Animal Capture Techniques
When discussing animal capture techniques, or more specifically, wildlife capture techniques, two types of capture are being referenced: physical capture and chemical immobilization. Physical capture broadly describes the use of devices such as traps, nets and snares which restrict an animal such that it can be handled or chemically immobilized. Chemical immobilization involves the direct use of sedatives and/or anesthetic drugs to render an animal unconscious or docile enough to be safely handled prior to capture. In such cases, the immobilizing drugs are delivered remotely.
By definition, both of these methods effectively result in the physical capture of an animal; chemical immobilization can precede the physical capture necessary to carry out research, medical or wildlife management procedures, whilst physical capture can precede chemical immobilization in order to further the same ends. For the purposes of this discussion, physical capture techniques will be detailed, as well as advantages and disadvantages associated with the various methods.
Physical Capture Methods
The type of physical capture methods will of course depend upon the species and need. Professionals are called upon to capture wildlife—typically wildlife managers and animal control officers—may be removing a raccoon from an attic in a residence, or they may be trapping bobcats for a research study on bobcat populations in the wild. Barring the necessity for direct chemical immobilization (in the case of a young adult bear that keeps wandering into a neighborhood, for example), nonlethal physical means of capture are most likely to be used.
Catchpoles are one of the most versatile tools used to capture and restrain many animals. A catchpole is a long stick with a cabled loop on one end that can be tightened via an integral mechanism. These are also frequently used by animal control officers to capture and restrain dogs and feral cats. The loop is placed over the animal’s head and the cable is tightened to hold the animal. Since come animals such as cats (domestic or wild) can become agitated and accidentally suffocate, many advocate placing the loop over the animal’s head as well as over one front leg. Some catchpoles also swivel, allowing the animal to twist without risking suffocation, and modified catchpoles are available for restraining snakes.1 In every case, the amount of time an animal spends in this type of restraint should be as short as possible.
Nets come in many forms, the most common being throw nets and hoop nets. A throw net is tossed over an animal, while a hoop net is attached to the end of a long handle and is used to scoop up the animal. In the case of throw nets, the net must be large enough to at least cover the animal, while a hoop net should be deep enough to allow the hoop to be twisted to restrain the animal in the bottom of the net (captured animals can climb out of shallow hoop nets). Mesh size is important as well, as an animal may force its head through and injure itself or strangle if the mesh is too large.1
Netting systems for larger animals, or to capture large numbers of animals such as birds are also commercially available. These are very versatile and can capture a wide variety of species. Netting systems commonly include cannon/rocket/air cannon nets, net guns, mist nets, drop nets, and hand nets.1,2 Some of these can be used to fire a net at an animal ballistically, usually from a ground vehicle or helicopter.
Live traps are effective devices for capturing many species, and are widely used by wildlife managers and animal control officers. Variations of live traps include cage traps, multiple capture traps and foothold traps. These traps are usually constructed of wire or plastic and come in many sizes and styles. They may open on one or both ends and have one or more compartments for multiple animals. The animal enters the cage and steps on a treadle, which causes the door to close behind it.1 Cage traps are easy to set and little site preparation is needed.
Advantages of live traps include being able to visually determine the animal that’s been trapped, and circumventing the risks associated with animals being preyed upon after capture. Disadvantages include the fact that live trapping is labor-intensive, the wrong animal can be captured and animals can die in traps due to exposure, or lack of food and/or water. Animals can also hurt themselves due to the stress of being restrained or while trying to escape.
Foothold traps restrain an animal by holding the foot. Foothold traps can be used on land and in the water. There are several different designs, including the coilspring trap, which is probably the most commonly used foothold trap, the longspring trap and the cylindrical foothold trap.1 Foothold traps are still used by some wildlife services for wildlife damage management, mostly involving wildlife that are causing damage to property, agriculture, and natural resources or protecting human health and safety. Because of the cruelty inherent in the use of steel-jaw traps however, they've been banned in many countries, and in several U.S. states.2 In other states in the U.S., there are legal restrictions on the jaw spread of foothold traps.
Bird Capture Techniques
Capture techniques designed for wild birds such as waterfowl, shorebirds and other wetland species are of particular importance for reasons of disease research and conservation. The capture of wild birds is strictly controlled in most countries, and those engaged in capture activities should always be aware of and comply with local, state and federal laws regarding these activities and obtain all the required permits well in advance.1 As mentioned earlier, net trapping is often used in the capture of birds.
Corral traps (which are also used to trap feral hogs) are large, temporary fenced enclosures with an entrance that can be closed after birds are guided into the trap. Birds are typically driven into the trap by a team of handlers. This technique is often used to capture flightless birds (e.g., geese or other waterfowl during their annual molt, or pre-flight colonial birds).1
Funnel traps are traps consisting of a wire cage or enclosure with one or more funnel shaped entrances which the birds can enter, but have difficulty exiting. Mesh netting can be placed over enclosure traps to prevent birds escaping over the wire fence when handlers approach. A baited funnel trap can be deployed or constructed on land or in water shallow enough for foraging by dabbling ducks, coots and waders.1
Dive-in traps are usually baited traps that are effective for capturing aquatic diving birds. Dive-in traps can be constructed in relatively shallow water habitats that are frequented by diving birds and accessible to handlers in boats or waders. Dive-in trap design is similar to that of the funnel trap. In general, dive-in traps are only effective in wetland habitats, but may be used in permanent water bodies of adequate depth or tidally influenced wetlands.1
Capture and Stress
Stress is the biological reaction to any adverse stimulus, internal or external, that tend to disturb an animal’s internal homeostasis.1 Stress alters an animal’s normal physiology and can induce pathological states. In this context, stress is usually caused by excessive exertion or fear during capture. The many unfamiliar events that occur during these procedures can lead to both psychological stress as well as the physical stress of muscular exertion.1,2 This exertion may result in damage that can lead to development of a pathological state.
Capture myopathy (or CM; alternative names include post-capture myopathy, stress myopathy and transport myopathy3) is a stress-induced condition most frequently encountered in wild animals. It frequently occurs following prolonged and intense chases or manipulations. The cause for capture myopathy is likely a combination of fear and anxiety accompanied by muscle exertion.
Capture myopathy has been recognized in numerous wild species, including fish, birds and cetaceans. Clinical signs of capture myopathy can vary depending on the species and the cause of exertion.3 The method of capture and restraint is also a determinant in occurrences of CM. The available literature states that capture myopathy may result in sudden death, or that clinical signs may develop hours, days, or up to two months following capture.4 The clinical signs during early onset include elevated respiratory rate, heart rate, and body temperature. Body temperature increases during exertion, with higher temperatures being associated with death due to CM. Muscle spasms, stiffness and lameness are also clear signs of CM. Animals often become recumbent and may stumble. If dark red-colored urine is noted, this is an indication that the animal's muscles are breaking down and that its kidneys have been severely affected.3,4 Death of the animal usually follows. If the animal survives the acute stage of the condition, scarring of heart and skeletal muscle tissue may permanently debilitate the animal. Upon necropsy, light-colored skeletal and cardiac muscle is indicative of capture myopathy being the cause of death.
There is no treatment for capture myopathy, prevention being the best method of avoiding this condition. Care should be taken in case of handling of animals that tend to be more susceptible to capture myopathy. The team in the field should be thoroughly aware of the risks of capture myopathy and make every effort to prevent its occurrence. The negative effects that capture may have on an animal's health should always be considered before beginning a capture. Capture methods that minimize animal stress, struggling and handling time should always be utilized.
Interested in learning more about safe capture? The San Diego Zoo now offers courses in safe capture techniques and best practices. Learn reliable, safe, and effective techniques for the species you work with and the scenarios you encounter!
1Animal Care and Use Committee (1998) Guidelines for the Capture, Handling, and Care of Mammals as Approved by the American Society of Mammalogists. In: J. Mammology 79:1416-1431.
2Hubert, W., et. al. Passive Capture Techniques (2012). Nebraska Cooperative Fish & Wildlife Research Unit, Staff Publications, 111.
3Friend, M., Thomas, N. J. Field Manual of Wildlife Diseases. In: Field Manual of Wildlife Diseases, United States Geological Survey, 361-368.
4Williams, E. S., Thorne, E. T. 1996. Exertional Myopathy (Capture Myopathy). Noninfectious Diseases of Wildlife, Second Edition, 181-193 Iowa State University Press, Ames, Iowa, USA.
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