POTENTIAL ANIMAL WELFARE ISSUES IN WILDLIFE RESEARCH
In general, the impact of wildlife research on animal welfare depends on whether the animal needs to be captured and whether the research involves invasive or lethal methods. Specifically, the use of lethal techniques for tissue sampling and collection of voucher specimens has a long-standing tradition in wildlife research. However, apart from the obvious harm to the individual animal, removing a key member of a group in species with complex social formations can result in impaired well-being among the remaining individuals1.
Capturing and trapping
In contrast to laboratory animals, free-living animals are not accustomed to interactions with humans, making any capture or handling highly stressful2. For instance, Cattet et al. (2006)3 demonstrated that grizzly bears (Ursus arctos) subjected to repeated captures exhibited significant differences in their body condition compared to bears captured only once. The stress of capture can even lead to capture myopathy, a metabolic muscle disease that often results in death4, 5. Additionally, capture can alter an animal’s behaviour, which might significantly impact data collected in behavioural and recapture studies. For example, Rode et al. (2014)6 found that polar bears (Ursus maritimus) displayed reduced activity and movement rates 3.5 days after capture. Linhart et al. (2012)7 showed that willow warblers (Phylloscopus trochilus) could recall capture events involving mist nets even after a year and learn to avoid them. Apart from stress and behavioural impacts, capturing can also cause physical harm, ranging from skin abrasions to broken limbs8, 9, 10. Trapped animals are also more vulnerable to predation11.
Blood and tissue sampling
Common methods used for DNA collection in genetic research include blood and tissue sampling, such as toe-clipping or fin-clipping. Blood is also frequently utilized to assess levels of potential detrimental elements, such as heavy metals, and in physiology studies to measure hormonal levels. However, blood sampling can be challenging for small animals, such as zebrafish (Danio rerio)12, and has even been associated with lower survival rates during the first year after sampling in American cliff swallows (Petrochelidon pyrrhonota)13. Fin-clipping is often employed for DNA sampling in fish. This procedure is, however, painful and may impact fish survival14, 15, 16.
Marking
Wildlife research often requires marking animals to gather data on behaviour, survival, reproduction, or home range size. Virtually all marking methods require capture, which is stressful for wild animals, and many methods also result in tissue damage. Common marking techniques include, for instance, hot- or freeze-branding, mutilations, tags and bands, and the use of radio-transmitters.
Branding
Hot-branding and freeze-branding, traditionally used for marking cattle and horses, have been adapted for marking pinnipeds. Not surprisingly, hot-branding is a painful procedure, leading to behavioural changes in the marked animals17. Public concerns about animal welfare have resulted in lawsuits and the withdrawal of research permits for sea lion studies involving hot-branding18. Additionally, the development of skin tumours following freeze- or hot-branding has been observed in cattle19, which raises caution regarding wildlife branding as well.
Mutilations
Toe clipping is a classic method for marking small vertebrates such as lizards, amphibians, and rodents. Unique marking is achieved by clipping toes in different combinations on different limbs. Although considered harmless by some researchers,20, 21 toe-clipping has been shown to reduce survival rates22. It also impairs locomotor performance, endurance, and the clinging performance of pad-bearing lizards23.
Tags and bands
Another common method of marking animals is with tags or bands. Tags can be made from various materials, typically metal or plastic, and often include alphanumeric codes for individual or group recognition. Marking and attaching tags usually require immobilization of larger animals, and the procedure can be painful24, 25. In small animals such as fish, tagging can also affect their survival rates26, 27. Tags can be applied to different parts of the body depending on the animal’s anatomy, most commonly wings, fins, or flippers. Several studies have shown that tagged seabirds experience reduced return rates, provisioning behaviour and survival28, 29. Tags can increase swimming costs due to drag in seals30, and tagged penguins have been observed to face foraging difficulties during periods of low food abundance31. Moreover, tags have been reported to damage flippers of Adélie penguins (Pygoscelis adeliae)32, and modified diving behaviour and decreased survival in the first year after banding have been observed in little penguins (Eudyptula minor)33.
Radio-transmitters
Radiotelemetry has been crucial for tracking animal movements. This method involves the transmission of radio signals to locate a radio-transmitter attached to an animal. Radio-transmitters can be glued to the skin, designed as GPS collars or harnesses, or surgically implanted. For tracking mule deer (Odocoileus hemionus), elk (Cervus elaphus nelsoni) and moose (Alces alces) females, vaginal implant transmitters are also used34, 35, 36. Several issues have been identified with radio-transmitters. For example, Dixon et al. (2016)37 found evidence of decreased survival rates associated with harness-mounted satellite transmitters on falcons (Falco cherrug), and a recent study showed similar results in a shorebird (Calidris alpina schinzii)38. In passerine birds, entanglements with vegetation or body parts as well as non-entanglement injuries have been observed39. Recently, GPS devices have been reported to cause corneal opacity in ibises (Geronticus eremita)40.
Another issue is the method of attachment and the weight of the instrument. If a radio-transmitter is attached using glue, it can cause lesions and abrasions on the skin41. Studies have shown that heavy collars decrease the survival rate in caribou (Rangifer tarandus)42, and collar weight also affects the grazing behaviour of Burchell’s zebras (Equus burchelli antiquorum)43.
Particularly problematic is the use of implanted transmitters, as this involves additional trauma to the animal. A recent study44 demonstrated that transmitters implanted into the abdominal cavities of brown bears (Ursus arctos) performed poorly and were not biocompatible, leading to the death of several animals. Cases of mortality caused by implanted radio-transmitters have also been reported in European lynx (Lynx lynx)45, Harlequin ducks (Histrionicus histrionicus)46, and American badgers (Taxidea taxus)47.