Human Health and Ecological Risk Assessment

for the Use of Wildlife Damage Management Methods

by USDA-APHIS-Wildlife Services

Chapter II

The Use of Cage Traps in

Wildlife Damage Management

May 2017

Peer Reviewed Final

September 2019
i

USE OF CAGE TRAPS IN WILDLIFE DAMAGE MANAGEMENT

EXECUTIVE SUMMARY

USDA-APHIS-Wildlife Services (WS) Program uses cage traps to capture a variety of vertebrate animals for 

specific wildlife management projects, mostly where a need exists to resolve a wildlife damage situation. 

Wildlife can cause damage to property, agriculture, and natural resources or cause human health and safety 

concerns; for example, cage traps may be used to capture a skunk that is under a house or a for disease 

surveillance. WS uses cage traps extensively for wildlife damage management operations. Cage traps are 

used in many settings including urban and rural areas. WS personnel use cage traps in accordance with WS 

Directive 2.450. 

Potential human health and environmental risks from the proposed use of all types of cage traps including 

purse and box traps, and drive or herd style cage traps by WS has been evaluated by APHIS and determined 

that the risks to human health and the environment are negligible. Cage traps can capture nontarget species, 

but capture rates are low compared to overall take and nontarget species are often released from cage traps 

unharmed. Cage traps have minimal risks to people, pets, and nontarget species. WS will continue to support 

and conduct research and education that supports more humane and effective trapping methods and will 

implement these measures in programs, where appropriate, to further reduce risk to nontarget animals.

Table of Contents

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

1.1 Cage Traps.........................................................................................................................................................2

1.2 Drive/Herd Traps................................................................................................................................................7

1.3 Use Pattern ........................................................................................................................................................7

2 HAZARDS ..................................................................................................................................................................13

2.1 Human Health and Safety ................................................................................................................................13

2.2 Environmental .................................................................................................................................................14

3 RISKS........................................................................................................................................................................15

3.1 Human Health and Safety ................................................................................................................................15

3.2 Environmental .................................................................................................................................................17

4 UNCERTAINTIES AND CUMULATIVE EFFECTS..........................................................................................................19

5 SUMMARY ................................................................................................................................................................19

6 LITERATURE CITED...................................................................................................................................................19

7 PREPARERS..............................................................................................................................................................22

7.1 WS Methods Risk Assessment Committee .....................................................................................................22

7.2 Internal Reviewers ..........................................................................................................................................24

7.3 Peer Reviewers ...............................................................................................................................................24

7.3.1 Peer Reviewers Selected by the Association of Fish and Wildlife Agencies ...........................................24

7.3.2 Comments............................................................................................................................................24

Appendix 1. “Other Species” Included in Tables ...........................................................................................................26
1

1 INTRODUCTION

Cage traps are commonly used by the U.S. Department of Agriculture (USDA), Animal and Plant Health 

Inspection Service (APHIS), Wildlife Services (WS) Program to capture animals in wildlife damage 

management (WDM) activities. Cage traps come in a wide variety of styles and generally are of a particular 

design to accommodate the size of the target animal. They are designed to take advantage of the behavior or 

physical characteristic of the target animal. For example, box traps (Powell and Proulx 2003) can be made to 

capture a shrew (8 inches long) up to a black bear1 (up to 12 feet long) and may be baited with an attractant 

preferred by the target species, or set on target animal trails without bait. Standard cage traps such as box

traps, corral traps, clover traps, culvert traps, flight cage traps (e.g., pigeon walk-in traps, modified Australian 

crow traps for starlings), funnel traps (minnow traps), and suitcase traps are a few of the many designs of 

cage traps available. The wide variety of cage traps come with different doors and triggering mechanisms to

close the door or trap. Most of these traps are made of wire, Nylon mesh, or solid metal/plastic/wood walls, 

floors, ceilings and doors, but can be panels with no roof for animals that cannot climb, jump, or dig out 

quickly. Some of these traps are made on floats to live capture aquatic animals such as turtles and otters.

Another type of cage trap per se, is the drive or herd trap (Couey 1949, Addy 1956), which will also be 

discussed. Cage traps have been used for decades, if not centuries in some form or another, and are an 

effective method for trapping a wide variety of species.

In 1996 the Association of Fish and Wildlife Agencies (AFWA), working cooperatively with federal and 

private partners, embarked on a goal to develop voluntary Best Management Practices (BMPs) for 

trapping furbearers in the United States (Batcheller et al. 2000). The stated purpose and intent of AFWA 

in developing the BMPs was to: “Scientifically evaluate traps and trapping systems used for capturing

furbearers in the United States.” AFWA determined the best methods by species2

, but was primarily 

targeting harvest by private fur trappers and not take in WDM activities. Evaluations of trap performance 

were based on animal welfare, efficiency, capture rate, selectivity, practicality, safety, mechanical 

function, cost, quality, durability, weight, and maintenance requirements (Fall 2002). Science-based 

literature and research on the variety of traps and snares were used by AFWA to develop the BMPs. The 

evaluation of BMPs continues and BMPs are updated as research results warrant (AFWA 2017). BMPs 

were provided to state and federal wildlife agencies as well as trappers and the public in the form of a 

general overview for traps and trapping, and specifically the most efficient and humane methods for 

trapping 24 furbearer species in the United States (USA) (AFWA 2017). The goals were to promote

regulated trapping as a modern wildlife management tool, identify practical traps and trapping

techniques while continuing to improve efficiency, selectivity, and the welfare of trapped animals 

through research, to provide specifications for traps that meet BMP criteria for individual species in

various regions of the USA, to provide wildlife management and trap industry professionals with

information to evaluate trapping systems in the USA; and to instill public confidence in and maintain

public support for wildlife management and trapping through distribution of science-based

information. AFWA (2017) focused on private trappers and realized that trapping for depredation control 

was different. The BMP program utilizes international humane trapping standards consistent with the 

Agreement on International Humane Trapping Standards among Russia, Canada, and the European 

Union. WS has adopted these standards, where feasible, for trapping in the USA and conducts research 

on different trapping systems.

 1 See the Introduction to Risk Assessments – Chapter I for scientific names. These are only given if not used in that Section. 2 Furbearers with AFWA (2017) trapping BMPs include Virginia opossum, beaver, muskrat, nutria, Canada lynx, bobcat, coyote in Eastern U.S., 

coyote in Western U.S. (both eastern and western United States populations have own BMPs since eastern coyotes are larger as a result of 

hybridizing with wolves), gray wolves, red fox, swift/kit fox, arctic fox, gray fox, river otter, fisher, American marten, weasel (least, long-tailed, 

and short-tailed), mink, American badger, ringtail, raccoon, and striped skunk.
2

WS Policy (WS Directive 2.450, 09/24/2014)3 states that the use of the BMP trapping guidelines developed 

and promulgated by AFWA (2017) for private fur harvest and other trapping activities are valuable and should 

be followed as practical. WS uses the BMP guidelines as the basis for policy formulation, but recognizes that

some cage traps used in WDM are not commercially available and that not all devices recommended in the

BMP guidelines for general public-use meet the more stringent performance requirements, particularly for

efficiency and durability, for use in federal wildlife management activities. The Directive also discusses the fact 

that traps need to be set so that captured animals are not conspicuous to the public, particularly along public 

roads and trails; this reduces the possibility of a member of the public attempting to free an animal and getting 

injured and also to prevent trap theft. Cage traps are typically placed in areas where the public will not 

haphazardly stumble onto a trap or a trapped animal. The Directive also notes that agency cage trap

replacements are to be selected from those commercially available or equivalents listed in BMP regional 

guidelines for each species (AFWA 2017), unless changes are authorized by the WS Regional Director. 

1.1 Cage Traps

Cage traps (e.g., Figure 1) allow a target

animal(s)4 to enter inside an enclosure, but 

prevents the target animal from exiting once 

trapped. Cage traps are available in a variety 

of designs and sizes to live-capture different 

animals. The design and size of a cage trap are 

based on the size and behaviors of target 

animals. WS has used cage traps to 

successfully live-capture over 200 species of

animals, including mammals (e.g., raccoons, 

voles, monkeys, deer), birds (e.g., waterfowl, 

pigeons, starlings, crows), reptiles (e.g., 

snakes, turtles, iguanas, alligators), and fish

(Table 3). Cage traps are placed in areas 

where activity by the target animal is high

(e.g., along travel corridors), with the 

entrance to the trap easily accessible and 

baited with an attractant to entice the target 

animal inside. Attractants used in cage traps 

could include familiar scents, non-live food items, live bait such as birds or mice (held in a bait station), or 

another target animal (decoy trap).

Many cage traps are designed with a door5 that is held open by attaching the door to a pan, wire trigger, 

electronic beam, remote activating device, or other type of mechanism that can be activated once the animal 

is completely inside. When the target animal enters through a door to investigate the attractant, the pan, wire, 

or beam once tripped allows the opened door to quickly close with the animal trapped inside. Suitcase-style 

traps have a trigger or pan in the center of the trap and hinged panels that resemble an open suitcase when 

 3 All WS Policy Directives referenced in this document can be found @ http://www.aphis.usda.gov/wps/portal/aphis/ourfocus/wildlifedamage

under Wildlife Damage – WS Program Directives. 4 Depending on the trap-style, a trap may capture one or more animals. In the text, animal can refer to one or more. 5 Traps can have multiple entrances depending on the trap and the target species. Some bird traps have as many as four to six.

Figure 1. Standard box trap, often called a cage trap, set for a raccoon. 

The pan is in the rear and attached to the door by a metal rod. When the 

door closes, a hinge opens another flap that does not allow it to be 

opened from the inside.
3

set. When a target animal steps on the pan or trips the wire or trigger in the center of the trap to investigate 

the attractant, the side panels snap shut around the animal, which resembles a closed suitcase with the target 

animal live-captured inside. Other traps, such as funnel traps, allow animals to enter the trap through an 

opening that is larger at the beginning and progressively gets smaller as the animal moves towards the 

entrance into the trap. Once the target animal enters the trap, the opening in the trap is too narrow to allow 

animals to exit easily, or the opening is positioned in such a way that prevents exiting but allows other target 

animals to enter into the trap. Traps can also be designed with one-way doors that allow target animals to lift 

open or push through (e.g., hanging wires or bobs) a door as they enter into the trap to investigate an 

attractant, but once inside, the door is closed behind them and the animal is unable to exit, these types of 

traps are often multiple-catch traps. Another type of entrance is similar to an elevator where the weight of the 

animal drops it to a lower level where it can enter the cage.

Schemnitz et al. (2012) discusses cage traps extensively, along with the diversity of traps available to livecapture animals. Some of the more common cage traps used by WS to live-capture target animals are 

discussed in this document, but is not an exhaustive list of available cage traps that WS has used in the past

or could use in the future to live-capture target animals. However, the human and environmental risks and 

hazards associated with cage traps would be similar across the diversity of traps available since those traps 

operate under the same principle. The following are examples of specialized cage traps that are commonly 

used by WS to live-capture certain target animals. Their size and design are intended to target certain animal 

species and to exclude non-target animals.

 Box traps, often referred to generally as cage traps if they are 

made of wire mesh (Figures 1 and 2), are one of the more

common types of traps available to live-capture animals and the 

trap with the most diversity in size and design. Box traps are 

generally rectangular, as the name implies. Box traps are enclosed 

on all sides, except for a door or doors that allow entrance into 

the enclosure. Box traps are generally constructed using wire 

mesh, but sometime are enclosed using sheet metal or hard 

plastic. They have a range of sizes, which is dependent on the size 

of the target animal. Attractants, particularly edible baits, are often 

used with box traps to entice target animals into the enclosure.

The door or doors (some have doors at either end) to the 

enclosure are held open by a triggering mechanism, such as a pan 

or trip wire, or a remote control that closes the doors where the 

trap is viewed from a distance or with cameras. The attractant is normally placed on or beyond the 

triggering mechanism so the target animal has to step on or trip the mechanism to reach the attractant, 

which releases the door to close, and the animal is trapped inside the enclosure. However, where an 

operator is waiting to close the door from a remote area, feed may just be in the middle or away from the 

doors (these are commonly used for feral swine). Box traps are available to live-capture a variety of 

vertebrates from mammals to fish, but are most commonly used by WS to live-capture mammal and bird 

species that range in size from mice and voles to white-tailed deer and mountain lions. Box traps are 

generally portable and can be placed in areas frequently used by target animals, including in the water on 

floats for species such as waterfowl, otters and aquatic rodents. Traps with more than one door are 

usually used, especially, for animals that like to see the “other side” or the way through (e.g., rabbits).

Box style cage traps generally allow for the capture of one individual at a time, so their use can be labor 

intensive and costly.

Figure 2. Box cage trap with wings to 

guide animals into traps such as 

armadillos and feral chickens.
4

 Culvert traps are used to live-capture bears. Culvert traps are a type of large cylindrical trap with differing 

trigger systems and gravity doors. These are constructed of solid tubular metal (a culvert) and are on a 

wheeled platform or trailer for transport. The door to culvert traps is held open by a triggering mechanism 

that is located at the opposite end of the trap from the door. Attractants are often used with culvert traps 

to entice bears into the enclosure (bears do not mind investigating enclosed areas for food whereas other 

animals typically would not). Baits similar to those attracting nuisance bears may be used. The attractant 

is normally placed on or beyond the triggering mechanism so the target animal has to step on or trip the 

mechanism to reach the attractant. Upon contact the door closes and the animal is trapped inside the 

enclosure. Due to the size and weight of most culvert traps, they are primarily restricted for use near 

roadways, although models exist that may be disassembled and reconstructed in remote areas. Culvert 

traps are checked daily to address any bears live-captured.

 Clover traps are the most common cage trap for deer (Clover 1954). The Clover trap, named for the 

originator and not the shape, has been modified since the original design was developed, but has the 

appearance of a large box trap. They restrain deer once captured. The trap is portable with sides that

collapse and fold together for easy transport (Sparrowe and Springer 1970, Roper et al. 1971, 

McCullough 1975). Traps are placed in areas where activity by the target species is high and are baited 

with an attractant. When the target animal enters the cage trap to investigate the attractant, a pan or wire 

is triggered releasing the door and enclosing the animal inside the Clover trap. Clover traps are typically 

checked daily if not more often.

 Corral traps are generally used by WS to live-capture feral swine, and potentially other hoofed animals.

As the name implies, these look like corrals when constructed because they have open tops, which allows 

birds and other nontargets to come and go. Corral traps for feral swine are generally large circular traps 

consisting of panels anchored to the ground using steel posts with a door allowing entrance. Side panels 

are typically woven metal fencing, referred to as hog panels or cow panels. The entrances into the traps 

generally consist of a door that allows entry into the trap but prevents exit, or a guillotine-type door that 

are triggered usually from remote access (camera monitor and some type of remote switch to close the 

doors). The doors are often designed to allow swine to enter the trap continually allowing for the 

possibility of capturing multiple swine. The top of traps is often open, which allows most nontarget

species to escape, such as white-tailed deer. Some variation in design is expected based on the soil type, 

brush, and the number of swine expected to be captured. Corral traps are typically baited with food 

sources that are attractive to feral swine, such as corn. Corral traps for swine are semi-permanent traps 

that can be disassembled but are generally constructed and left in areas for extended periods. Doors, side 

panels, and steel posts are often heavy and bulky and may have to be carried long distances to areas 

where feral swine are active. If a remote control is used, swine can come and go as they please until the 

operator decides to close the doors when the desired number of animals are inside the trap.
5

 Walk-in and swim-in traps are similar to box traps with doors 

designed so that target animals can either push open the door to 

enter the trap, which promptly closes behind the animal or are made 

of funnels with open entrances that go into the trap which allow the 

target animal to enter, but once inside they go to the sides of the 

cage trap away from the funnel to try to get back out (Figure 3 and 

4). Entrances are fitted with repeating or revolving doors made of 

wire bobs that hang down (tied together as a wire panel or free 

hanging) or solid panels such as glass or wire mesh. The doors open 

inward but return to the closed position after the target animal enters 

the trap. Funnels are also placed on the outside parallel to the walls 

and taper inward so that the entrance into the trap is smaller than the 

entrance parallel to the outside wall. Walk-in 

traps are typically baited with a food 

attractant inside the trap with some sprinkled 

outside, particularly at the doorway 

entrances. As animals consume the limited 

amount of food attractant around the doors 

or entryways, they are drawn into the trap by 

the presence of larger amounts of food 

inside the trap. Animals are unable to push 

open the door once inside the trap. The 

design of the door allows multiple target 

animals to enter the trap. WS generally uses 

walk-in traps for bird species, such as 

pigeons and chickens. 

 Decoy traps and bait station traps are 

(Figure 5) mostly similar in size to walk-in 

traps, depending on the size of the target 

species. In both types of traps, live animals 

are maintained. Decoy traps are similar in 

design to the Australian Crow Trap as 

reported by McCracken (1972) and Johnson 

and Glahn (1994). Decoy traps are 

commonly rectangular and they are generally 

constructed of a wooden or metal frame and 

wire mesh or netting to form an enclosure, 

which can be constructed in a variety of 

sizes, depending on the target species and 

the number of birds likely to be captured.

Sides go up above the middle panel with the 

funnels and have perches to encourage birds 

to stay above the funnels so they do not try 

to escape. Decoy traps are commonly used 

by WS to target social flocking bird species such as crows, starlings, house sparrows and blackbirds.

Live decoy birds of the same species being targeted are usually placed in the trap with sufficient food and 

Figure 5. A brown tree snake cage trap made from a modified 

minnow trap. A live mouse is in an inner compartment that attracts 

the snake. These are multiple catch traps and can catch up to 15 

or 20 snakes. 

Figure 4. A swim-in trap with 3 mallards and a northern pintail.

Figure 3. Walk-in trap with a funnel 

entrance.
6

water to assure their survival. Perches are configured in the trap to allow birds to roost above the ground 

and in a more natural position. The feeding behavior and calls of the decoy birds attract other target birds 

to the trap. In addition, the traps are often baited with food attractants. Openings in the enclosure allow 

target birds to enter the enclosure to feed on the bait. Openings are generally placed at the top of the 

enclosure and are generally about the length and width of target bird species with their wings folded so 

birds can enter but are unable to exit with their wings extended as they are flying upwards toward the 

openings. Active decoy traps are monitored daily, every other day, or as appropriate, to address captured 

birds and to replenish bait and water. Depending on design, decoy traps can be portable or permanent.

Portable decoy traps generally consist of several parts and panels that require assembly once transported 

to a location where target animals are active.

Bait station traps are similar to decoy traps except that they have live bait rather than decoys and usually 

have funnels in the sides. Inside, live mice or chickens are kept in an inner cage which has an access 

door to feed and water them. The snakes, or other target animals, are attracted to the lure and scent, and 

enter, but are not able to get out because they typically go to the sides (Figure 5) and the entrance to the 

funnel is in the center of the trap. However, if a snake enters a trap with its tail still outside the trap, it will 

follow its tail back out (usually the cage that holds the prey is small enough to allow the snake to coil 

around it, thus pulling its tail inside).

 Swedish goshawk traps are used to live-capture hawks and owls. These traps can be portable or 

permanent and are baited similarly to a box trap that contains a live attractant, such as a pigeon or mouse.

The trapping mechanism consists of an “A” frame made of wood or metal along with a trigger that is 

mounted atop the bait cage. The frame is generally made of mesh wire or netting. The sides of the “A” 

are hinged so that the sides are held open in a “H” shape by a trigger that stretches the length of the trap.

The trigger mechanism is hinged in the middle. As a raptor enters into the trapping mechanism to 

investigate the lure in the bait trap, it lands on or brushes against the trigger, which collapses and allows 

the sides to close back into an “A” shape trapping the raptor inside (Meng 1971, Kenward and Marcstrom 

1983). Traps are monitored by personnel to quickly respond to live-captured raptors. The pigeons are in 

a separate compartment below the raptor and generally do get predated.

 Purse traps, suitcase traps or basket-type cage traps 

are designed to live-capture animals, primarily birds 

and mammals and have the appearance of a purse or 

suitcase when closed. These types of traps are 

typically constructed of a metal frame covered in 

netting to heavy-gauged wire that is hinged with 

springs. When set, the trap is opened to allow an 

animal to enter and the pan that triggers the trap to 

close is in the center of the trap. The trap is baited with 

an attractant, or live animal, so when the animal 

investigates the attractant or preys on the animal, the 

pan is triggered and the sides snap closed around 

them. Popular traps used to catch beaver include the 

Bailey and Hancock beaver traps. These traps 

generally set in shallow water, are some of the largest traps, and weigh about 25 pounds. They are 

relatively bulky to carry and maneuver. Of all cage traps, the Bailey (Figure 6) and Hancock traps for 

beaver and otter are fairly bulky and have the most potential for causing injury to those setting them. A 

Figure 6. Bailey trap, a purse trap, used primarily for 

trapping beaver. This purse trap has a size of 39” x 21” x 

~12” and weighs about 30 pounds.
7

popular trap to capture birds, especially raptors, is the bow-net trap. Bow nets consist of two semicircular bows as a frame with loose netting strung between the bows that are placed on the ground.

Hinges and springs connect the two semi-circular bows at their bases with one bow fixed to the ground.

The other semi-circular frame is folded and held together with the stake portion with a trigger or release 

mechanism (Bloom 1987, Hull and Bloom 2001).

 Nest box traps are used to capture breeding and post breeding European Starlings and other targeted 

secondary cavity-nesting6 birds (DeHaven and Guarino 1969, Knittle and Guarino 1976). With this trap, 

the door closes when the bird enters into the cavity. The cavity boxes are usually hung on the side of a 

building or on a tree, depending where the target species is located. WS has used these to capture 

Northern Flickers, European Starlings, House Sparrows, House Finches, Tree Swallows, and bluebirds.

The birds are alive when captured7

. Other nest box traps come in different designs. Some are open and 

placed directly on a nest with eggs to capture the adult (similar to a Swedish goshawk trap) and have 

been used by WS to capture gulls and blackbirds.

 Colony traps are multi-catch traps used to live-capture muskrats. There are various types of colony traps.

One common type of colony trap consists of a cylindrical tube of wire mesh with a one-way door on each 

end (Novak 1987). Colony traps are set at entrances to muskrat burrows or placed in muskrat travel lanes.

Colony traps are effective, relatively inexpensive, and easy to construct (Miller 1994). The stovepipe trap, 

a common type of colony trap, is usually made with sheet metal and may capture two to four muskrats 

on the first night (Miller 1994).

1.2 Drive/Herd Traps

Drive or herd traps are different from regular cage traps because animals have to actively be herded or driven 

to the pen or corral trap by people. People on foot and in boats, aircraft or other vehicles “drive” animals into

an area that narrows down naturally or artificially (fencing guides or wings of an appropriate size) until they 

are directed into a small confined area, a corral, usually made of some type of panels or heavy-gauged wire 

fencing where a door can be closed to keep them in the pen or corral. These are normally used for geese 

when they are flightless during their primary molt. Other species that can be trapped in drive traps include 

hooved mammals, feral waterfowl because they typically cannot fly or fly well, and jackrabbits, small rodents, 

and snakes. Typically, people surround the animals opposite the pen and may use cage panels, ropes, or 

chains between them to keep animals headed in the direction of the enclosure (Figure 7). People normally 

walk slowly to allow time for animals to keep moving in front of them. Once to the pen or corral, it is closed 

and the animals are then processed.

1.3 Use Pattern 

From FY118 to FY15, WS used cage traps to capture 226,264 target animals of 45 species (Tables 1a, 1b, and 

1c). WS caught target animals in decoy traps (64% of capture), a variety of box traps (29%), snake traps 

(4%), feral swine corral traps (1%), goshawk traps (1%), purse or suitcase traps (0.6%), and culvert traps 

 6 Secondary cavity-nesters do not excavate the cavity themselves, but use those created by another animal (e.g. woodpecker). 7 Another type of nest box trap uses a snap trap inside which kills the target bird, but will be discussed under quick kill traps. 8 FY11 equals the federal Fiscal Year 2011 which is October 1, 2010-September 30, 2011 (the year is denoted by FY11, FY12, and so on and is 

the federal Fiscal Year for 2011, 2012, and so on.
8

(0.3%). WS captured 2,939 nontarget species of 161 

species, which was 1.3% of the total take of all 

animals in cage traps; nontarget species were taken in

box traps (84% of nontarget captures), decoy traps 

(12%), culvert traps (2%), snake traps (1%), suitcase 

traps (0.4%), goshawk traps (0.3%), and feral swine 

corral traps (0.1%). Mammals accounted for 20% of 

the target take in cage traps (Table 1), birds 78% 

(Tables 2a and 2b), and reptiles, amphibians and fish 

(2%) (Table 3). 

WS targets several mammalian species with cage 

traps, including federally listed threatened and 

endangered (T&E) species (Table 1). Mammals are 

captured in cage traps to protect a variety of resources 

including livestock, livestock health, feed, crops, 

property, natural resources, and human health and 

safety from wildlife strikes at airports and reducing 

potential for disease such as rabies. In fact, over 50% 

of the cage trap captures are for rabies surveillance 

following the distribution of oral rabies vaccine baits

targeting mostly raccoons, skunks, other predators, 

and rabbits. The Virginia opossum is generally 

considered a nontarget in the oral rabies vaccination 

program because it is a mammal that rarely contracts 

the disease. Thus, opossums have a high nontarget 

capture rate. Opossums did account for the highest 

number of all vertebrates captured in cage traps or 

51% of all nontarget vertebrates captured by WS 

between FY11 and FY15. Depending on the species, 

its abundance, whether it is invasive or not, and the 

damage situation, target mammals may be 

euthanized, relocated, or released after disease 

sampling/banding. However, most target species are 

euthanized. Of the mammals euthanized, 40% were 

invasive species (Table 1).

More birds are captured by WS with cage traps than 

the other vertebrates at 78% of all target species 

captured with cage traps (Tables 2a and b). Birds are 

captured in cage traps to protect a variety of 

resources including livestock, feed, crops, property 

including aircraft, natural resources including the 

federally endangered Kirtland’s warbler (Setophaga ruticilla) from brown-headed cowbirds, human health and 

safety from wildlife strikes at airports, and reducing potential for disease. Depending on the species, its 

abundance, whether it is invasive or not, and the damage situation, target birds may be euthanized, relocated, 

or released after disease sampling/banding.

Figure 7. Standard goose drive where geese are herded with 

boats from water and people walking on land. Slowly the 

geese are herded to a pen which has wings coming away 

from it in a “V.” The geese are enclosed in a pen and handled

for their predetermined disposition (relocated, freed, or 

euthanized). 
9

Table 1. The annual average number target and nontarget mammals captured by WS with cage traps in 

WDM from FY11 to FY15 throughout the United States (USA).

* Invasive species ** Nontarget livestock ^Invasive sp. in some areas – W USA # Three invasive sp. (9 killed) 1

Includes species with a total take, including Target (T) and Nontarget (NT) take, less than 10 for each species and not a T&E sp., or sensitive. Animals 

killed or released with an average annual take over a 5-year period less than 1 are given in decimals and those one or more rounded to whole numbers.

MAMMAL SPECIES CAPTURED WITH CAGE TRAPS

SPECIES TARGET NONTARGET

Killed Released Killed Released

Virginia Opossum^ 1,761 336 9 1,501

Feral/Free-roaming Cat* 630 505 2 209

Bobcat 43 1 0.2 0.6

Mountain Lion 31 0 0 0.4

Small Asian Mongoose* 2,003 1 0 0

Coyote^ 20 2 0 0.2

Feral/Free-Roaming Dog* 4 23 0.2 8

Red Fox^ 42 11 0.2 3

Common Gray Fox 166 21 0.4 78

Black Bear 148 539 0.2 3

- Louisiana Black BearT&E 0 4 0 0

Grizzly BearT&E 0 2 0 0

River Otter 15 2 0 4

Fisher 0.4 10 0 5

Raccoon 7,482 8,144 9 101

Striped Skunk 4,460 291 5 11

Other Predator (11T, 9NT – 13 sp.) 1 27 4 1 9

Feral Swine* 9,057 40 0.2 0.4

Collared Peccary 0 7 0.8 11

Mule Deer (incl. Black-tailed Deer) 0 10 0 0.4

White-tailed Deer (captive* and wild) 0.4 0 2 8

Feral Goat* 0 10 0 0

Other Hoofed Mammal (1T, 2NT – 3 sp.)** 1 0.4 0 0 2

Beaver^ 759 121 0 1

Nutria* 156 3 0 0

Muskrat 107 0.2 0.6 32

Woodchuck 129 11 0 83

Yellow-bellied Marmot 5 6 0 0

California Ground Squirrel 1,632 1 0.4 20

Rock Squirrel 252 3 0 5

Meadow Vole 27 0.8 0 0

Prairie Vole 1 32 0 0

Western Gray Squirrel 4 5 0 2

Eastern Gray Squirrel^ 34 10 2 44

Eastern Fox Squirrel^ 24 17 0 19

Red Squirrel 0.6 2 0.2 11

Douglas’ Squirrel 0.2 10 0 0

North American Deermouse 113 0.8 0 0

White-footed Deermouse 14 160 0 0

House Mouse* 231 21 0 0

Brown (Norway) Rat* 52 1 1 3

Black Rat* 1,189 4 0 0.2

North American Porcupine 10 1 0.8 14

Desert Cottontail 310 12 0.2 33

Eastern Cottontail^ 83 10 0.8 69

Other Rodent & Rabbit (29T#, 15NT -33 sp.) 1 44 6 0.6 20

Nine-banded Armadillo 68 2 1 5

Vagrant Shrew 14 0 0 0

Other Shrew/Bat (4T - 4 sp.) 1 0.8 0 0 0

AVE. ANNUAL MAMMALS TAKEN (87T, 56NT – 97 sp.) 31,150 10,403 38 2,316

% TARGET AND NONTARGET MAMMALS TAKEN 70.9% 23.7% 0.1% 5.3%
10

Most birds targeted with cage traps are euthanized. Of the euthanized target birds, 92% were invasive species 

(Table 2a and b). Comparatively, 5% of the nontarget birds were invasive species, but 24% of the nontarget 

birds killed were invasive. The birds captured in cage traps by WS are divided into Tables 2a (non-passerine 

birds) and 2b (passerine or songbirds). 

Table 2a. The annual average number target and nontarget non-passerine (not songbirds) birds controlled by WS with 

cage traps in WDM from FY11 to FY15 throughout the USA.

* Invasive species ^Invasive species in some areas 1

Include species with all take less than 10 and not a threatened, endangered, sensitive or highly invasive species are summarized with the total number

of species targeted (T), taken as nontargets (NT), and included in the row (# species). The “Risk Assessment Introduction” Chapter has all of the 

species taken listed and their scientific names. Animals killed or released with an average annual take over a 5-year period less than 1 are given in 

decimals and those one or more rounded to whole numbers.

NON-PASSERINE BIRD SPECIES CAPTURED WITH CAGE TRAPS

SPECIES TARGET NONTARGET

Killed Released Killed Released

Rock Pigeon* 26,299 66 0.6 0.2

Island Collared-Dove* 153 14 0 0

Eurasian Collared-Dove* 584 0.6 0.2 12

Spotted Dove* 1,563 9 0 0

Zebra Dove (Barred Ground-Dove)* 1,326 2 0 0

Mourning Dove^ 968 398 4 83

White-winged Dove 0.4 2 3 28

Other Doves (2NT - 2sp.)1 0 0 0 2

Great Black-backed Gull 24 0 0 0

Herring Gull 147 0 0 0.2

Other Larids (5T, 1NT - 5 sp.) 1 6 0.8 0 0.2

Black-bellied Whistling-Duck 0 0.2 2 8

Canada Goose 4 29 0.2 0

Mallard (incl. 0.2 lethal take of feral domestic mallard*) 25 170 0.2 1

Green-winged Teal 0.8 10 0 0

Other Waterfowl (8T, 2NT - 8 sp.) 1 1 28 0.2 1.8

Turkey Vulture 113 1 1 4

Black Vulture 2,739 2 0 0

Sharp-shinned Hawk 0.8 11 0 2

Cooper’s Hawk 7 162 1 5

Northern Harrier 0.2 27 0 0.2

Bald Eagle 0 1 0 0.4

Red-shouldered Hawk 0.2 14 0 0

Red-tailed Hawk 87 770 0 0.4

Rough-legged Hawk 0 16 0 0

Golden Eagle 0 0.4 0 0

Barn Owl 2 152 0 0

Snowy Owl 0 75 0 0

Great Horned Owl 2 140 0 0.4

American Kestrel 28 320 0.8 6

Other Raptor (10T, 3NT - 11 sp.) 1 1 40 0.2 2

Waterbird/Wading Bird/Shorebird (1T, 4NT - 5 sp.) 1 0.2 0 0 1

Wild Turkey 55 17 0 5

Black Francolin* 153 0 0 0

Gray Francolin* 227 0 0 0

Erckel's Francolin* 89 0 0 0

Red Junglefowl* 174 0 0 0

- Feral Domestic Chicken* 858 6 0 0.6

Ring-necked Pheasant* 11 19 0.2 0

Other Gallinaceous Bird (1T*, 2NT - 3 sp.) 1 0.2 0.2 0 3

Woodpeckers/Parakeets (6T, 3NT - 7sp.) 1 9 0 0 0.6

Ave. Annual Non-Passerine Birds Taken (64T, 36 NT – 74 sp.) 1 35,658 2,503 14 167

% of total take of Non-Passerine Species 93.0% 6.5% <0.1% 0.4%
11

Table 2b. The annual average number target and nontarget passerine (songbirds) birds controlled by WS with cage traps 

in WDM from FY11 to FY15 throughout the USA.

PASSERINE BIRD SPECIES CAPTURED WITH CAGE TRAPS

SPECIES TARGET NONTARGET

Killed Released Killed Released

European Starling* 116,275 272 6 1

Red-winged Blackbird 2,085 8 3 3

Yellow-headed Blackbird 35 17 0 2

Brewer’s Blackbird 803 0.2 0 0

Common Grackle 100 0.2 1 10

Great-tailed Grackle 10 0 0.4 0

Boat-tailed Grackle 0.4 0 0 0

Brown-headed Cowbird 7,598 13 0 0.4

Blue Jay 0.2 0.4 0.4 26

American Crow 126 0.8 2 1

Other Corvids (4T, 3NT - 5 sp.)1 13 2 0.2 11

Tree Swallow 2 0 3 12

Other Aerialists (1T, 1NT - 2 sp.)

1 0.6 0 0 1

Western Kingbird 13 21 0.2 21

California Towhee 16 7 0.4 0.4

Savannah Sparrow 0.8 41 0.4 41

Song Sparrow 0 6 0 9

White-crowned Sparrow 179 1 0 0.6

Dark-eyed Junco 0 1 0 91

Northern Mockingbird^ 14 19 2 26

Eastern Bluebird 0 0 1 20

Northern Cardinal^ 85 76 0.2 2

House Finch^ 337 0 0 10

Other Passerine (10T, 26NT - 29 sp.) 1 5 18 1 25

Unidentified Bird 0 0 0 0.8

Common Myna* 481 0 0 0

Java Sparrow* 5,990 0 0 0

Red-crested Cardinal* 1,191 0 0 0

House Sparrow* 2,305 6 2 0.8

Eurasian Tree Sparrow* 253 10 0 0

Other Invasive Passerines (4T - 4 sp.)* 1 7 0 0 0

Ave. Annual Passerine Birds Taken (44 T, 50 NT – 66 sp.) 137,925 520 23 315

% of total take of Passerine Species 99.4% 0.4% <0.1% 0.2%

AVE. ANNUAL All BIRDS TAKEN (108T, 86NT-140 sp.) 173,583 3,023 37 482

% TARGET AND NONTARGET BIRDS TAKEN 98.0% 1.7% <0.1% 0.3%

* Invasive species ^Invasive species in some areas 1

Species with a total take less than 10 and not a threatened, endangered, or sensitive species are summarized with the total number of species targeted 

(T), taken as nontargets (NT), and included in the row (some are both targets and nontargets). The “Risk Assessment Introduction” Chapter has all of 

the species taken listed and their scientific names. Animals killed or released with an average annual take over a 5-year period less than 1 are given in 

decimals and those one or more rounded to whole numbers.

WS also targets several reptilian species and few amphibians and fish (only the common carp) with cage 

traps, and these accounted for 4% of the target take between FY11 and FY15 (Table 3). Reptiles are captured 

in cage traps to protect a variety of resources, but primarily property, natural resources, and human health 

and safety. Depending on the species, its abundance, whether it is invasive or not, and the damage situation, 

target reptiles may be euthanized, relocated, or released. However, most are euthanized. Of the euthanized 

reptiles, almost 100% were invasive species with 95% of the reptiles targeted being the brown tree snake

(Table 3). The brown tree snake is an invasive species on Guam where it has eliminated all but two of the 

native forest bird species. Most brown tree snakes are captured in modified minnow traps that have funnels 

on both ends with doors added at the end of the funnel so that they cannot get back out because they easily 

escape without them (figure 2). A live house mouse is the attractant inside the cage, but it is in a compartment 

where it is fed regularly. The scent that the live mice produce helps attract the snakes. Since the mouse is not 

eaten, these become multi-catch traps and several snakes can be caught in one trap.
12

Table 3. The annual average number target and nontarget reptiles, amphibians, and fish captured by WS with cage traps 

in WDM from FY11 to FY15throughout the USA.

REPTILES, AMPHIBIANS, AND FISH CAPTURED WITH CAGE TRAPS

SPECIES TARGET NONTARGET

Killed Released Killed Released

Common Snapping Turtle^ 0.4 36 0 5

Eastern Box Turtle 0 0.4 0 21

Northern Painted Turtle 0 66 0 5

Pond Slider^ 9 58 0 2

Black Spinytail Iguana* 171 0 0 0

Green Iguana* 12 0 0 0

Mangrove Monitor* 0 0 0 15

Brown Tree Snake* 7,570 144 0 0

Other Reptiles (11T, 8NT – 15 sp.) 1 7 11 2 3

American Bullfrog^ 0 0 0.2 0.2

Common Carp* 21 0 0.2 0

Channel Catfish^ 0 0 0 11

Other Fish (3NT - 3 sp.) 1 0 0 0 2

AVE. ANNUAL OTHER SPECIES TAKEN (20T, 19NT, 29 sp.) 7,790 315 2 64

% TARGET AND NONTARGET OTHER SPECIES TAKEN 95.3% 3.9% <0.1% 0.8%

* Invasive species ** One invasive (0.2 killed) ^Invasive species in some areas – western USA

+ Two invasive (3 killed) # One invasive sp. (6 killed) 1

Species with a total take less than 10 and not a threatened, endangered, sensitive or highly invasive species are summarized with the total number of 

species targeted (T), taken as nontargets (NT), and included in the row (# species). The “Risk Assessment Introduction” Chapter has all of the species 

taken listed and their scientific names. Animals killed or released with an average annual take over a 5-year period less than 1 are given in decimals 

and those one or more rounded to whole numbers.

Animal capture trap night is a standard comparison measurement of effectiveness or selectivity for all types 

of mammal traps that remain in place for one or more nights. The standard is to compare the number of 

animals captured with 1000 trap nights. Cage traps were used between FY11 to FY15 for a total of 6,856,538 

trap nights annually, or 6,857 1000 trap nights. An annual average of 229,203 target and non-target animals 

were captured in cage traps between FY11 and FY15 for a total of 33.4/1000 trap nights. Target capture was 

33.0/1000 trap nights at 98.7% of all take which is a highly effective method with minimal numbers of 

nontarget species capture (0.4/1000 trap nights) at 1.3%. These figures represent a high effectiveness rating 

for target animal capture with a very low take of nontarget animals. However, with that said, it should be noted 

that many traps for birds can catch several to a hundred in a day, not making this a great comparison to other 

methods.

Drive or herd traps are another type of cage trap, but requires the presence of people to make them work.

Between FY11 and FY15, WS used drive traps to capture 18,268 target animals representing 12 species (Table 

4). Of the 18,267 target captures, 13% were relocated; some States relocate Canada geese to waterfowl 

management areas, but fewer of these are available every year. Three nontarget species, an average of 2 

annually, were taken during the 5 years because most can be excluded when herding animals towards the 

pen. The nontarget captures were released at the capture location. About 99% of the target captures were 

“resident” Canada Geese, which are introduced nesters throughout much of the USA when they are captured.

They can cause extensive damage at parks (figure 3). In fact, most all operations were conducted for Canada 

geese and other waterfowl were caught during Canada goose roundups.
13

Table 4. The annual average number target and nontarget animals captured by WS with drive/herd traps in WDM from 

FY11 to FY15 throughout the USA.

ANIMALS CAPTURED WITH DRIVE/HERD TRAPS FROM FY11 TO FY15

SPECIES TARGET NONTARGET

Killed Released Killed Released

Gray Francolin* 0.8 0 0 0

Feral Domestic Goose* 47 18 0 0

Canada Goose 15,846 2,214 0 0

Mallard 23 57 0 0

- Feral Domestic Mallard* 33 9 0 0

Feral Domestic Muscovy* 9 3 0 0

Other Waterfowl (7T, 3 NT, 10 sp.)1 0.2 8 0 2

ANNUAL AVE. TOTAL ANIMALS TAKEN (12T, 3NT - 15 sp.) 15,959 2,309 0 2

% OF ALL TARGET AND NONTARGET SPECIES TAKEN 87.4% 12.6% 0 0.01%

1

Species with a total take less than 10 and not a threatened, endangered, or sensitive species are summarized with the total number of species targeted 

(T), taken as nontargets (NT), and included in the row (some are both targets and nontargets). Animals killed or released with an average annual take 

over a 5-year period less than 1 are given in decimals and those one or more rounded to whole numbers. The “Risk Assessment Introduction” Chapter 

has all of the species taken listed and their scientific names.

* Invasive species. 

2 HAZARDS

2.1 Human Health and Safety

Human health and safety hazards associated with cage traps include potential cuts or abrasions from loose 

wires or snags, sharp edges on the equipment, or strains from moving cage traps, especially those that are 

heavier such as the beaver Hancock and Bailey traps. It is possible with some designs that the hand could be 

pinched by the door. However, most injuries occur while transporting, setting, or maintaining cage traps.

Muscle strains could also occur during the construction or placement of corral traps for feral swine, since the 

wire mesh panels, door, and steel posts are heavy and cumbersome to handle. Corral traps used to livecapture waterfowl can also be cumbersome due to their size but are generally constructed of netting and a 

lightweight frame to reduce weight. The removal of animals from cage traps may lead to bites or scratches.

Hancock traps and Bailey traps are heavy, bulky traps that are constructed of metal frames and metal wire, 

which could cause muscle strain during transport and while setting the trap. Hancock traps and Bailey traps 

can weigh up to 30 or more pounds. Hancock traps and Bailey traps could pose additional hazards as 

employees set the trap if the trap inadvertently snaps shut during the setting process. During research 

projects conducted by Muller-Schwarze and Hoggart (2005) targeting beavers, they reported that Hancock 

traps inadvertently closed many times injuring their technicians; they gave examples of injuries including the 

hand of an experienced technician being pinched between the edges of the two halves of the trap and another 

bruised the face of a novice technician. The safety mechanism for Hancock traps is located next to the trigger 

mechanism, which requires people to reach inside the set trap to release the safety mechanism and fully 

activate the trap. Muller-Schwarze and Hoggart (2005) recommended modifying the trigger mechanism and 

the safety mechanism of Hancock traps by moving the safety mechanism to the edges of the trap, which 

allows the trap to be activated without reaching inside the set trap to release the safety mechanism. After 

retrofitting their Hancock traps with new trigger mechanisms, Muller-Schwarze and Hoggart (2005) used the 

modified Hancock trap in the field for six years without any accidents.

Live-captured animals may also bite or scratch people as they tend to the trap or encounter the trap. Handling 

of wildlife from cage traps could also result in hazards associated with disease and parasite transmission 
14

from wildlife (Animal Care Use Committee 1998). The same injury hazards extend to the public who encounter 

and tamper with traps placed by WS.

2.2 Environmental

Cage traps are mechanical methods that are employed to live-capture animals and are not methods that would 

contaminate water or result in the bioaccumulation of chemicals or other hazardous materials. Lures and food 

attractants are sometimes used to encourage target animals to enter inside traps; however, relatively small 

quantities are used and those items are not considered hazardous. Food attractants consist of food items that 

are preferred by target animals. For example, whole kernel corn could be used outside and inside a trap set 

to capture feral swine, deer, or pigeons. Whole eggs could be used inside a box trap to attract striped skunks 

or marshmallows could be used to encourage a raccoon to enter a trap. Food attractants could also consist 

of animals that are placed inside of cage traps alive to attract target animals. For example, pigeons or mice 

are often used as attractants for traps that target raptors, since mice and pigeons are prey items for raptors.

Lures could include liquid attractants that mimic another target animal’s presence. For example, beaver castor 

is derived from glands within a beaver and used to attract other beaver. Lures could also consist of individual 

animals of the target species and often works for species of birds that are social and feed together. Target 

animals that are placed inside a live-trap to attract other target animals are often referred to as “decoys.” For 

example, a pigeon is often placed inside a walk-in trap designed to live-capture other pigeons. Other pigeons 

are attracted by the presence of the pigeon and food in the trap. Blackbirds are often used in decoy traps to 

attract target bird species to the traps. Therefore, lures and attractants used to attract other target animals 

would not be substances that would bioaccumulate in the environment and those attractants would not cause 

environmental harm.

Hazards to animals captured in cage traps include stress, injury, and death. Injuries can occur to the captured 

animals (Beringer et al. 1996, Haulton et al. 2001, Peterson et al. 2003) and rarely to the user. Most cage 

traps are checked daily which reduces the time for injuries to occur. White et al. (1991) demonstrated that 

red fox held in cage traps of a box-style had elevated levels of the stress hormones, adrenocorticotropin and 

cortisol, as well as other physiological impacts when compared to fox not held in cages. Some animals may 

struggle to escape and they may become injured or break teeth. Blundell et al. (1999) reported swelling and 

abrasions to appendages of river otter live-captured in Hancock traps and serious damage to teeth, 

presumably from otters chewing on the metal to escape. Powell and Proulx (2003) reported abrasions to the 

muzzles of animals live-captured in cage traps. Mowat et al. (1994) noted injuries to lynx that were livecaptured in box traps that ranged from broken or split claws to superficial cuts on the nose, and rarely on the 

face. Mowat et al. (1994) considered those injuries to lynx that occurred from capture in box traps to be 

minor. Of the nontargets live-captured in box traps during a study conducted by Mowat et al. (1994), only 

one fox suffered injury from a cut on the foot, which was considered minor. Finally, the death of captured 

animals could occur because of environmental conditions, such as extreme temperatures or exposure to rain.

Euthanasia of animals could be necessary when the animal is unlikely to survive due to a trap related injury.

Target and nontarget species captured by WS are listed in Tables 1, 2, 3 and 4.

As a result of concerns regarding injuries and death of animals from foothold traps, snares, and other traps 

including cage traps, the Association of Fish and Wildlife Agencies (AFWA), along with federal and private 

partners working cooperatively, embarked on a goal to develop voluntary Best Management Practices (BMP) 

for trapping furbearers in the United States (Batcheller et al. 2000, AFWA 2017). Results of their research 

(AFWA 2017) were provided to state and federal wildlife agencies as well as trappers and the public in the 

form of a general overview on BMPs for traps and trapping. AFWA (2017) focused on private trappers and 
15

realized that trapping to control depredation was different. However, WS has adopted these standards, where 

possible, for trapping in the USA and conducts research on different trapping systems. Cage traps were 

included in much of the research.

WS Policy (WS Directive 2.450, 09/24/2014) states that the use of the BMP trapping guidelines developed 

and promulgated by AFWA (2017) for private fur harvest and other trapping activities are valuable and should 

be followed as practical. WS utilizes the BMP guidelines as the basis for policy formulation, but recognizes 

that some devices used in wildlife damage management are not commercially available and that not all devices 

recommended in the BMP guidelines for general public use meet the more stringent performance 

requirements, particularly for efficiency and durability, for use in Federal wildlife management activities.

3 RISKS

WS Policy (WS Directive 2.450, 09/24/2014) states that the use of the BMP trapping guidelines developed 

and promulgated by AFWA (2017) for private fur harvest and other trapping activities are valuable and should 

be followed as practical. WS follows the BMPs for cage traps, which primarily discuss the size of the door 

opening, and cage material specifications for cage traps.

3.1 Human Health and Safety

WS employees are knowledgeable in the use of methods available for WDM, the wildlife species responsible 

for causing damage or threats, and WS directives. WS employees whose duties involve animal capture 

participate in a trapper education course (see WS Directive 2.450). That knowledge is incorporated into the 

decision-making process inherent with the WS’ Decision Model that would be applied when addressing 

requests for assistance (see WS Directive 2.201). When employing traps in WDM, WS employees consider 

risks to public safety based on location and method, especially those that could be hazardous to the public.

For example, risks to human safety from the use of cage trap methods would likely be lower in rural areas 

that were less densely populated or on private property where the public has limited access. Consideration is

also given to the location where WDM activities are conducted based on property ownership. If locations 

where methods are used is on private property in rural areas where access to the property could be controlled 

and monitored, the risks to human safety from the use of cage traps would likely be less. If damage 

management activities occurred at public parks or near other public use areas, then risks of the public 

encountering and subsequently tampering with cage traps and the corresponding risk to human safety would 

increase. Activities would generally be conducted early mornings or night when human activity was minimal 

or in areas closed to the public where human activities was minimal. (e.g., in areas closed to the public).

Use and placement of cage traps by WS would comply with applicable laws, regulations, and authorizing 

permits (see WS Directive 2.210, WS Directive 2.450). Traps would not be used unless appropriate 

authorization was granted by the landowner (see WS Directive 2.450). Cage traps used by WS are labeled 

with an attached WS – U.S. Govt. tag or stamped directly on the trap.

Cage traps are mechanical methods that are activated by an animal entering into the trap; therefore, if left 

undisturbed by the public, cage traps would not pose a human safety concern. However, risks could occur if 

the public tampers with traps placed by WS. If the public tampers with traps, the risks and hazards of injury 

would be similar to those risks and hazards from the use of those methods by WS employees. Risks of injuries 

associated with cage traps and box traps could occur incidentally from transporting, placing, and checking 

traps.
16

WS field and office employees filed an annual average of 79 Office of Workmen’s Compensation (OWCP) 

claims for strained backs, lacerations, animal bites, burns, and other injuries that occurred on the job from 

FY13 to FY15. Of these, an annual average of 2.0 (0.7 lacerations, 0.3 illness, and 0.3 sprain) were related to 

cage traps and 0.3 (0.3 compression/contusion to elbow from slip-fall) for herd traps. Additionally, WS 

employees had an average of 19 injuries from falls, slips, twists, and repetitive activities that resulted in 

lacerations, sprains, contusions, strains, compression bruises, and fractures that were associated with field 

activities, but the injury was not readily associated with any specific activity such as setting cage traps. 

Considering the number of employees (~1,900), these claims are relatively few for the number of hours spent 

afield (the OWCP claims from FY13 to FY15 also includes office employees and injuries such as carpal tunnel 

syndrome). Thus, risks of setting cage traps are relatively minor to employees.

The risk of injury from captured animals is also minimal. Typically, employees dispatch target animals

captured in cage traps with a gunshot to the brain9

. The highest risk is typically from animals that are trapped 

in cage or drive traps that are not staked, but are attached to drags; employees may accidentally come across 

a hidden animal that is trapped when approaching the location of the set. Few employees over many years 

have been injured by such captured animals. A more obvious risk is associated with the release of captured 

animals. WS employees usually carry a catch-pole (a pole with a cable loop that can hold an animal prior to 

release). Catch-poles are very effective in handling wildlife, but an animal’s behavior following release, though 

mostly predictable, is a primary concern. If an animal is too large, is in an area where the use of firearms 

would cause a safety concern, or is being trapped for a research project, an animal may be immobilized or 

euthanized with drugs; though usually not a problem, drugged animals can also be a risk10 which will be 

discussed separately under the Immobilization and Euthanasia Risk Assessment. 

From FY13 to FY15, WS operational field personnel averaged 3 bites or injuries annually from animals and 

some of these were from trapped animals. One, a feral cat, was captured in a cage trap and bit the WS

employee while transferring custody to a local animal shelter. Another black bear in a culvert trap bit a WS 

employee on the hand before being released after relocation. Additionally, a coyote captured in a foothold trap 

bit an employee before it was euthanized. Another bite was from a feral cat that had been caught and released 

from a foothold trap; the cat bit the WS employee while it was in the process of being transferred to a local 

animal shelter. Two WS employees were bit by feral or free-roaming dogs being hand gathered, but one 

escaped capture. Finally, a bat that was caught by a person from another agency bit a WS employee while the 

bat was being sampled for a variety of diseases (primarily rabies). 

To analyze the risk of animal bites, context is needed. WS operations annually killed 43,576 and released 

11,432 predators with methods conducive to being bitten from FY13 to FY15. Thus, an average of 2.3 bite 

incidents were related to capturing them alive while hand gathering (0.7), transferring custody to another 

agency after capture (0.7), relocating an animal (0.3), in the process of euthanizing a live-captured animal 

(0.3), and while handling an animal for disease sampling (0.3). For bite incidents that occurred from released 

animals (2.0), WS had a ratio of one bite per 5,700 releases. For animals to be euthanized, the ratio was much 

less at 1 bite for 145,000 animals killed. Overall, the bite ratio was 1 bite for every 18,000 animals captured 

with live-capture methods. This is a low risk. 

 9 WS personnel are trained and certified to use firearms which results rapid euthanasia and this is discussed in the Firearms Risk Assessment. 10 WS personnel are trained and certified to use immobilization and euthanasia drugs and risks associated with their use are discussed in the 

Immobilization and Euthanasia Drug Risk Assessment.
17

Two other bites (0.7/year) occurred from dogs at private residences while WS personnel were making contact 

with people requesting WS assistance. It should be noted that 2 bites in three years occurred as dog attacks; 

this again is a minimal number as the Centers for Disease Control (2015) estimates 4.5 million dog bites 

alone occur annually throughout the USA. Thus again, we believe these risks are low and well within the 

norms.

In addition to field personnel, from FY13 to FY15, NWRC personnel received an annual average of 1.0 animal 

bites or injuries from research animals with bites from a skunk (0.3) and a rat (0.3), and a bone fracture from 

feral swine (0.3). Lab animal bites typically come from caged animals during routine maintenance or research. 

It is not known whether these particular animals were from trapped animals from research that was being 

carried out in the field. 

WS personnel could be exposed to animals carrying diseases such as rabies. All recorded bites from FY13 to 

FY15 and an annual average of two lacerations/splashes were from potentially diseased animals (e.g., rabies). 

Only two bites in three years (0.7) were from animals in known cage traps. These bites had the potential for 

transmitting the rabies virus. None of the animals involved in the incidents was identified as subsequently 

rabid with the exception of fluids from tissue from a known rabid skunk that splashed into the eye of a 

researcher. Thus, a potential for 5 animals per year caused concern potentially for exposure to rabies from 

FY13 to FY15. Personnel that have the potential for exposure to rabid animals, have the option of obtaining 

the rabies prophylactic series with follow up boosters to reduce the potential for contracting the disease if 

exposed through a bite, laceration, or contact with animal fluids. General exposure to animals is common for 

many WS employees, but considering the number of animals captured or handled, the risk of contracting a 

wildlife-borne disease is minimal. As discussed, WS attempts to place cage traps in areas where exposure to 

the public is minimal.

Thus, considering the number of employees and the types of injuries, it is believed that the risk of injury to 

WS personnel is minimal. WS employees engaged in trapping receive trapper education training to reduce 

risk of injury. WS personnel use gloves11 and job aids including stake pullers and trap setter devices to 

minimize injury risk. However, setting traps sometimes requires free hands and gloves may not be used.

3.2 Environmental

Both target and nontarget animals could be captured when using cage traps. Environmental risks are limited 

to the capture of nontarget animals. However, trap design, trap size, attractants, and trap placement can 

minimize the risk of non-target capture. Cage traps generally allow the safe release of nontarget species and 

result in a lower potential for stress and injury compared to other trapping methods such as foothold traps 

(Mowat et al. 1994, Powell and Proulx 2003, Kolbe et al. 2003, Schutz et al. 2006, Iossa et al. 2007, MunozIgualada et el. 2008). The total nontarget take from cage traps was 1.2%, a minimal number, with 97% of 

these being released. Of the 2,939 nontarget species captured and freed or killed (Tables 2, 3a, 3b, and 4), 

the most common nontarget species were opossums (51%), feral house cats (7%), raccoons (4%), darkeyed juncos (3%), mourning doves (3%), woodchucks (3%), common gray foxes (3%), and eastern 

cottontails (2%). These were the only species with nontarget captures above 50 throughout the USA; all of 

these species are abundant within their range – most are found throughout the eastern USA and much of the 

West, if not all. Thus, this is a very low risk to nontarget species.

 11 Setting traps may sometimes require free hands and gloves may not be worn at all times.
18

Data from other studies have demonstrated similar rates of nontarget captures from cage traps while other 

studies have reported higher nontarget capture rates. However, mortality rates are low and population level 

nontarget impacts were not anticipated from cage trapping efforts (Gosling et al 1988, Baker et al. 2001, Way 

et al 2002, Short et al. 2002, Shivik et al., 2005, Iossa et al. 2007). Variability in non-target capture and 

mortality rates will be dependent on the target animal and ability to implement cage trapping measures that 

are species-specific that reduce nontarget captures. The risk to nontarget animals is minimized by WS 

implementing measures that increase selectivity and reduce capture time. For example, the adoption and 

advancement of electronic signaling devices have been shown to reduce the holding time for trapped animals 

reducing the potential for stress and other impacts to nontarget animals (Larkin et al. 2003, Benevides et al. 

2008, Darrow and Shivik 2008, Will et al. 2010). Signals sent from traps to remote devices such as cell phones 

not only serve to reduce the holding time for captured animals but also allow personnel to collect more 

accurate data regarding trapping, ensure compliance with regulations regarding trap monitoring and address 

animal welfare concerns. The use of the appropriate cage trap size and design; trap placement; and the 

selection of bait or lure applicable to the target animal reduce the risk of the capture of non-target species

(Baker and Clarke 1988, Andrzejewski and Owadowska 1994, Jojola et al. 2009, Phillips and Winchell 2011).

Proper trap maintenance and minimizing trap check intervals allow for the safe release of non-target species.

WS recognizes the Best Management Practices (BMP’s) for trapping as developed by the Association of Fish 

and Wildlife Agencies that emphasizes animal welfare, efficiency, selectivity, practicality, and safety and as 

practical will utilize these guidelines when conducting trapping programs (AFWA 2017). WS also continues 

to support research and methods that are humane and selective towards the target animal by developing 

baits, lures and attractants specific to the target animal while also improving on trap design and facilitating 

the development of more efficient trap monitoring methods (Huot and Bergman 2007, Fagerstone and Keirn 

2012).

The risk of capturing nontarget animals exists even with these mitigating factors in place, but the risk is 

reduced and will continue to be reduced as further regulatory and scientific information becomes available on 

trap selectivity. From FY11 to FY15, WS took an average annual total of 244,534 target animals (98.8%) with 

cage and drive/herd traps and 2,941 nontarget animals (1.2%). An average of 77 nontarget animals, taken in

cage traps, was euthanized (0.03%) between FY11 and FY15. Finally, WS did not take any nontarget 

threatened and endangered species in cage traps, but did 2 bald eagles accidentally between FY11 and FY15 

that were released. WS did target an average of 0.4 grizzly bears and 0.6 Louisiana black bears, 1 bald eagle, 

0.4 golden eagles annually from FY11 to FY15; all of these were targeted and taken with the appropriate permit 

(all were released unharmed). Thus, the risk to nontarget species and in particular T&E species is negligible

using cage traps. 

Of concern is the potential for animals to succumb to environmental conditions, such as heat and cold, while 

held in cage traps. WS personnel consider placement (e.g., cage traps are placed in shaded areas where 

possible during warmer months to avoid heat exposure), the necessary food and water for decoy animals in 

decoy traps, and time between trap checks. A new development that will make cage traps more efficient, while 

minimizing the time an animal is in a cage trap, is a remote cage trap monitor that alerts the user that an 

animal is captured or the trap is closed. Few animals trapped in cage traps die of exposure.
19

4 UNCERTAINTIES AND CUMULATIVE IMPACTS

Uncertainty in this risk assessment is negligible as WS has over 100 years using cage traps for WDM activities 

and understands potential risks of using the variety of cage traps available. The knowledge gained from this 

experience has helped reduce uncertainties. 

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

in National Environmental Policy Act documents (USDA 2017) such as WS (2017) and found not to be 

significant to any native species population. Additionally, the “Introduction to Risk Assessments for Methods 

Used in Wildlife Damage Management” looks at all take from all WDM activities by WS and none shows a 

significant level of take for any native species. From a human health perspective, the use of cage traps in 

WDM will not have any known cumulative impacts.

5 SUMMARY

WS uses cage traps as a component of an integrated approach to managing wildlife issues for several 

vertebrate pest species. APHIS WS works cooperatively with other natural resource agencies at the state, 

national and international level to develop effective and humane trapping measures while minimizing exposure 

to human health and nontarget animals. Cage traps offer a comparatively low risk to human health and the 

environment compared to other trapping methods, but their use is specific to those animals where aversion 

to entering a trap can be minimized. Advancements in the design of cage traps and the response time to 

handling caged animals have resulted in more effective and humane trapping of target animals while 

dramatically reducing the potential for nontarget captures. WS will continue to support and conduct research 

that supports more humane and effective trapping methods, and implement these measures in their 

programs, where appropriate, to further reduce risk to nontarget animals.

Overall, the evaluation of risks to human health and safety and the environment from the use of cage traps 

are very minimal. WS personnel are professional with their use of cage traps and work to minimize the 

identified potential risks.

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7 PREPARERS

7.1 APHIS WS Methods Risk Assessment Committee

Writers for “Use of Cage Traps in Wildlife Damage Management Risk Assessment”:

Writer: Thomas C. 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. Thirty-two years of 

service in APHIS Wildlife Services including operations and research in CO for research and OR, GU, CA, OK, and 

NV 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. Expert in preparing environmental documents for WS programs to comply with the National 
23

Environmental Policy Act and the Endangered Species Act. For cage traps specifically, have used all types of cage

traps in WDM and supervised employees that used them in their duties. 

Primary Writer: 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. Seventeen 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.

Editors/Contributors for “Use of Cage Traps in Wildlife Damage Management Risk Assessment”:

Editor: Nikeeya Ali

Position: USDA-APHIS-Wildlife Services (WS), Summer Intern 2017

Education: BS in Communications, Journalism, South Carolina State University 

Experience: Three years as a staff writer for The Collegian Newspaper, one year as Editor-in-Chief. Skilled in production, 

video editing. Previously edited Risk Assessments for USDA-APHIS-WS.

Reviewer: 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/Contributor: 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: Thirteen 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: Fan Wang-Cahill 

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

Environmental Health Specialist

Riverdale, MD

Education: B.S. Biology and M.S. Hydrobiology - Jinan University, Guangzhou, China; Ph.D. Botany (Ultrastructure/Cell 

Biology) – Miami University

Experience: Joined APHIS in 2012, preparing human health risk assessments and providing assistance on 

environmental compliance. Prior experience before joining APHIS includes 18 years environmental consulting 

experience specializing in human health risk assessments for environmental contaminants at Superfund, Resource 

Conservation and Recovery Act (RCRA), and state-regulated contaminated facilities.

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
24

Experience: Eight 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.

Data Contributor: Joey Millison

Position: USDA-APHIS-WS Information and Technology (IT), Junior Applications Developer

Education: Information and Technology coursework from various sources

Experience: Eleven years of experience in APHIS, WS Management Information System (MIS) Group. Retrieves WS field 

data from the MIS for writers, reviewers, and editors.

7.2 Internal Reviewers

USDA APHIS Wildlife Services

Reviewer: Gary Littauer

Position: USDA-APHIS-WS, Assistant Regional Director/Supervisory Wildlife Biologist, Fort Collins, CO

Education: BS Wildlife Management Iowa State Univ., MS Biology, New Mexico State University

Experience: Special expertise in wildlife biology, ecology, and damage management including supervising an aerial 

operation program. Thirty years of service for APHIS-WS in TX, MS, and NM in a wide variety of programs (livestock, 

aquaculture, property, human health and safety, and natural resource protection) including predator, beaver, and 

rodent damage management activities.

7.3 Peer Review 

The Office of Management and Budget requires agencies to have peer review guidelines for scientific 

documents. The APHIS guidelines were followed to have “The Use of Cage Traps in Wildlife Damage 

Management Risk Assessment” peer reviewed. WS worked with the Association of Fish and Wildlife Agencies 

to have experts review the documents. 

7.3.1 Peer Review Agencies Selected by the Association of Fish and Wildlife Agencies

Reviewer: Association of Fish and Wildlife Agencies 

Reviewer: California Department of Fish and Wildlife 

Reviewer: Michigan Department of Natural Resources 

7.3.2 Comments

Comments regarding concerns with the risk assessment and a response:

1. Comment: Why are some animals in fractions in the tables?

Response: Clarification was added below each table that “Animals killed or released with an average annual 

take over a 5-year period less than 1 are given in decimals and those one or more rounded to whole numbers.”.

Comments received not requiring a response.

1. Comment: Commenters provided general overall support for the contents of this Risk Assessment.

2. Comment: The document adequately outlines potential consequences of the use of cage traps, description of 

operating procedures and mitigations to negative consequences is sufficient to allow WS decision makers the 
25

ability to make informed decisions about the continued use of cage traps, Assumptions and uncertainties are 

clearly stated, references selected are appropriate.

3. Comment: Commenter stated that “I liked seeing all the numbers documenting target vs non-target captures 

as well as success per trap nights and such. I don’t have anything more to add.”
26

Appendix 1. “Other Species” Included in Tables.

Table 1

Other predator = swift fox, kit fox, American marten, least weasel, long-tailed weasel, short-tailed weasel, mink, badger, 

ringtail, hog-nosed skunk, hooded skunk, eastern spotted skunk, and western spotted skunks. 

Other hoofed mammal = American elk, Philippine deer* and feral cattle*

Other rodent and rabbit = mountain beaver, black-tailed prairie dog, white-tailed prairie dog, Richardson’s ground 

squirrel, Belding’s ground squirrel, Columbia ground squirrel, thirteen-lined ground squirrel, Mexican ground 

squirrel, round-tailed ground squirrel, golden-mantled ground squirrel, eastern chipmunk, least chipmunk, Botta’s 

pocket gopher, woodland vole, southern red-backed vole, Ord’s kangaroo rat, Abert’s squirrel, southern flying

squirrel, Gambian rat*, desert woodrat, dusky-footed woodrat, eastern woodrat, Mexican woodrat, bushy-tailed 

woodrat, Mexican woodrat, Pacific rat*, Desmarest’s Hutia, mountain cottontail, New England cottontail, 

Appalachian cottontail, European rabbit*, snowshoe hare, European hare* and black-tailed jackrabbit

Other mammal = Asian house shrew*, northern short-tailed shrew, eastern mole and 1 sp. Unidentified bat (from 13 

different species NM – 0.2 lethal take).

Table 2a

Other dove = Inca dove and common ground-dove

Other larid = laughing gull, ring-billed gull, California gull, glaucous-winged gull and western gull

Other waterfowl = wood duck, gadwall, American wigeon, American black duck, blue-winged teal, cinnamon teal, 

northern shoveler and northern pintail

Other raptor = broad-winged hawk, Swainson’s hawk, ferruginous hawk, eastern screech-owl, barred owl, burrowing 

owl, long-eared owl, short-eared owl, caracara, merlin, prairie falcon and peregrine falcon

Other wading bird/shorebird = American bittern, black-crowned night-heron, cattle egret*, great blue heron and Pacific 

golden-plover

Other gallinaceous bird = northern bobwhite, ruffed grouse and common peafowl* 

Other forest bird = red-headed woodpecker, Gila woodpecker, red-bellied woodpecker, downy woodpecker, hairy 

woodpecker, northern flicker and monk parakeet

Table 2b

Other corvid = Steller’s jay, California scrub-jay, black-billed magpie, fish crow and common raven

Other aerialist = purple martin and barn swallow

Other passerine = Say’s phoebe, great crested flycatcher, loggerhead shrike, eastern towhee, chipping sparrow, field 

sparrow, grasshopper sparrow, white-throated sparrow, golden-crowned sparrow, eastern meadowlark, western 

meadowlark, Baltimore oriole, hooded oriole, Carolina chickadee, tufted titmouse, cactus wren, house wren, whitebreasted nuthatch, gray catbird, brown thrasher, curve-billed thrasher, wood thrush, American robin, purple finch, 

American goldfinch, ovenbird, palm warbler, black-headed grosbeak and rose-breasted grosbeak

Other invasive passerine = red-vented bulbul*, red avadavat, nutmeg mannikin and saffron finch*

Table 3

Other reptiles = American alligator, gopher tortoise, Blanding’s turtle, Florida box turtle, northern map turtle, eastern 

mud turtle, common musk turtle, spiny softshell, common five-lined skink, Argentine black and white tegu*, eastern 

kingsnake, gophersnake, southern watersnake, cottonmouth and western diamond-backed rattlesnake

Other fish = northern pikeminnow, largemouth bass and bluegill

Table 4

Other waterfowl = snow goose, Ross’s goose, wood duck, gadwall, American wigeon, blue-winged teal, cinnamon teal, 

northern pintail, redhead and ruddy duck