Wildlife Services

Protecting People 

Protecting Agriculture 

Protecting Wildlife

National Wildlife Research Center

FY 2017

Methods Development and Population

Management of Vultures and Invasive Wildlife

Contact Information:

Dr. Michael Avery, 

Research Wildlife Biologist 

Florida Field Station 

2820 East University Avenue 

Gainesville, FL 32641 

Phone: (352) 375-2229 

FAX: (352) 377-5559 

Email:

michael.l.avery@aphis.usda.gov 

Website: www.aphis.usda.gov/

wildlifedamage/nwrc/ 

Groups Affected:

Air travelers

Airlines

Airports

Archaeological site managers

Broadcast and communication

tower owners and operators

Business owners

City managers

Electric utility companies

Endangered species

conservationists and managers

Health authorities

Homeowners

Military installations

Natural resource managers

Tourists

Water managers (management

districts)

Wildlife managers

Major Cooperators:

Biosecurity

Queensland/Department of

Primary Industries

Florida Department of

Environmental Protection (or state

parks)

Florida Fish and Wildlife

Conservation Commission

National Park Service

University of California-Davis

University of Colorado School of

Public Health

University of Florida

University of Southern Queensland

U.S. Air Force

U.S. Fish and Wildlife Service

U.S. Geological Survey

U.S. Navy

Wildlife Services Operations

National Wildlife Research Center Scientists Address Problems Associated with 

Invasive and Overabundant Wildlife Populations

Wildlife Services' (WS) National Wildlife Research Center (NWRC) is the only Federal research

organization devoted exclusively to resolving conflicts between people and wildlife through the

development of effective, selective, and socially responsible methods, tools, and techniques. Scientists 

with NWRC's field station in Gainesville, Florida, conduct research to resolve problems caused by 

invasive species and overabundant native species. This 26-acre research facility includes large 

outdoor test pens and aviaries which allow research to be conducted under natural environmental

conditions. 

As land-use patterns change and people move into previously uninhabited areas, wildlife conflicts,

inevitably, increase. Of growing concern are problems associated with some abundant native bird

species, such as vultures, gulls and crows, which readily adapt to urban and suburban settings.

Additionally, populations of invasive or non-native species, such as feral pigeons, monk parakeets,

Burmese pythons, feral swine and Argentine tegu lizards, continue to grow with harmful impacts to

native ecosystems and human health and safety.

Applying Science & Expertise to Wildlife Challenges

Feral Swine Impacts to Rangelands. — Grazing lands in central Florida are a mosaic of sown

pastures, native grasslands, wetlands, and woodlands that offer a variety of important ecosystem

services. Feral swine damage to these areas negatively impacts economic productivity and biodiversity.

In a recent study, NWRC and University of Florida researchers looked at the specific impacts of feral

swine damage in pastures and grasslands. They found that feral swine rooting in native grassland

pastures reduced the number of plant species, while rooting in sown pastures increased the number of

plant species. In both sown pastures and native grasslands, swine rooting altered plant communities

and reduced agricultural productivity. Forage grasses were mainly associated with unrooted areas,

whereas low-quality forage or nuisance species dominated rooted areas. The researchers estimated

that more than 300,000 hectares (about 741,000 acres) of pasture and forage are lost to feral swine

rooting in central Florida each year, amounting to a $2 million loss in cattle production. More stringent

programs to manage feral swine populations could minimize the negative impact of their rooting on

valuable grazing lands.

Protecting Endangered Sea Turtle Nests From Predation. — On Florida's Keewaydin Island,

raccoon and feral swine predation poses major threats to sea turtle nests. Using 6 years of nesting

data for endangered sea turtles, NWRC researchers partnered with WS Operations and the

Conservancy of South Florida to study the impacts of feral swine and raccoon predation on nests.

Researchers also examined the benefits of eradicating feral swine from the island and caging sea turtle

nests to protect them from predation. Swine began preying on nests midway through the 2007 nesting 

season and destroyed all sea turtle nests on the island. The swine were later eradicated before the 

2008 nesting season. Eradication costs totaled $14,020, while the value of the hatchlings lost to 

swine predation in 2007 was 27 times higher at $379,100. When studying the benefits of caging sea 

turtle nests, researchers found that from 2005 to 2010, raccoon predation rates for caged nests were 

significantly lower than for uncaged nests every year except 2009, when little raccoon predation 

occurred. For feral swine, caging did not prevent predation, but caged nests remained intact almost 12 

days longer than uncaged nests. In short, eggs in caged nests have a greater chance of hatching 

before feral swine eat them. Researchers note the use of cages and other barriers as well as the 

removal of predators are effective strategies for protecting not only sea turtle eggs, but also other 

threatened and endangered plants and animals.

Evaluation of Invasive Reptile Management and Research. — Invasive or non-native reptiles and

amphibians have been in Florida for over 135 years, and their populations have increased quickly in

the last half century. Exotic snakes, lizards, frogs, turtles, and crocodilians are all breeding in Florida.

NWRC researchers led a team of scientists and managers to identify the invasive reptile species with 

United States Department of Agriculture 

Animal and Plant Health Inspection Service
the greatest ecological threats to Florida and find out the most 

useful ways to reduce their damage. They evaluated 37 

invasive reptile species and scored them based on their impacts 

to endangered or threatened species, eradication potential, stage 

of invasion (localized versus widespread), and adaptability. 

Results showed seven species with the highest potential for 

negative impact: Argentine giant tegu lizard, Burmese python, 

Nile monitor lizard, North African python, spectacled caiman, 

black spiny-tailed iguana, and yellow anaconda. Next, the 

team looked at vulnerabilities in each species that might be 

exploited for control purposes and the overall potential for 

successful management. They recommended the Nile monitor, 

black spiny-tailed iguana, and Argentine giant tegu for further 

research on management methods. Developing new tools for 

these species, along with practical management programs, 

have the highest probability of success in some areas.

Role of Genetic Diversity on Monk Parakeets' Successful

Invasion. — Invasive species cause millions of dollars in

damages every year. Identifying characteristics that make a

species a successful invader may help to prevent its spread.

Several studies have investigated the impact of genetic diversity

on species' abilities to establish themselves in new environments.

It is thought that a more genetically diverse founder population is

more likely to include individuals with traits that are better suited

to the new environment, making it more successful. To examine

this concept, NWRC and university scientists, as well as experts

from Australia, Canada, and Spain, compared genetic data

collected from native monk parakeet populations in South

America with data from invasive populations in the United States,

Europe, and Africa. Results showed that genetic diversity varied 

among the invasive populations and was overall lower than in the 

native populations. The low genetic diversity observed in 

invader populations does not support the hypothesis that high 

genetic variation inherently favors biological invasion or that 

invasion is favored by the combining or mixing of genetic 

variation from multiple source populations. In the case of 

invasive monk parakeets, other traits like their ability to build 

their own nests instead of relying on cavities for breeding, 

their tolerance of human disturbances, and their flexible and 

diverse diets may be responsible for their success.

Indexing Abundance of Voles in Artichoke Fields. — 

NWRC researchers compared two types of materials—nontoxic,

grain-based wax bait blocks and artichoke bracts (modified fleshy

leaves)—to see their effectiveness as chewing mediums to record

vole presence and index their populations. Researchers also

compared presence-absence observations of chewing on bait

blocks to the total percent chewed, as well as three sizes of

observation grids (4x4, 5x5, or 6x6 meters), to see which

recording methods best tracked population abundance. After

intense trapping, they determined the actual number of voles in

the area to better assess the different methods. Results showed

that bait blocks were better than artichoke bracts and continuous

measuring was better than presence-absence observations for

accurately determining vole abundance. All three grid sizes

worked well to track the number of known voles; however,

researchers caution that the largest grid size may be best if vole

abundance is unknown or low.

Documenting Feral Swine Impacts to Archeological

Resources. — Feral swine damage native plants and animals,

agriculture, infrastructure, and spread diseases. Another

important, but lesser known impact, is their disturbance to

archaeological sites. Of the 293 archaeological sites in 

Florida inspected by NWRC researchers and collaborators 

over a six year period, 42 percent had experienced swine 

disturbance. The areas of disturbance mapped within three historic 

homestead sites showed 5 to 26 percent of the total site surface 

area had been rooted. Artifacts were located at depths of less 

than 10 cm and less than 20 cm at 85 percent and 90 

percent of the sites, respectively. Feral swine rooting

commonly exceeds 20 cm in depth, making the great majority 

of the sites vulnerable to artifact damage or displacement.

Selected Publications:

Bankovich, B., E. Boughton, R.Boughton, M.L. Avery, and S.M.

Wisely. 2016. Plant community shifts caused by feral swine

rooting devalue Florida rangeland. Agriculture, Ecosystems and

Environment 220:45-54. doi: 10.1016/jagee.2015.12.027. 

Edelaar, P., S. Roques, E.A. Hobson, A. Goncalves da Silva, M.L.

Avery, M.A. Russello, J.C. Senar, T.F. Wright, M. Carrete, and J.L.

Tella. 2015. Shared genetic diversity across the global invasive

range of the monk parakeet suggests a common restricted

geographic origin and the possibility of convergent selection.

Molecular Ecology 24:2164-2176. doi: 10.1111/mec.13157. 

Engeman, R.M. and M.L. Avery. 2016. Prioritizing management

and research actions against invasive reptiles in Florida: A

collaboration by an expert panel. Herp Alliance and

USDA/WS/National Wildlife Research Center, Fort Collins, CO. 

Engeman, R.M., R.A. Baldwin, and D.I. Stetson. 2016. Guiding

the management of an agricultural pest: Indexing abundance of

California meadow voles in artichoke fields. Crop Protection 88:

53-57. doi: 10.1016/j.cropro.2016.05.013.

Engeman, R.M., D. Addison, and J.C. Griffin. 2016. Defending

against disparate marine turtle nest predators: nesting success

benefits from eradicating invasive feral swine and caging nests

from raccoons. Oryx 50(2):289-295. doi:

10.1017/S0030605324000805. 

Engeman, R. M., J. S. Meyer, and J. B. Allen. 2017. Prevalence of

feral swine disturbance at important archaeological sites over a

large landscape in Florida. Scientific Reports 7, 40287. DOI:

10.1038/srep40287

Major Research Accomplishments:

WS research estimated that more than 300,000 hectares

(about 741,000 acres) of pasture and forage are lost to feral

swine rooting in central Florida each year, amounting to a $2

million loss in cattle production.

WS research found the use of cages and barriers, as well 

as the removal of feral swine and raccoons, are effective

strategies for protecting endangered sea turtle eggs.

WS evaluated 37 invasive reptile species in Florida and 

identified seven species with the highest potential for negative 

impact: Argentine giant tegu lizard, Burmese python, Nile 

monitor lizard, North African python, spectacled caiman, black 

spiny-tailed iguana, and yellow anaconda.

WS analysis of invasive monk parakeet genetics showed that

invasive populations had lower genetic diversity than native

populations. 

WS experts determined bait blocks were better than artichoke 

bracts, and continuous measuring was better than presenceabsence observations, for determining vole abundance.

WS research documented extensie impactst to archaeological 

resources from feral swine rooting.

The U.S. Department of Agriculture is an equal opportunity employment provider and employer

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