Specimen Procurement


Although many areas of mammalian research do not require specimens (e.g., behavioral studies), many others do. Furthermore, many studies where specimens are not preserved for the study itself do require the taking and preservation of voucher specimens. Any student of mammalogy should be able to prepare adequate study specimens. This section concerns the collection of such specimens.

Keep in mind that in healthy populations of animals, a large number are going to die "before their time". Specimens taken for scientific purposes usually are replaced by other individuals that otherwise would not have survived. Mostly subjective information from areas near universities that have been trapped heavily for rodents over a period of many decades indicate no harmful effects on the populations.

The days are long past when researchers could collect at will. There is red tape at almost every step. Most states require a scientific collecting, usually issued by the department of game and fish or its equivalent. Mammals covered by laws requiring permits usually include most or all mammals. Permits for threatened or endangered species are almost never issued (for obvious reasons). Some collecting (e.g., from national parks) require federal permits. Some states require registration of particular types of collecting gear(e.g., mist nets). Texas has in place a nongame license ($18 plus the person must have a Texas hunting license) to possess more than 25 specimens of non-game wildlife.

Requirements for scientific collecting permits vary from state to state, but usually require an association with an institution such as a university, museum, research center, or environmental company; there usually also is a requirement that animals collected under the permit be deposited in an institution that will make the specimens available to all qualified persons. This usually means a university and/or museum.

Since the outbreak of hantavirus in 1993, it's also recognized that there is some danger involved in collecting. Hantaviruses are carried by rodents of the family Cricetidae, subfamilies Neotominae and Sigmodontinae. Primary hosts of concern are the deer mouse (Peromyscus maniculatus), white-footed mouse (P. leucopus), and hispid cotton rat (Sigmodon hispidus). Hantavirus is not the only danger: rabies, tularemia, and bubonic plague (which is endemic in the Southwest), for example, pose some degree of danger. Some mammals also are capable of inflicting painful bites. The American Society of Mammalogists has GUIDELINES OF THE AMERICAN SOCIETY OF MAMMALOGISTS FOR THE USE OF WILD MAMMALS IN RESEARCH available.

There are a number of techniques for collecting mammals, including hand capture, live traps, kill traps, mist nets, pitfall traps, and shooting. To a degree, the size and habits of an animal determine the methodology. Also keep in mind the limitations imposed by the scientific collecting permit. Hand capture usually is limited to small mammals such as mice or shrews. Most suitable rodents are nocturnal, and the usual methodology is to walk an area with a lantern and several helpers. When a rodent is seen, it is run down on foot (sometimes even successfully). Live traps are take-offs on the old box trap. An animal is lured inside of a container (usually by bait) and triggers the closure of the trap. The most commonly used live trap is the Sherman Trap, although there are other, similar traps on the market. This is a steel or aluminum, rectangular, enclosed box; some types can be folded for easy transportation. One end of the trap can be set to be held down by a lip on a treadle. Bait is placed on the treadle, and when the animal steps on the far end of it, the animal's weight frees the door to snap shut, trapping the animal. The opposite end of the trap can be opened to retrieve the animal. These traps are primarily for animals up to the size of packrats and ground squirrels. Similar types (such as Hav-a-Hart) are of open wire construction and are made in much larger sizes. A different type of live trap consists of a segment of plastic pipe blocked by crossed wires at one end and by a metal flap that can open inward by not outwards at the other end. The pipe is placed into a burrow so that an animal attempting to exit moves into the pipe but then is unable to backtrack.

Care should be taken to insure protection of animals in live traps. In cold weather, some type of bedding material should be supplied to allow the animal to get off of cold metal, etc. In hot weather, traps for nocturnal animals should be checked before the sun has a chance to heat up the trap; traps for diurnal mammals should be checked frequently.

Kill traps are primarily of the type familiar to most people as "mouse trap" types. A flat piece of wood has a spring-loaded kill bar with a triggering device on its upper surface. Jiggling the bait pad (usually baited with chewed oatmeal, but some people prefer peanut butter or a mixture of oats and peanut butter) releases the kill bar. The ordinary mouse type obtainable at hardware stores, etc., is so small that the kill bar almost always damages the skull of mouse-size mammals. Since the skull is the most useful part of the skeleton in systematics, this is undesirable. To lessen damage, the Museum Special was created. This is a larger trap for mice. A standard rat trap is used for ground squirrel and packrat-sized rodents. Failure to check traps for long periods of time may result in ant damage, scavenging by other animals, or decay.

Several varieties of kill traps are used for pocket gophers and moles. The pocket gopher types fit into the gopher burrows and are triggered by the gopher pressing itself or a load of dirt against a trigger. Sprung, the trap skewers the animal in the chest region. Mole traps are placed on the surface over a mole tunnel, with the tunnel collapsed. When the mole pushes through, raising the roof, a trigger against the surface sends a spring-loaded set of prongs into the mole. Neither of these types of traps are pleasant for either the victim or the perpetrator.

Mist nets are fine nylon nets widely used to capture birds, but also the most important tool for capturing bats. The nets are long (to 60 feet or more) with several stringers that are stretched between poles. The net itself, so fine as to be almost invisible and giving a very weak echo, hangs loosely from the stringers, forming elongate "pockets". Nets usually are strung over water for bats (bats drink on the wing), though natural passageways through vegetation, etc., also are utilized. A bat hitting the net either falls into the pocket (which pretty much closes because of the weight of the animal) or becomes entwined. Nets should be attended at all times.

Pitfall traps are cans or other containers sunk into the substratum so that the lip is even with the surface. Usually a cover (such as a flat rock) is placed over the opening, raised enough by other objects as to allow an animal access. Small mammals are used to seeking cover under objects; the idea here is that in seeking cover, the animal will fall into the container. The container must either be deep enough to prevent the trapped animal from jumping out or, in some cases, water is placed in the bottom of the trap. In specialized situations, such as trapping for shrews in rockflows, the pitfall trap may be covered by several feet of rock or other filler material.

Shooting is utilized frequently for diurnal animals the size of ground squirrels and up. The most commonly utilized gun is a .410 shotgun with the smallest sized shot available for small animals and larger shot for larger prey. For very small mammals, .22 cal. dust shot sometimes is used. Shooting is not ideal for collecting because of the damage done to the specimen, but may be necessary in some cases because of trap shyness or limitations on the time available for collecting.


Last Update: 5 Feb 2008

Centennial Museum and Department of Biological Sciences, The University of Texas at El Paso