By: Shelby McCay, Student Technician
Texas A&M Natural Resources Institute
Wild pigs (Sus scrofa) are considered opportunistic omnivores – meaning they will consume both plant and animal food sources available to them throughout the year. The vast majority of a wild pigs diet consists of plant materials (Figure 1), and an important, seasonal food source for wild pigs are mast crops (acorns, fruits or beans). Common mast producing species in Texas include oaks, hickories, honey mesquite, prickly pear cactus and persimmon. This article will highlight the research that has been conducted on wild pig competition with native wildlife for mast, the effects mast has on wild pig population trends and how wild pigs’ consumption of mast can influence forest composition.
Figure 1. Wild pig diet composition6. *Other materials may include debris, garbage, lichen, rocks/gravel, soil/sand, etc.
Consumption of Mast
and Competition with Wildlife
Mast crops represent a high-quality food source for wildlife
and are consumed by many native Texas species including white-tailed deer, wild
turkeys, collared peccaries and multiple small mammal species, including
squirrels and rodents. Honey mesquite
pods contain high concentrations of carbohydrates, some protein and several
minerals, including sodium, calcium, iron, and zinc9. Acorns of both white and red-oak species (Figure
2) are high in fat and carbohydrates, and contain some vitamins and minerals,
including calcium and phosphorus8, 15. Acorns of the red-oak group have a high
concentration of phenolics and tannins15, which are compounds that
can reduce palatability to wildlife.
Figure 2. Red Oak species vs. White Oak species. Red oaks generally have pointed tips on their leaves and white oaks generally have more rounded tips on their leaves. (Images Credit: Robert O'Brien, Texas A&M Forest Service)
Due to the variable environments and unpredictable levels of
rainfall in Texas, mast crop production can vary widely between individual
plants, species and years. For example,
acorns from trees in the red-oak group are considered semi-annual producers
since they take approximately 15 months (two growing seasons) to mature,
whereas acorns in the white-oak group are considered annual producers since
they only take approximately 3 months to mature (one growing season)12. These crops are often available in large
quantities for limited periods of time, mainly in the fall and winter months. Because mast crops often are distributed
unevenly across the landscape, there is potential for competition among various
species of wildlife for these resources5.
To
test this hypothesis, researchers at the Caesar Kleberg Wildlife Research
Institute conducted an experiment to compare levels of mast intake between
multiple native wildlife species (white-tailed deer, wild turkeys, collared
peccaries, raccoons) and wild pigs by offering these various mast crops and
measuring the rate of intake and total amount consumed by each species. Results of the study found that wild pigs can
consume mast at an equal or higher rate than native species when consuming
mesquite pods and live oak acorns, and had the capability of eating the
relatively larger, astringent, red oak acorns that were rejected by raccoons
and wild turkeys. The rates of intake
and the ability of wild pigs to displace native wildlife species from feeding
sites2 suggests that wild pigs can compete effectively with wildlife
for mast crops5.
As stated above, wild pigs are opportunistic omnivores and
are able to readily shift their diet between browse, mast and animal food
sources throughout the year. Many native
wildlife species, on the other hand, are very specialized in their diets and
are unable to shift to new food sources when their usual ones run out. During productive years, this is generally
not an issue, but in years where resources are scarce wild pigs can exhaust food
supplies required by native wildlife, leaving these species with few options to
survive.
Acorns also contain the essential amino acid lysine, which is a primary determinant of milk production in domestic sows 19. Lysine concentrations in sow diets greatly influence offspring growth rates19. Therefore, litters born in a productive acorn crop year will have increased growth and future reproductive capability over litters born in unproductive years7.
In order to investigate this further, a study was conducted by researchers from Rice University and Texas A&M University over 7 years using exclusion plots in select areas of the Big Thicket National Preserve in Texas16. Results of the study found that mast producing species (hickory, oak, and tupelo) responded positively to wild pig exclusion and there was increased the diversity of woody plants in the forest understory, especially mast crop producing species, in exclusion plots versus non-exclusion plots16. In the non-exclusion plots, tree diversity was lower due to Chinese Tallow invasions, which were more than twice as abundant as in exclusion plots16. Increased wild pig management activities may be desirable in forests where mast producing species are the predominant part of the plant community and invasive plant species are present.
Conclusion
Overall, the relationship between native wildlife, wild pigs and mast crop species has been shown to be complex and incredibly interconnected. Wild pigs can effectively compete with native wildlife for these resources and exploit mast crops that many species find unpalatable, increasing their competitive advantage through increased fertility and reproduction. Exotic, invasive wild pigs also have the potential to change the species composition and diversity of forests through their consumption of mast crops, destruction of habitat and proliferation of invasive plant species. Continued wild pig control and damage abatement efforts remain imperative to keep both native wildlife and plant communities healthy and functioning.
Wild Pig Population
Dynamics and Mast Intake
Mast crops are an important component in population dynamics
of many species, including white-tailed deer, small mammals and wild pigs1,
11, 13, 18. The growth rate of
wild pig populations has been shown to be correlated to the seasonal
availability of mast producing tree species3, and the yield of both
previous and current mast crops influences the timing of reproduction and the
proportion of reproducing sows in a given year14.
A European research team conducted a long-term monitoring
study of two populations of wild pigs, one on a 14,800 acre fenced preserve in
Italy with low levels of mast crop production and low hunting pressure and the
other on a 27,200 acre forest in France with high levels of mast crop
production and high hunting pressure to assess how mast crops affect the reproductive
output of sows7. Results of
the study found that in both populations, abundant mast crop availability
increased body mass, and reproduction. Abundant
mast crop availability also led to direct increase in fertility, indicating
that wild pig sows adjust their reproductive output to track resource
availability7. Thus, sows
born in years with high mast crop production should be heavier the next
breeding season and potentially have higher fertility levels and larger litter
sizes than sows born in years with low mast crop production7 (Figure 3).
Figure 3. Research showed increased fertility and litter size in wild pigs with access to abundant mast crops.
Acorns also contain the essential amino acid lysine, which is a primary determinant of milk production in domestic sows 19. Lysine concentrations in sow diets greatly influence offspring growth rates19. Therefore, litters born in a productive acorn crop year will have increased growth and future reproductive capability over litters born in unproductive years7.
Forest Dynamics
Wild pigs may impact the diversity of tree species found in
forests through their consumption of mast crops and their destructive rooting
behavior. Since seed number and seed
size are generally negatively correlated10, mast producing species
may be more sensitive to consumption by wild pigs simply because they are
unable to produce as many seeds as small-seeded species such as grasses16. Rooting behavior can increase abundance of
small-seeded and invasive species such as Chinese Tallow (Triadica sebifera) by creating favorable soil conditions and
reducing competition from large-seeded species16. In order to investigate this further, a study was conducted by researchers from Rice University and Texas A&M University over 7 years using exclusion plots in select areas of the Big Thicket National Preserve in Texas16. Results of the study found that mast producing species (hickory, oak, and tupelo) responded positively to wild pig exclusion and there was increased the diversity of woody plants in the forest understory, especially mast crop producing species, in exclusion plots versus non-exclusion plots16. In the non-exclusion plots, tree diversity was lower due to Chinese Tallow invasions, which were more than twice as abundant as in exclusion plots16. Increased wild pig management activities may be desirable in forests where mast producing species are the predominant part of the plant community and invasive plant species are present.
Conclusion
Overall, the relationship between native wildlife, wild pigs and mast crop species has been shown to be complex and incredibly interconnected. Wild pigs can effectively compete with native wildlife for these resources and exploit mast crops that many species find unpalatable, increasing their competitive advantage through increased fertility and reproduction. Exotic, invasive wild pigs also have the potential to change the species composition and diversity of forests through their consumption of mast crops, destruction of habitat and proliferation of invasive plant species. Continued wild pig control and damage abatement efforts remain imperative to keep both native wildlife and plant communities healthy and functioning.
Wild pig resources listed below are available at the AgriLife Bookstore
– L-5523 Recognizing Feral Hog Sign
– L-5524 Corral Traps for Capturing Feral Hogs
– L-5524 Corral Traps for Capturing Feral Hogs
– L-5525 Box Traps for Capturing Feral Hogs
– L-5526 Placing and Baiting Feral Hog Traps
– L-5527 Door Modifications for Feral Hog Traps
– L-5528 Snaring Feral Hog
– L-5529 Making a Feral Hog Snare
– SP-419 Feral Hogs Impact Ground-nesting Birds
– SP-420 Feral Hog Laws and Regulations
– SP-421 Feral Hogs and Disease Concerns
– SP-422 Feral Hogs and Water Quality in Plum Creek
– SP-423 Feral Hog Transportation Regulations
– L-5533 Using Fences to Exclude Feral Hogs from Wildlife Feeding Stations
– WF-030 Reducing non-target species interference while trapping wild pigs
Click here for additional resources on wild pigs
_____________________________________________________________________________________________
For educational programming or technical assistance with wild pigs please contact:
Josh Helcel, 512-554-3785, josh.helcel@tamu.edu
Literature Cited
1 Barber,
D.W. and Coblentz, B.E. 1987. Diet, nutrition and conception in feral pigs on
Santa Catalina Island. Journal of Wildlife Management. 51: 306-317.
2 Berger, J.
1985. Interspecific interactions and dominance among wild Great Basin
ungulates. Journal of Mammalogy 66:571–573.
3 Bieber, C.
and Ruf, T. 2005. Population dynamics in wild boar Sus scrofa: ecology, elasticity of growth rate and implications for
the management of pulsed resource consumers. Journal of Applied Ecology. 42:
1203-1213.
4 Elston,
J.J. and Hewitt, D.G. 2010. Comparative digestion of food among wildlife in
Texas: Implications for competition. The Southwestern Naturalist. 55: 67-77.
5 Elston,
J.J. and Hewitt, D.G. 2010. Intake of mast by wildlife in Texas and the
potential for competition with wild boars. The Southwestern Naturalist.
55:57-66.
6 eXtension. 2012. Food Habits of Feral Hogs. http://articles.extension.org/pages/63655/food-habits-of-feral-hogs.
7 Gamelon,
M., Focardi, S., Baubet, E., Brandt, S., Franzetti, B., Ronchi, F., Venner, S.,
Saether, B. and Gaillard, J. 2017. Reproductive allocation in pulsed‑resource environments: a comparative study in two populations
of wild boar. Oecologia. 183: 1065-1076.
8 Goodrum,
P.D., Reid, V.H. and Boyd, C.E. 1971. Acorn yields, characteristics and
management criteria of oaks for wildlife. Journal of Wildlife Management. 35:
520-532.
9 Harden,
M.L., and Zolfaghari, R. 1988. Nutritive composition of green and ripe pods of
honey mesquite (Prosopis glandulosa, Fabaceae). Economic Botany 42:522–532.
10 Leishman,
M.R. 2001. Does the seed size/number trade-off model determine plant community
structure? An assessment of the model mechanisms and their generality. Oikos
93: 294–302.
11 McShea,
W.J., and Schwede, G.1993. Variable acorn crops: responses of white-tailed deer
and other mast consumers. Journal of Mammalogy 74: 999–1006.
12 Pierce
II, R.A., Dwyer, J., Stelzer, H. and Coggeshall, M. 2017. Managing Oaks for
Acorn Production to Benefit Wildlife in Missouri. http://extension.missouri.edu/p/g9414.
13 Scarlett,
T.L. 2004. Acorn production and winter reproduction in white-footed mice
(Peromyscus leucopus) in a southern Piedmont forest. Southeastern Naturalist
3:483–494.
14 Servanty,
S., Gaillard, J.M., Toïgo, C., Brandt, S., and Baubet, E. 2009. Pulsed resources
and climate-induced variation in the reproductive traits of wild boar under
high hunting pressure. Journal of Animal Ecology 78:1278–1290.
15 Short,
H.L., and Epps Jr., E.A. 1976. Nutrient quality and digestibility of seeds and
fruits from southern forests. Journal of Wildlife Management 40: 283–289
16 Siemann,
E., Carillo, J.A., Gabler, C.A., Zipp, R. and Rogers, W.E. 2006. Experimental
test of the impacts of feral hogs on forest dynamics and processes in the
southeastern US. Forest Ecology and Management. 258: 546-553.
17 Timmons,
J.B., Alldredge, B., Roger, W.E., and Cathey, J.C. 2012. Feral Hogs Negatively
Affect Native Plant Communities. Texas AgriLife Extension. SP-467.
18 Wentworth,
J.M., Johnson, A.S, Hale, P. E., and Kammermeyer, K.E. 1992. Relationships of
acorn abundance and deer herd characteristics in the southern Appalachians.
Southern Journal of Applied Forestry 16:5–8.
19 Yang, H.,
Pettigrew, J.E., Johnston, L.J., Shurson, G.C., and Walker, R.D. 2000.
Lactational and subsequent reproductive responses of lactating sows to dietary
lysine (protein) concentration. Journal of Animal Science 78:348–357.