Feral pig manuscript 050908 FINAL by wanghonghx


									 1   (Aiming for Journal of Applied Ecology)

 2   Spatial modeling of feral swine to determine effective population control methods

 3   J.L. Burton, M. Drigo, Y. Li, A.L. Peralta, J.S. Salzer, K. Varala, J. Westervelt, B.H. Hannon


 5   Summary

 6   1. Feral swine (Sus scrofa) are a destructive invasive species with high reproductive success.

 7   Through controlling swine populations, conservation of native species and overall decrease in

 8   habitat disturbance can be achieved.

 9   2. Controlling feral swine populations has been challenging due to their high fecundity,

10   generalist diet, and overall resilience to anthropogenic disturbance. Modeling provided a way to

11   test population control methods of hunting and sterilization techniques. Simulations are aimed to

12   guide selective implementation of management strategies that are very costly and challenging to

13   test in the field.

14   3. A combination of constant hunting pressure and oral contraceptive delivery through baiting

15   has been shown by this model to be the most effective control method for feral swine populations.

16   Under these pressures, the feral swine population is maintained at low numbers.

17   Key-words: feral swine, spatial modeling, population control, Fort Benning, Georgia (USA)


19   Introduction

20           Feral swine (Sus scrofa) are a non-native species that have successfully proliferated in

21   many habitats in the United States. This invasive species causes ecosystem disturbance due to

22   predation on native plants and animals, and destruction of landscapes and habitat due to their

23   natural rooting behavior (Graves, 1984). The highly adaptable nature and unusually high

 1   reproductive fitness of feral swine contributes to their success as an invasive species (Mauget,

 2   Barrett & Spitz, 1991). The challenge in managing feral swine populations is in identifying and

 3   administering the most efficient and most effective control techniques. To circumvent the

 4   difficulty in implementing population control methods in the field, modeling can offer insight

 5   and aid predictions to guide management strategies for more successful outcomes.

 6          Feral swine have been observed to increase destructive rooting behavior as the

 7   availability of high quality above-ground food sources, such as mast crops (tree nuts), decreases

 8   (Graves, 1984). During the winter when mast is available, it is the preferred food of feral swine

 9   (Adkins & Harveson, 2006), comprising a majority of the diet (Graves). The diet of feral swine

10   is not limited to the mast crop and ranges widely to include roots, herbaceous material, and small

11   vertebrates and invertebrates (Taylor, 1991). Acorns and other tree nuts are a source of high

12   quality nutrition because of their high fat and carbohydrate content (Graves, 1984). The diets of

13   males and females do not significantly differ (Adkins & Harveson, 2006). Grass and forb intake

14   increases in the summertime (Adkins & Harveson, 2006); however, grasses alone are suspected

15   to provide insufficient nutrition for feral swine (Graves, 1984). Roots, tubers, and herbaceous

16   material comprise up to two-thirds of the summer diet, while the remainder includes mast,

17   vertebrate, and invertebrate fauna, bait, or other materials (Adkins & Harveson, 2006). As food

18   availability varies, swine will also feed heavily on items such as earthworms, carrion, frogs,

19   leeches, insects, eggs, small mammals, agricultural crops, and garbage (Graves, 1984; Hanson &

20   Karstad, 1959; Herrero et al., 2006).

21          In areas such as Fort Benning, Georgia, USA, invasive feral swine are of particular

22   concern due to destruction of habitats specific to species at risk and species that are threatened

23   and endangered (TES). Feral swine at Fort Benning do not appear to be at carrying capacity

 1   (Jolley, 2007). The current population at Fort Benning is not vulnerable to food limitation

 2   because mast productivity is consistently abundant.

 3          Humans are the primary predator of feral swine and have the largest impact on population

 4   control; however coyotes, bobcats, mountain lions, large raptors and feral dogs are known to

 5   prey especially on young pigs. Mortality during the first 3 months of life is extremely high

 6   (Hanson, 2006). A bounty program at Fort Benning began in June 2007, but even under

 7   increased hunting pressure, this feral swine population can be sustained as long as food source is

 8   not limiting.

 9          Swine are considered a reproductively prolific species. The longevity of feral swine is at

10   least 15 years, and no reproductive senescence has been noted. Female reproductive maturity

11   typically occurs around six months and depends on nutrition and on exposure to other females in

12   estrus (Pedersen, 2007). While boars are physiologically capable of breeding around 5 months,

13   their fertility continues to increase over a period of several months. Competition is observed

14   among boars attempting to breed (Pedersen, 2007). Breeding is considered non-seasonal (Jolley,

15   2007); however, timing is heavily dependent on food availability, especially during mast crop

16   season (Graves, 1984; Jolley, 2007; Matschke, 1964; Mauget, Barrett & Spitz, 1991). Fertility

17   has not been observed to be density-dependent as long as the population remains in good

18   nutritional condition (Jolley, 2007). At Fort Benning, a bimodal breeding distribution is

19   observed with the majority of births occurring in March and from July through November.

20          Litter size varies from as few as three piglets to as many as thirteen, with a sex ratio of

21   1:1. The average litter for young sows is significantly smaller than for older ones, with first and

22   second parities producing an average of 4.8 piglets, while subsequent litters average 6.4 (Hanson,

23   2006). Male and female fertility is negatively affected by inadequate nutrition (Matschke, 1964)

 1   and heat stress (Jolley, 2007). Piglets are weaned at two to three months of age, and sows enter

 2   estrus one week later. With a gestation of 114 days, the minimum birthing interval is 19.3 weeks.

 3   Under favorable conditions sows are observed to produce approximately two litters annually.

 4          Sow groups, or sounders, are typically comprised of one to three sows and their piglets

 5   with an average of 2.59 sows (Hanson, 2006). When food is scarce, they may become much

 6   larger. Males typically remain with the sounder until they reach sexual maturity. Mature boars

 7   generally do not live in groups, though they congregate at breeding time to follow sounders

 8   during estrus (Pedersen, 2007).

 9          Food availability also influences home range and movement of feral swine (Graves,

10   1984). Swine are observed to occupy every habitat type available, although cover can be

11   essential for habitat selection depending on hunting pressure (Graves, 1984). Range data vary

12   widely with estimated ranges as small as 304 acres or as large as 6175 acres (Graves, 1984;

13   Hanson & Karstad, 1959). Boar range size is approximately double that of sounders, and the

14   sizes of both appear to depend on food and water availability (Hanson & Karstad, 1959). Feral

15   swine exhibit strong fidelity to their home ranges (Graves, 1984), generally leaving only when

16   food (Kurz & Marchint, 1972) and water (Graves, 1984; Taylor, 1991) are inadequate, or to

17   breed (Graves, 1984), and returning when conditions are suitable again. At Fort Benning, swine

18   are observed to move to wetland areas in the summertime and into woodlands during the winter

19   when the mast crop becomes available. From approximately one month prior to birthing until

20   piglets are about four weeks old, the sow moves away from the sounder (Hanson & Karstad,

21   1959) and occupies a much smaller range (Kurz & Marchint, 1972). No significant differences

22   in daily movement are observed between sexes, both of which travel 0.4 to 0.7 miles daily

23   depending on the availability of food and water (Kurz & Marchint, 1972).

 1          The challenge in assessing total population density has hindered the assessment of

 2   population control methods (Hanson, 2006). Radio collar studies have only supplied a narrow

 3   range of information (Hanson, 2006; Jolley, 2007). Several techniques have been implemented in

 4   the field, but no solution has been found to be effective universally. The proposed model will

 5   allow for the determination of the most ideal control strategy given the geographic and seasonal

 6   features of the landscape. In the present study, spatial modeling of feral swine population

 7   dynamics was used to assess efficacy of various population control strategies. Included in the

 8   model is a combination of known parameters on feral swine population distribution as well as

 9   potential control methods that are currently in use and/or have the potential to be implemented in

10   the future. More research is needed to more accurately assess the effects of control methods. The

11   specific objectives of this project were to use modeling to track population dynamics of a feral

12   pig population, and to test the effectiveness of control methods that have been difficult to

13   implement in the field. The expense and logistical challenges of field research are prohibitive.

14   Information from models can guide management strategies with possibilities that have not been

15   tested individually or in combination (e.g. hunting + sterilization).

16          Control can be implemented through several different techniques. When considering

17   control methods, several factors should be identified: 1) method of distribution over the

18   landscape, 2) population to target (gender and/or species specific), 3) route of administration, and

19   4) effectiveness over time. Because it is difficult to test various population control methods and

20   the intensity and combination of these methods, constructing models to test these control

21   methods is useful. Based on feral pig demography, reproduction, and hunting data specific to

22   Fort Benning, (1) how would implementing a lethal control program affect the feral swine

23   population over time?, (2) how would introduction of a contraceptive affect the feral swine

 1   population over time? What is the ideal method of delivery?, and (3) how would the

 2   combination of sterilization and lethal control programs affect the feral pig population?

 3   This model will be applicable to other feral swine populations and control methods at other

 4   locations despite the specificity of the location tested in this model. We hypothesize that the best

 5   swine control options will be a combination of lethal control in conjunction with effective

 6   contraception implementation.


 8   Materials and methods

 9   An agent-based model was developed to simulate effects of feral swine population growth with

10   varying control options (NetLogo, Version 4.0.2). Reproductive parameters (birth and death rate,

11   sex ratio, age of reproductive maturity) were based on information specific to Fort Benning,

12   Georgia, USA. Simulations of swine movement and patch preference were based on information

13   regarding food and land use preferences (Adkins & Harveson, 2006; Graves, 1984; Hanson &

14   Karstad, 1959; Herrero et al., 2006; Kurz & Marchint, 1972; Taylor, 1991). Parameters that were

15   permanently applied to each run were reproductive parameters (sex ratio of newborns, maximum

16   number of females in sounder, sexual maturity, minimal interval between breeding) and some

17   control method parameters (hunter kill rate and bait station success rate). Parameters that were

18   adjustable in the model interface included some reproductive parameters and mostly

19   incorporated details to change population control methods, which included sterilizing and killing

20   individuals. Table 1 is a summary of parameters included in the model. Control methods chosen

21   represent possibilities for control and some are not currently available for implementation (e.g.

22   sterilization control methods). Simulations of control methods included individual effects of

 1   hunting, injectable sterilization, bait-delivered oral sterilization, and bait station placement of

 2   oral contraceptive. The combination of hunting and sterilization techniques was also simulated.

 3          Fort Benning maps of land cover and soil type were incorporated into the model. A

 4   landscape representing 400 x 400 patches with a patch size of 45 x 45 m was used in the model.

 5   Because swine movement is driven by water and food availability, seasonality was incorporated

 6   into the model through use of soil and land cover maps to calculate for soil water storage based

 7   on precipitation and potential evapotranspiration. In addition, food-driven movement was based

 8   on the nutritional requirements of the individual and the availability of food in a patch. Patches

 9   containing more water or food were more attractive to pigs than those containing less of these

10   resources.



13   Four “breeds” were defined: pigs (male swine), sounders (female swine), hunters, and stations.

14   The time step is one week. The main body of the script contains two parts: “Setup” and “Go”.

15   “Setup” is called at the beginning of each run to initialize the “world” and set values of global

16   variables which include number of fertile females, number of sterile females, number of boars,

17   time of bait placement, number of hunters, number of swine that die from causes other than

18   control methods, frequency of bait placement (every week, month, year), female and male pigs

19   born, and group female pigs into sounders.

20       “Go” initializes the time steps. In each time step, sounder movements and structure

21   modifications are modeled first. Structure modifications include aging of individual pigs and

22   regrouping of mature females and mature males that leave sounders. New sounders are formed

23   by those mature females. Individual pig events, which include death and giving birth, are then

 1   simulated. A female pig gives birth if the following four requirements are satisfied: (1) female is

 2   sexually mature, (2) presence of mature, male pig within certain radius, (3) female has not been

 3   sterilized by any control method, and (4) female is not pregnant. In addition, the number of

 4   piglets in a litter is dependent on the female pig’s previous breeding history, as the first and

 5   second birthing events produce less piglets than subsequent births. The sex ratio of newborn pigs

 6   is 1:1. Piglets stay in the mother’s sounder until they reach maturity. Pigs die at a set age/sex

 7   specific death rate, which is derived from all current mortality factors observed in Fort Benning

 8   (Hanson, 2006). Observed post-weaning mortality rates for feral swine at Fort Benning are

 9   provided in Table 1.



12   Land cover, and soil maps specific to Fort Benning were incorporated into the model. Water

13   capacity values for each soil type were used to calculate seasonality on a monthly basis. Under

14   the “Setup” procedure, precipitation for average, dry, and wet years is defined. Under the “Go”

15   procedure, a function “calculate evapotranspiration” is called. This function contains all the

16   procedures for seasonality. Average temperature per month is calculated based on the following

17   trigonometric expression of average temperature: y = 10 sin (0.5236 * number of the month -

18   2.09) + 18. Using the average temperature, annual heat index is calculated. These values are used

19   to calculate the unadjusted potential evaporanspiration value, which is adjusted by multiplying

20   by a correction factor for location (30’ latitude) (Richard et al., 1998).

21       On the basis of adjusted potential evapotranspiration and precipitation for the current year

22   (average, dry, or wet), the amount of water in the soil is calculated for each patch. If there is

23   excess water (e.g. more water than a given soil can hold at its maximum), it goes into run-off and

 1   the storage of water stays at the maximum. If soil is not at water holding capacity, water storage

 2   decreases until it reaches 0. Water storage cannot be less than 0. If water storage appears to be

 3   less than 0, this value goes into “shortage” category and 0 goes into storage.



 6   In addition to water availability, food-driven movement was modeled. Because feral swine are

 7   observed to thrive on nearly any combination of nutritional resources, but clearly prefer mast,

 8   food-driven movement based on relative attractiveness of patches was used in the model. The

 9   availability of surface water was also factored in.

10       Mast energy content was reported in one study to be 1.32 kcal/g wet weight (Burns & Viers,

11   1973). The caloric density of acorns is between 2.5 and 3.2 kcal (CalorieKing.com) and the mast

12   density in Fort Benning woodlands of 40 grams/square meter (Jolley, 2007) was incorporated

13   into the model. Based on these figures a range of 52.8 to 126.2 kcal per square meter of acorns

14   was calculated.

15       Caloric requirements of feral swine were extrapolated based on calculations provided by the

16   American Veterinary Medical Association for the energy requirements of dogs performing “light

17   work”. The formula for metabolic energy requirement in this category is 2*[70*(body weight in

18   kg)0.75]. Based on average body weights for boars (130 pounds), sows under one year (60

19   pounds), and older sows (110 pounds), metabolic energy requirements of 2984, 1671, and 2632

20   kcal/day, respectively, were calculated. During the final month of gestation, 3744 kcal/day was

21   the calculated requirement for sows. Piglets’ requirements were calculated to require an average

22   of 519 kcal/day at one week of age, and 819 kcal/day at four weeks of age.



 2   Different population control methods include hunting, injectable sterilization , oral baits, and bait

 3   stations were incorporated to assess efficacy of feral swine population control (Table 2).

 4   Hunting – Hunters were introduced into the “world” at a set number. Bounty number in the

 5   model represents the number of hunters that are introduced into the “world” and move randomly

 6   three times per time step. The hunters are given a percent chance of shooting pigs within a given

 7   radius. This user-defined figure is referred to as “kill-radius”. Hunter presence will result in

 8   death of a user-defined percentage of male and female pigs within the kill radius. A higher

 9   percentage of death within the kill-radius translates to increased effectiveness of hunters.

10   Injectable sterilization – Hunters are also used to administer an injectable pharmaceutical to

11   sterilize female pigs. Users can switch between “sterilize or kill” on the interface and manipulate

12   the effectiveness by altering the percent chance of shooting to sterilize a pig within the kill-

13   radius.

14   Baits – Oral baits are used to sterilize or kill feral swine. The initial modeled baits are

15   techniques and methods previously used in field trials for swine population control (Table 2).

16   The oral baits are distributed by one of three methods; hand placement on the ground, aerial

17   dropping from a small aircraft, or stationary bait stations of concentrated bait densities.

18             The difference between ground and aerial placement of baits is in the density and

19   effectiveness. Ground placement of baits reaches a higher density of baits/area and a more

20   precise distance between baits, ultimately leading to a higher effectiveness of sterilization. Baits

21   are placed in the “world” with a precise density and distance from each other that can be

22   manipulated by the user to simulate ground or aerial distribution techniques. The baits are

23   placed within a range set by the user or set at random. The baits are placed every 4 time steps to

 1   simulate monthly bait placement. Each female pig that contacts a patch containing bait has the

 2   same likelihood of becoming sterile.

 3           Stations are introduced into the “world” and randomly distributed. The patches

 4   containing stations have high energy so that pigs, both male and female, have a higher chance of

 5   congregating around the bait stations. Pigs within a certain range of each station can either be

 6   killed or sterilized (females only) depending on user-specified settings. A “radius-of-effect” is

 7   created around each station. The effectiveness of the bait station (percent of pigs within effective

 8   radius that become sterile) can be manipulated by the user.



11   Combinations of feral swine control methods were simulated to test efficacy of methods on the

12   current known values for the Fort Benning feral swine population. Simulations were run 3 times

13   for 5 years each to monitor immediate impacts of control methods. Each control method was run

14   individually with varied dynamics to evaluate outcome with altered variables such as efficacy

15   and kill-radius. The final population size was recorded and compared between treatment methods.

16   Treatment methods were used in combination to test for interactions and outcomes.



19   The effects of different control methods on final feral swine population size were tested using an

20   analysis of variance (ANOVA). Swine population were considered significantly different if P <

21   0.05.

22   Not yet included in model: Modifications to be made to the model before final submission:

23   -Increase # of replicate runs to 10 and increase projections to 20 years.

 1   -Swine movement will more accurately represent swine behavior.

 2   -Test effect of bait/euthanize control treatment.

 3   -Validation of the model with observational data.


 5   Results

 6   Control methods that included hunting, injectable sterilization, and oral baiting to sterilize were

 7   simulated and final population numbers were provided in Table 3. Hunting at unfeasibly high

 8   rates (hunters = 100/week) was the most effective control method. In addition, injectable

 9   sterilization was effective at controlling the population but only at very high hunting pressure.

10   Bait stations and oral bait placement in a 100 x 100 patch area (4.5 km x 4.5 km) were not

11   effective. However, oral baiting in a 400 x 400 patch area (18 km x 18 km) did reduce swine

12   numbers, but as with the intense hunting treatment, this is not feasible. Shooting to kill or

13   sterilize does appear to provide more effective swine control than oral baiting methods.

14          The combination of baiting oral contraceptive in a 100 x 100 patch area while hunting

15   (even as few as 30 hunters a week) is much more feasible. Results from this trial show that the

16   swine population is controlled and does not increase rapidly after 5 years (Table 3).

17          Future simulations will be run in the context of the Fort Benning map. This will allow

18   our model to be specifically targeted to the movement of pigs at Fort Benning and the outcomes

19   of control methods in this system.


21   Discussion

22   As a result of the difficulty in testing feral swine population control methods in the field,

23   modeling provides an ideal way to test current and not yet developed control methods. The

 1   objective of this study was to use modeling to guide in-field implementation of control strategies

 2   and to help focus research efforts on methods that would produce the most successful outcome in

 3   the field. Preliminary results agree with our posed hypothesis that the swine population is most

 4   effectively and efficiently controlled by a combination of hunting and oral contraceptive baiting.

 5          Future modeling simulations will incorporate drought years without supplemental baiting.

 6   Currently, hunters heavily supplement food supplies at Fort Benning, Georgia, (Ditchkoff,

 7   personal communication) through baiting the swine at the rate of about 20,000 pounds of food

 8   per month (Sparklin, personal communication). These simulations will provide information on

 9   the response of the swine population to water and food stress without being confounded by

10   current practices of food supplementation through baiting practices by hunters. In addition,

11   sterilization of males will be simulated to test whether this method, which is not currently

12   developed, is a more effective sterilization technique. Projecting the model to 20 years will

13   provide more information on the effects of control methods through time. The 5-year simulations

14   provide a realistic implementation and response time to observe results quickly. Although we

15   have found no simple, clear control method to eliminate feral swine, this model provides

16   valuable information for those interested in controlling feral swine populations not only at Fort

17   Benning but throughout other invaded areas.


19   Acknowledgements

20   The authors would like to thank Dr. Stephen Ditchkoff at Auburn University, Dr. Bill Sparklin at

21   Montana State University, and Mark Thornton at Fort Benning for their expertise regarding the

22   Fort Benning feral swine population. We would also like to thank Bruce MacAllister at US Army

23   Corps of Engineers Construction Engineering Research Laboratory.


 2   References

 3   Adkins, R.N. & Harveson, L.A. (2006) Summer diets of feral hogs in the Davis Mountains,

 4          Texas. Southwestern Naturalist, 51(4), 578-80.

 5   Burns, T.A. & Viers, C.E. (1973) Caloric and moisture-content values of selected fruits and mast.

 6          Journal of Wildlife Management, 37(4), 585-87.

 7   Fleming, P.J.S., Choquenot, D. & Mason, R.J. (2000) Aerial baiting of feral pigs (Sus scrofa) for

 8          the control of exotic disease in the semi-arid rangelands of New South Wales. Wildlife

 9          Research, 27(5), 531-37.

10   Graves, H.B. (1984) Behavior and ecology of wild and feral swine (Sus scrofa). Journal of

11          Animal Science, 58(2), 482-92.

12   Hanson, L.B. (2006) Demography of feral pig populations at Fort Benning, Georgia, Auburn

13          University, Auburn, AL.

14   Hanson, R.P. & Karstad, L. (1959) Feral swine in the southeastern United States. Jour Wildlife

15          Management, 23((1)), 64-74.

16   Herrero, J., Garcia-Serrano, A., Couto, S., Ortuno, V.M. & Garcia-Gonzalez, R. (2006) Diet of

17          wild boar Sus scrofa L. and crop damage in an intensive agroecosystem. European

18          Journal of Wildlife Research, 52(4), 245-50.

19   Jolley, D.B. (2007) Reproduction and herpetofauna depredation of feral pigs at Fort Benning,

20          Georgia, Auburn University, Auburn, AL.

21   Kavanaugh, D.M. & Linhart, S.B. (2000) A modified bait for oral delivery of biological agents

22          to raccoons and feral swine. Journal of Wildlife Diseases, 36(1), 86-91.

23   Killian, G., Miller, L., Rhyan, J. & Doten, H. (2006) Immunocontraception of Florida feral swine

 1          with a single-dose GnRH vaccine. American Journal of Reproductive Immunology, 55(5),

 2          378-84.

 3   Kurz, J.C. & Marchint, R.I. (1972) Radiotelemetry studies of feral hogs in South Carolina.

 4          Journal of Wildlife Management, 36(4), 1240-48.

 5   Locke, S.L., Cook, M.W., Harveson, L.A., Davis, D.S., Lopez, R.R., Silvy, N.J. & Fraker, M.A.

 6          (2007) Effectiveness of Spayvac (R) for reducing white-tailed deer fertility. Journal of

 7          Wildlife Diseases, 43, 726-30.

 8   Matschke, G.H. (1964). The influence of oak mast on European wild hog reproduction. In

 9          Proceedings Annual Conference Southeast Association of Game and Fish Commission,

10          Vol. 18.

11   Mauget, R., Barrett, R.H. & Spitz, F. (1991) Reproductive biology of the wild Suidae. Biology of

12          Suidae., 49-64.

13   Mitchell, J. (1998) The effectiveness of aerial baiting for control of feral pigs (Sus scrofa) in

14          north Queensland. Wildlife Research, 25(3), 297-303.

15   Pedersen, L.J. (2007) Sexual behaviour in female pigs. Hormones and Behavior, 52(1), 64-69.

16   Richard, A., Pereira, L., Raes, D. & Smith, M. (1998). Crop Evapotranspiration - Guidelines for

17          Computing Crop Water Requirements. FAO Irrigation and Drainage.

18          Taylor, R.B. (1991). The feral hog in Texas. In Federal Aid Report Series Number 28.

19          Texas Parks and Wildlife, Austin.

20   Twigg, L.E., Lowe, T. & Martin, G. (2007) Bait consumption by, and 1080-based control of,

21          feral pigs in the Mediterranean climatic region of south-western Australia. Wildlife

22          Research, 34(2), 125-39.






















21   Table 1. Parameters included in model. Some parameters are constant or adjustable in the model.
                                                           Not adjustable in     Adjustable in
     Parameter                                Value
                                                           interface             interface
     Average sounder size                           2.59                                  x
     Female:male ratio in beginning             53 to 47                                  x

                                             > 3 mature
    Threshold for sounder splitting                                 x
    Age female reach mature                           24             x
    Age male reach mature                             32             x
    First & second delivery               4.8 pigs/litter            x
    Secondary delivery                               6.4             x
    Sex ratio of new born baby                    1 to 1             x
    Minimum interval between
                                              19 weeks               x
    Beginning female size                             48                      x
    Sows under one year old                       0.311              x
    Sows over one year                               0.2             x
    Boars under one year                          0.207              x
    *Breeding-radius                                100                       x
    *Hunter shooting success rate                  50%               x
    *Station success rate                          50%               x
    *Bait density                                     54                      x
    *Bounty                                           75                      x
    *Shelf-time                                        1                      x
    *Effectiveness (bait)                             80                      x
    *Hunting-radius                                   10                      x
    *Number-of-stations                               20                      x
    *Radius-station                                   57                      x
    Parameters not designated with "*" directly represent literature values
    *Indicates values that were chosen by authors and were guided by
    literature values

Table 2. Description of population control methods tested in model.
Methods of
Control              Target Sex   Delivery Method       Description             Outcome                 References                Model
Hunting              Female &     Hunters               All sexes and age       Pigs are killed         Benning hunting data      1) Contact with hunter over a
                     Male                               are hunted                                      2007, personal            short period of time will kill
                                                                                                        communication             males and females; 2) Kill radius
                                                                                                                                  around hunter in which a
                                                                                                                                  percentage of swine within this
                                                                                                                                  radius will be killed; 3) Hunters
                                                                                                                                  are not stationary.
Oral Contraceptive   Female       Dropped aerially at   Bait containing         Sterilization of        (Fleming, Choquenot &     1) Placed in a pattern over
                                  measured distances    pharmaceutical          females                 Mason, 2000; Mitchell,    landscape in measured distance
                                                        contraceptive                                   1998)                     and density; 2) Percentage of
                                                                                                                                  females in contact becomes
                                                                                                                                  sterile, males are unaffected; 3)
                                                                                                                                  Baits are removed from
                                                                                                                                  environment over a 72 hour
                                                                                                                                  period to represent consumption
                                                                                                                                  by swine and other animals.
Oral Contraceptive   Female       Distributed from      Bait containing         Sterilization of        (Fleming, Choquenot &     1) Same as aerial baiting (see
                                  ground with highly    pharmaceutical          females                 Mason, 2000; Mitchell,    above) but without randomness
                                  accurate spacing      contraceptive                                   1998)                     of placement and at higher
Oral Contraceptive   Female       Bait stations         Bait stations will be   Sterilization of        (Kavanaugh & Linhart,     1) Stations placed in few
                                                        set up for certain      females                 2000; Twigg, Lowe &       locations at one point in time,
                                                        time period and                                 Martin, 2007)             swine will be spatially attracted
                                                        continuously                                                              to bait stations; 2) Sterilization
                                                        stocked with bait                                                         of percentage of females within a
                                                        containing oral                                                           radius of stations; 3) Stations are
                                                        contraceptive                                                             stationary.
Injectable           Female       Dart gun              Injectable dose of      Sterilization of        (Killian et al., 2006;    1) Contact with contraceptive-
Contraceptive                                           pZP (porcine zona       females for period of   Locke et al., 2007)       hunter over a short period of time
Vaccine                                                 pellucida)              time (1-2 years)        (white-tailed deer with   will sterilize female; 2)
                                                                                                        SpayVac)                  Sterilization radius around
                                                                                                                                  sterilizing-hunter in which a
                                                                                                                                  percentage of swine within this
                                                                                                                                  radius will be killed; 3)
                                                                                                                                  Sterilizing-hunters are not

Table 3. Results of swine control method simulations.
 Methods of
 Control               Population size after 5 years
                       Effectiveness = 50     Effectiveness = 50        Effectiveness = 50
                       Hunters = 50           Hunters = 75              Hunters = 100
 Hunting                               2274                      575                      149
 Injectable            Effectiveness = 50     Effectiveness = 50        Effectiveness = 50
 Contraceptive         Hunters = 50           Hunters = 75              Hunters = 100
 Vaccine                               4099                      440                      514
 Oral Contraceptive Effectiveness = 80        Effectiveness = 80        Effectiveness = 80
 &                     100x100 patches        300x300 patches           400x400 patches
 Bait placement                       6930+                    2970+                   2480+
 Oral Contraceptive Effectiveness = 80        Effectiveness = 80        Effectiveness = 80
 &                     Bait station = 10      Bait station = 20         Bait station = 30
 Bait station                        13400+                  11700+                    7250+
 Oral Contraceptive Effectiveness = 80        Effectiveness = 80        Effectiveness = 80
 &                     Hunters = 30           Hunters = 40              Hunters = 50
 Hunting                               3520                     2760                    1297
 "+" after a number indicates that the population is still increasing


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