National Wildlife Research Center (NWRC)

Project Accomplishments 2008

Movements of Feral Swine Relative to Aerial Control in South Texas—Aerial control is widely used by private landowners and WS officials in Texas to reduce feral swine damage.  However, no studies have been conducted on the impacts of aerial control on movements of surviving feral swine in the United States.  A scientist from the NWRC field station in Kingsville, Texas, conducted a study to evaluate whether aerial control of feral swine alters movements of surviving feral swine.  The scientist placed Global Positioning System (GPS) collars on 13 feral swine on a property experiencing extensive damage in south Texas, just prior to the initiation of an aerial control exercise.  These efforts, which included almost 6 hours of flight time, resulted in the removal of 151 feral swine on approximately 2,023 ha.  Of the nine animals on site during aerial control, two males and two females moved outside their home range a mean distance of 1/2 a mile.  However, all of these animals returned to within their home range the same day.  A preliminary analysis of the results indicated only minor, short-term feral swine movements in response to aerial control.  The results indicate that this technique may be useful in the event of a foreign animal disease outbreak.

A Genetic Evaluation of Feral Swine Ancestry in Texas—Feral swine descend from domestic swine that were released or escaped and have adapted to the wild.  Feral swine have been present in the United States for over 200 years, but have recently increased dramatically in number.  Texas has the largest population of feral swine, with current estimates at more than 1.5 million.  Feral swine are susceptible to diseases that affect wildlife, livestock, and humans, raising serious concerns about the role of feral swine in the maintenance and transmission of disease.  However, predictions of disease transmission by feral swine are hampered by a lack of information on their behavioral ecology.  As a result, estimates of contact rates and other vital information for disease risk models and management are tenuous at best.  NWRC biologists from the Center’s Kingsville, Texas, field station collaborated with Texas A&M University as part of a graduate student project to investigate the mating behavior of feral swine as a means of estimating rates of contact among individual animals. 

The biologists obtained tissue samples from free-ranging pregnant sows, extracted DNA, and constructed multilocus genotypes based on a panel of 12 DNA microsatellite markers.  Biologists collected 64 tissue samples from pregnant sows containing 345 fetuses.  They found evidence for multiple paternities in 21 of the 64 litters (33 percent).  Most of the litters were from McMullen and San Patricio counties, with the animals having 38 percent and 39 percent of multiple paternity occurrences, respectively.  The high rate of promiscuity (~33 percent of litters sired by >1 boar) suggests that the risk of feral swine transmitting diseases that are spread by direct contact (e.g., pseudorabies and brucellosis) is significant.  These results demonstrate the value of molecular techniques in providing insight into difficult wildlife management problems and supply timely information for predicting disease transmission within feral swine.

Evaluation of Strawberry-Flavored PIGOUT® Baits for Feral Swine—Few studies have examined baits as oral delivery systems of biological agents to feral swine in the United States.  Previous NWRC studies found that there was high removal and ingestion of both fish-flavored and vegetable-flavored PIGOUT® baits by feral swine in southern Texas, but that nontarget animals also removed and ingested the baits.  NWRC scientists initiated research to identify swine-specific attractants as alternate bait flavors.  The scientists identified strawberry flavoring as one such product that could be incorporated into a bait matrix intended for feral swine.  They compared feral swine and nontarget animal visitation, contact, and removal rates of five different PIGOUT bait treatments in southern Texas: (1) fish flavored, (2) vegetable flavored, (3) vegetable plus strawberry flavored, (4) vegetable flavored plus synthetic fermented egg, and (5) fish flavored plus synthetic fermented egg.  The trials involved using an automated camera system to monitor baits hand-placed at 120 locations for each treatment.  NWRC monitored the baits for up to four nights to determine species-specific visitation, contact, and removal rates.  All treatment baits experienced unusually high removal by rodents.

AI in Wild Raccoon Populations—Raccoons are common, widespread, and mobile, and they frequently come into contact with wild waterfowl, agricultural operations, and human activity.  NWRC scientists captured raccoons and analyzed blood samples to determine their exposure to AI.  Serosurvey results showed that raccoons are exposed to AI virus and develop antibodies based on that exposure.  The researchers found that antibodies to AI subtypes H10N7, H4N6, H4N2, H3, and H1 have a wide geographic variation in seroprevalence.  Analyses of the cellular receptors for influenza virus revealed that raccoons have both avian and human type receptors.  Experimental infection studies with captive raccoons confirmed that raccoons become infected with avian and human adapted influenza viruses, shed infectious virus, and can transmit virus to naïve raccoons.  Accordingly, raccoons have the potential for co-infection with multiple subtypes of influenza viruses and genetic reassortment, which could possibly result in the creation of novel influenza strains.

Survival and Movements of Translocated White-tailed Deer in Southern Texas—Translocation of white-tailed deer has become popular in southern Texas, yet its effectiveness for establishing populations in new areas is undocumented.  NWRC biologists evaluated the survival, movements, and body condition of 51 white-tailed deer translocated into a partially fenced property (2,000 ha) and an unfenced property (4,000 ha) in south Texas.  Cumulatively, 39 percent of all deer survived and remained on the release areas.  Annual survival was lower (59 percent) in the partially fenced property compared to the unfenced property (74 percent).  However, more deer left the unfenced property (60 percent) than the partially fenced property (15 percent).  Young (1.5 to 3.5 years of age), translocated males had below average antler gain, body condition scores, and rump fat measurements as compared to native males.  Results of this study give wildlife managers a basis for evaluating translocations as a tool to achieve their management goals.

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Kingsville, TX, Field Station