RODENTS: Roof Rats
Fig. 1. Roof rat, Rattus
Damage Prevention and Control Methods
Many control methods are
essentially the same for roof rats as for Norway rats.
The roof rat (Rattus
rattus, Fig. 1) is one of two introduced rats found in
the contiguous 48 states. The Norway rat (R. norvegicus)
is the other species and is better known because of its
widespread distribution. A third rat species, the
Polynesian rat (R. exulans) is present in the Hawaiian
Islands but not on the mainland. Rattus rattus is
commonly known as the roof rat, black rat, and ship rat.
Roof rats were common on early sailing ships and
apparently arrived in North America by that route. This
rat has a long history as a carrier of plague.
Three subspecies have been
named, and these are generally identified by their fur
color: (1) the black rat (R. rattus rattus Linnaeus) is
black with a gray belly; (2) the Alexandrine rat (R.
rattus alexandrinus Geoffroy) has an agouti (brownish
streaked with gray) back and gray belly; and (3) the
fruit rat (R. rattus frugivorus Rafinesque), has an
agouti back and white belly. The reliability of using
coloration to identify the subspecies is questionable,
and little significance can be attributed to subspecies
differentiations. In some areas the subspecies are not
distinct because more than one subspecies has probably
been introduced and crossbreeding among them is a common
occurrence. Roof rats cannot, however, cross with Norway
rats or any native rodent species.
Some of the key
differences between roof and Norway rats are given in
Table 1. An illustration of differences is provided in
figure 2 of the chapter on Norway rats.
Table 1. Identifying
characteristics of adult rats.
Roof rats range along the
lower half of the East Coast and throughout the Gulf
States upward into Arkansas. They also exist all along
the Pacific Coast and are found on the Hawaiian Islands
(Fig. 2). The roof rat is more at home in warm climates,
and apparently less adaptable, than the Norway rat,
which is why it has not spread throughout the country.
Its worldwide geographic distribution suggests that it
is much more suited to tropical and semitropical
climates. In rare instances, isolated populations are
found in areas not within their normal distribution
range in the United States. Most of the states in the US
interior are free of roof rats, but isolated
infestations, probably stemming from infested cargo
shipments, can occur.
Roof rats are more aerial than Norway rats in their
habitat selection and often live in trees or on
vine-covered fences. Landscaped residential or
industrial areas provide good habitat, as does riparian
vegetation of riverbanks and streams. Parks with natural
and artificial ponds, or reservoirs may also be
infested. Roof rats will often move into sugarcane and
citrus groves. They are sometimes found living in rice
fields or around poultry or other farm buildings as well
as in industrial sites where food and shelter are
Roof rats frequently enter
buildings from the roof or from accesses near overhead
utility lines, which they use to travel from area to
area. They are often found living on the second floor of
a warehouse in which Norway rats occupy the first or
basement floor. Once established, they readily breed and
thrive within buildings, just as Norway rats do. They
have also been found living in sewer systems, but this
is not common.
The food habits of roof
rats outdoors in some respects resemble those of tree
squirrels, since they prefer a wide variety of fruit and
nuts. They also feed on a variety of vegetative parts of
ornamental and native plant materials. Like Norway rats,
they are omnivorous and, if necessary, will feed on
almost anything. In food-processing and storage
facilities, they will feed on nearly all food items,
though their food preferences may differ from those of
Norway rats. They do very well on feed provided for
domestic animals such as swine, dairy cows, and
chickens, as well as on dog and cat food. There is often
a correlation between rat problems and the keeping of
dogs, especially where dogs are fed outdoors. Roof rats
usually require water daily, though their local diet may
provide an adequate amount if it is high in water
Control methods must
reflect an understanding of the roof rat’s habitat
requirements, reproductive capabilities, food habits,
life history, behavior, senses, movements, and the
dynamics of its population structure. Without this
knowledge, both time and money are wasted, and the
chances of failure are increased.
Unfortunately, the rat’s
great adaptability to varying environmental conditions
can sometimes make this information elusive.
The young are born in a
nest about 21 to 23 days after conception. At birth they
are hairless, and their eyes are closed. The 5 to 8
young in the litter develop rapidly, growing hair within
a week. Between 9 and 14 days, their eyes open, and they
begin to explore for food and move about near their
nest. In the third week they begin to take solid food.
The number of litters depends on the area and varies
with nearness to the limit of their climatic range,
availability of nutritious food, density of the local
rat population, and the age of the rat. Typically, 3 or
more litters are produced annually.
The young may continue to
nurse until 4 or 5 weeks old. By this time they have
learned what is good to eat by experimenting with
potential food items and by imitating their mother.
Young rats generally
cannot be trapped until about 1 month old. At about 3
months of age they are completely independent of the
mother and are reproductively mature.
Breeding seasons vary in
different areas. In tropical or semitropical regions,
the season may be nearly year-round. Usually the peaks
in breeding occur in the spring and fall. Roof rats
prefer to nest in locations off of the ground and rarely
dig burrows for living quarters if off-the-ground sites
Rats usually begin
searching for food shortly after sunset. If the food is
in an exposed area and too large to be eaten quickly,
but not too large to be moved, they will usually carry
it to a hiding place before eating it. Many rats may
cache or hoard considerable amounts of solid food, which
they eat later. Such caches may be found in a dismantled
wood pile, attic, or behind boxes in a garage.
When necessary, roof rats
will travel considerable distances (100 to 300 feet [30
to 90 m]) for food. They may live in the landscaping of
one residence and feed at another. They can often be
seen at night running along overhead utility lines or
fences. They may live in trees, such as palm, or in
attics, and climb down to a food source. Traditional
baiting or trapping on the ground or floor may intercept
very few roof rats unless bait and/or traps are placed
at the very points that rats traverse from above to a
food resource. Roof rats have a strong tendency to avoid
new objects in their environment and this neophobia can
influence control efforts, for it may take several days
before they will approach a bait station or trap.
Neophobia is more pronounced in roof rats than in Norway
rats. Some roof rat populations are skittish and will
modify their travel routes and feeding locations if
severely and frequently disturbed. Disturbances such as
habitat modifications should be avoided until the
population is under control.
Rats rely more on their
keen senses of smell, taste, touch, and hearing than on
vision. They are considered to be color-blind,
responding only to the degree of lightness and darkness
They use their keen sense
of smell to locate and select food items, identify
territories and travel routes, and recognize other rats,
especially those of the opposite sex. Taste perception
of rats is good; once rats locate food, the taste will
determine their food preferences.
Touch is an important
sense in rats. The long, sensitive whiskers (vibrissae)
near their nose and the guard hairs on their body are
used as tactile sensors. The whiskers and guard hairs
enable the animals to travel adjacent to walls in the
dark and in burrows.
Roof rats also have an
excellent sense of balance. They use their tails for
balance while traveling along overhead utility lines.
They move faster than Norway rats and are very agile
climbers, which enables them to quickly escape
predators. Their keen sense of hearing also aids in
their ability to detect and escape danger.
The social behavior of
free-living roof rats is very difficult to study and, as
a result, has received less attention than that of
Norway rats. Most information on this subject comes from
populations confined in cages or outdoor pens.
Rats tend to segregate
themselves socially in both space and time. The more
dominant individuals occupy the better habitats and feed
whenever they like, whereas the less fortunate
individuals may have to occupy marginal habitat and feed
when the more dominant rats are not present.
Knowledge is limited on
interspecific competition between the different genera
and species of rats. At least in some parts of the
United States and elsewhere in the world, the methods
used to control rats have reduced Norway rat populations
but have permitted roof rats to become more prominent,
apparently because they are more difficult to control.
Elsewhere, reports indicate that roof rats are slowly
disappearing from localized areas for no apparent
It has often been said
that Norway rats will displace roof rats whenever they
come together, but the evidence is not altogether
Rat densities (numbers of
rats in a given area) are determined primarily by the
suitability of the habitat—the amount of available
nutritional and palatable food and nearby protective
cover (shelter or harborage).
The great adaptability of
rats to human-created environments and the high
fertility rate of rats make for quick recuperation of
their populations. A control operation, therefore, must
reduce numbers to a very low level; otherwise, rats will
not only reproduce rapidly, but often quickly exceed
their former density for a short period of time.
Unless the suitability of
the rat’s habitat is destroyed by modifying the
landscaping, improving sanitation, and rat-proofing,
control methods must be unrelenting if they are to be
and Damage Identification
Nature of Damage
In food-processing and
food-storage facilities, roof rats do about the same
type of damage as Norway rats, and damage is visually
hard to differentiate. In residences where rats may be
living in the attic and feeding outdoors, the damage may
be restricted to tearing up insulation for nesting or
gnawing electrical wiring. Sometimes rats get into the
kitchen area and feed on stored foods. If living under a
refrigerator or freezer, they may disable the unit by
gnawing the electrical wires. In landscaped yards they
often live in overgrown shrubbery or vines, feeding on
ornamentals, vegetables, fruits, and nuts. Snails are a
favorite food, but don’t expect roof rats to eliminate a
garden snail problem. In some situations, pet food and
poorly managed garbage may represent a major food
In some agricultural
areas, roof rats cause significant losses of tree crops
such as citrus and avocados and, to a lesser extent,
walnuts, almonds, and other nuts. They often eat all the
pulp from oranges while the fruit is still hanging on
the tree, leaving only the empty rind. With lemons they
may eat only the rind and leave the hanging fruit
intact. They may eat the bark of smaller citrus branches
and girdle them. In sugarcane, they move into the field
as the cane matures and feed on the cane stalks. While
they may not kill the stalk outright, secondary
organisms generally invade and reduce the sugar quality.
Norway rats are a common mammalian pest of rice, but
sometimes roof rats also feed on newly planted seed or
the seedling as it emerges. Other vegetable, melon,
berry, and fruit crops occasionally suffer relatively
minor damage when adjacent to infested habitat such as
Like the Norway rat, the
roof rat is implicated in the transmission of a number
of diseases to humans, including murine typhus,
leptospirosis, salmonellosis (food poisoning), rat-bite
fever, and plague. It is also capable of transmitting a
number of diseases to domestic animals and is suspected
in the transference of ectoparasites from one place to
The nature of damage to
outdoor vegetation can often provide clues as to whether
it is caused by the roof or Norway rat. Other rat signs
may also assist, but be aware that both species may be
present. Setting a trap to collect a few specimens may
be the only sure way to identify the rat or rats
involved. Out-of-doors, roof rats may be present in low
to moderate numbers with little sign in the way of
tracks or droppings or runs and burrows.
There is less tendency to
see droppings, urine, or tracks on the floor in
buildings because rats may live overhead between floors,
above false ceilings, or in utility spaces, and venture
down to feed or obtain food. In food-storage facilities,
the most prominent sign may be smudge marks, the result
of oil and dirt rubbing off of their fur as they travel
along their aerial routes.
The adequate inspection of
a large facility for the presence and location of roof
rats often requires a nighttime search when the facility
is normally shut down. Use a powerful flashlight to spot
rats and to determine travel routes for the best
locations to set baits and traps. Sounds in the attic
are often the first indication of the presence of roof
rats in a residence. When everyone is asleep and the
house is quiet, the rats can be heard scurrying about.
Roof rats are not
protected by law and can be controlled any time with
mechanical or chemical methods. Pesticides must be
registered for rat control by federal and/or state
authorities and used in accordance with label
Prevention and Control Methods
The damage control methods
used for roof rats are essentially the same as for
Norway rats. However, a few differences must be taken
against roof rats, pay close attention to the roof and
roof line areas to assure all accesses are closed. Plug
or seal all openings of greater than 1/2 inch (1.3 cm)
diameter with concrete mortar, steel wool, or metal
flashing. Rodent-proofing against roof rats usually
requires more time to find entry points than for Norway
rats because of their greater climbing ability.
Eliminate vines growing on buildings and, when feasible,
overhanging tree limbs that may be used as travel
Attach rat guards to
overhead utility wires and maintain them regularly. Rat
guards are not without problems, however, because they
may fray the insulation and cause short circuits.
The elimination of food
and water through good warehouse sanitation can do much
to reduce rodent infestation. Store pet food in sealed
containers and do not leave it out at night. Use proper
garbage and refuse disposal containers and implement
exterior sanitation programs. Emphasis should be placed
on the removal of as much harborage as is practical. For
further information see Norway Rats.
vine-covered trees and fences, and vine ground cover
make ideal harborage for roof rats. Severe pruning
and/or removal of certain ornamentals are often required
to obtain a degree of lasting rat control. Remove
preharvest fruits or nuts that drop in backyards. Strip
and destroy all unwanted fruit when the harvest period
In tree crops, some
cultural practices can be helpful. When practical,
remove extraneous vegetation adjacent to the crop that
may provide shelter for rats. Citrus trees, having very
low hanging skirts, are more prone to damage because
they provide rats with protection. Prune to raise the
skirts and remove any nests constructed in the trees. A
vegetation-free margin around the grove will slow rat
invasions because rats are more susceptible to predation
when crossing unfamiliar open areas.
Rats have acute hearing
and can readily detect noises. They may be frightened by
sound-producing devices for awhile but they become
accustomed to constant and frequently repeated sounds
quickly. High-frequency sound-producing devices are
advertised for frightening rats, but almost no research
exists on their effects specifically on roof rats. It is
unlikely, however, they will be any more effective for
roof rats than for Norway rats. These devices must be
viewed with considerable skepticism, because research
has not proven them effective.
Lights (flashing or
continuously on) may repel rats at first, but rats will
quickly acclimate to them.
Products sold as general
animal repellents, based on taste and/or odor, are
sometimes advertised to repel animals, including rats,
from garbage bags. The efficacy of such products for
rats is generally lacking. No chemical repellents are
specifically registered for rat control.
Rodenticides were once
categorized as acute (single-dose) or chronic (multipledose)
toxicants. However, the complexity in mode of action of
newer materials makes these classifications outdated. A
preferred categorization would be “anticoagulants” and
“non-anticoagulants” or “other rodenticides.”
(slow-acting, chronic toxicants). Roof rats are
susceptible to all of the various anticoagulant
rodenticides, but less so than Norway rats. Generally, a
few more feedings are necessary to produce death with
the first-generation anticoagulants (warfarin, pindone,
diphacinone, and chlorophacinone) but this is less
significant with the second-generation anticoagulants (bromadiolone
and brodifacoum). All anticoagulants provide excellent
roof rat control when prepared in acceptable baits. A
new second-generation anticoagulant, difethialone, is
presently being developed and EPA registration is
anticipated in the near future.
A few instances of
first-generation anticoagulant resistance have been
reported in roof rats; although not common, it may be
underestimated because so few resistance studies have
been conducted on this species. Resistance is of little
consequence in the control of roof rats, especially with
the newer rodenticides presently available. Where
anticoagulant resistance is known or suspected, the use
of first-generation anticoagulants should be avoided in
favor of the second-generation anticoagulants or one of
the nonanticoagulant rodenticides like bromethalin or
The older rodenticides, formerly referred to as acute
toxicants, such as arsenic, phosphorus, red squill, and
ANTU, are either no longer registered or of little
importance in rat control. The latter two were
ineffective for roof rats. Newer rodenticides are much
more efficacious and have resulted in the phasing out of
these older materials over the last 20 years.
At present there are three
rodenticides—zinc phosphide, cholecalciferol (vitamin
D3), and bromethalin—registered and available for roof
rat control. Since none of these are anticoagulants, all
can be used to control anticoagulant resistant
populations of roof rats.
Roof rats can be
controlled with the same baits used for Norway rats.
Most commercial baits are registered for both species of
rats and for house mice, but often they are less
acceptable to roof rats than to the other species. For
best results, try several baits to find out which one
rats consume most. No rat bait ingredient is universally
highly acceptable, and regional differences are the rule
rather than the exception.
Pelleted or loose cereal
anticoagulant baits are used extensively in
tamper-resistant bait boxes or stations for a permanent
baiting program for Norway rats and house mice. They may
not be effective on roof rats, however, because of their
usual placement. Bait stations are sometimes difficult
to place for roof rat control because of the rodents’
overhead traveling characteristics. Anticoagulant
paraffin-type bait blocks provide an alternative to bait
stations containing pelleted or loose cereal bait. Bait
blocks are easy to place in small areas and
difficult-to-reach locations out of the way of children,
pets, and nontarget species. Where label instructions
permit, small blocks can be placed or fastened on
rafters, ledges, or even attached to tree limbs, where
they are readily accessible to the arboreal rats.
Some of the
first-generation anticoagulants (pindone and warfarin)
are available as soluble rodenticides from which water
baits can be prepared. Liquid baits may be an effective
alternative in situations where normal baits are not
readily accepted, especially where water is scarce or
where rats must travel some distance to reach water.
In controlling roof rats
with rodenticides, a sharp distinction must be made
between control in and around buildings and control away
from buildings such as in landfills and dumps, along
drainage ditches and streams, in sewer water evaporation
ponds, and in parks. Control of roof rat damage in
agriculture represents yet another scenario.
Distinctions must be made as to which rodenticide
(registered product) to use, the method of application
or placement, and the amount of bait to apply. For
example, only zinc phosphide can be applied on the
ground to control rats in sugarcane or macadamia
orchards, and the sec-ond-generation anticoagulants,
cholecalciferol and bromethalin, can be used only in and
around buildings, not around crops or away from
buildings even in noncrop situations. Selection of
rodenticides and bait products must be done according to
label instructions. Labels will specify where and under
what conditions the bait can be used. Specifications may
vary depending on bait manufacturer even though the
active ingredient may be the same. The product label is
the law and dictates the product’s location of use and
Tracking powders play an important role in structural
rodent control. They are particularly useful for house
mouse control in situations where other methods seem
less appropriate. Certain first-generation
anticoagulants are registered as tracking powders for
roof rat control; however, none of the second generation
materials are so registered. Their use for roof rats is
limited to control within structures because roof rats
rarely produce burrows.
Tracking powders are used
much less often for roof rats than for Norway rats
because roof rats frequent overhead areas within
buildings. It is difficult to find suitable places to
lay the tracking powder that will not create a potential
problem of contaminating food or materials below the
Tracking powders can be
placed in voids behind walls, near points of entry, and
in well-defined trails. Tunnel boxes or bait boxes
specially designed to expose a layer of toxic powder
will reduce potential contamination problems and may
actually increase effectiveness. Some type of clean food
can be used to entice the rats to the boxes, or the
tracking powders can be used in conjunction with an
anticoagulant bait, with both placed in the same
Since roof rats rarely dig
burrows, burrow fumigants are of limited use; however,
if they have constructed burrows, then fumigants that
are effective on Norway rats, such as aluminum phosphide
and gas cartridges, will be effective on roof rats.
Where an entire warehouse may be fumigated for insect
control with a material such as methyl bromide, all rats
and mice that are present will be killed. The fumigation
of structures, truck trailers, or rail cars should only
be done by a licensed pest control operator who is
trained in fumigation techniques. Rodent-infested
pallets of goods can be tarped and fumigated on an
individual or collective basis.
Trapping is an effective
alternative to pesticides and recommended in some
situations. It is recommended for use in homes because,
unlike with poison baits, there is no risk of a rat
dying in an inaccessible place and creating an odor
common wooden snap traps that are effective for Norway
rats are effective for roof rats. Raisins, prunes,
peanut butter, nutmeats, and gumdrops make good baits
and are often better than meat or cat food baits. The
commercially available, expanded plastic treadle traps,
such as the Victor Professional Rat Trap, are
particularly effective if properly located in
well-traveled paths. They need not be baited. Place
traps where they will intercept rats on their way to
food, such as on overhead beams, pipes, ledges, or sills
frequently used as travel routes (Fig. 3). Some traps
should be placed on the floor, but more should be placed
above floor level (for example, on top of stacked
commodities). In homes, the attic and garage rafters
close to the infestation are the best trapping sites.
Pocket gopher box-type
traps (such as the DK-2 Gopher Getter) can be modified
to catch rats by reversing the action of the trigger.
Presently, only one such modified trap (Critter
Control’s Custom Squirrel & Rat Trap) is commercially
available. These kill traps are often baited with whole
nuts and are most useful in trapping rats in trees.
Their design makes them more rat-specific when used
out-of-doors than ordinary snap traps that sometimes
take birds. Caution should be taken to avoid trapping
nontarget species such as tree squirrels.
Wire-mesh, live traps
(Tomahawk®, Havahart®) are available for trapping rats.
Rats that are captured should be humanely destroyed and
not released elsewhere because of their role in disease
transmission, damage potential, and detrimental effect
on native wildlife.
Glue boards will catch
roof rats, but, like traps, they must be located on
beams, rafters, and along other travel routes, making
them more difficult to place effectively for roof rats
than for Norway rats or house mice. In general, glue
boards are more effective for house mice than for either
of the rat species.
Where legal and not
hazardous, shooting of roof rats is effective at dusk as
they travel along utility lines. Air rifles, pellet
guns, and .22-caliber rifles loaded with bird shot are
most often used. Shooting is rarely effective by itself
and should be done in conjunction with trapping or
In urban settings, cats
and owls prey on roof rats but have little if any effect
on well-established populations. In some situations in
which the rats have been eliminated, cats that are good
hunters may prevent reinfestation.
In agricultural settings,
weasels, foxes, coyotes, and other predators prey on
roof rats, but their take is inconsequential as a
population control factor. Because roof rats are fast
and agile, they are not easy prey for mammalian or avian
Economics of Damage and Control
Roof rats undoubtedly
cause millions of dollars a year in losses of food and
feed and from damaging structures and other gnawable
materials. On a nationwide basis, roof rats cause far
less economic loss than Norway rats because of their
There are approximately
30,000 professional structural pest control operators in
the United States and about 70% of these are primarily
involved in general pest control, which includes rodent
control. It is difficult to estimate how much is spent
in structural pest control specifically for roof rats
because estimates generally group rodents together.
avocados, and macadamia nuts are the agricultural crops
that suffer the greatest losses. In Hawaii, annual
macadamia loss has recently been estimated at between $2
million and $4 million.
I wish to acknowledge my
colleague, Dr. Walter E. Howard, for information taken
from his publication The Rat: Its Biology and Control,
Division of Agricultural Sciences, University of
California, Leaflet 2896 (30 pp.), coauthored with R. E.
Marsh. I also wish to express my thanks to Dr. Robert
Timm, who authored the chapter on Norway rats. To avoid
duplication of information, this chapter relies on the
more detailed control methods presented in the chapter
Figure 1 from C. W.
Schwartz and E. R. Schwartz (1981). The Wild Mammals of
Missouri, rev. ed. Univ. Missouri Press, Columbia. 356
Figures 2 and 3 from
Howard and Marsh (1980), adapted by David Thornhill.
For Additional Information
Dutson, V. J. 1974. The association of the roof rat (Rattus
rattus) with the Himalayan blackberry (Rubus discolor)
and Algerian ivy (Hedera canariensis) in California.
Proc. Vertebr. Pest Conf. 6:41-48.
Frantz, S. C., and D. E.
Davis. 1991. Bionomics and integrated pest management of
commensal rodents. Pages 243-313 in J. R. Gorham, ed.
Ecology and management of food-industry pests. US Food
Drug Admin. Tech. Bull. Assoc. Official Analytical Chem.
Howard, W. E., and R. E.
Marsh. 1980. The rat: its biology and control. Div.
Agric. Sci., Publ. 2896, Univ. California. 30 pp.
Jackson, W. B. 1990. Rats
and mice. Pages 9-85 in A. Mallis, ed. Handbook of pest
control. Franzak & Foster Co., Cleveland, Ohio.
Kaukeinen, D. E. 1984.
Resistance; what we need to know. Pest Manage.
Khan, J. A. 1974.
Laboratory experiments on the food preferences of the
black rat (Rattus rattus L.). Zool. J. Linnean Soc.
Lefebvre, L. W., R. M.
Engeman, D. G. Decker, and N. R. Holler. 1989.
Relationship of roof rat population indices with damage
to sugarcane. Wildl. Soc. Bull. 17:41-45.
Marsh, R. E., and R. O.
Baker. 1987. Roof rat control—a real challenge. Pest
Meehan, A. P. 1984. Rats
and mice: their biology and control. Rentokil Ltd. E.
Grinstead, United Kingdom. 383 pp.
Recht, M. A., R. Geck, G.
L. Challet, and J. P. Webb. 1988. The effect of habitat
management and toxic bait placement on the movement and
home range activities of telemetered Rattus rattus in
Orange County, California. Bull. Soc. Vector Ecol.
Thompson, P. H. 1984.
Horsing around with roof rats in rural outbuildings.
Pest Control 52(8):36-38,40.
Tobin, M. E. 1992. Rodent
damage in Hawaiian macadamia orchards. Proc. Vertebr.
Pest Conf. 15:272-276.
Weber, W. J. 1982.
Diseases transmitted by rats and mice. Thomson Publ.,
Fresno, California. 182 pp.
Zdunowski, G. 1980.
Environmental manipulation in roof rat control programs.
Proc. Vertebr. Pest Conf. 9:74-79.
Scott E. Hygnstrom; Robert
M. Timm; Gary E. Larson
PREVENTION AND CONTROL OF
WILDLIFE DAMAGE — 1994
Division Institute of Agriculture and Natural Resources
University of Nebraska -Lincoln
United States Department
of Agriculture Animal and Plant Health Inspection
Service Animal Damage Control