of control was practiced. If the kill or birth control rate changed from
year to year the population did not stabilize, but fluctuated in response

to the variable control in effect. If the level of control exceeded the
capacity of the population for compensations in birth and natural loss tates,
the population did not stabilize but declined toward zero.

Under field conditions it is rare for exactly the same rate of control
to be achieved from year to year; the population therefore, does not stabilize.
Likewise the carrying capacity of the coyote habitat may change from one
year to the next, and this also prevents stabilization of numbers,

The effects of killing coyotes on the population were studied by a
series of runs ranging from no control to 75 percent annual control kill
(table 3). The values shown are at stability, when the previously uncontrolled
population had fully responded to the control level under test. (See years
9 to 11 in table 2, for example.) In table 3 each value representing a
specific number of coyotes was rounded to the nearest whole number, For
this reason, some of the numbers do not cross check.

As shown in table 3, killing coyotes affects every variable of the
coyote population. Some parameters were affected more than others. As the
Percentage of coyotes killed annually increased, the breeding population (Cb)
decreased, while the maximum population (Cm) increased slightly due to
increased numbers of pups (P) born. As the control kill (Kt) increased
natural losses (Nt) decreased, The effects of population reduction on the
Proportion of females breeding (By,Ba), litter size (4), and natural loss
rates (Np,Na) were forecast in figures 2 to 4, but are reiterated so that
tesults can be analyzed.

One variable which changed only slightly with control intensity was
the number of breeding females (Fl). This resulted from increased propor-
tions of females breeding (By,Ba) as the breeding population (Cb) was
teduced. Knowlton (1972) pointed out that the greatest adjustments in
Productivity of local coyote populations may result from variations in
the percentage of yearlings becoming sexually mature. In our model this
is simulated by the proportion of yearling females with litters (By).
However, the relative frequency of yearlings in the breeding population (Cy/
Cb) also increases with control intensity, The net contribution of yearling
females to reproduction is given by Py, the proportion of pups produced by

17



LITERATURE CITED
Adams, C. C.
1930, Rational predatory animal control, Jour, Mammalogy 11(3):353-358,
Anderson, F. M., G. E. Connolly, A. N. Halter, and W. M. Longhurst.

1974, A computer simulation study of deer in Mendocino County, California.

Oregon Agric, Exp. Sta. Tech. Bull. 130:72 pp.
Balser, D. S.

1964, Management of predator populations with antifertility agents.
Jour. Wildl, Manage. 28(2):352-358.

Cain, S. A., J. A. Kadlec, D. L. Allen, R. A. Cooley, M. G. Hornocker,

A. S. Leopold, and F. H. Wagner.

1972. Predator control -- 1971. Report to the Council on Environmental
Quality and the Department of the Interior by the Advisory Comittee
on Predator Control:207 pp.

Gier, H. T.
1968. Coyotes in Kansas, Kansas Agric, Exp. Sta. Bull, 393:118 pp.
Henderson, F. R.

1972. Controlling coyote damage, Kans. State Univ. Coop. Ext. Serv. Publ.

No. C=397:24 pp.
Knowlton, F. F.

1972. Preliminary interpretations of coyote population mechanics with some

management implications. Jour. Wildl. Manage. 36(2) 369-382.
Linhart, S. B. and F. F. Knowlton.

1967. Determining age of coyotes by tooth cementum layers. Jour. Wildl.
Manage. 31(2):362-365,

Linhart, S. B., H. H. Brusman, and D. S. Balser.

1968. Field evaluation of an antifertility agent, stilbestrol, for
inhibiiting coyote reproduction. Trans. N. Amer. Wildl. Conf,
33:316~326.

Swick, C. D.

1974. Operational management plan for the coyote. Part I. Inventory.

Final Progress Report, Federal Aid in Wildlife Restoration, Project

W-54-R-5 and 6. California Dept. of Fish and Game, Sacramento,
Ca. 30 pp.

34


Table 1, Variables for the coyote population dynamics model.

Variable Symbol Relation to other variables

Yearling coyotes at breeding Cy Cy(t) = P(t - 1) - Pk(t - 1) -
Pn(t - 1)

Adult coyotes at breeding Ca GaCt) = Cb(t - 1) - Ak(t = 1) -
An(t ~ 1)

Minimum (breeding) population Cb Cb = Cy + Ca

Relative density at breeding D,* d= Cb/100

Proportion of yearling females by! By = £D)

with litters

Proportion of adult females Bat Ba = £D)

with litters

Breeding females (number with ri? Fl = 0.5(1 - 8) (ByCy + BaCa)

litters)

Proportion of breeding females S$ Specified by investigator

suppressed

Litter size cal Le D,

Pups born P P = L(F1)

Proportion of pups produced by Py Py = (0.5L)(1 ~ 8) @yCy)/P

yearling females

Maximum population Cm Cm = Cb + P

Proportion of coyotes killed K Specified by investigator

in control

Pups killed by control: Pk Pk = P(K)

Adults killed by control Ak Ak = Cb(K)

Total control kill Ke Kt = Pk + Ak

Proportion of pups in control Kr Kr = Pk/Kt

kill

Control kill as proportion of Kb Kb = Kt/Cb

breeding population

*D, expresses the breeding population as a fraction of the breeding

population in the absence of control.

These values increase as Dy decreases. The functions are described in

Figures 2 and 3,
4

Assumes a 50:50 sex ratio at breeding.

11



Table 4, Simulation of effects of birth suppression by chemosterilants on a

coyote population.

PERCENTAGE OF BREEDING FEMALES
SUPPRESSED ANNUALLY (S)

Variables* 0 20 40 60 80 95

erncne Annual values at population stability---------—-~

cy 40.00 37.00 34,00 29.00 21,00 5.00
eb 100,00 99.00 97.00 92.00 79.00 32.00
By 0.10 a. 0,14 0.20 0,36 0.70°
Ba 0.70 0.70 0.71 0.73 0.79 0.90°
FL 23.00 19.00 15.00 10.00 5.00 1.00
4,50 4.50 4.80 5.30 6.40 9.00°

104.00 87.00 71.00 54.00 34.00 6.00

Py 0.09 0.08 0.10 Q.11 0.14 0.13
cm 204.00 186.00 168.00 146,00 113.00 39.00
Kt 0.00 0.00 0.00 0.00 0.00 0.00
Np 0.61 0.57 0.53 0.47 0.39 0. 20
Na 0.40 0.37 0.35 0.32 0.27 0.16

Nt 104.00 86.00 71.00 54.00 34.00 6.00

*For explanation of symbols see table 1.

‘population declined slowly after year 20 but appeared stable by year 50.
Values show are for year 50.

Values generated in model exceeded and therefore were replaced by specified
maximum values,

$

21



to affect overall coyote numbers but locally it may be stimulating the rate
of reproduction,
INTRODUCTION

Killing coyotes, primarily because they prey on livestock, has been
widely practiced in the western United States for many years. Tremendous
sums have been spent on trapping, poison bait programs, shooting, den hunting,
the Humane Coyote Getter, and M-44 devices (Cain, et al. 1972). Control
objectives have apparently shifted from extermination (Adams, 1930), to
population reduction ("prophylactic control"), to selective removal of problem
animals (Cain, et al., 1972). In addition to the federal control program
carried out by the U.S. Fish and Wildlife Service and its cooperators, fur
trappers and sport hunters take many coyotes. In California alone sport
hunters are estimated to take over 80,000 coyotes annually (Swick, 1974).
However, coyote numbers seem to be increasing over much of the West (U.S.
Congress, 1973; page 58) in spite of all these efforts.

Considering this history it is logical to wonder what the effect of
control actually is on coyote populations. Cain, et al. (1972) questioned
whether control activities influenced overall coyote densities in some states
even when 1080 (sodium monofluoroacetate) poison stations were commonly used.
Young and Jackson (1951; page 156) have described the effectiveness of
trapping and poisoning "like digging a hole in the ocean." Detailed study
of this matter has been surprisingly limited in relation to the magnitude
of the control effort,

This paper describes the development and use of a simple simulation
model to examine the probable effects of control on coyote populations.

DESCRIPTION OF THE SIMULATION MODEL

In this model the population consists of a seasonally variable number
of coyotes. Natural coyote populations are of the "birth-pulse' type, with
births occurring at one season while deaths occur the year round (Gier, 1968;
Knowlton, 1972). Numbers are lowest after the breeding season (just before
the birth pulse) and highest just after the birth pulse. We have simulated
the annual population cycle in three steps: births, control mortality, and
natural mortality which includes all other types of mortality. In effect,
the take of coyotes by sport hunters and fur trappers is additive to the number


To determine the age would require one canine tooth from each coyote for
laboratory counts of cementum layers (Linhart and Knowlton, 1967). This
would not be necessary for animals which were obviously juvenile. Uterine
examinations for reproduction data can readily be done in the field.
Regardless of the time of year, the presence of placental scars will reveal
that pups were born in the previous breeding season. The number of scars
indicates the number of pups produced (Gier, 1968).
EFFECTS OF COYOTE CONTROL ON NONTARGET SPECIES

Several of the effective coyote killing techniques in present use are
not completely selective for coyotes, The catch of foxes, raccoons, skunks,
and other nontarget animals in coyote traps is grounds for much opposition
to predator control (U.S. Congress, 1973; pages 320-342). While we did
not include these nontarget animals in our model, we wish to point out that
the principles of population dynamics demonstrated for coyotes apply to
other animal species as well. It is likely that most, if not all, popula~
tions of nontarget animals possess the ability to compensate for man-caused
mortality by increased birth and reduced natural loss rates, just as coyotes
do, Also the natural losses in the populations of these nontarget species
should be similar to those of coyotes so that population turnover is high
and the effects of removing a few additional animals inadvertently would
be insignificant and difficult to even detect.

If this is true, predator control programs are not likely to eradicate
or even seriously affect the nontarget species. As a matter of record,
governmental animal control programs have not significantly threatened the
future of a single animal species, endangered or not (U.S. Congress, 19733
pages 380-382), None of this is to excuse the indiscriminant destruction
of wildlife, but only to point out that the incidental catch of nontarget
animals in predator control programs is not, of itself, grounds for termi~
nating predator control in areas of proven need.

CONCLUSION
This report discusses the level of control needed for eradication of
coyote populations and the feasibility of achieving such control, We emphat—
ically DO NOT recommend eradication as the preferred coyote management
strategy. Eradication is the limit of control intensity at the opposite end

of the scale from no control. Both limits are important reference points to

32



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24


If an ideal birth control (chemosterilant) chemical or combination
of chemicals could be developed, one dosage would sterilize either males
or females for life. However, the chemosterilants tested to date are effec~
tive only on females during a short period in the breeding cycle and they
must receive dosages each year. Likewise we did not concern ourselves with
the problems of bait distribution or Environmental Protection Agency regis-
tration of the chemicals.

In this model we have examined the effects of birth suppression in
a series of runs in which from 0 to 95 percent of the normally breeding
females were prevented from having litters (table 4), No other form of
control was practiced. All values representing coyote numbers were rounded

to the nearest whole number. For this reason some of the numbers in table

4 may not cross check.

The effects of birth suppression on the coyote population differed in
several respects from the effects of killing coyotes. As the intensity of
birth suppression increased, the breeding population (Cb) declined slightly
(up to S = 0.6), but the number of pups born (P) dropped nearly 50 percent
(table 4). These results contrasted sharply with the effects of increasing
the control kill (table 3), which caused a marked decline in the breeding
population (Cb) but an increase in the number of pups born (P). The net
effects of these differences were that the maximum coyote population (Cm)
declined with increased birth suppression (table 4) but increased with the
control kill (up to K = 60 percent, table 3).

We believe the key to the different population responses to these two
kinds of control is the reproductive potential of young females. As shown
in table 3, the proportion of yearlings (Cy) in the breeding population (Cb)
increased with the control kill. The percentage of females with litters also
increased, with the potential of yearlings (By) greater than that of adults
(Ba). The composite effect of these variations is that the proportion of
pups produced by yearling females (Py) increased with the control kill.

Turning again to the results of birth suppression (table 4), we see that
Py is virtually constant at all levels of suppression. Not only does the
proportion of yearlings in the breeding population (Cy/Cb) decline as $

increases, but the increase in the proportion of yearlings breeding (By) is

20


to compare with intermediate levels of control. Our aim in this paper is to
evaluate the effects of various management strategies and to elucidate their
consequences,

Killing coyotes unselectively with the techniques presently available,
is not a very feasible means of reducing populations over broad geographical
areas. This report suggests that other means should be found to reduce
coyote depredations, and that better understanding of coyote population
dynamics is required.

ACKNOWLEDGEMENTS

We wish to thank M. Cummings and D, Wade, Cooperative Extension, and
E, Garton, Division of Environmental Studies, University of California,
Davis, who contributed to the validation phase of model development and
provided valuable suggestions for the improvement of the manuscript. Also
we wish to thank B, Weiss for clerical assistance and M. Vann, Director of
Animal Control for Mendocino County for providing control data for the

county.

33



Np = (PB - Cy)/P (Symbols defined in table 1.)

As previously stated, this model assumes a breeding population of 100
coyotes each year in the absence of control (assumptions 1 and 8*). If the
adults are replaced solely by pups surviving to be yearlings (assumption 3),
and the adult mortality rate is 40 percent (Knowlton, 1972), then short
yearlings must comprise 40 percent of the breeding population. Therefore,
cy = 40.

The number of pups born depends on the number of breeding females and
the average litter size (P = L x Fl, table 1). In a breeding population of
60 adults and 40 yearlings with a 50:50 sex ratio (assumptions 8 and 5),
there are 30 adult females and 20 yearling females. If 70 percent of the
adult females and 10 percent of the yearlings produce litters, as estimated
in figure 2 @, = 1.0), the uncontrolled population contains 23 breeding
females, If the litter size 1s 4.5 (fig. 3, Dy = 1.0), the number of pups
born (P) is 103.5. From these estimates, in the uncontrolled population
Np = (103.5 - 40)/103.5 = 0.614.

This estimate differs from the value of 0.67 proposed by Knowlton (1972)
primarily because we used separate pregnancy rates for yearling and adult
females, while Knowlton used one value for all females.

As in the case of adult natural mortality, we feel the natural loss rate
of pups will decline as the population is reduced by control but will never
be under 10 percent. For the pup natural mortality function (fig. 4) we set
the value in the uncontrolled population @, = 1,0) at 0.614, as calculated
above, declining toward 10 percent as Dy approaches 0. The resulting func-
tion is described by the equation Np = 0.104 + 0.51 @,) as calculated by
least squares regression techniques.

Discussion of birth and death functions

The functions shown in figures 2 to 4 are the most important variables

in this model. We reemphasize that the form of these functions is largely

speculative, although each is based on the best available data. During
the formulation and validation phases of model development, the functions
were changed several times. It became apparent that minor changes would

not alter our conclusions significantly, Although additional research is

*Refer to numbered assumptions on page 5.

15



various control intensities has not been fully determined. However, in
this model it was necessary to mathematically define these functional rela~
tionships. Since it would have been impossible to identify and separately
quantify each environmental factor affecting births and natural losses,

the relative density was used as a proxy variable encompassing all the
density dependent effects. The relative density is simply the number of
coyotes in the population expressed as a fraction of the number which would
have been present in the absence of control. When no control is practiced
the relative density is one, and birth and natural loss rates are unchanged.
As the population is reduced by control, the relative density is also reduced,
causing corresponding changes in the birth and natural loss rates which

are functionally related to relative density.

Five parameters in this model vary with relative density: the pregnancy
rates for adult (Ba) and yearling (By) female coyotes, the average litter
size (L), and natural mortality rates for adults (Na) and pups (Np).
Detailed descriptions of the functions follow:

Adult pregnancy rate (Ba)

It has been shown that 60 to 90 percent of the adult female coyotes
produce litters (Gier, 1968; Knowlton, 1972). For this model all coyotes
older than yearlings (12 months of age when pups are born) are considered
to be adults. We assume that, in the average year, 70 percent of the adult

females produce litters in an uncontrolled population (relative density = 1),
and that this pregnancy rate increases to 90 percent as the population is
teduced by control to half the precontrol density (fig. 2). We take 90
percent as the biological limit for this parameter, so the adult pregnancy
rate remains at 90 percent for all relative densities below 0.5. The adult
pregnancy rate function from D, = 1.0 to Dy = 0.5 is described by the

1
equation:

Ba = 1.1 - 0.4 Dy
which was calculated by least squares regression techniques.

Yearling pregnancy rate (By)

The fraction of yearling female coyotes bearing litters may range from
0 to 70 percent (Gier, 1968). Breeding yearlings are those which bear pups
at about 12 months of age. We suggest that in an uncontrolled population



is reasonable and we had independently estimated the breeding population at
about 4,000 animals before learning of Vann's work.

Vann reported that although coyotes may be found throughout the livestock
ranges of Mendocino County, not all of the county is subject to intensive
control. Occasional den hunting or calling is done in many areas, but only
about 25 percent of the county is worked intensively. The areas of greatest
coyote density, particularly public lands, receive little or no control.

Widespread, intensive predator control is not possible in this couty
because of limited funds and public opposition to control in excess of proven
needs, Therefore, the control strategy is to concentrate on areas where
livestock losses to predators are most serious. These often are ranches
adjacent to wild lands too steep or too brushy to support livestock. Such
wild lands apparently serve as "coyote reservoirs," providing a ready source
of animals to replace those taken by trappers from the livestock ranges
nearby. Under these circumstances, the trappers take as many coyotes as
possible from the immediate problem areas, They also work the "refuge"
areas, particularly by den hunting, in an attempt to minimize the numbers
of coyotes available to repopulate the problem areas.

The number of coyotes taken by Mendocino County trappers is quite con-
stant from year to year. During the five year period 1970 to 1974 an average
of 334 coyotes was taken each year. The yearly totals ranged from 303 to
363 during this period, In addition to the coyotes removed by county trappers,
perhaps 50 per year are taken by deer hunters, sport hunters, and callers.
Few, if any, are taken for fur. Comparing the coyote control program in
Mendocino County to the output (table 3) of our theoretical model, it is
evident that the overall control kill is quite low. Taking the estimated
breeding population (Cb) of 4135 coyotes and the estimated control kill
(Kt) of 384 per year (334 by trappers and 50 by sport hunters) as explained
above, the control kill amounts to 9 percent of the breeding population.
This kill ratio (Kb) is low in relation to the values for Kb in table 3,
suggesting that the actual kill rate (K) in Mendocino County is about 5
percent of the maximum population.

In addition to the kill ratio (Kb), we also determined the average
coyote litter size in the county from trappers' reports indicating the

30


The techniques presently used for coyote control include trapping, the
"N-44" cyanide ejector device in some areas, shooting both on the ground and
from aircraft, and den hunting. The relative effectiveness of these methods
may differ with the intensity of control. Efforts to reduce the population
by trapping or aerial shooting just before breeding would probably decline
in effectiveness proportional to the decline in the breeding population (Cb)
as control levels increase (table 3). However, the number of females with
litters (Fl), and presumably the number of dens, declines only slightly with
increasing control (table 3). Therefore, it appears that den hunting should
remain quite effective even at high rates of control, Aerial shooting has
proven very effective in areas of sparse cover but cannot be relied upon in
brushy or timbered areas.

As mentioned earlier, the take of coyotes in many areas by sport hunting
may greatly exceed the number removed through deliberate control programs,
Likewise, in some places bounties are still being paid as an incentive to
kill coyotes, Considering the strong compensatory reproductive response
of coyote populations to reduction, if control, sport, and bounty hunting
collectively do not reduce numbers annually on a continuing basis by at
least 75 percent, no sustained decline in the population can be achieved.
Therefore, to summarize, in most situations, killing coyotes at rates below
75 percent may merely stimulate reproduction and aggravate the problem by
increasing the seasonal population pressure on the food supply, With such
increased competition for food, it is reasonable to expect coyotes to turn
more to alternative food sources such as livestock. From this standpoint
chemosterilants may be especially useful if they can be applied effectively,
since they do not tend to cause increased food competition.

: INDICATORS OF CONTROL INTENSITY

Since reliable estimates of coyote numbers are notoriously difficult
to obtain, the information needed to plan intelligent predator management
programs is not usually available. In most areas we simply do not know how
the control kill relates to the size of the population, or even whether
coyote numbers are increasing or decreasing. However, there are several ©
statistics measurable from the control kill which can serve as indices to
the level of control actually being achieved. Perhaps the most useful of

these are measures of reproductive success.

27



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of coyotes killed by federal, state, county agencies or private individuals
For purposes of this model all of these
Tt

to alleviate livestock depredations.
forms of coyote removal are lumped together under control mortality.
should be realized, however, that sport hunting and fur trapping are non-
selective in their removal of coyotes from the population whereas coyote

killing to alleviate livestock losses tends to be focused on localized problem

areas and on individual "killer" coyotes. The coyotes remaining at the end
of the year constitute the breeding population for the next year. These
events are related schematically in figure 1.

Our simulated population differs from actual populations in several
respects. For example, we describe the minimum population (just before
whelping) as the breeding population. Actually the population at breeding
might be substantially higher than the minimum population, depending on
natural and control loss during gestation. In this model, breeding is
significant only in terms of the numbers of pups born, and this is a function

of the minimum population.

As noted above, we have simulated the annual coyote population cycle
in three steps: births, control mortality, and other "natural" mortality.
Though in reality all forms of mortality may occur throughout the year,
considerable abstraction from this pattern was needed in the model to keep
the calculations within reasonable limits. In each year the control kill
numbers are taken from the maximum population. Natural losses are then cal-
culated for the animals surviving control. The justification for this is
that intensive control, in the form of den hunting, often is applied to the
maximum population. If pups are not killed in their dens, survival is thought
be be high until fall (Knowlton 1972). In the model, both control and natural
losses are calculated once each year, The whelping season also is compressed
into a single calculation each year, even though in nature it may last several
weeks. .

_ In our model two forms of human intervention ("control") in the coyote
population are considered: coyotes may be killed or females may be prevented
from having pups through the use of chemosterilants. Either or both forms
of intervention may be applied in any combination of rates. In the absence

of "control," the model simulates the dynamics of a population that is
affected only by natural losses. The control kill and birth suppression



needed to define the functions more precisely, the model is so constructed
that improved or refined functions can be substituted for the present ones,
CONTROL KILL RATES

Coyote pups are thought to be less wary than adults and therefore more
likely to be taken by trappers. With this in mind, our model allowed pups
and adults to be killed at different rates. Theoretically, pups and adults
could be killed at any combination of rates. To limit the number of combina-
tions simulated, we sought to take pups and adults in the proportions
actually expected in operational control programs. Wade (personal communica-
tion)* indicated that as the intensity of control increases, the proportion
of pups in the total control kill also increases. Considering all methods
of direct control efforts, pups would be expected to comprise little mre
than half of the kill at low control levels. Under the most intensive control
as many as 80 percent of the coyotes taken might be pups. We found that
by taking the same percentages of pups and adults present in the population,
the composition of the control kill changed as expected when the intensity
of control was increased. This is attributed to the increase in the birth
tate as the intensity of control increased. After it became apparent that
different kill rates for pups and adults would not be needed, the program
was simplified to apply a single kill rate to both pups and adults.

EFFECTS OF CONTROL ON THE SIMULATED COYOTE POPULATION

Figure 1 shows the two kinds of human intervention or "control" that "J
be applied to coyote populations -~ birth control or direct killing. We have
tested the impacts of both kinds of control, both singly and in combination.

The general response of our simulated coyote population to control is
illustrated in table 2. Each run began with a previously uncontrolled
population of 100 coyotes at breeding. As control was applied in the first
year coyote numbers were reduced, causing compensatory changes in birth and
natural loss rates in subsequent years. If the control kill was held year
after year at a constant percentage of the population, as shown in table 2,
the population stabilized within a few years at a lower density than was the

case in the absence of control, This occurred regardless of which form

*D, A. Wade, Extension Wildlife Specialist, Animal Damage Control, University
of California, Davis.

16


(5) The sex ratio of both pups and adults is 50:50.

(6) There is no sex~specific mortality; i.e., natural and control
losses consist of equal numbers of males and females, both among
pups and adults.

(7) Control loss rates apply to the maximum population. Natural
loss rates apply to the coyotes surviving control.

(8) Each run begins with 100 coyotes at breeding time, 60 adults and
40 yearlings. (The reason for this age composition is given in
the description of the natural mortality functions.)

The coyote population model diagrammed in figure 1 represents a set of
variables related to one another by simple functions and difference equations.
The variables and their interrelationships are listed in table 1. For details
of programming and calculations see Appendix.

BIRTH AND NATURAL LOSS FUNCTIONS

We believe that birth rates are higher and natural loss rates lower in
an intensively controlled coyote population than in an uncontrolled population.
We agree with the concept that intensive population reduction alleviates the
constraints that ordinarily limit numbers in an uncontrolled population,

In our view these constraints (density~dependent variables) consist most
importantly of intraspecific competition for limited resources, primarily
food. Likewise competition for other habitat resources, such as favored
denning sites, may increase with density and serve to limit reproductive
success. Social stress in relation to density may also have a bearing in
this regard as would transmission of diseases and parasites. Whatever the
specific natural limiting factors are, it is known that both pregnancy rates
(Gier, 1968) and litter size (Knowlton, 1972) vary with control intensity
and environmental conditions, While environmental conditions for coyotes
may be influenced by weather or land use practices, intensive control also
appears to enhance environmental conditions for the surviving coyotes. As
explained by Henderson (1972), . . "reducing the numbers of predators makes
it easier for the remaining predators to survive the winter and come through
in better shape."

While it is accepted that control can induce increased birth and natural
survival rates in coyote populations, the magnitude of these effects at


limited because the breeding population remains near pre-control levels,
Birth suppression thus provides a "double~barrelled" effect, directly
limiting the maximum population (Cm) by restricting the number of pups born
(P), and indirectly preventing increased breeding by young females by
restricting the relative numbers (Cy/Cb) and breeding success (Cy) of
yearlings.

Livestock losses to coyotes are said to be particularly serious during
spring and summer because of the food requirements of the pups (Wade, 1973).
In this connection the birth suppression approach is particularly attractive
because it reduces the number of pups born and presumably the depredations
associated with the feeding of pups. In contrast, increased killing of
coyotes might actually increase depredations near den sites, as the number
of breeding females (Fl) remains nearly constant while the litter size (L)
increases with the control kill (table 3). The critical relationship may
be the level of competition for available food resources in relation to
coyote density.

Since birth suppression offers real advantages over more traditional
means of coyote control, it is unfortunate that this approach has not yet
been perfected to the point of field application, While initial trials were
promising (Balser 1964), later tests were less successful (Linhart, et al.,
1968). The main constraints appeared to be consumption of baits by
nontarget animals, many coyotes are not exposed to baits, and the drug used,
diethylstilbestrol, is only effective in the female coyote for a limited
period, There may be hope for future developments, but at present birth
control is not a viable alternative to existing control methods.

THE EFFECTS OF INTEGRATED CONTROL (BIRTH SUPPRESSION + KILLING)
ON THE COYOTE POPULATION

It seems unlikely that birth control will supplant conventional methods
of coyote control, at least in the near future, and even with an effective
birth suppression program it is likely that some coyotes would still have
to be killed in chronic depredation areas, Therefore, we have tested the
effects of killing and birth control combined (table 5). The two kinds
of control might be applied in any ‘combination of rates, but in table 5 the
alternatives are limited to equal percentage rates for both kinds of control


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Journal Title: Bulletin - Division of Agricultural
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Article Author: University of California (System);
United States G.E. Connolly & W.M. Longhurst
Article Title: The effects of control on coyote
populations: A simulation model

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Q, = 1.0), 10 percent of the yearlings breed, and that this rate increases
to 70 percent as the population is reduced by control to half the precontrol
density (fig. 2). With 70 percent set as the biological limit for this
Parameter, the yearling pregnancy rate remains at 70 percent for all relative
densities below 0.5. The relationship from DL = 1.0 to Dy = 0.5 is described
by the equation

By = 1.3 - 1.2 Dy
which was calculated by least squares regression procedures,
Litter size (L)

Published estimates of average litter size range from 2,8 to 8.9
pups per litter (Knowlton, 1972). However, litters of 12 or more pups are
not uncommon, Wade (1975) records 16 litters containing 154 pups taken by
Benton Whitman in Yakima and Columbia counties, Washington, in 1955, for an
average of 9.6 per litter.

We propose an average litter size of 4,5 in an uncontrolled population
, = 1.0), increasing to 9 pups per litter as the population is reduced to
half the precontrol density (Figure 3). With 9 set as the maximum for this
parameter, the litter size remains at this level for ali relative densities
below 0.5. The relationship from Dy = 1.0 to Dy = 0.5 is given by the equa-
tion L= 13.5 - 9 (D,); which was also calculated by least squares procedures,
Relative density (Djs Do)

In this model the birth functions are based on relative density at
breeding @,)- This relates breeding success to the density dependent
constraints operative at the time of breeding. Because the breeding portion
of the uncontrolled population always contains 100 coyotes, the denomina-
tor for calculating Dy is always 100 (table 1).

for mortality calculations, a different reference point was needed for
relative density. Both pups and adults die, but only the animals surviving
control are susceptible to natural mortality. The relative density after
control (@,) is based on the numbers of animals susceptible to natural
mortality. As this value is 203.5 coyotes each year in the uncontrolled
population, the denominator for calculating Dy is always 203.5 (table 1),
Adult natural mortality (Na)

Knowlton (1972) estimated that in the absence of control the annual

mortality rate was about 40 percent, We feel that this rate will decline



PROPORTION OF FEMALE COYOTES WITH LITTERS (Ba, By)

Figure 2,

PROPORTIONS OF FEMALE COYOTES BREEDING IN RELATION
TO DENSITY

ADULTS (Ba)

YEARLINGS (By)

L L i 1

8 7

RELATIVE

6 5 4 3
DENSITY (D))


chapparal thickets, which provide good escape cover for coyotes. Vehicle
access in many areas is restricted by the steep terrain and dense vegetation.
Approximately 20 percent of the county is public land (ilational Forest or
National Resource Land) where little livestock grazing or predator control
is practiced,

About half of Mendocino County is grazed by livestock, and coyotes
occur on virtually all of the livestock ranges. Coyotes have preyed on live-
stock, particularly hseep, in this part of the state since the early days of
European settlement. A predatory animal control program has been carried out
under county auspices for the past 30 years and the area has been divided
into six districts with a full-time hunter trapper working -ach district.
The trappers are supervised by the Director of Animal Control. lost of the
coyotes are taken by steel traps and den hunting, but some calling employing
sirens or commercial predator calls is done as well. M-44 devices were also
used until banned by the executive order in 1972. Wo other toxicants have
been used recently. Aerial hunting is not practical in this area because of
the dense vegetation and steep terrain.

In 1973-74 the Mendocino County Animal Control Department made an
estimate of the numbers of coyotes in the county (Vann, personal communica~
tion).* Each trapper district was evaluated by sections, with the trappers
giving their best estimate of the coyote population in each section. Areas
not being trapped were inspected by the Director and the numbers of coyotes
were estimated from scat counts, tracks, sightings, and den numbers. The
estimates for all areas were summarized for a total breeding population of
about 4,135 coyotes for the entire county.

When this estimate was made it was thought to be conservative. Director
M. Vann now believes (March, 1975) that the previous estimate should be
revised upwards by several hundred. Approximately 50 percent of the county,
including all areas east of highway US 101, is heavily populated by coyotes
and an additional 30 percent is lightly populated. While it is difficult

to verify Vann's estimate of coyote numbers in the county, we believe it

*M. Vann, Director of Animal Control, Mendocino County.

29



Our work suggests that the proportion of yearlings in the breeding
‘population (Cy/Cb), the proportion of females with litters (Cy,Ba), the
litter size (L), the proportion of pups in the control kill (Kr), and the
ratio between the control kill and breeding population (Kb) all vary with the
intensity of control (table 3). Several of these rates can be determined
by examination of the carcasses of coyotes killed in control programs, and of
the results compared with table 3 or other estimates to infer the actual
control level. Probably the most indicative data would be the yearling
pregnancy rate (By) and the litter size (L). All of these measures vary
with environmental conditions as well as control intensity. To separate
these influences would require sampling of uncontrolled coyote populations
to establish baseline data for comparison with the controlled populations.
Annual samples of coyotes for a period of years would also be desirable
to estimate the range of variability associated with year to year changes in
environmental conditions.

Predator control administrators frequently cite the number of aninals
killed as a measure of control effectiveness, While this statistic is often
the only one available, it has little meaning unless it can be related to
the number of coyotes remaining in the population. Whenever an estimate
of the breeding population (Cb) is available, the control kill (Kt) may
be expressed as a fraction of the breeding population to obtain a better
index of control effectiveness. As noted earlier (table 3) this ratio (Kb)
should exceed 3.0 1£ control is maintaining the population below half of
its normal (uncontrolled) density.

COYOTE CONTROL IN MENDOCINO COUNTY, CALIFORNIA

This section describes actual coyote control as practiced in Mendocino
County and relates this control program to our model, Mendocino County
was chosen as an example because of our experience on coyote studies at
the University of California, Hopland Field Station within this county.

Mendocino County contains 3,500 square miles of rugged forest and range
lands in north coastal California. Dense redwood and Douglas fir forests
cover much of the coastal half of the county. The eastern half is a mosaic
of grassland, oak woodland, hardwood, chaparral, and coniferous forest types.

The grassy openings grazed by livestock are typically close to woods or

28



tates are specified arbitrarily by the investigators at the beginning of

each run (or at the beginning of each year if desired). Reproductive and
natural loss rates are generated within the model and are variable with coyote
density, as described in detail later.

This coyote model may be called an "if-then" simulator. That is, if
a specified set of initial conditions is true, then over time a certain set
of results will follow. If a specified control level is pursued over time
the population will eventually stabilize at a level different than that when
no control is practiced. Various population parameters can then be compared
with similar values from an uncontrolled population to infer the effect of
that level of control on the coyote population. The concepts of this model
are generally similar to those employed by us in a deer simulation model
(Anderson, et al., 1974).

This model is an abstract representation of a complex biosystem. Like
any other model it is a simplification of real phenomena and requires certain
assumptions. Some of these assumptions are implicit in figure 1. Others
follow:

(1) In the absence of control, the population is stable, both in

numbers and age structure. The population occupies an area
of unspecified size which has sufficient resources to sustain
a breeding population of just 100 coyotes each year. For
simplicity the carrying capacity of this area for coyotes

is assumed to be constant year after year. In reality, the
carrying capacity varies with climate, food supplies and other
factors beyond the scope of this model.

(2) In the model the population contains two age classes: pups

(from birth to 12 months of age), and adults (over 12 months
old). As the whelping season approaches, the pups of the
previous year are called yearlings to distinguish them from
the newborn pups.

(3) Adult recruitment is limited to pups which survive their first

year. Immigration and emigration either do not occur: or occur

at equivalent rates.
(4) Birth and death rates are constant for adult coyotes of all ages.



yearling females. This value ranged from less than 10 percent in the
uncontrolled population to almost 75 percent before an extinction level of
control was reached, Tor this reason we concur with Knowlton (1972) that
the greatest potential for increased reproduction lies with the yearling age
class.

Several authors have described the seeming futility of attempting to
reduce coyote numbers by killing coyotes (Young and Jackson, 1951; Cain, et
al., 1972; Henderson, 1972). In table 3 perhaps the best indication of this
is Kb, which expresses the annual control kill as a fraction of the breeding
population. A value of 1.0 for this parameter means that the annual control
kill equals the breeding population. Note that a kill of about three coyotes
fpr every animal at breeding would be needed to hold the breeding population
(Cb) below 50 percent of the pre-control level. Even if this figure is not
precise it is apparent that a very high kill rate is needed to eliminate
coyotes.

Our model. suggests that coyotes through compensatory reproduction can
withstand an annual control level of 70 percent, but not 75 percent, However,
even at the 75 percent control level, the population persisted more than
50 years. We must point out that to achieve these results, 75 percent of
the coyotes must be removed in each and every year. When 75 percent were
taken in four of every Five years, with no control in the fifth year, the
breeding population (Cb) fluctuated between 28 and 76 coyotes with an average
of 42 and the control kill (Kt) averaged 102 animals per year.

EFFECTS OF BIRTH SUPPRESSION ON THE COYOTE POPULATION

Limiting coyote numbers by inhibiting reproduction with antifertility
agents rather than killing them directly is an attractive idea, at least
in theory, As pointed out by Balser (1964, page 356), "It may be more
practical to prevent animals from being born than to reduce their numbers after
they are partially or fully grown and established in a secure environment,"
Suppressing reproduction might also prevent the comensating increase in
reproduction associated with killing coyotes. Most importantly, antifertility
agents might be more acceptable to the public than large scale coyote killing
programs, especially if people were adequately informed on the biological
facts about coyote populations,

19



APPENDIX
PROGRAMMING AND CALCULATIONS

The relationships shown in figure 1 and table 1 of the main text of this

paper were programmed for solution on a Wang Model 360 electronic calculator

with Model CP~l1 card programming attachment. In its final version the

program contained 152 steps. The sequence of calculations was as follows:

1

10.
dl.
12.
13,
14,
is.
16.
7
18.
19.
20,
al.

Store initial values for Cy, Ca, Cb, and K (refer to table 1
for explanation of symbols). In each run the initial values
for Cy, Ca, and Cb were 40, 60, and 100, respectively.
Insert program card 1.

Calculate and store Dy

Calculate By.

Apply By to Cy to determine the number of yearling females
with litters.

Calculate Ba,

Apply Ba to Ca to determine the number of adult females with
litters.

Sum numbers of yearling and adult females with litters to
determine Fl.

In runs where part of the breeding females are subjected to
chemosterilization, apply S to Fl to determine the value of
Fl after birth suppression.

Calculate L.

Calculate P,

Calculate Cn.

Remove program card 1; insert card 2.

Calculate Pk and subtract it from P.

Calculate Ak and subtract it from Cb.

Calculate and store Dy.

Calculate Np,

Apply Np to (P ~ Pk) to determine Pn.

Subtract Pn from (P - Pk) to determine Cy for the next year.
Calculate Na,

Apply Na to (Cb ~ Ak) to determine An.

Subtract An from (Cb - Ak) to determine Ca for the next year,

36


22. Add Cy and Ca (from steps 18 and 21) to determine Cb for the
next year.

23, Remove program card 2,

Steps 2-23 constitute one annual cycle in the coyote model, To begin

the next year the user returns to step 2. As calculated in steps 18, 21,
and 22, the initial values for Cy, Ca, and Cb for the next year are in
storage. Two program cards were required to accommodate the entire model.
Card 1 covered reproduction and card 2 the mortality phase of the model.

Throughout this model the calculations were sequential and endogenous;
i.e., each step proceeded from values calculated and stored previously.

The only exceptions to this were as follows:

A, To begin a run four initial values were stored (step 1).

B. STOP commands were used throughout the program to permit
monitoring the calculations, Whenever Dy < 0.5 the calculated
values of By, Ba, and L (steps 4, 6, and 9) exceeded the
specified maxima (figs. 2 and 3). In such cases each excessive
value was replaced by the specified maximum before the calcula~
tions were continued.

C. Step 8a was used only in runs where part of the females were
prevented from breeding. This step was performed manually
because the limited storage capacity of the Wang 360 prevented
storing the value of S.

The Wang 360 calculator used in this study features visual display of
results. No output is printed. In using this model it was necessary to copy
the output as displayed (see table 2, for example). In practice it was found
that the calculations were made as fast as the operator could change cards
and copy the results. This procedure was slower than it would have been on
a high speed computer, but was much more efficient in the formulation,
validation, and programming stages.

The output from this model (table 2) does not include all the variables
shown in table 1, However, the variables not explicit tn the model can
readily be calculated from the output. In early stages of model development
all the variables in table 1 were included as output but it soon became
apparent that it would be more efficient to limit the program to essentials,
calculating the other variables from the output after the model reached

stability.
37



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THE EFFECTS OF CONTROL OW COYOTE POPULATIONS: A SIMULATION mopent??

Guy E. Connolly, Staff Research Associate, Division of Wildlife and Fisheres
Biology, University of California, Davis

William M. Longhurst, Wildlife Biologist, Division of Wildlife and Fisheries
Biology, University of California, Davis

ABSTRACT: According to a model developed to simulate coyote population
dynamics, the primary effect of killing coyotes is to reduce the density of
the population thereby stimulating density-dependent changes in birth and
natural mortality rates.

Tests of varying levels of control kills showed that a coyote population
can maintain itself and even increase its numbers except at the very highest
levels of control. If 75 percent of the coyotes are killed each year, the
population can be exterminated in slightly over 50 years.

Birth control combined with killing coyotes directly reduced both the
breeding and maximum populations more than when either method was used
separately, However, birth control is not yet feasible for field operations.

In this model, coyote populations reduced by intensive control recovered
to precontrol densities within three to five years after control was termi-
nated, Under current conditions, considering the restrictions placed upon
control methods, coyote densities probably cannot be significantly reduced
except in limited geographical areas.

The yearling pregnancy rate and the mean litter size are probably the
best criteria for indicating the level of control, although the proportion
of yearlings in the breeding population, the proportion of pups in the
control kill, and the ratio between the control kill and breeding population
also vary with the intensity of control.

Coyote control data from Mendocino County, California, were compared

with the model output. The existing county control program does not appear

lsubmitted for Publication April 30, 1975.

an contribution from Western Regional Research Project W-123, Evaluating
Management of Predators in Relation to Domestic Animals.

Spresent address: U. S. Fish and Wildlife Service, Twin Falls, Idaho



Table 1. (continued)

Variable Symbol Relation to other variables
Relative density after control Dp,” Dy = (Cm ~ Kt) /203.5
Proportion of pups dying of Np? Np = £D,
natural causes .
Proportion of adults dying of Na! Na = £D,
natural causes “
Pups dying of natural causes Pn Pn = Np(@ - Pk)
Adults dying of natural causes An An = Na(Cb - Ak)
Total natural mortality Nt Nt = Pn + An
Pups at year end cy(t + 1) Cy(t + 1) = P(t) ~ Pk(t) -
Pn(t)
Adults at year end Ca(t + 1) Ca(t + 1) = Ch(t) - Ak(t) -
An(t)
Total year end population Cb(t + 1) cb(t + 1) = Cm(t) - Ket) -
Ne (t)

Ww, *
Dy expresses the population surviving control (Also = population susceptible
to natural losses) as a fraction of the maximum population in the absence of

control,

“these values decrease as Dy decreases, The functions are described in
Figure 4,

as the population is reduced by control but it will never be lower than

10 percent. For the purpose of this model we set the adult natural mortality
rate at 40 percent in the uncontrolled population @, = 1.0), declining
toward 10 percent as Dy approaches 0 (fig. 4). The relationship

Na= 0.1 + 0.3 Dy) was calculated using least squares regression techniques.
Pup natural mortality (Np)

For the uncontrolled coyote population Q, = 1.0), this rate was
calculated from the assumptions and rates for other parameters given
previously, It is apparent that in a stable population with no control, the
pup natural mortality rate can be calculated from the number of pups born

and the number of pups surviving to one year of age:

12


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14


COOPERATIVE EXTENSION UNIVERSITY OF CALIFORNIA

This information is provided by Cooperative Extension, an educational agency of the University of
California and the United States Department of Agriculture.

Support for Cooperative Extension is supplied by federal, state, and county governments. Cooperative
Extension provides the people of California with the latest scientific information in agriculture and
family consumer sciences, It also sponsors the 4 H Youth Program,

Cooperative Extension representatives, serving 56 counties in California, are known as farm, home or
youth advisors. Their offices usually are located in the county seat. They will be happy tv provide you
with information in their fields of work,

Cover photo credit:
U. S. Fish and Wildlife Service,
Department of the Interior

The University of Califomia’s Cooperative Extension programs are
available to all, without rogard to race, color, or national origin.

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the United
States Deportment of Agriculture, James B, Kendrick, Jr., Director, Cooperative Extension, University of Calilernia,


U. S. Congress, House of Representatives.

1973. In: Predatory animals, Hearings before the Subcommittee on
Fisheries and Wildlife Conservation and the Environment of the
Committee on Merchant Marine and Fisheries. Mar. 19-20. Serial
93-2, Washington, D. C,: U. S, Govt. Printing Office, 397 pp,

Wade, D. A.

1973. Control of damage by coyotes and some other carnivores. Golo, Stz

Univ. Coop. Ext. Serv. Bull, 482a:16 pp.
Young, S. P. and H. H, T. Jackson,
1951. The clever coyote. Stackpole Co., Harrisburg, Pa. 411 pp.



within each run. As in previous tables the values representing numbers of
coyotes were rounded to the nearest whole number.

In general, the results of integrated control are intermediate between
those obtained with either birth control or killing applied separately.
Integated control (table 5) reduced the breeding coyote population (Cb) more
effectively than when either control method was applied separately (tables 3
and 4). However, the consequences of reducing the breeding population
include increased productivity of yearling females (By) and increased litter
size (L), which lead to more pups born (P) under integrated control (table
5) than would be the case with birth control only (table 4), There appears
to be a trade-off relationship between the breeding population (Cb) and
number of pups born (P), in that it is hard to minimize both parameters
simultaneously. The breeding population can be reduced by a heavy control
kill, but at the cost of increased reproduction and increased maximum popula-
tion. Conversely, the number of pups produced (P) can be reduced most by
birth control in a breeding population kept as large as possible. Of the
strategies tested so far in our model, the best prospect for reducing both
breeding and maximum populations would be integrated control at the highest

practicable rate.
RECOVERY OF COYOTE POPULATIONS FROM CONTROL

One aspect of coyote population dynamics which has received little
study is the capacity of a heavily controlled population to increase after
control is terminated. This was simulated for two different levels
of control -- 50 percent and 75 percent annual control kill for 20 years —-
followed by as many years without control as were required for the population
to recover to the precontrol level. The response of the breeding population
(Cb) to these treatments is shown in figure 5.

The population from which 50 percent of the coyotes were removed annually
stabilized after 6 years with a breeding population (Cb) of 72, coyotes each
year. Other parameters of this controlled population at stability are given
in table 3 (K = 50 percent). After control was terminated the population
recovered to its precontrol level in 3 years (fig. 5). By the beginning
of the fourth year after control was stopped, the numbers of yearlings and
adults in the breeding population were similar to those in the pre+control

population.

23



sf UNIVERSITY LiBRARY

) “UNIVERSITY OF ARKANSAS

Saye FAYETTEVILLE, ARKANSAS 72701

. THE EFFECTS OF CONTROL

ON
COYOTE POPULATIONS

Division of Agricultural Sciences BULLETIN
UNIVERSITY OF CALIFORNIA 1872

PRINTED AUGUST 1975



numbers of unborn pups in pregnant females. Twenty-nine litters were
reported from 1968 through March 1975. The fetal counts ranged from two to
11 with an average of 5.4 pups per females. Thirteen of the 29 litters
contained five pups each. Referring again to table 3, an average litter
size (L) of 5.4 would be expected when approximately 25 percent of the
coyotes are killed each year. This is a substantially higher control rate
than that indicated by the kill ratio (Kb) as determined above. However,
the litter size estimate (L) is biased toward that portion of the county
where control is intensive, while the kill ratio (Kb) represents the entire
county. This illustrates the difficulty of applying a simple model assuming
a uniform control rate to field conditions where the actual control rate
varies locally. Nevertheless this comparison agrees with our concept of the
“hot spot" pattern of control effectiveness and suggests that effects are
most evident in the immediate areas of intensive control, We conclude

that coyote control as practiced in Mendocino County has little impact on
overall coyote numbers.

We have no recommendations to improve the effectiveness of predator
control in Mendocino County for reducing livestock losses. Such recommenda-
tions would depend on cost effectiveness data beyond the scope of this study.
If, as we believe, the existing program removes predators from problem areas
without significantly influencing overall coyote numbers, it may be con-
sidered to serve the interests of both ranchers and preservationists.
However, there is room for improvement in the collection of data from the
animals taken in control,

As noted earlier, a number of statistics measurable from the control
kill can serve as indices to the level of control being achieved. These
include the proportion of yearlings in the breeding population (Cy/Cb in
tables 1, 3), the proportion of females with litters (By, Ba), the litter
size (L), the proportion of pups in the control kill (Kr), and the ratio
between the control kill and breeding population (Kb), With the exception
of the kill ratio (Kb) and litter size (1), as discussed above, little
information of this kind exists in Mendocino County.

This information could be determined if the age, reproductive status,

and litter size were recorded for each coyote taken by control officers.

31



Previously we noted that coyotes would be exterminated 1f 75 percent
were killed each year (table 3). After 20 years at this level of control
the breeding population was reduced to nine coyotes (fig. 5). However, in
our model the response to cessation of control was rapid. The breeding popu-
dation regained the precontrol density by the end of the fifth year after
control was terminated. If this projected recovery rate is accurate, there
is no need for concern that the coyote may become a rare or endangered species.

THE FEASIBILITY OF REDUCING COYOTE NUMBERS BY CONTROL

We have shown that coyotes could conceivably be exterminated if
sufficient numbers are killed for a sufficient number of years. However,
there is a great difference between killing coyotes in a computer and killing
them in the field.

In field operations the effort needed to take each coyote increases
with the intensity of control as a result of reduced density. Field opera—
tions usually cannot be planned to obtain specified: percentage kill rates,
but only to apply control within the limits of available funds and manpower.
Fortunately (or unfortunately, depending upon one's point of view) it is
usually beyond the range of economic feasibility to apply enough control
to exterminate the coyote, Because of limited resources, predator control
agencies generally concentrate their efforts in areas where depredations
on livestock are most severe, This "hot-spot" control pattern leaves mst
of the coyotes subject to light control, so that surplus animals are available
to repopulate the areas where control is heavy.

Animal control specialists generally agree that poisons were the most
effective means of reducing coyote populations. Prior to the presidential
ban (President's Executive Order Number 11643 of February 8, 1972), about
80 percent of all predatory animals killed in federal control programs were
taken with toxicants (Bureau of Sport Fisheries and Wildlife, 1973). Cain,
et al. (1972, page 42) reported that the use of 1080 may have caused coyote
populations to decline in seven western states. The Cain committee also
concluded that generalized coyote population control may be the most effective
approach to reducing livestock losses. Whatever teh desirability of such
control, we do not believe substantial coyote reductions can usually be
effected over broad areas without the use of toxicants. As shown in tables
3 to 5, coyotes will persist except with the most intensive control.

26



Figure 3.
COYOTE LITTER SIZE RELATED TO COYOTE DENSITY

i 1 ! J i ! i Lt
io 9 8 7 6 5 4 3 2

RELATIVE DENSITY (Dj)

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