Wolf Management in the 21st Century:
From Public Input to Sterilization
L. David Mech, Steven H. Fritts,
Michael E. Nelson*
Fig. 1. Trend in numbers of wolves trapped by a federal
livestock depredation-control program in Minnesota
Methods Of Alleviating Wolf Damages
for losses to wolves
possible role of vasectomy
Table 1. Pack sizes of vasectomized wolves in the Superior
National Forest, Minnesota after vasectomies.
Human-population increase and land development portend
increasing conflict with large predators. Concurrently, changes and
diversification of human attitudes are bringing increased disagreement about
wildlife management. Animal-rights advocacy resulting from urbanization of human
populations conflicts with traditional wildlife management. These forces focus
more on wolves than on other wildlife because of strong public and media
interest in wolves. Thus wolf management in the future will come under even
greater public scrutiny, involve more public input, and may have greater
restrictions imposed on it. This will lead to increased complexity in wolf
management including more zoning, more experimentation with lethal and
non-lethal capture techniques and alternate methods of alleviating damage to
pets, livestock, and large ungulate herds, and greater public and private
subsidy of wolf damage. One form of non-lethal control of wolf populations that
may hold some promise is direct sterilization of males to reduce the biotic
potential of the wolf population. Experimental vasectomy of five wild male
wolves from four packs in Minnesota indicates that sterile males will continue
to hold mates and territories, which would be necessary if sterilization is to
be a viable technique for assisting with population control. If sterile males
held territories but failed to produce pups, such territories might contain only
about a third the number of wolves as fertile pack territories. Because wolves
are long-lived in unexploited populations and their territories are large,
direct sterilization of relatively few animals each year might significantly
As the twentieth century draws to a close, the gray wolf Canis lupus
is more widely distributed in Europe and in the contiguous 48 United States than
it has been for more than three decades (Promberger and Schroder 1993, Mech et
al. 1994). The species has made a comeback in Italy, Spain, Portugal, and
Poland, is increasing in Finland, Norway and Sweden, and has begun to colonize
France and Germany. In the U.S., the wolf has recolonized northern Wisconsin,
Michigan, and Montana and is attempting to recolonize North and South Dakota,
Washington, Idaho, and Wyoming. A reintroduction program is planned for central
Idaho and Yellowstone National Park (Wyoming), and an Environmental Impact
Statement is being prepared for the possibility of reintroducing the Mexican
gray wolf to the southwestern U.S. Meanwhile, Minnesota, Canada, Alaska, much of
Asia, eastern Europe, and the Mideast still harbor high numbers of wolves (Ginsburg
and MacDonald 1990).
At the same time, the human population continues to increase, and land use by
humans is intensifying in most areas. The potential for conflict between wolves
and humans is increasing, especially in the more accessible regions, where
wolves were exterminated three to four decades ago and are now returning. For
example, between 1988 and 1993 the number of wolves killed in Minnesota by
depredation control personnel increased 127% (Fig. 1). In Spain, annual
compensation for damages by wolves now totals one million U.S. dollars (Vila et
al. 1993). Because wolves are prolific (Mech 1970) and can disperse distances
exceeding 800 km (Fritts 1983, Gese and Mech 1991), conflicts will probably
continue to increase, and intensive wolf management will become increasingly
Fig. 1. Trend
in numbers of wolves trapped by a federal government
livestock depredation-control program in Minnesota
(Fritts et al. 1992,
B. Paul, 1994, personal communication).
An important new factor that will also greatly complicate wolf management is
the decrease in proportion of the public that hunts, traps, or raises livestock
and the increase in animal welfare and animal rights sentiment. Such changes
will make lethal wolf control less acceptable. Furthermore, public sentiment
against the steel-jawed foot trap and the neck snare further hinder wolf control
and will become more important in the future. Because poison also has been
banned or is socially unacceptable in many countries, the number of techniques
available for lethal control of wolves has been greatly reduced (Cluff and
Alternate Methods Of Alleviating Wolf Damages
In addition to wolf control, other techniques to minimize damage from wolves
might be instituted such as the electric fence (Dorrance and Bourne 1980, Eles
1986, Nass and Theade 1988), and guarding dogs (Coppinger 1987, Coppinger and
Coppinger 1994) both of which have some value in certain situations. Aversive
conditioning has also been tested, with few definitive results (Guastavson and
Nicolaus 1987). However, neither these nor any other technique is yet available
to consistently protect livestock from wolf depredations on extensive open
ranges, and none is even being tested. Thus in most areas, lethal wolf control
will still be necessary.
Where wolf populations are low and each individual is important to population
recovery but some depredations on domestic animals are occurring, translocation
of problem animals may be useful. However, based on experiments in Minnesota,
wolves must be moved at least 70 km or they will return to their capture area
(Fritts et al. 1984). Where wolf populations are large and secure, translocation
has little value to the population.
Losses to Wolves
Compensation for livestock losses is another method of dealing with wolf
depredations. However, it really is only useful when wolf populations are low
and attempts are being made to restore the species to an area. After a large
enough population is established, compensation payments only serve to subsidize
the wolves. If the compensation program is successful, payments will only
increase. At some point the public may object to its funds going to subsidize
increasing numbers of wolves. In such cases, private organizations may choose to
make the compensation payments as is now being done in the western United States
(Fischer et al. 1994). Conceivably, payments by private individuals or
organizations may become more important in the future.
As wolf-human conflict intensifies and greater restrictions are placed on wolf
control, wolf management will have to become increasingly efficient. This will
probably mean tailoring wolf management to the needs of specific areas, and
intensification of zoning. Zoning can be useful to wolf management in two ways.
First, certain areas can be set aside where wolves can either be allowed to live
or prevented from inhabiting. Or in certain zones wolves could be allowed to
reach only a certain density before being subject to control. Secondly, areas
can be zoned in such a way that at certain times lethal wolf control can be
applied to some zones but not to others. Both approaches to zoning have been
applied to northern Minnesota wolf range since 1978 (Fritts et al. 1992). Wolves
are allowed to inhabit some zones without being subject to control, whereas they
are subject to control in other zones. However even in zones where control is
allowed, certain criteria must be met before control is initiated. In this way,
a legally protected population of wolves numbering from 1,200 to 2,000 (Fuller
et al. 1992) has been maintained without much public discontent for about
200,000 USD per year, 75% of which goes toward lethal wolf control, and the rest
towards compensation for livestock losses.
On the other hand, if wolf-human conflicts, public payments for compensation, or
illegal taking of wolves reach high enough levels, some of the restricted or
banned methods of lethal wolf control may be reinstated. Alternatively,
techniques such as public hunting, which may also be publicly disapproved of,
may seem more acceptable than the use of poison, steel-foot traps, or illegal
taking. Three such cycles of protection and persecution have been documented for
the wolf in Poland (Okarma 1992).
Because the Minnesota wolf population has saturated most of the wilderness
and continues to increase, more wolves are currently inhabiting agricultural
lands. Thus depredation control costs and compensation costs continue to rise.
For example, when wolf numbers increased from about 1,600 in 1988 (Fuller et al.
1992) to probably 2,000 in 1994, the number of depredation complaints, the
amount of compensation paid, and number of wolves trapped for depredation
control increased disproportionately (Fig.
1). Presumably in Minnesota, Spain, Italy, and elsewhere, the public
eventually will object to the cost of subsidizing wolves and demand wolf
population reduction in certain areas.
One of the most effective approaches to wolf management is to educate the public
about wolf biology and management. Misconceptions about wolves, both negative
and positive, tend to cause people to hold extreme views about wolf protection.
Generally, agricultural cultures in current or recent wolf range tend to view
wolves far more negatively than urbanites, who tend to deify the animal and
object to wolf control. Promoting accurate, objective information about the wolf
will be a constant need in the 21st century just as it is at present. If
successful, however, it will greatly facilitate ecologically sound wolf
Wolf control or reduction can be done by the government or the public or some
combination. If the control involves the public, it could be by sport hunting or
trapping with various regulations such as seasons, zones, methods of capture,
limits, etc. All these methods have been used in the past either on wolves or
other species and they will have relevance in the future depending on various
Possible Role of Vasectomy
Another possibility of controlling wolf populations, at least in certain areas,
could be through the use of vasectomy to reduce a population's reproductive
potential. Because most wolf packs contain a single breeding pair (Mech 1970,
Harrington et al. 1982) and breeding pairs hold territories (Rothman and Mech
1979), sterilizing members of each of several pairs could result in an
attenuated wolf population. The only practical method of sterilizing wild wolves
at present is by live-trapping the males and vasectomizing them.
The question remains, however, as to whether sterilized pairs lacking pups
would continue to hold territories. Intact pairs, of course, hold territories
long enough to produce pups (Rothman and Mech 1979, Fritts and Mech 1981).
However, some wolf pairs that do not produce pups sometimes break up and leave
their territory (Mech 1987, Mech and Seal 1987). If vasectomized pairs did so,
then sterilization would have little lasting effect, for other lone wolves would
soon fill the vacant territories (Rothman and Mech 1979, Fritts and Mech 1981).
To determine whether vasectomized wolf pairs would continue to hold
territories, we conducted an experiment in the Superior National Forest of
northeastern Minnesota from 1987 through 1994. During summers 1987 and 1988,
five adult male wolves, weighing 32-38 kg and with testis lengths 3.0-3.9 cm
were live-trapped from four packs, transported to a veterinary lab, and
surgically vasectomized. Veterinarians removed large portions of the vas
deferens of each. The animals were then radio-collared, released in their
territories, and followed by aerial radio-tracking approximately weekly and
their presence in packs, pairs and territories was observed. We observed
post-vasectomy pack sizes of the four packs for 1,3, 4, and 7 years respectively
Table 1. Pack sizes of vasectomized wolves
in the Superior
Minnesota after vasectomies.1
Maximum Sizes of
Packs with Vasectomized Wolves
1. Wolves 35, 77, and 79 were vasectomized in summer 1987; 119 and 129,
in summer 1988.
2. Killed by other wolves in July 1988; the only observation of this pack
after the 1988 whelping season was of 4 adult wolves in July.
3. Members of the same pack; one possible observation of pups was made
with this pack on 2 November 1988.
4. Dispersed 18 km, paired with female and held new territory until
The effectiveness of the vasectomies in sterilizing males cannot be fully
documented because there were other pack members present which could have been
breeding males. However, the sterilization technique used is standard for dogs,
and the veterinarians who performed the vasectomies were practiced at the
technique. Only one possible observation of pups was made, and that observation
was questionable. In all years, the pack size either remained the same or
decreased after the males were vasectomized (Table 1).
All of the vasectomized wolves for all the years observed remained in
territories until they died or their transmitters expired. One wolf spent two
years in one pack territory after being vasectomized, then dispersed about 18 km
and bonded with a female; the pair held its new territory for 2 years until the
male was killed. Another vasectomized wolf remained in his territory for 7 years
after being vasectomized (Table 1). The evidence obtained in this study
demonstrates that vasectomized wolves do not necessarily lose pair-bonds or
territories; one wolf even formed a new pair bond.
The greatest disadvantage of the vasectomy technique is that individual
wolves must be captured and handled. However, chemical vasectomy involving the
non-surgical injection of sclerosing agents directly into the epididymides
(Freeman and Coffey 1973, Pineda and Hepler 1981), which the authors learned
about after this study, could be applied by wildlife biologists in the field.
This technique would make vasectomy far more practical.
Thus it may be possible to vasectomize wolves around local livestock herds
sustaining chronic losses from wolves and reduce the local wolf population by as
much as 2/3 given that wolves usually produce an average of 4-6 pups per litter
(Mech 1970). This should also reduce depredations considerably because a litter
of pups would quadruple a wolf pair's need for food. Situations may also arise
in which it would be preferable to vasectomize members of non-depredating pairs
rather than remove them and risk their territories being filled by others who
Furthermore, as a general wolf-population-control measure, vasectomizing a
certain percentage of a population would tend to reduce its biotic potential and
its size for periods of several years. If each year, a certain percentage of the
wolf population was sterilized, population growth and recolonization of new
areas could be curtailed while a reservoir wolf population was maintained. Field
studies and wolf-population modeling would give reasonable insights into the
approximate percentage of each population that might need vasectomizing so that
a given wolf population might be adjusted to a desired level.
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problem of maintaining wolf populations in areas where they do not compete
seriously with human beings but restricting them from locales where they do.
Rather, some combination of prescription management, fine-grained zoning, public
education, lethal control, compensation payments, translocations,
livestock-protection measures, and possibly sterilization, seems to be the
approach managers will have to use.
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* Mech, L. David, Steven H. Fritts, and Michael E. Nelson. 1996. Wolf Management In The 21st Century: From Public Input to Sterilization. Journal of Wildlife Research 1(2):195-198. Jamestown, ND: Northern Prairie Wildlife Research Center. Website: < http://www.npwrc.usgs.gov/resource/2000/ >.
Study funded by the U. S. Fish and Wildlife Service and the U. S. D.
A. North Central Forest Experiment Station.