlife biologist at the U.S. Fish and Wildlife Service Florida Panther
Refuge in Naples, Fla.
The heavily forested,
urbanized Northeast has the most deer collisions, but the South has its
share too. In South Carolina, four people died in deer collisions and
420 were injured during 2001. Last October, two Ohio residents were killed
when their car struck a deer near Myrtle Beach.
Even so, South Carolina’s
one million deer are a major economic asset to rural areas. Deer hunters
annually spend $200 million in retail sales during South Carolina’s
harvest season, which typically reduces herds by nearly a third. “The
positive aspects of a deer population far exceed the negative aspects,”
says Charles Ruth, DNR deer project supervisor. “Rural counties really
rely on the economics of deer hunting.”
the growing drumbeat of conflict with wild creatures?
In a word, sprawl. Seeking the country life, Americans are building homes
farther out in the boondocks and commuting back to jobs at the metropolitan
edge. “In the Southeast, conflicts are all due to urban encroachment,”
says Agnew. “Animals have run out of places to go.”
Growing numbers of
Americans flock to second homes, vacation hideaways, and gated retirement
communities surrounded by woods. These low-density developments are connected
to urban centers by road and highway networks, which break up and isolate
habitat for most large mammals, particularly predators.
Americans with urban
values are moving ever deeper into the countryside, extending the so-called
“urban-wildland interface” or “suburban-rural interface.”
“As that interface
increases, we’re going to have more conflicts between animals and
people,” says Johnny Stowe, DNR heritage preserve manager. “A
lot of people can now afford to live in the country and commute into the
city. But most of these people are urban, with urban values. They get
upset when animals do what animals do naturally, usually barging in to
get something to eat. They are not willing to deal with the animals themselves
and they expect the state or a private contractor to take care of it.
Thirty-five years ago, the people who lived in the countryside were country
people, and if they had a problem with an animal, they took care of it.”
Vast wooded buffers
once surrounded DNR’s coastal wildlife preserves. But urban growth
is squeezing the Lewis Ocean Bay Heritage Preserve near Myrtle Beach and
the Victoria Bluff Heritage Preserve on Hilton Head Island. “Those
preserves,” says Stowe, “will be huge challenges because of
the people around them.”
Some city people
reject measures to control wild animals. The problem is that large predators,
unless they’re hunted or managed wisely, can kill you. “When
we populate an area that is typically (big) cat country,” says Richardson,
“animals get used to seeing us, and after a while they experiment
and try to taste us. This is true of bears, alligators, and cougars. When
animals lose their fear, they become dangerous.”
Many Americans believe
that habitat and wildlife have steadily disappeared throughout the United
States over the past century. But that’s only partly true. In the
eastern third of the United States, forested habitat and many wildlife
populations have improved, but only because conditions were so dreadful
to begin with.
By 1800, the eastern
seaboard’s forests were already aggressively converted to farms and
timber lots. Most Americans were subsistence farmers who conducted “slash
and burn” agriculture. They cut and burned the forest, grew crops
for a few years until the fertility was exhausted, and abandoned the land.
Forests were cleared for shipbuilding products and charcoal for home heating
in towns and cities.
noticed wild-game declines by the 1830s. In England, the crown owned wildlife,
but in the United States it was common property, and anyone was free to
shoot wild animals for food or profit. Market hunters, who sold meat and
feathers to urban markets, began decimating bird and mammal populations.
During the nineteenth
century, agriculture for international markets intensified, particularly
in the South. On the eve of the Civil War, there were tens of thousands
of small farms and hundreds of giant cotton plantations in the Carolinas.
King Cotton’s reign continued long after Reconstruction, though southern
farmers and planters drew lower profits. South Carolina’s cotton
agricultural output more than doubled between 1860 and 1890. Prices for
cotton, however, fell. Northern railroad syndicates controlled transportation
networks and price mechanisms for southern commodities.
To survive, farmers
overworked the land, using heavy doses of fertilizer and tilling marginal
soils, causing severe erosion. Meanwhile, farmers and logging companies
cut down vast forests east of the Mississippi River, and commercial hunting
By 1900, many wildlife
species neared extinction, including white-tailed deer, wild turkey, and
black bear. In response, conservationists lobbied to outlaw hunting of
threatened species and then slowly nurtured them back in some areas by
restocking, setting bounties on predators, and catch-limits for hunters
and trappers. Game-conservation laws aided some species but harmed others.
Predators such as the coyote and cougar were hunted out of the South and
East, and the red wolf was driven almost to extinction.
Then suddenly the
southern agricultural economy fell apart. In the 1920s, the boll weevil
and a long drought crushed U.S. cotton agriculture. About 40 percent of
South Carolina’s 19 million acres were so exhausted that they were
declared “destroyed” in 1934. Hungry rural people killed wild
creatures for food, and many game populations struggled.
Farmers during the
nineteenth century fled New England’s rocky soils for western farms
or factory jobs in towns and cities. The South followed a similar pattern
in the 1920s and ‘30s. Tens of thousands of black farmers left South
Carolina, and many white farmers gave up too.
quickly returned to forest. Since then, the eastern third of the United
States has been home to one of the world’s most remarkable reforestations.
In a book reissued in 2002, Douglas MacCleery of the U.S. Forest Service
describes the eastern woodlands’ comeback: “By the 1960s and
1970s, the pattern of forest, field, and pastures (in the Appalachians
and in many other areas of the South and the East) was similar to that
prior to 1800.”
That is, the extent
of forest and agricultural land in many parts of the South and East in
Vietnam War-era America was comparable to that when George Washington
served as U.S. president.
During the twentieth
century, rural population drain, agricultural stagnation, the modern conservation
movement, and hunting regulations set the stage for an extraordinary rebirth
for some wildlife species in the eastern third of the United States. Several
thousand white-tailed deer roamed South Carolina in 1900. This population
grew to 30,000 to 40,000 by the 1960s—when it grew exponentially
to a million by the late 1990s, says Ruth. The wild turkey was virtually
extinct during the Depression; now four million inhabit eastern and southern
Yet few modern forests
provide the rich habitat they once did, Pickett points out. Many eastern
and southern forests are immature in ecological function, lacking the
complexity found in more mature woodlands. After logging, the forest canopy
grows back fairly quickly. But the intricate, complex groundcover—wildflowers,
lichens, mushrooms, and small bushes—don’t return for a much
longer period. Nor do the animals that rely on specialized groundcover.
This is particularly true of the South Carolina coastal plain’s pine
plantations, which replaced biodiversity-rich longleaf pine forests.
forests may look great,” says Pickett, “but they often have
a very low biodiversity structure. Just because we have all these forests
doesn’t mean we have all this habitat.”
Humans today have
unprecedented influence on the future of wild creatures. Either on purpose
or by accident, we often determine which species survive and which fade
into the background or face extinction. Our manipulations of the environment
alter animals’ behaviors and sometimes even their evolutionary tracks.
We could be the world’s
dominant evolutionary force, argues Palumbi, the Stanford University biologist.
With applications of antibiotics and pesticides, intense commercial fishing,
and species introductions, people have caused extremely swift evolutionary
changes in bacteria, insects, and wild fish. Under intense harvesting
pressure, for example, pink salmon have rapidly evolved smaller bodies.
The larger fish were caught in nets, causing a genetic change so that
new generations grow more slowly.
and wild fish reproduce rapidly and in large numbers, so generations of
change can be readily observed, and natural selection in the wild can
be documented. These creatures rely on genetically based adaptation mechanisms
to cope with new conditions.
Land animals, by
contrast, have relatively large brains, which offer mechanisms other than
genetics to confront challenges. Instead of genetic evolution alone, terrestrial
animals can evolve behaviorally. “Cultural behavior can be learned
within a group,” says Palumbi, “and that behavior can be passed
down like a cultural legacy from generation to generation.”
A raccoon routinely
begging for food at someone’s back porch soon brings along her young,
which learn to beg too. If this behavior is rewarded long enough, it is
passed down culturally, says Palumbi.
Mountain lions and
other large predators also learn quickly—too quickly—about friendly,
curious humans fascinated by big cats. “We should never attempt to
associate with them,” says Richardson. “Every time they see
us, they should run. When they stop running and start walking toward us,
we’re in trouble.”
But as humans have
continued dominion over the natural world, the creatures most likely to
survive have been those attuned culturally to our habits and tastes. A
few species, such as raccoon and opossum, may have even lost some of their
feral—or wild—instincts. “Some of these animals are becoming
more like commensals”—like rats and mice that rely on and live
in close proximity to humans, says Greg Yarrow, a Clemson University wildlife
It’s not uncommon
for such species to alter their behaviors to a degree that they begin
adapting physiologically. “Some animals reproduce differently in
urban environments, with more litters per year and larger litters,”
Americans have encouraged
booming populations of nuisance species, yet many of us feel uneasy taking
steps to control them.
Beginning in the
1960s, some environmentalists began to view any human management of nature
as destructive, and animal-rights groups condemned killing of animals
for sport or to manage wildlife populations. In recent years, animal-rights
activists have thwarted efforts by some localities to kill white-tailed
deer in urban and suburban areas.
As a result, some
wildlife managers have tried to control nuisance deer using various types
of fertility control. Some attempts at fertility control have shown promise,
but these have generally focused on small numbers of deer in isolated
settings. Until a researcher develops an effective long-term fertility-control
method that is easy to use, hunters will continue to provide the best
opportunity to control herds. “Killing deer is currently the best
management tool,” says Ruth. “Yet some people say, ‘Don’t
South Carolina hunters
have successfully controlled deer herds in rural parts of the state. South
Carolina has one of the least restrictive deer-hunting regulatory structures
in the nation, including seasons, bag limits, and methods.
But hunting isn’t
practical in urbanized areas, particularly along the coast. Hunters don’t
want to shoot guns near houses, and city ordinances prohibit discharging
firearms. Now some coastal residents complain about abundant deer, while
their neighbors want to protect them. “In many coastal areas where
there is development, we don’t hunt anymore, so the deer herds get
tremendous,” says Priscilla M. Wright, DNR wildlife assistance coordinator.
After a protracted
lawsuit by animal-welfare activists, DNR and the managers of the gated
community Sea Pines on Hilton Head Island are proceeding with a deer-management
program to kill some animals with sharpshooters.
Perhaps top predators—such
as coyote, wolf, bobcat, and cougar—should be further encouraged
or reintroduced to prevent small predators and herbivores from getting
out of control, some experts say. Red wolves have been reintroduced in
North Carolina, and gray wolves have been re-established in the Northern
Coyotes, which proliferate
without direct help from man, could already be culling deer herds along
some suburban-rural edges. Human and coyote populations have grown rapidly
during the past 15 years in New York’s Hudson Highlands 50 miles
north of New York City, a popular second-home and weekend destination.
But, surprisingly, deer populations have not increased in comparable numbers.
Scientists theorize that coyotes are preying on very young deer, especially
fawns less than a few months old.
“Now that deer
are becoming a suburban problem, the coyotes might actually help to maintain
ecological health,” says Fred Koontz, director of the New York Bioscape
Initiative, a research and education project based in Palisades, New York.
“The suburban-rural interface is where you’ll likely have bigger
concentrations of coyote,” says Koontz, “and it’s at these
interfaces where coyotes could play a role in balancing the deer populations.”
Mountain lions meanwhile
are steadily migrating from western states to the Midwest, attracted by
vast numbers of deer. Confirmed lion sightings or their roadside carcasses
have been found in Nebraska, Kansas, North Dakota, Iowa, and Minnesota.
you will see puma in South Carolina,” says Paul Beier, a wildlife
ecologist at Northern Arizona University, who has extensively studied
It might take 50
years or more for mountain lions to migrate naturally to South Carolina,
or five to 10 years if the Florida panther is reintroduced into northern
Florida under a proposed U.S. Fish and Wildlife plan. Environmentalists
and resource managers have hoped to return the panther to its historic
range in the South, which includes the coastal plain of South Carolina
between Savannah and Charleston and the western third of the state.
More mountain lions
in the South and East would diminish deer numbers, says Beier. “Most
attempts to model the dynamics suggest that deer herds are probably 10
percent to 25 percent lower with the top predator in the system. There
would still be a lot of deer left for hunters and wildlife viewers.”
Top predators help
preserve ecosystem functions and contribute to richer biodiversity. Mountain
lions not only limit overabundant herbivores, which can destroy native
plants, but these large cats also devour smaller predators like raccoons,
which feast on songbird eggs and thus suppress some bird populations.
Mountain lions, of
course, are dangerous if people are careless around them. As author Anne
Matthews points out in a recent book: “For a hungry young mountain
lion, humans and deer pose similar problems in hunting: same size, same
weight, same tendency to bolt when confronted. But deer run faster.”
Richardson, the Florida
panther expert, argues that big cats can be safely integrated into places
in the South and the East where sufficient habitat has been preserved.
The Florida panther lives without incident in South Florida’s remaining
wild areas adjacent to densely populated cities.
Still, mountain lions
must be hunted or otherwise managed to remind them that humans are dangerous.
“We need to keep these animals wild,” says Richardson. “When
they get used to us, we start having troubles. That’s why wild areas
are so important. Wild areas are for our protection as much as for the
That’s the paradox
of the modern relationship between humans and wild creatures. For wildness
to thrive, people must manage it intensively, recreating or sustaining
natural processes and functions. Leaving wildness to its own devices usually
means that it will disappear—or turn around and bite us.
Follow a few simple
rules to avoid conflicts with most nuisance species, says Priscilla M.
Wright, S.C. Department of Natural Resources wildlife assistance coordinator.
put out food for wildlife. “I can’t tell you how many people
put out food for foxes,” says Wright. “People think they’re
cute and that the poor things don’t have anywhere to get food. But
foxes do carry rabies.” If you put out food, you’re encouraging
young animals to migrate to where people live, and that’s cruel,
she says. “You’re taking away the animals’ ability to take
care of themselves.”
Second, put garbage
cans behind a locked door or strap down garbage lids with bungee cords,
so raccoons can’t get to them.
with native plants to discourage deer invasions. Consider using pine straw
instead of planting peonies and other plants that deer
prefer to eat.
Many species of hawks,
owls, eagles, and falcons are generalists, which means they can adapt
quickly when one source of food disappears or when nesting sites are disrupted.
raptors’ habitat) don’t have to be fatally disruptive,”
says James D. Elliott, Jr., executive director of the S.C. Center for
Birds of Prey. “It’s a matter of understanding the ecology of
the birds you’re dealing with. Raptors can adapt, but it’s a
question of whether you’re making changes at a crucial time in their
nesting and breeding cycle. The scale and pace of development can be too
large and fast, shocking the population, so the birds don’t have
a chance to modify their behavior. We often don’t allow time for
them to adjust.”
Many raptors can
adapt to dramatic changes to their environment, but only if the changes
occur outside nesting and breeding schedules. Thus a developer can cut
down an historically favored nest site if this change happens when the
birds are not breeding, so the birds have time to find another place,
Some raptors are
so adaptable that they thrive in the nation’s biggest cities. In
1970, the peregrine falcon was an endangered species, with only 300 pairs
nationwide. Now falcons nest and hunt in New York City, Baltimore, Chicago,
Seattle, and other cities, swooping among high buildings to catch pigeons.
But raptors with
specialized feeding or nesting requirements are struggling. Take the snail
kite, which eats freshwater snails in Florida. When swamps are drained,
the freshwater snails disappear, and the snail kite cannot switch to another
food source, says Elliott. Now the snail kite is classified as endangered
in Florida. Other raptors that have lost population due to habitat loss
include the southeastern American kestrel, the spotted owl, and the burrowing
of urban ecology
once believed that the only environments worth studying were remote and
“pristine,” untouched by human hands. Ecologists ignored urban
areas except as places where people had destroyed nature.
But this began to
change in the mid-1970s, when scientists began acknowledging that humans
had altered virtually every environment in the continental United States
by hunting, harvesting, ranching, and farming. “All of these landscapes
were formed by fire, cattle, people of different cultures,” says
Christine Alfsen-Norodom, the coordinator of Columbia University and UNESCO’s
joint program on the biosphere and society. Today, the United States “is
heavily impacted by humans from coast to coast.”
In other words, human
influences on nature are a matter of degree, and people are embedded in
all natural processes. Such ideas led some scientists to explore a new
frontier of research: urban ecology.
are surprisingly rich biologically. For example, bird diversity in the
Phoenix metro area is actually higher than that in the surrounding desert,
as is total bird abundance. Many bird species are attracted to the city
where water and other resources are more consistently available than in
the desert. Birds especially prefer sewage treatment plants and detention
basins, where plant productivity flourishes.
the number of species (in a given place) is not that instructive,”
says Steward Pickett, senior scientist at the Institute of Ecosystem Studies,
based in Millbrook, New York, and project director of the National Science
Foundation’s Long Term Ecological Research Program (LTER) in Baltimore.
The agency is supporting the nation’s two major, interdisciplinary
urban-ecology studies in Phoenix and Baltimore.
by itself doesn’t mean all that much,” says Pickett. “You
really have to know what the species are and what the species do, and
that’s the hard part of ecology.”
In both the Baltimore
and Phoenix metro areas, non-native nuisance species predominate, according
to LTER research. Two hundred bird species have been documented in Phoenix,
but one-quarter of them are exotics like house sparrows, starlings, and
rock doves. “A few of these urban specialists are very efficient
at using resources of the city,” says Madhusudan Katti, a post-doctoral
research associate at Arizona State University. “They are more flexible
and can out-compete native species.”
environments are altering many birds’ physiology. A bird’s hormonal
clock coincides breeding with warmer weather and longer spring days so
that newborns arrive at times of greater food availability. The urban
environment, however, is altering these hormonal clocks. Fossil-fuel burning
increases local temperatures in large metro areas, creating microclimates
where spring starts sooner. Some bird species have begun their spring
breeding earlier in the city than in the desert, and their breeding seems
to last longer. Some species breed more than once each year in urbanized
places, so they build up higher densities there.
But “not all
bird species are capable of altering their reproductive systems”
to accommodate urban living, says Katti. “Some birds have hormonal
systems that are very tightly coupled with day length,” so they are
less flexible and therefore have difficulty competing in the city. “The
ones that do well are more flexible.” Meanwhile, the birds that lack
flexibility fade in population, at least in urban places.
Bears in the Backyard,
Deer in the Driveway. Washington, D.C.: International Association of Fish
and Wildlife Agencies, 1999.
Resolving Human-Wildlife Conflicts: The Science of Wildlife Damage
Management. Boca Raton, Fla.: Lewis Press, 2002.
Harden, Blaine. “Deer
Draw Cougars Ever Eastward.” New York Times, Nov. 12, 2002.
W. American Forests: A History of Resiliency and Recovery. Durham,
N.C.: Forest History Society, 2002.
Matthews, Anne. Wild
Nights: Nature Returns to the City. New York: North Point Press, 2001.
McKibben, Bill. “An
Explosion of Green.” Atlantic Monthly, April 1995.
Paige, L.C. America’s
Wildlife: The Challenge Ahead. Washington, D.C.: International Association
of Fish and Wildlife Agencies, 2000.
R. The Evolution Explosion: How Humans Cause Rapid Evolutionary Change.
New York: Norton, 2001
Reven, Andrew C.
“Out of Control, Deer Send Ecosystem into Chaos.” New York
Times, Nov. 12, 2002.
Ecological Research Program:
Long-Term Ecological Research Program:
Extension Wildlife Program: