Human Health and Ecological Risk Assessment

for the Use of Wildlife Damage Management Methods

by APHIS-Wildlife Services

Chapter XXII

USE OF EXCLUSION

IN WILDLIFE DAMAGE MANAGEMENT

August 2022
i

USE OF EXCLUSION IN WILDLIFE DAMAGE MANAGEMENT 

EXECUTIVE SUMMARY

USDA-Animal and Plant Health Inspection Service (APHIS)-Wildlife Services (WS) uses 

exclusion as a wildlife damage management method to remove, exclude, or limit the access of 

various vertebrate animals from specific areas to resolve wildlife damage situations. Exclusion 

methods include fencing, netting, wires, wire mesh, overhead netting, anti-perching devices, and 

several other barriers. Wildlife can cause damage to property, agriculture, and natural resources 

or cause human health and safety concerns, and exclusion is often used to eliminate wildlife 

access to these resources. Exclusion is used in commercial, urban, and rural settings targeting. 

many wildlife species including deer, rabbits, feral swine, coyotes, wolves, and numerous bird 

species. WS personnel generally recommend exclusion methods to resource owners, not being 

involved in their implantation, but WS does occasionally use and construct exclusionary devices

to resolve wildlife damage. For example, WS has used exclusion methods at airports to minimize 

aircraft strikes with wildlife or worked in the field to install fladry to keep wolves from killing 

livestock.

APHIS evaluated the potential human health and environmental risks from WS use of exclusion 

methods in wildlife damage management and determined that the risks to human health and the 

environment are negligible. Risks to workers are low based on WS personnel being trained in the 

proper use and set up of exclusion devices and wildlife handling in accordance with WS Directive 

2.635. Risks to the general population are negligible because site selection and timing minimize 

public exposure. Exclusion devices are used to decrease wildlife interactions with resources and 

are not methods that would contaminate water or result in the bioaccumulation of chemicals or 

other hazardous materials. Environmental hazards associated with exclusion devices generally 

are limited to the unintentional injury or death of target and nontarget species. Training WS staff 

in animal handling techniques reduces the risks of injury or death to target and nontarget species. 

Risks are negligible for nontarget fish and wildlife due to WS utilizing only the exclusion device 

specific to the resource to be protected.
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TABLE OF CONTENTS

1 INTRODUCTION........................................................................................................................................1

1.1 Exclusion Methods ..............................................................................................................................1

1.1.1 Fences .........................................................................................................................................1

1.1.2 Netting..........................................................................................................................................3

1.1.3 Overhead Wires ...........................................................................................................................3

1.1.4 Fladry ...........................................................................................................................................4

1.1.5 Anti-perching Devices ..................................................................................................................4

1.1.6 One Way Doors............................................................................................................................5

1.1.7 Fill/Seal Gaps...............................................................................................................................5

1.1.8 Entrance Barriers .........................................................................................................................5

1.2 Use Pattern for Exclusion Barriers......................................................................................................6

2 HAZARDS..................................................................................................................................................7

2.1 Human Health and Safety Hazards ....................................................................................................7

2.2 Ecological Hazards .............................................................................................................................7

3 RISKS.........................................................................................................................................................8

3.1 Human Health and Safety Risks .........................................................................................................8

3.2 Ecological Risks ..................................................................................................................................9

4 UNCERTAINTIES AND CUMULATIVE EFFECTS....................................................................................9

5 SUMMARY.................................................................................................................................................9

6 LITERATURE CITED.................................................................................................................................9

7 PREPARERS...........................................................................................................................................12

7.1 APHIS WS Methods Risk Assessment Committee ..........................................................................12

7.2 Internal Reviewers ............................................................................................................................14
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1 INTRODUCTION 

Exclusion devices are used by the United States Department of Agriculture (USDA), Animal and 

Plant Health Inspection Service (APHIS), Wildlife Services (WS) Program to eliminate and control 

unwanted access or interaction with animals in wildlife damage management (WDM). Exclusion 

methods form some type of barrier that minimizes or stops access to wildlife species from gaining 

access to protected resources. The selection of exclusion method(s) reflects the target animal 

being excluded from an area, their size, susceptibility to self-injury and the type of damage such 

as feeding, chewing, roosting or nesting. The ability of the target animal to penetrate specific 

barriers, animal motivation, behavioral characteristics of the animal, and economics are used to 

determine the type of exclusion barrier used. The level of protection necessary to eliminate or 

reduce damage permanently such as gaining access to a building or water sources on an airport, 

seasonally such as preventing access to livestock or crops while vulnerable, or for short term 

such as reducing access to wildlife during migration. Exclusion can be cost-effective, but this 

depends on the cost of materials and installation labor compared to the resource protected and 

anticipated damage.

Wildlife such as deer1 and feral swine, can cause damage to gardens and recently planted or 

ripening crops. Birds, such as gulls, geese, and fruit-eating birds like robins, cedar waxwings, and 

house finches, can cause significant damage to crops such as grains, corn, fruits, and nuts. The 

wide variation of exclusion barriers can help accommodate specific areas of interest, for example, 

unwanted wildlife at airports. Fencing and anti-perching devices are used at airports to decrease 

deer, coyotes, and other mammals on the airfield and decrease perching locations for hawks and 

owls. Items used for exclusion can vary in size, durability, height, material, and purpose. Although 

fencing is a very common exclusion barrier, bird netting, wire mesh, and anti-perching devices

will also be discussed. 

1.1 Exclusion Methods

Exclusion methods vary depending on the species targeted, efficacy, cost, and ease of use. The 

following methods describe ways to exclude animals from certain areas or resources and their 

efficacy.

1.1.1 Fences 

Fences exclude or contain animals by providing a physical barrier, a physiological barrier (via 

behavioral conditioning), or a combination of both. Some fences provide a physical barrier that 

prevents animals from passing over, through, or under them (e.g., woven wire fences). Electric 

fencing, however, provides a minimal physical barrier instead, relying on an electric shock to deter 

animals (McKillop and Sibly 1988, Curtis et al. 1994). Fencing can be a reliable way to exclude 

wildlife from designated areas. Though it can be labor-intensive, costly to assemble, and require 

occasional maintenance, fencing often lasts for many years. Fencing is good for protecting 

orchards, landscapes, vineyards, and tree nurseries. Fencing is cost-effective and practical when

protecting small landscapes, gardens, orchards, and larger areas that may contain crops or other 

agricultural products of high value. For areas of lower economic value, the labor required for the 

construction of fencing and maintenance should be considered. Fencing is effective in deterring 

deer and other pest animals. 

1 Scientific names for species are given in the text only for species not discussed in the Wildlife Damage Management Methods Risk Assessment 

Introduction.
2 

Non-Electric Fencing is often erected to

exclude sites from wildlife. Depending on the 

target animal, non-electric fencing may be a 

more viable option. Wire fencing is nonelectrical fencing consisting of woven metal 

wires that create a pattern that forms a physical 

barrier. Wire fencing is ideal for areas that have 

moderate to high mammal damage (e.g., deer, 

feral swine) (Curtis et al. 1994, Hone and 

Atkinson 1983, Isleib 1995). Fences can be

used to slow the spread of disease 

transmission, especially from animals such as 

deer or feral swine (Lavelle et al. 2011). 

Non-electrical fencing for deer should be at 

least eight feet high. Once erected, this fencing 

may require occasional maintenance to fix breaches created by fallen debris such as trees or 

limbs. A commonly used type of wire fencing is chain-link fencing and fixed knot fencing. These 

types of fences provide effective closures around structures and gardens. Another type of nonelectrical fencing that is cheaper and effective for areas where damage pressure is light to 

moderate is plastic deer fencing or polypropylene fencing. Polypropylene fencing (Figure 1) is a 

heavy plastic mesh that can be used as an exclusion method in gardens, crops, and individual 

plants. It offers high flexibility and contours to the ground easily. Because of this flexibility, the 

polypropylene fencing can sag and can be supported with posts every 10 to 15 feet (3.2-4.1 m)

using ties. This type of temporary fencing is best when long-term protection is unnecessary, and 

a less expensive option can be used. Polypropylene fences can last for about ten years, rolled 

up, and stored, whereas metal fencing may last as long as thirty years but is more permanent. 

Holes can form in the mesh and must be monitored for proper maintenance (Day and MacGibbon 

2007). 

Wire Mesh Fencing is available in many different forms: woven wire, chain link, welded wire, "v" 

mesh, and rigid mesh panels (VerCauteren et al. 2006). Wire mesh costs vary based on durability, 

lifespan, construction, and weight. Chain link fencing and wire fence panels are the most 

expensive, with welded wire being the least expensive. Woven-wire fence made of 12.5 

galvanized high-tensile steel is an ideal exclusionary material for ungulates such as deer. When 

manufactured with tension curves on horizontal wires, the fence material has the elasticity to 

minimize harm to an animal impacting it and facilitates installation on uneven terrain (Bryant et al. 

1993). The addition of a skirt going outwards a few feet at the bottom in an “L-shape” prevents 

animals from digging under the barrier to get into restricted areas. Wire mesh fencing is often 

used to minimize wildlife-vehicle collisions along highways with high traffic volume within 

migration corridors. A 7.9-foot (2.4m) wire-mesh fence along an interstate in Wyoming was 

effective in reducing collisions when used in conjunction with underpasses (Ward 1982) and 

reduced deer-vehicle collisions by 80% along a highway in Banff National Park, Alberta, Canada 

(Clevenger et al. 2001). Wire cages are often used for protecting individual plants that can be

browsed by herbivores or rubbed against by antlered animals. Wire cages and plastic mesh 

screens are commonly used to protect endangered species nest, such as sea turtles, from beach 

foraging mammalian predators. (Phillott 2020, Kurz et al. 2012).

Electric Fencing has historically been used for containing livestock and restricting wildlife from 

an area or commodity. When considering electric fences, factors such as voltage requirements, 

fence configuration, charge configuration, seasonal fences, and attractants should be examined.

Figure 1: Polypropylene fencing or deer fencing is 

commonly used in areas where deer damage is low;

this fencing is cost effective and a deterrent for deer. 
3

It is important to know the physical capabilities and behavioral aspects of the target animal to 

provide an efficient electric fence barrier. For example, standard fence designs used to contain 

livestock typically include three- to six-strand barbed wire and single and multi-strand electric wire. 

It is also common for post and rail and stockade type fencing to be used to contain livestock. This 

fencing proves effective for livestock, but it would not be ideal to exclude white-tailed deer

(VerCauteren et al. 2006). Electric fencing primarily function as a psychological barrier due the 

electric shock as opposed to a physical barrier. The electricity is used as a deterrent for animals

to prevent them from wanting to cross the fenced area. For example, an adequate voltage to deter 

deer would be a minimum charge of 3,000 volts and would be most effective on high-tensile wire 

and poly-tape materials (Matschke et al. 1984, Duffy et al. 1988, Curtis et al. 1994). Electric 

fencing can last up to thirty years and be less expensive than woven wire fencing.

Electric fencing contains animals or pests with bad climbing abilities, such as rabbits, hares, and 

ferrets. Electric fencing does not effectively contain animals with good climbing and jumping 

abilities, such as deer, coyotes, and foxes (Day and MacGibbon 2007). The most basic electric 

fencing design consists of wires that conduct an electric charge and are supported by posts made 

from wood, metal, or plastic and a charging system that supplies an electric current to the fence 

wires. Some or all of the wires on an electric fence conduct electricity. Animals must be grounded 

to get shocked, touch either a ground wire or a charged wire simultaneously or touch a charged 

wire and the ground grounded with a grounding rod. Electric fencing should not be used in 

residential areas. It is important to identify an electric current running through the fence to prevent 

injury to people, so warning signs are of high importance. The wires used for the electric fencing 

should be smooth and charged using a commercially available fence charger. The shock they 

administer is intermittent, therefore, safe for humans and animals. Direct current and barbed wire 

should never be used for electric fences because their use may cause electrocution. Electric

fencing may be baited with attractants, so the target animal is more likely to make contact with 

the fencing and get shocked. It is important to keep the fence baited to encourage the target 

animal to touch the fence; once the fence stops being baited, the target animal may try to get into 

the fence. Once crops have been sampled, it is almost impossible to keep target animals out of 

the crop. To help prevent collision or injury to nontarget animals, using brightly colored flags or 

tin cans to help with the visibility of the fence is important.

1.1.2 Netting

Netting is used as a barrier to exclude smaller birds from high-value crops (Tillman et al. 2000), 

buildings (Slater 1998), and aquaculture (Taber 2002). Bird-exclusion netting can be highly 

effective in reducing bird damage. However, the high cost of materials and labor for installation 

can be cost-prohibitive for lower-value commodities. Netting is commonly used for flocking bird 

species such as pigeons, blackbirds, swallows, starlings, and wading birds such as herons and 

egrets.

1.1.3 Overhead Wires 

Overhead wires, steel or monofilament, are another exclusion device used in WDM. Wires can 

be easier to erect than installing netting and is often more cost-effective for smaller projects,

though large ones covering more than several hundred square feet adjacent to dams have been 

erected to protect T&E fish species on the Columbia River. Wire is constructed in parallel lines 

over the site that needs to be protected. Wire has also become an effective tool in eliminating the 

access of gulls and other birds from sites (Solman 1994). A diameter of 0.03 in (0.8mm or 20 
4 

gauge2) or greater is recommended if steel wire is used. When using monofilament (a single 

strand of material, commonly plastic, with 100-pound test), it is important to test the line to make 

sure it is strong enough to handle the weight of landing or collision. 

Lines can be made visible for birds by using aluminum foil or other reflective objects that can be 

hung from the line. But often, the element of surprise is a sufficient tactic to keep birds from landing 

and perching on the lines. It is important to consider the species of bird that is the target animal 

to ensure that wire spacing effectively eliminates access for birds into restricted areas. It is also 

important to note that wire is not as effective on smaller birds. Wire should be checked daily for 

debris, tears, or objects or birds entangled in the line. This method is considered more costeffective than bird netting (Duffney 2006, Pochop et al. 1990).

1.1.4 Fladry

Fladry is a barrier device explicitly used for predators, such as coyotes and wolves. Fladry is used 

to alleviate predation on livestock by taking advantage of wolf and coyote fear of unfamiliar items 

on the landscape (Windell et al. 2021, Young et al. 2019). Fladry consists of a continuous rope 

strand with strips of flagging sewn or tied at 20 in (50 cm) intervals and strung 20 in (50 cm) from 

the ground for wolves. Closer spacing of fladry has been shown to be more effective with coyotes 

(11 in, 28 cm) (Young et al. 2019). Turbo fladry is modified from typical fladry by carrying an 

electric charge along the rope. Recent testing of turbo fladry conducted by the WS Feral Swine 

Task Force (unpublished data) to protect crops from feral swine damage had positive results.

Fladry can protect prairie dog colonies, black-footed ferrets, and livestock, especially at critical 

seasons (e.g., calving) (Windell et al. 2021).

1.1.5 Anti-perching Devices

Anti-perching devices include porcupine wire (e.g., 

Nixilite®, Bird-Flite®, and Cat-claw®), floppy wire 

(Daddi Long LegsTM and Bird Barrier Coil®), springtensioned wires, and shock strips. These types of 

devices can be used to keep birds from perching in 

particular areas (Figure 2). They are often attached 

to fences, signs, light fixtures, and ledges at 

airports and other areas where birds are not 

desired (Seamans et al. 2007). These devices help 

reduce roosting and loafing and associated bird 

fecal accumulation, which can deface resources 

due to its acidity. If bird fecal matter accumulates 

on top of buildings or other surfaces, it can become 

a human health and safety hazard and damage 

resources such as bridges and statues over time. 

Anti-perching devices can be effective at repelling 

birds. Still, issues such as debris build-up from a lack of maintenance, misshapen rods or wires 

from weather or larger animals, normal wear-and-tear, and nonfunctioning electrical systems for 

electrical wires and mats can reduce efficacy. 

Anti-landing devices include floating plastic balls called Euro-Matic Bird BallsTM that have been 

used at airport, mine, sewage treatment, sludge, and livestock waste settling ponds to keep birds 

2

 Wire gauge goes down as wire gets wider such as from 20 ga. to 8 ga.

Figure 2. Example of an anti-perching device (e.g., 

Nixilite®) installed on a ledge to keep pigeons from 

landing.
5 

from landing on ponds, many that may succumb to the toxicants or spread them around. Water 

on airports attract birds like gulls that are strike hazards. The balls are an effective barrier to keep 

birds from using the water source (Advanced Water Treatment Technologies 2017). WS typically 

recommends these and does not use these operationally. Once installed, the bird balls can last 

and provide other benefits to the users other than just repelling birds.

1.1.6 One Way Doors

One-way door cages (Figure 3) are an exclusion barrier 

used to remove pests from structures or burrows. The trap 

blocks an opening into an enclosure, preventing re-entry

into the structure or burrow. The one-way door is designed 

with a slant to encourage animals to push the door to enter 

the cage, and as it shuts behind them, they remain 

enclosed in the cage or trap. Baiting provides an attractant 

to get the target animal to enter the trap, but it is 

unnecessary. Understanding the size of the target animal 

is important to determine the size of the cage. It is also 

important to know how many one-way door cages you may 

need to exclude all target animals.

1.1.7 Fill/Seal Gaps

Gaps that allow wildlife to enter areas where they are not 

wanted are sometimes filled with wire mesh, sheet metal, 

patching compounds, chalking, concrete, steel wool, dirt, or 

other materials that prevent entry. Rodents can fit through 

about any hole they can get their head through (e.g., house mice and brown rats can squeeze 

through any opening greater than 0.25 inches and 0.5 inches, respectively). The more durable 

the product, the more likely it will repel the animal. Some will just be reopened (rodents gnaw 

through many materials, predators and rodents dig under fences, and birds such as woodpeckers 

can drill new holes). Wildlife should be removed from the area of concern prior to sealing access 

points to avoid trapping wildlife inside structures. Today, new buildings, bridges, and other 

structures often limit typical pest species' nesting areas and access points.

1.1.8 Entrance Barriers

Entrance barricades of various kinds are used to exclude 

several bird species such as starlings, pigeons, and house 

sparrows from dwellings, storage areas, gardens, or other 

areas. Heavy plastic strips hung vertically in open 

doorways (Figure 7) have been successful in some 

situations in excluding birds from warehouses and 

buildings, especially used for indoor feeding or housing of 

livestock (Johnson and Glahn 1994), a biosecurity 

measure. Plastic strips, however, can prevent or 

substantially hinder the filling of feed troughs or feed 

platforms at livestock feeding facilities. Such strips can also 

be covered up when the feed is poured into the trough by 

the feed truck. They are not practical for open-air feedlot 

Figure 3: One-way doors allow target 

animals to exit structures without the ability 

to regain entrance, so they may be

removed. 

Figure 4. Entrance barricade to deter birds.
6 

operations that are not housed in buildings. Metal flashing or hardware cloth may be used to 

prevent entry of wildlife into buildings or roosting areas.

1.2 Use Pattern for Exclusion 

WS minimally uses barriers to remove or block access to wildlife, including filling holes under 

fences, using one-way door cages to remove animals, fladry, and wire mesh or plastic netting to 

keep species from accessing areas. Because it is difficult to determine the number of animals

repelled from the use of exclusion barriers, few entries are recoded in the MIS3. Additionally, these 

techniques are generally recommended to the property owner rather than installed by WS. From 

FY164-FY20, an annual average of 337 animals were repelled or evicted from areas in 9 states 

and 1 territory.

Table 1. The annual average number of target species repelled with barriers used by WS in wildlife damage 

management from FY16 through FY20. 

ANNUAL AVERAGE SPECIES REPELLED WITH BARRIERS

Species* Repelled/Exited States Where Used

Fill Crawl Hole

Black Bear 0.2 AK

Coyote 2 CA

Fill Crawl Hole Total (2 sp.) 2 2 States

One-way-door

Virginia Opossum 0.8 CA

Northern Raccoon 12 CA

Striped Skunk 75 CA

California Ground Squirrel 40 CA

One-way Door Total (4 sp.) 127 1 State

Nest/Roost Wire Mesh

Brazilian Free-tailed Bat 202 TX

Canada Goose 1 MA

Pelagic Cormorant 0.8 OR

Osprey 2 FL WV

European Starling 1 PA

Nest/Roost Wire Mesh Total (5 sp.) 207 6 States

Plastic Netting

Trumpeter Swan 0.4 IA

Barn Swallow 0.4 PR

Plastic Netting Total (2 sp.) 0.8 1 State, 1 Territory

TOTAL (13 sp.) 337 9 States, 1 Territory

* Introduced species 

Data recorded between FY11 and FY15 was less, with an annual average of 32 animals repelled. 

Feral pigeons (0.8 dispersed) were excluded from building nest sites. Mixed blackbird species (26 

dispersed) were blocked from roost sites. Ospreys (0.4 dispersed) were excluded using netting 

at the Space Center; this was an attempt to block nesting structures so nesting would not 

continue. Burrowing owls (0.4 dispersed) were excluded using one-way doors on ground squirrel 

burrows on an airfield where they are a strike hazard. Coyotes (1) were blocked with barriers at 

crawl-through spaces under fencing that led into the air operations area of an airport. Striped 

3 MIS - Computer-based Management Information System used for tracking APHIS-WS-WDM activities nationwide. 

Throughout the text, data for a year (i.e., FY11 (next footnote)) will be given and is from the MIS. MIS reports will not 

be referenced in the text or Literature Cited Section because MIS reports are not kept on file. A database is kept that 

allows queries to be made to retrieve the information needed.

4 FY16 equals the federal Fiscal Year 2016 which is October 1, 2015-September 30, 2016.
7

skunks (2) were excluded through one-way doors used under residences. Eastern gray squirrels 

and fox squirrels (0.6 dispersed each) were excluded from nesting areas at industrial sites. 

Exclusion barriers used by WS require labor, monitoring, and occasional maintenance. Barriers 

must be monitored to ensure no debris, entangled animals, or breaks and tears in the materials

have occurred. 

2 HAZARDS

2.1 Human Health and Safety Hazards

Human health and safety hazards associated with exclusion barriers include potential cuts or 

abrasions from loose wires, snags, or sharp edges on the equipment, electric shock from 

electrified fences, and possible strain from labor and maneuvering of materials. Most injuries 

occur while setting, or maintaining exclusion barriers, due to the labor of erecting these structures 

to perform efficiently. Muscle strains could also occur during the construction or placement of 

exclusion barriers because of the large fencing sheets or moving of structural supports. Cuts and 

abrasions are common when using barbed wire or other materials that may contain sharp edges, 

sharp points, and other deterrents. Removing target and nontarget animals from exclusion 

barriers may lead to bites or scratches. It is important to wear proper protective gear and evaluate 

the situation for safety concerns.

Handling wildlife entangled or caught on/in exclusion barriers could also result in hazards 

associated with disease and parasite transmission from target and nontarget wildlife (Animal Care 

Use Committee 1998, WS Directive 2.635). For example, target animals such as white-tailed deer 

and other ungulates can be hosts for diseases such as bovine tuberculosis (Schmitt et al. 1997), 

chronic wasting disease (Miller et al. 1998), brucellosis (Rhyan 2000), and Lyme disease. Chronic 

wasting disease (CWD) is a prion disease of elk, white-tailed deer, mule deer, and moose and is 

transmitted through direct contact and other means (Miller et al. 2004). Bovine tuberculosis is a 

bacterial disease established in wild white-tailed deer herds in northern Michigan and can be 

readily transmitted to cattle through direct contamination or environmental contamination 

(Kaneene et al. 2002). White-tailed deer also serve as a host for the primary vector of Lyme 

disease. Reducing the concentration of deer can reduce the occurrence of Lyme disease in 

humans (Kilpatrick and LaBonte 2003). The recent increase in outbreaks has emphasized the 

importance and need for exclusion devices to reduce potential disease transmission between 

domestic and wild animals and humans. The same injury and disease hazards extend to the 

public who encounter and tamper with animals that are caught in exclusion barriers placed by 

WS.

2.2 Ecological Hazards

Ecological hazards associated with exclusion barriers include capture, injury, or death to 

nontarget animals. These ecological hazards can be avoided by monitoring exclusion barriers 

and maintaining the condition of the materials used. It is important to understand other animals 

may come into contact with the exclusion barrier. It is common for nontarget animals to get injured 

and entangled by colliding with exclusion barriers when attempting to pass through or under 

barriers. Allowing for the barriers to be visible can keep nontarget animals from colliding with the 

barriers and getting entangled. Using bright markers or making sure posts are closer together can 

help many animals prevent possible injury. Materials used around bodies of water should be 

closely monitored due to the possibility of contamination and harm to nontarget wildlife through 

ingestion and strangulation. Another environmental risk that exclusion barriers can cause is the 
8

disruption of emigration and immigration (Nielsen et al. 1997). Exclusion barriers can disrupt the 

movement of animals such as deer, causing detrimental effects on wildlife migration (Owen and 

Owen 1980). Fencing can cause hazards to grouse due to collisions with wires in rangeland 

habitat. These hazards can be mitigated with fence-marking methods (Stevens et al. 2012).

3 RISKS

3.1 Human Health and Safety Risks

Human health and safety can be affected by unwanted target animals through interactions on 

roadways and in areas where aircraft are present such as airports. Exclusion barriers can prevent 

the risk of animals causing automobile collisions and aircraft malfunctions, which can damage 

property and cause human casualties. This is a very common issue on roadways as deer often 

graze in fields parallel to roadways that may have high traffic volume. It was estimated that deervehicle collisions cost approximately $1.6 billion annually (Conover 2002). White-tailed deer were 

also determined to be the most hazardous mammal on airport runways, causing an estimated 

$52,909,864 in damage per aircraft collision between 1990-2020 (Dolbeer et al. 2021).

Human health and safety can also be compromised with animal interaction because many 

animals can have diseases that are zoonotic to humans and domestic animals. White-tailed deer,

in particular, are common carriers of diseases such as chronic wasting disease (CWD), bovine 

tuberculosis, and Lyme disease (DeNicola et al. 2000). Chronic wasting disease is easily spread 

from elk, white-tailed deer, and mule deer. It is spread through direct contact and can be spread 

through indirect contacts, such as environmental contamination. Livestock can potentially transfer 

CWD to humans and domesticated animals. Feral swine can carry zoonotic diseases to humans,

including brucellosis, bovine tuberculosis, and leptospirosis, among others (Brown et al. 2018). 

Exclusion barriers help eliminate access or interaction from potentially contaminated animals to 

other animals and humans. Lyme disease can easily be transmitted from animals to humans, 

causing a need to reduce the concentration of deer in unwanted areas (Kilpatrick and LaBonte 

2003). Canada goose conflicts in the eastern United States include intensive foraging and 

localized (aquatic and terrestrial) fecal contamination in recreation areas (Conover and Chasko 

1985). The close proximity of geese and humans increases the risk associated with pathogenic 

bacteria prevalent in Canada goose feces (Kullas et al. 2002).

During FY16-FY20, WS employees had an annual average of 2.6 injuries from falls, slips, and 

repetitive activities that resulted in lacerations, sprains, contusions, strains, and bruises 

associated with field activities, specifically related to exclusion activities. These were mainly due 

to installing posts for temporary fencing, one injury due to removing an eagle from netting 

excluding birds from a fish hatchery, and two tick exposures installing fencing and fladry in the 

field. Considering the number of WS employees (~1,900), these claims are relatively few for the 

number of hours spent afield. Thus, the risks of deploying exclusion devices are relatively minor 

to employees.

Overall, risks to workers are low based on WS personnel being trained in the proper use and set 

up of exclusion devices and wildlife handling in accordance with WS Directive 2.635. Risks to the 

general population are negligible because site selection and activity timing minimize public 

exposure.
9

3.2 Ecological Risks

Ecological risks include risks to all nontarget animals. When target animals are being excluded 

from areas that are often their feeding grounds, it is not common for them to find another location 

to feed. They will often move to a nearby unprotected area (Isleib 1995). The addition of habitat 

loss may cause the target animal to concentrate in smaller areas. This could cause existing 

damage to become greater and increase the likelihood of disease transmission to nontarget and 

domestic animals. There can also be risks involved in areas of high stress, which can cause the 

ability of human health hazards to increase. For example, stressed deer are driven by non-typical 

behaviors, and under certain circumstances (e.g., being pursued by a hunter), they will penetrate 

exclusion barriers such as fences that would typically deter them (Bryant et al. 1993, Conover 

2002). The stress that target and nontarget animals can exhibit when being excluded can lead to 

unintentional death or injury.

Risks to nontarget animals are minimized by proper placement and selectivity of barriers. WS 

recommends the appropriate barrier for the situation to prevent nontarget effects, or by adding 

marking materials to reduce hazards to nontarget species from barriers.

4 UNCERTAINTIES AND CUMULATIVE EFFECTS

Uncertainty in this risk assessment is negligible as APHIS-WS has used various styles of 

exclusion barriers for WDM activities and understands the potential risks of erecting and 

maintaining exclusion barriers. The knowledge gained from this experience has helped reduce 

risks associated with exclusion barriers, especially regarding human health and safety due to 

encounters with entangled or injured animals and injuries due to exclusion barriers such as 

fencing, both electric and non-electric, and neglected maintenance. 

Cumulative impacts could occur to target and nontarget animals. However, cumulative impacts 

are addressed in National Environmental Policy Act documents and found not to be significant to 

any native species population. Additionally, the "Introduction to WS Methods Risk Assessments,"

Chapter 1 gives all species taken by WS from FY11 to FY15 and shows no significant impacts 

from a population standpoint. From a human health perspective, the use of exclusion barriers in 

WDM will not have any known cumulative impacts.

5 SUMMARY

The use of exclusion methods in WDM is an effective and nonlethal method for protecting crops, 

livestock, and other agricultural and domestic products. Exclusion barriers, such as fencing, wire, 

netting, spikes, etc., are exceptional in maintaining health, safety, and value in structures, 

gardens, orchards, and livestock production areas. Exclusion barriers are often a tool in an 

integrated wildlife damage management program. It is important to understand the efficiency of 

any exclusion barrier is limited to material, proper maintenance, effectiveness in excluding 

animals based on physical and behavioral characteristics, and overall motivation of the target 

animal to penetrate a specific exclusion barrier. 

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7 PREPARERS

7.1 APHIS WS Methods Risk Assessment Committee

Writers for "Use of Exclusion in Wildlife Damage Management":

Primary Writer: Thomas Hall 

Position: USDA-APHIS-WS, Operational Support Staff, Staff Wildlife Biologist, Fort Collins, CO

Education: BS Biology (Natural History) and BA Psychology – Fort Lewis College; MS Wildlife Ecology –

Oklahoma State University

Experience: Special expertise in wildlife biology, identification, ecology, and damage management. Thirtyseven years of service in APHIS Wildlife Services including operations and research in DC, CO for 

research and OR, GU, CA, OK, NV, CO for operations conducting a wide variety of programs including 

bird damage research and management, livestock protection (predators and birds), invasive species 

management, wildlife hazard management at airports, property and natural resource protection 

including waterfowl, brown tree snake, feral swine, rodent, and beaver damage management. Used 

and instructed cooperators in the use of exclusion methods. 

Primary Writer: Jasmine Scott

Position: USDA-APHIS-WS, Biological Technician Summer Intern 2017, Pocatello, ID

Education: Pursuing BS degree in Animal Sciences with a concentration in Wildlife, Tuskegee University
13

Experience: One year as a writer for Tuskegee University’s The Odyssey Online News Platform. During 

internship at the USDA-APHIS Pocatello Supply Depot, revised and reformatted Standard Operating 

Procedures (SOP) and Manufacturing Procedures (MP).

Writer: Shelagh DeLiberto

Position: USDA-APHIS-Wildlife Services (WS), National Wildlife Research Center (NWRC), Wildlife 

Biologist, Fort Collins, CO

Education: BA Biology and Environmental Science – Ithaca College; MS Wildlife Biology – Colorado State 

University

Experience: Nineteen years of service in APHIS conducting wildlife research including bird damage 

research and management, property and natural resource protection including waterfowl, 

woodpeckers, feral swine. Five years of experience in preparing categorical exclusions and 

environmental analyses in compliance with the National Environmental Policy Act.

Editors/Contributors for "Use of Exclusion in Wildlife Damage Management Risk 

Assessment":

Editor: Michael Green 

Position: USDA-APHIS-Wildlife Services (WS), Environmental Coordinator, Fredrick, MD

Education: BS Wildlife and Fisheries Sciences, University of Tennessee

Experience: Special expertise in wildlife biology, ecology, and damage management. Eleven years of work 

experience with WS in MD and VA. Experienced in a wide range of program activities including nutria 

eradication, airport wildlife management, and wildlife damage management to protect livestock, 

aquaculture, public safety, and natural resources. Served as staff biologist in WS Headquarters for 

two years.

Editor: Andrea Lemay

Position: USDA-APHIS-Policy and Program Development (PPD), Environmental and Risk Analysis 

Services (ERAS), Biological Scientist, Raleigh, NC

Education: BS Plant and Soil Science (Biotechnology) - University of Massachusetts; MS Plant Pathology 

-North Carolina State University 

Experience: Fourteen years of service in APHIS conducting risk analysis. Four years of experience in 

preparing environmental analyses in compliance with the National Environmental Policy Act. 

Editor/Contributor: Jim Warren

Position: USDA-APHIS-Policy and Program Development (PPD), Environmental and Risk Analysis 

Services (ERAS), Environmental Toxicologist, Little Rock, AR 

Education: B.S. Forest Ecology and M.S. Entomology – University of Missouri; Ph.D. Environmental 

Toxicology – Clemson University

Experience: Nine years of experience working for APHIS preparing ecological risk assessments and 

providing assistance on environmental compliance. Prior experience before joining APHIS includes 

other government and private sector work regarding ecological risk assessments related to various 

environmental regulations.

Editor: Ryan Wimberly 

Position: USDA-APHIS-WS, Operational Support Staff, Staff Wildlife Biologist, Madison, TN

Education: BS Wildlife Management and Ecology – Northwest Missouri State University

Experience: Special expertise in wildlife biology, ecology, and damage management. Eighteen years of 

service with APHIS Wildlife Services, including operations and research, conducting a wide variety of 

programs, including bird damage research and management, livestock protection, invasive species 

management, wildlife hazard management at airports, property, and natural resource protection. 

Expert in preparing environmental documents for WS programs to comply with the National 

Environmental Policy Act and the Endangered Species Act.
14

7.2 Internal Reviewers

Editor: Odin Stephens

Position: USDA-APHIS-Wildlife Services (WS), GA State Director, Athens, GA

Education: BS Business Management – University of Georgia, MS Wildlife Management –

University of Georgia 

Experience: Seventeen years of service in APHIS Wildlife Services including operations in VA 

and GA conducting wildlife damage management programs including livestock protection, 

wildlife hazard management at airports and rabies management. Specific wildlife damage 

management experience with a variety of species including feral swine, white-tailed deer, 

Canada geese, coyotes, beavers, and vultures,