How Do Vets Capture Wild Animals?

Veterinarians are often called upon to help capture wild animals unharmed, to relocate animals and to safely release animals from traps during the course of their work. This may include veterinarians who are consulted by animal control personnel, veterinarians who work with biologists in the area of research or wildlife veterinarians whose primary focus is wildlife.

Wildlife researchers, fish and wildlife services and animal management personnel in national parks regularly immobilize wild animals to mark them for later identification, to provide veterinary treatment or to relocate them from overpopulated areas. Marking can involve ear notching, tagging and banding or radio-transmitter attachment. In recent years, the immobilization of wild animals for the fitting of tags and markers has increased dramatically due to the management and conservation objectives of regulatory and government agencies.

The capture of wild animals is necessary for the purposes of conservation, research and wildlife management. “Immobilization” is a term that is often used synonymously with the “capture”, since both refer to the forced restriction of movement of all or part of an animal’s body, either by physical or chemical means.¹ Immobilization is used to facilitate the manipulation of an animal, either for human and/or the animal benefit’s. This is a common practice in many animal management procedures.

Physical immobilization methods usually involve traps to restrain the animal (e.g., cage traps, box traps, nets, snares, leg-hold traps). Chemical immobilization is achieved using sedative and anesthetic drugs which have a range of intended effects. These can include sedatives and muscle relaxants which produce a widespread muscular paralysis while the animal is fully conscious, or they may produce unconsciousness with anesthesia, depending on the need, length and invasiveness of the required procedure.

Wild Animal Capture: Ethical Concerns

The immobilization of an undomesticated (exotic, wild) and/or anxious animal carries the potential to cause considerable stress. When animals are immobilized, they often undergo a series of acute stressors including pursuit, restraint, pain, fear and anxiety. All of these are capable of inducing harmful physiological responses and pathological changes.¹ Repeated stressors, such as those imposed on wild animals in laboratory or field settings have been known to lead to unfortunate outcomes.

Animals in physical traps can experience stress similar to being caught by a predator. Unfortunately, their struggle to escape may continue until they are released from the trap. Traps are sometimes set in remote locations, and a trapped animal may be left unattended for long periods of time. In the case of some traps and restraint devices (e.g., snares, steel-jaw leg-hold traps), physical injury of target and non-target species is also a risk.

Chemical immobilization can represent different risks. Immobilizing drugs have the potential to disturb normal regulatory systems, particularly respiratory and thermo-regulation, which in turn can lead to negative outcomes such as respiratory depression, overheating (hyperthermia), lowered blood pH (acidosis) and oxygen deficit (hypoxemia).¹ These can give rise to neurological or myocardial problems and organ failure. A long chase by ground or air for the purposes of darting an animal can lead to extreme muscular activity and hyperthermia, as well as capture myopathy, which is a potentially fatal outcome.

Veterinarians in wildlife medicine administer anesthetic drugs using different types of delivery systems. There are different approaches to administering drugs in chemical restraint procedures: oral, hand-held injection, pole syringe and darts. If an animal is large, dangerous or uncooperative, remote delivery systems using blow darts, gunpowder explosive darts or compressed gas projectors are the most suitable choices. Typically, the veterinarian will select the best drug or drug formulation for each situation according to the physiology and behavior of the animal, as well as the practitioner’s experience and professional preference.

Drugs used for immobilization can behave differently in combination, as well as in individual animals depending on their physiological status (e.g., health, age, size, sex). In the field, drug dosages often have to be estimated for animals of unknown weight. When drugs are remotely delivered via darts to a moving animal, the delivery of a correct dosage can be difficult to control, and such scenarios are routine occurrences when wild animals are immobilized via chemical means.

Chemical Immobilization Particulars

With the exception of the trapping of smaller nuisance animals for the purposes of animal control, in the U.S., chemical immobilization has become the method of choice for capture in many instances, particularly for large species. Given the improvements in drugs and drug combinations used in wildlife immobilization in recent years, the efficacy of this modality and the reduction of attendant stress factors it offers have shown it to be safer, more humane and far more effective than trapping.

In cases of chemical immobilization of wildlife, the veterinarian’s role is also has regulatory aspects, as the drugs used in chemical immobilization are regulated by the U.S. Drug Enforcement Agency (DEA). Any parties engaging in the chemical immobilization of wildlife must work in concert with a prescribing veterinarian, whether the veterinarian is part of the capture team, a consultant or on staff at a given facility.

The immobilization of large or potentially dangerous wild animals may pose significant challenges, presenting risks for both the team in the field and target animals. This means that drug choices and combinations must be of proven safety for each species and calculated for the weight, age, and physiological condition of the target animal. Further, invasive procedures such as surgery are often necessary in the field and in research settings. Thus, the role of the veterinarian in the capture of wild animals can be quite expansive in its nature.

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!