Technical Note: Breakaway Collars, Timed Collar Releases, and Expansion Collars
Transmitters for mammals are often attached using a collar. Most collars have adjustment ranges that allow fitting to an animal's neck and once deployed collar circumference remains fixed. Some collar materials, such as leather, tend to stretch, shrink, and eventually decay. Other collar materials such as those typically used by Telonics are much more durable, retaining their size and flexibility for years under a variety of conditions.
Many collars have been put on animals with recognition that those collars would stay on the animal for its lifetime. When collars are put on adult animals, and when expected transmitter longevity is measured in years, this is still seen as an appropriate approach by many. However, increasing numbers of researchers want collars that fall off after the useful operational life of the unit has been achieved. Some applications also require or benefit from collars that expand while on the animal. Over the years, Telonics has worked with biologists to develop different types of expandable, breakaway, and expandable/breakaway collars to meet specific design criteria and study goals. More recently we have developed microprocessor controlled releases that can be programmed to release a collar at a precise time. Many users now include such timed releases on their collars so that collars do not predictably remain on animals for long periods following the collar’s useful life. This technology has now been expanded such that when used with the specific Telonics collars that operate through the Iridium satellite system users can remotely command collar release. Such collar releases, when paired with VHF transmitters included as a portion of the overall unit on the animal, also facilitate collar retrieval, which can allow downloading of information that was not transmitted and/or refurbishment of the electronics into a new collar.
The most basic breakaway collar designs are based on a degradable link that allows the collar to fall away after some period of time. The biggest difficulty with such designs is predicting how long the degradable link will remain intact given the wide range of species, habitats, and environments where they may be used. A different set of problems is faced when wanting to instrument juvenile animals that will be growing during the period of interest. With such applications some type of expandable collar is required, or another attachment method such as an ear-tag is used. Most such expandable collars need only to expand once as the animal grows. There are also applications where repeated expansion and contraction of the collar over several years is desired; e.g. collars placed on male ungulates that experience seasonal swelling of neck circumference during rut, or species such as bears that can undergo significant weight gain and loss related to hibernation. Such specialized collars can have complicated designs and be difficult to construct. There are instances where both expansion and breakaway mechanisms are desired and those two technologies can be combined in collars that first expand and then fall away.
Brief discussions of these various collar types follows:
Micro-processor controlled collar releases can provide precisely-timed release dates and times, and when paired with specific Iridium systems allow the ability to remotely trigger release. Such releases continue to prove themselves in field applications and an increasing number of users elect to include them in collars they purchase and deploy. However, even with these precisely-timed, designed, and tested devices users should be aware of limitations. The releases themselves come with some cost in dollars, weight, and space on the collar. Because of this they may not be available or selected for all applications. Further, it must be recognized that when putting a device on wildlife, that device is subject to a variety of abuse, often including temperature cycling and extremes, wetting or submergence, and physical abuse such as impact or chewing. Such factors can result in the devices not performing as intended.
Breakaway Collars include some type of degradable link, which is expected to breakaway over some period of time. A limitation of such collars is that variations in the environment between areas or years can result in large variation in retention times for the collars. Breakaway depends on the amount of abrasion, temperature cycling and extremes, moisture, UV exposure, and other abuse as varies among species, individuals, environments, and years. Despite such limitations, some users find that this approach meets their requirements and include this type of breakaway in their collars. This kind of breakaway mechanism is usually less expensive than microprocessor-controlled releases, but with the required perspective that breakaway times may vary substantially.
Expandable Collars are designed to expand as an animal grows or has seasonal changes in neck circumference. This presents a series of design challenges. Often, a first priority of an expandable collar is that it expands easily enough to avoid harm to the animal. However, collars designed to expand are necessarily easier for the animal to remove than a collar of fixed circumference. Collars may prematurely expand because of neck rubbing, scratching, social interactions, or even the mass of the transmitter moving as an animal runs. The use of expandable collars may increase the danger of an animal catching a foot while scratching, or stepping into the collar while feeding. Increasing resistance to expansion increases the possibility that the collar will not expand at the desired time. Reasonable success has been achieved with collars that expand as young ungulates grow, but successful use has been more limited with dexterous species such as felids or canids. Repeated collar expansion and contraction is frequently desired for animals which have seasonal neck expansion, but such cycling is more difficult to achieve than only expansion because many materials and designs do not contract to original size and shape after being continuously expanded for days, weeks, or longer.
Expandable/Breakaway Collars combine aspects of expandable and breakaway collars, with the advantages and limitations of both.
Various articles have been published describing collar designs, with most of those described being at least moderately successful for the particular use described (most people do not publish failures). Our experience working with various species in a variety of environments has sometimes shown large differences in performance of a particular collar design depending on species, age, climate, habitat, and even behavior of specific populations or individuals. For example, latex tubing used as a breakaway mechanism in some collars is degraded by UV light. Such collars usually do not last as long in open areas where they are exposed to large amounts of UV radiation as they do in heavily forested areas which receive much less exposure. Likewise, the amount of diurnal versus nocturnal activity can influence retention time. Slight variations in material, threads, number of stitches, etc. can similarly impact performance of other types of expandable, breakaway, and expandable/breakaway collars.
Users should be aware that with most expandable or breakaway collars a variation in performance needs to be expected. Some collars fall off prematurely and others remain on longer than desired. The professional staff at Telonics has a pool of knowledge gained from years of experience, though we do not have all the answers. Therefore, we encourage you to share your information with us so that we may share it with others. If you have the perfect expandable collar, or a good one, or something you tried that was a miserable failure, we would like to know.