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1 ~
Vampire Bat Control
in Latin Arnenca
To find an effective control agent that affects only the species of concern
normally requires knowledge of the life history of the target species. The
current control of vampire bats in Latin America rests on the following
aspects of the biology of the bats: they are much more susceptible than
cattle to the action of anticoagulants, they roost extremely close to each
other, they groom each other, their rate of reproduction is low, they do
not migrate, and they forage only in the absence of moonlight. These
pieces of information were acquired in a search for control methods, and
they yielded methods that are effective and that have minimal or no effect
on nontarget species. The approach in this case was to find and use weak
links in the life history of the animal in question. It also reflects an attempt
to save money by comparing the cost and availabilities of various chem-
icals.
151
OCR for page 152
Case Stucly
G. CLAY MITCHELL, Denver Wildlife Research Center, Denver,
Colorado
INTRODUCTION
When the Conquistadors arrived in Mexico in 1527, their horses were
immediately attacked by the common vampire bat, Desmodus rotundas
(Molina Solis, 18961. Over four centuries later, Bernardo Villa (1969)
made the following statement after reviewing the vampire bat problem in
Brazil: "No notable success has been achieved in controlling bats of the
family Desmodontidae, particularly the species Desmodus rotundus, in
any of the countries of tropical America."
Of the three species of vampire bats, only the common vampire, the
subject of this review, is economically damaging. The others, Diphylla
ecaudata and Diaemus youngii, have specialized feeding habits, preferring
to feed on the blood of birds (Uieda, 1982; Villa, 19661. Vampire bats
range from tropical Mexico to northern Argentina and northern Chile, and
they cost the Latin American livestock industry $350 million a year: $100
million in direct losses to rabies and $250 million in secondary losses,
such as reduction in milk production and secondary infections (Kverno
and Mitchell, 1976~. In addition, several humans die each year of rabies
transmitted by vampire bats (Beer, 1975; Irons et al., 1957; Venters et
al., 1954).
Previous attempts to reduce vampire bat populations in Latin America
have been ineffective, dangerous, destructive, impractical, too localized,
or too expensive. Methods tried included the use of flame throwers in
Trinidad (Greenhall, 1970), the dynamiting of several thousand caves in
the State of Grande do Sul, Brazil (Villa, 1969), the placement of a
strychnine-syrup mixture at old bite sites (Greenhall, 1963), the gassing
of thousands of caves in Latin America (Arteche, 1969), the use of Jap-
anese mist nets (Dalquest, 1954; Greenhall, 1963), and the placement of
traps at the entrances of caves (Constantine, 19691. Bats have also been
killed with clubs or firearms in stables and dwellings where they attack
their prey (Constantine, 19701.
In 1967, under the authority of the Foreign Assistance Act, the U.S.
Agency for International Development (AID) asked the U.S. Department
of the Interior's Fish and Wildlife Service to conduct research on vertebrate
pests (rodents, pest birds, and vampire bats) in developing countries. In
152
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VAMPIRE BAT CONTROL IN LATIN AMERICA
153
June 1968, the Service's Denver Wildlife Research Center (DWRC) ini-
tiated a program of research on the vampire bat problem under the auspices
of AID. The program consisted of two phases: (1) research conducted by
a laboratory team at DWRC and a field team at the Instituto Nacional de
Investigaciones Pecuarias in Palo Alto, Mexico; and (2) a utilization and
training phase, developed after species-specific control methods were
available.
THE ENVIRONMENTAL PROBLEMS
The main objective of the program was to increase livestock production
in Latin America by reducing vampire bat populations. The main envi-
ronmental problems were how to accomplish this objective without de-
stroying habitat, contaminating the environment with pesticides, destroying
desirable species, and adversely affecting an endangered species, the white-
winged vampire (Diaemus youngii). It was most important to develop
species-specific control methods that were effective, inexpensive, and safe
and required little training to apply.
APPROACHES TO CONTROLLING VAMPIRE BATS
When this project began, the morphology, physiology, and distribution
of vampires (primarily Desmodus) were reasonably well known, but little
was known of their social structure, behavior, movement, population
dynamics, and interspecific relationships, and no techniques were avail-
able for determining their relative or absolute abundance (Linhart, 1975~.
Hence, the proposed initial research was aimed at acquiring some knowl-
edge of the behavior and ecology of vampires.
The following studies were undertaken during the research phase from
1969 to 1973:
· Pharmacological evaluation of chemical agents, such as toxicants and
substances that alter physiology or behavior, for controlling vampire bats.
O Laboratory evaluation of techniques for applying control agents, in-
cluding feeding and grooming behavior of captive vampires, carrier com-
pounds or liquid vehicles for application of control agents to livestock,
and the application of control agents directly to livestock.
o Field evaluation of techniques for applying control, including devices
for applying carrier agents and their persistence on livestock, feeding
behavior of free-ranging vampires, and treatment of cattle with control
agents.
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154
SELECTED CASE STUDIES
· Estimation of actual numbers and repopulation or recovery rates of
natural populations of vampire bats.
Additional studies focused on vampire bat movements, sensory mech-
anisms associated with locating prey, and pharmacological hazards as-
sociated with the application of control agents to livestock.
Ecology of Vampire Bats
Research identified two potential weak links in vampires. First, Des-
moclus produce only one or possibly two young each year (Burns, 1970),
although each has a potential longevity of 13-14 years (Linhart, 1973;
Trapido, 19461. Therefore, population recovery after reduction by control
is slow. Second, vampire populations are concentrated near herds of live-
stock to which they fly nightly (Constantine, 19701.
Vampires do not migrate, although they can move locally during the
breeding season (Burns and Flores Crespo, 19751. They forage every night,
except when there is a full moon, but only during the darkest part of the
night, either before the moon rises or after it sets (Flores Crespo et al.,
19721. Finally, vampire bats form mobile communities that use multiple
roosts; the number of vampires in a colony might remain the same, but
there can be nightly exchange of individuals among roosts (Mitchell et
al., 19731. The most practical time to capture bats in mist nets set around
corralled cattle is during the week after a full moon, when the period of
complete darkness is still short.
Development of Control Methods
Two species-specific control methods for reducing vampire bat popu-
lations were developed in this project: the systemic method, in which
cattle are treated with a chemical; and the topical method, in which cap-
tured vampire bats are treated with the same chemical.
Systemic Method. The idea of treating cattle with systemic toxicants
originated at a Communicable Disease Center (CDC) laboratory working
on bats and rabies in Las Cruces, New Mexico. Denny G. Constantine,
a CDC veterinarian, was told that a Bayer systemic insecticide, Neguvon,
would kill vampire bats. He treated cattle with Neguvon, but no vampires
that fed on the treated cattle died. Although Neguvon did not kill vampires
in Constantine's experiments, other systemic insecticides recommended
by the U.S. Department of Agriculture (USDA) Livestock Insects Inves-
tigations Laboratory were tested. The recommendations on agents and
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VAMPIRE BAT CONTROL IN LATIN AMERICA
155
dosages were based on margins of safety for cattle. These compounds
were tested in Mexico, and one of them, Famophos, gave positive results.
In the laboratory, cattle were treated with a 13.2% pour-on formulation
of Famophos recommended for the control of screwworm larvae and
sucking flies. All vampire bats that fed on these treated cattle died (Mitchell
et al., 1970, 197 11. However, research with Famophos was discontinued,
because it was not available in Latin America and it was prohibitively
expensive.
When it was shown that vampires could be killed with a systemic
insecticide, DWRC scientists began looking at other substances that could
be administered to cattle, especially anticoagulants. Because they bind to
blood proteins, anticoagulants are excreted by the cow very slowly and
are available longer than most other chemicals for the bat to ingest with
a blood meal. Bats ingest about 50% of their body weight in blood at
each feeding and concentrate it by excreting water (Breidenstein, 1982),
so finding a dose of anticoagulant lethal to the bat but not harmful to
cattle appeared feasible.
Treating cattle with the anticoagulant actually selected, diphenadione,
at a concentration of 1.0 mg/kg gave a wide margin of safety for the cattle
and killed all the vampires that fed on blood taken from the treated cattle
up to 72 hours after treatment. Diphenadione was not retained in the liver
of treated animals, as was another effective anticoagulant, chlorophaci-
none (Bullard et al., 1970, 19711.
In 1971, diphenadione was administered with a balling gun to cattle in
Mexico. Results were good at Rancho Huichi (90.2% reduction in fresh
bites) and poor at Rancho Don Tomas (20% reduction in fresh bites)
(Mitchell et al., 19711. The poor results at Rancho Don Tomas were
attributed to weather that reduced the normal foraging activities of the
bats. In 1972, diphenadione was again field-tested in Mexico, but was
administered intraruminally with a syringe; this test reduced biting by 93%
(Thompson et al., 19721.
Topical Method. The idea of topical treatment was based on the like-
lihood that bats would ingest a toxicant while grooming. Similar behavior
is a basis of common methods of rat control. Greenhall (1965) reported
that vampires are thorough groomers and spend a considerable amount of
time in this activity. Captive vampires were observed to spend some 2
hours per day grooming (Flores Crespo et al., 1971a) enough time for
a control compound on the fur to be ingested.
To determine whether there would be sufficient contact between the
vampire and its prey for the vampire to receive the chemical from a cow's
skin and whether the vampire has a preferred biting area, 49 feedings
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SELECTED CASE STUDIES
were observed in a bat-proof corral under laboratory conditions. Of the
49 bites, 27 were made in the hoof region while the cattle were standing,
and 22 on various parts of the body while they were lying down; moreover,
each feeding entailed minimal contact between the vampire and its prey
(Flores Crespo et al., 1971b). As a followup to the laboratory study,
vampires were observed with Starlight night-vision telescopes, which elec-
tronically magnify available light, while they fed under natural conditions.
Vampires were observed while feeding under normal conditions on three
races of cattle Brahma, Charolais, and Holstein. Approximately one-
third of the bats landed on the Brahma before biting and feeding, and
31% on the Charolais, but 85% landed directly on the Holstein. Only on
the Holstein was there a preferred area for biting: 74.5~o of the bites were
on the neck (Flores Crespo et al., 19741.
Almost all cattle in the geographical range of vampire bats are Brahma.
Because the Brahma are on open range and because only 21% of the
vampires that fed on Brahma cattle fed on their necks, the idea of applying
a control compound to an appropriate area of the prey animal was discarded
as impractical.
An alternative topical method would be to apply the toxicant to the bat
itself. While writing a manuscript on grooming, DWRC biologist Samuel
B. Linhart recognized that vampires are extensive groomers and roost in
compact groups separate from beneficial bats in the same cave. Hence, a
substance placed on the fur of a captured bat might be passed to other
bats in the colony once the treated bat returned to the roost. These ideas
led Linhart to develop the topical method now in use.
On the basis of the recommendations of DWRC specialists, four chem-
icals were tested for toxicity to vampire bats. Chlorophacinone, an anti-
coagulant, was the most toxic. Ten carriers were evaluated by mixing
them with a dye and applying them to the dorsal surface of vampire bats.
Bats were checked several times a day to determine the persistence of the
carriers. Three carriers were selected for additional study: a saturated
solution of acetone and an acrylic polyester fluorescent paint pigment;
petroleum jelly; and a mixture of abalyn (a resin), mineral oil, and poly-
ethylene (Epoline- 101. For each candidate carrier, one vampire was treated
with a mixture of carrier and a dye and then introduced into a simulated
roost containing 19 other vampires. The roost was checked several times
a day to determine the degree of transfer among colony members by
grooming. Petroleum jelly was superior to the other carriers.
In the final test with the simulated roost, 50 mg of chlorophacinone
was mixed with 1.5 ml of petroleum jelly and applied to the dorsal surface
of one vampire. This vampire was put into the roost with 19 other bats.
The carrier bat was found dead on the morning after reintroduction into
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VAMPIRE BAT CONTROL IN LATIN AMERICA
157
the roost, and 18 of the 19 other bats died 5-19 days after reintroduction
(Linhart, 19701.
Several field tests confirmed these results. Vampire bats captured in
two caves were treated with a mixture of 50 mg of chlorophacinone and
1.5 ml of petroleum jelly. Six vampires captured in one cave were treated
and released; later, 94 dead vampires were found a ratio of 15-16 vam-
pires killed to each one treated. After 2 weeks, the caves contained only
one live vampire (Linhart et al., 1972~. In another test, bats were captured
in mist nets as they flew in to feed on corralled cattle on two ranches,
were treated with the control mixture, and were released. Two weeks
later, vampire bites on the same cattle had decreased by 95% (Linhart et
al., 19721.
At first, all vampires captured were treated with the chlorophacinone-
petroleum jelly mixture. Later, it was determined that one treated bat would
kill 19 others in the roost. There is a high correlation between the number
of fresh bites on members of a herd and the number of vampires feeding on
the herd. If a herd had 100 fresh bites, the vampire population was estimated
to be 100 and only five bats were treated.
There were two reasons for changing the control chemical from chloro-
phacinone to diphenadione. First, other anticoagulants were as effective as
chlorophacinone in controlling vampire bat populations with the topical method.
Second, diphenadione was available for manufacture, because the patent had
e.~nir~rl The aloe natent is held bv the U.S. Government. which gives per
~A~J~- ~ A4~ In_ r~_~ Rev .,_ -_ ~ ~.~ . ~ ~ . . _ i_
mission to anyone to use the chemical as a vampiricidal agent.
Although the topical method is more difficult to use than the systemic
method, because it requires night work and the proper identification and
treatment of only vampires, it is sometimes the preferred method. Injection
of the anticoagulant into the rumen is the easiest way to administer it;
but, of the animals commonly attacked by vampires, only cattle have a
rumen and can be treated this way. If other livestock or humans are being
attacked, the topical method is recommended.
Another control method, application of anticoagulants to roost walls,
was evaluated in a pilot study in Mexico. Diphenadione in petroleum jelly
was placed at vampire roost sites in a tunnel and in a mine (Mitchell et
al., 1971, 19721. In both cases, all the vampires were killed. Four non-
hematophagous bats also died in the tunnel. In view of these results,
control of vampire bats by treating roosts was not recommended.
Control Techniques
Systemic Treatment of Cattle with Diphenadione. Diphenadione is
injected into cattle intraruminally at l.O mg/kg of body weight. The drug
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158
SELECTED CASE STUDIES
is absorbed and circulates in the blood. Any vampire bat that feeds on a
properly treated animal within 72 hours after treatment receives a lethal
dose of the drug. Treating all cattle in a herd reduces biting by 90-95%
(Thompson et al., 19721.
Topical Treatment of Vampire Bats with Diphenadione. Vampire bats
are captured with mist nets that are set around corralled cattle or at cave
entrances. Approximately l.S ml of a diphenadione-petroleum jelly mix-
ture is placed on the dorsal surface of each captured bat, and the bat is
released. The bats return to their roost, and, because they live in compact
colonies, pass the chemical from one to another. The bats die after in-
gesting the chemical during grooming (Linhart et al., 19721. For every
treated bat, approximately 20 vampires die at the roost.
Vaccines
Although topical or systemic use of anticoagulants can reduce the num-
ber of bites by up to 96%, and thus reduce secondary losses by a similar
amount, rabies can still occur among unvaccinated cattle even when the
bat population is reduced. Therefore, both cattle vaccination and bat pop-
ulation control are recommended if the aim is to eliminate the disease,
rather than only to reduce cattle losses to an acceptable point (Lord, 19801.
Piccinini (1977) used both vaccines and anticoagulants in a 500 km2
area in the State of Pernambuco, Brazil. In the 2 years before control,
17,870 cattle were in the study area, 2,342 were not protected by vaccines,
and 140 died of rabies. After application of both control methods, the
vampire population was reduced by 96.1%. In the 2 years after control,
17,431 cattle were in the area, 4,848 were not vaccinated, and only 2
died of rabies. This shows that reduction of the vampire population gives
cattle some protection from rabies without the use of vaccines. It should
be noted that the treatments in Piccinini's study were made by scientists;
the results might be less impressive under normal operational field con-
ditions.
KINDS OF ECOLOGICAL KNOWLEDGE USED
Ecological Facts
Ecological and physiological facts were obtained from published lit-
erature and from the observations of experienced people in the field.
Experiments were done in simulated and natural situations and yielded
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VAMPIRE BAT CONTROL IN LATIN AMERICA
159
much knowledge of the life history and behavior of vampire bats. The
ecological observations provided the basis of the control programs.
Pilot Studies
The studies of topical anticoagulants in simulated roosts constitute an
example of the successful use of analog studies, and the pilot tests of both
systemic and topical anticoagulants were important in the development of
practical control programs. The studies did not all lead directly to such
cessful control, but the ones that "failed" enabled workers to avoid ex-
pensive and ineffective methods.
Project as Experiment
Experience gained in the utilization phase led to improvements in the
procedures. During that phase, one problem was encountered in Nicara-
gua, where 9 of 14 calves died after treatment with diphenadione (1.0 ma/
kg). These calves were less than 3 months old and lacked a fully functional
rumen. Further tests showed that calves without a functioning rumen
should not be treated (Elias et al., 19784.
UTILIZATION AND TRAINING
From 1974 to 1978, AID funded DWRC biologists to develop a utili-
z.ation or training phase for vampire bat control. It wanted DWRC to take
the control methods to Latin American cattlemen and to continue adaptive
research to answer questions that could arise. Initially, DWRC biologists
conducted training seminars in Latin America, often involving teams of
veterinarians organized to vaccinate cattle. The basic training tool was a
pamphlet, Chemical Control of Vampire Bats, published in Spanish, Eng-
lish, and Portuguese (Mitchell and Burns, 1973a,b, 19781. Later, the Peace
Corps in Belize (Mitchell et al., 1975, 1976) and the Pan American Health
Organization in Venezuela. Trinidad, and Surinam (Mitchell et al., 1974)
became involved. In-country training also occurred. For example, 125
veterinarians from 19 states were trained in Brazil (Mitchell et al., 19764.
In 1976, Rodrigo Gonzales presented results of the campaign in Nicaragua
at an international conference (Gonzales and Mitchell, 1976), and the
Nicaraguan government hosted a seminar on vampire bat control, attended
by 46 people from 11 countries (Mitchell et al., 19761.
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160
SELECTED CASE STUDIES
EFFECTIVENESS OF THE PROGRAM
After the publication of our control methods, new questions arose. The
possibility of hazards to other bats from use of the topical method was
suggested (Turner, 19751. Killing of nonhematophagous bats where vam-
pires have been controlled topically has not been reported, and none was
killed in the many field tests conducted. Brazilian workers controlled
vampires in 3,062 caves and never found a nonhematophagous bat killed
by the topical method (Mitchell et al., 19761.
The topical method was field-tested in every Latin American country
exposed to vampire predation. Results were consistent: 90-95% reduction
in the vampire population. The systemic method of treating cattle with
diphenadione is even more specific in that it kills only the vampires that
are attacking cattle. If cattle are treated with the recommended dosage,
1.0 mg/kg, no chemical is passed in the milk, and residues in tissue are
negligible (Bullard and Thompson, 1977; Bullard et al., 1976, 19771.
With sound management and husbandry practices in Ecuador, the killing
of vampire bats had no effect on milk production. In Nicaragua, under
more tropical conditions, mink production increased by 16% (Thompson
et al., 19771.
These methods of vampire bat control are very effective even when
applied by nonprofessionals. For example, in Nicaragua, 20 high-school
graduates were trained to apply the control methods over 4 years. They
examined 270,825 cattle on 2,124 ranches and found 123,376 fresh vam-
pire bites. They treated 148,142 of the cattle and 2,696 vampires and
reduced fresh bites by 90% to about 12,000. The annual benefit to farmers
from the vampire bat control program in Nicaragua was US$2,414,158,
and annual costs, $129,750, for a very favorable benefit-to-cost ratio of
about 18.6:1 (Badger and Schmidt, 19791.
ACKNOWLEDGMENTS
Although I prepared this case study, the solution to the problem is based
on an accumulation of many scientific experiments conducted by a host
of scientists. Much of the work was done by DWRC scientists in an array
of disciplines, including wildlife biology, pharmacology, animal psy-
chology, statistics, physiology, electronics, chemistry, nutrition, and ecol-
ogy. Undoubtedly, this multidisciplinary approach was influential in solving
the problem.
Thanks go to Bernardo Villa, Master Zoologist at the University of
Mexico, for sharing his vast knowledge of bats.
I also wish to give special thanks to Charles Ladenheim (AID retired),
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VAMPIRE BAT CONTROL IN LATIN AMERICA
161
who had the insight to support the transition from a research project to
an operational program. Research cannot be considered accomplished or
successful until its results are made known and implemented in this
case, by the small producers of livestock in Latin America.
Funds for this research were provided to DWRC by AID under Partic-
ipating Agency Service Agreements RA (ID) 01-67 and ID-TAB-000-10-
76.
Reference to trade names in this review does not imply U.S. government
endorsement.
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Irons, G. V., R. B. Eads, J. E. Grimes, and A. Conklin. 1957. The public health importance
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Lord, R. D. 1980. An ecological strategy for controlling bovine rabies through elimination
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Ministry of Agriculture, EMBRAPA, Coronel Pacheco, Braz.
Mitchell, G. C., R. Flores Crespo, R. J. Burns, S. Said Fernandez, and S. B. Linhart.
1970. Vampire Bats: Rabies Transmission and Livestock Production in Latin America.
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Committee Comment
The control of pests is a common theme in humans' attempts to live in
a world populated with animals and plants, and that theme is reflected in
several of the cases discussed in this report (Chapters 14, 15, and 244.
Many serious pests are controlled only poorly, despite great expense; those
controlled successfully usually have idiosyncrasies of life history that make
them vulnerable, and successful control depends on detailed knowledge
of those idiosyncrasies.
Early attempts to control vampires did not rely on knowledge of the
animals' natural history; they were ineffective and destructive. The re-
sulting careful and thorough research into the natural history of vampires
by the Denver Wildlife Research Center (DWRC) exemplifies an approach
OCR for page 164
164
SELECTED CASE STUDIES
that is usually needed for pest control; the idiosyncrasies discovered rep-
resent a certain amount of the luck that so often seems to accompany
successful cases.
DWRC biologists studied the behavior, dispersal, physiology, and ecol-
ogy of vampires, using field and laboratory experiments and observations.
These studies and literature review revealed important aspects of vampires'
natural history that made them susceptible to control. Two of these aspects
commonly help in pest control: the bats have a low reproductive rate,
which meant that less powerful control would be needed to keep their
numbers down, and they do not migrate.
Successful control also depended on several idiosyncrasies. The bats,
because of their diet of blood, are much more susceptible to anticoagulants
than cattle are. They forage only on dark nights, so when the moon rises
shortly after sunset or sets shortly before sunrise, their activity is confined
to short periods, and that makes them easier to trap. They roost extremely
close to each other and they groom each other both characteristics that
favor transfer of vampiricides between individuals and that make it un-
necessary to treat more than a few members of each roost.
Thus, successful control in this case depended on thorough research
into the pests' natural history, which is nearly always needed, and on the
vulnerabilities that the research revealed. The vulnerable points might not
exist, but in the absence of thorough research they will almost surely not
be found.
Representative terms from entire chapter:
vampire bat
