They represent only a very small percentage of all animal experiments, and yet they are sometimes used to defend animal experiments in general: experiments on animals for the purpose of species preservation (1, 2). While the vast majority of animal experiments are kept strictly in secret and genuine images and footages can be accessed only through undercover investigations, animal experiments in species-preservation are handled almost openly.

Hardly any wildlife documentary is without scenes showing wild animals being captured to be measured, tagged or fitted with transmitters. Blood or tissue samples are taken, rings placed on legs, clips on wings, collars hung around necks or backpacks strapped on. These manipulations appear harmless to viewers, and after all the research is said to benefit species preservation — thus the animals.

This article aims to show that such animal experiments — and by definition these interventions are experiments — are by no means indispensable for species preservation, and that they often critically impair the individual animals involved. Furthermore, there are numerous innovative methods available that cause no harm to animals and can yield meaningful results.

Publicly visible animal experiment: A grey goose with a huge neck collar in a park in Braunschweig, Germany. ©DAAE 

The importance of species preservation

The loss of species, also known as the biodiversity crisis, describes the rapid disappearance of animal and plant species on Earth. In recent decades, species loss has accelerated dramatically. It is estimated that extinction today occurs up to 1,000 times faster than the natural average (3). The main causes are human activities such as habitat destruction, environmental pollution, climate change and the excessive use of natural resources.

Studying the way of living and behaviour of wild animals is essential in order to understand the ecosystems in which they live and to implement protective measures. Equally important is studying animals’ adaptability to new or altered habitats, whether due to climate change or human interventions, so that appropriate measures for their protection can be taken.

Species preservation aims to preserve the diversity of animal and plant species on our planet. This biodiversity is crucial for the balance and stability of our ecosystems. Thus, species preservation is not only significant for nature but also for us humans.

Number of animal experiments in the area of wildlife research / species preservation

In Germany the number of animals recorded for this area varies significantly from year to year. Regarding the percentage, it is only a small part of all animal experiments. However, the statistics only cover vertebrates and cephalopods. Insects, crustaceans, worms and other invertebrates are not recorded.

	2018	2019	2020	2021	2022	2023
Mice	6,351	2,444	1,744	9	8	6
Chicken	0	0	150	629	1,878	0
Other birds	108	232	495	345	645	769
Reptiles	0	0	66	44	0	0
Frogs	0	0	0	990	0	0
Other Amphibia	651	0	0	0	0	0
Salmon, trout an others	6,881	0	0	14,320	1,552	5,398
Other fish		152,212	20,865	10,109	5,646	9,656
Other animals	97	46	260	131	255	507
Total	14,088	154,934	23,580	26,577	9,984	16,336
Percentage	0.66%	7.03%	1.2%	1.4%	0.58%	1.1%

Table 1: Number of animals used in animal experiments in Germany for the purpose of ‘species preservation’ and percentage of the total number (4).

Apart from a particularly high use of fish in 2019, between 10,000 and 26,000 animals were used for species-preservation in the past five years. In the EU and Norway in 2022 it was nearly half a million animals, which corresponds to 5.85% of the total number (5).

Capture of wild animals

Typically, capturing is the prerequisite for subsequent data collection. Measuring size and weight, taking blood and tissue samples, and attaching tags or transmitters are only possible if the animal is first caught. This happens in birds, bats and fish with various nets and traps. Other animals are caught in live traps or with snares. Fish are sometimes also caught by angling. For larger animals, anaesthetising darting fired from a distance is often used — partly for safety reasons for the humans involved.

Birds suffer from fear and panic when being captured. ©sevaljevic AdobeStock_233278426

In contrast to domestic animals, wild animals are not accustomed to human proximity or movement restriction. Numerous studies show that capture of wild animals can lead to substantial physical and psychological stress — regardless of whether anaesthesia is used. These damages range from injuries and long-term health issues and behavioural changes to death (6-11).

For example, grizzly bears (Ursus arctos) and American black bears (Ursus americanus) which were captured using helicopter-darting, barrel traps or foot snares showed reduced movement behaviour after capture, which only normalised after 3–6 weeks. Bears caught twice fared worse physically than bears caught only once (6).

The frequency of capture ranges from one-time for studies on species distribution to repeated captures over days, weeks, months or years — for measuring energy use or later retrieval of transmitters. That capture frequency influences animals is shown also in another example: wild reindeer (Rangifer tarandus platyrhynchus) when captured once, showed a short-term increase in the stress hormone cortisol; but multiple captures (4 times in 6 weeks) led female animals to have fewer offspring in the following summer (7).

Among some of the bears caught via foot snare (see above), severe physical damage occurred — they developed so-called “capture myopathy.” This muscle disease caused by capture stress was first described in 1964 in Hunter antelopes (Beatragus hunteri) and has since become a worldwide problem in all capture and relocation operations of wild animals (8).

Within hours or a few days a shock syndrome can appear. The animals show unstable gait, apathy, trembling, lameness up to paralysis; death often occurs due to kidney failure. Primarily affected are various mammals including marine mammals such as whales and dolphins, as well as birds. Fish, amphibians and reptiles are affected in individual cases. It has also been observed that animals survive the first capture well, but on the second they develop capture myopathy and die (8).

Triggers appear not only to be the stress of immobilization, but also noises of cars or helicopters, human proximity and manipulations such as measurements and attaching transmitters. With measures like sedatives, rest and cooling attempts are made to minimize risk of capture myopathy, but it still occurs repeatedly. Many examples exist in the literature. For instance, in Spain four little bustards (Tetrax tetrax) were caught with foot snares, to strap backpacks with transmitters onto them. One bird died after a day because it entangled a leg in the straps, the other three had difficulties walking and flying and died within 5-8 days of capture myopathy (9).

Proximity to humans and being handled even affect butterflies. Thus larvae, pupae and adult stages of the monarch butterfly showed elevated heart rates after 3-minute gentle handling (10).

The stress experience due to capture and release in wild animals can also lead to dramatic late consequences. There are numerous reports according to which animals could less effectively defend against predators, starved because they ate less, reproduced less or died from infections due to weakened immunity (11).

Frequent invasive research methods in wild animals

1. Samples of blood, tissue and stomach content

Blood and tissue samples are taken from wild animals to determine their genetic status and various metrics such as blood sugar, hormone levels or content of toxic substances like pesticides or heavy metals. In larger animals a blood sample can be taken via puncture of a vein in the legs, wings, neck or tail. But in small animals blood sampling is difficult and mutilations are accepted. In turtles and small birds such as hummingbirds toe-nails may be cut off to obtain a drop of blood (12). If at the same time a marking is to be done, e.g., in frogs and lizards whole toes (13) may be clipped or in fish one or more fins cut off (14).

To study the diet composition of animals, they are either killed or caught and their stomach flushed. For example, in unaesthetised frogs a tube is inserted through the mouth and oesophagus into the stomach and water is pumped in with a syringe. The water with stomach contents emerging from the mouth is collected. This is repeated until no stomach content is flushed out (15).

2. Marking 

Animals are marked in various ways so that individual animals can be distinguished during observation and repeated capture. There are less traumatic methods like fur‐cuts (individual patterns cut in the fur) or colouring of fur or body parts (16). But many invasive marking methods are common that cause injuries and mutilations of animals (16,17). In all cases the traumatic experience of capture is the prerequisite for the subsequent marking.

2.1. Mutilations

Toe-clipping (i.e., cutting off toes) in differing positions and numbers is standard in “laboratory” mice under 7 days. Among wild living mice it is rather the exception, but still happens (17). In some mouse species this leads to a low recapture rate (17), suggesting that the animals associate capture with the pain of mutilation. By contrast, toe-clipping in amphibians and lizards as well as fin-clipping (cutting off fins) in fish is a usual marking method (14).

2.2. Branding

Branding of cattle and horses with a hot iron has a centuries-old tradition. Burns of third degree are inflicted to ensure permanent marking through scar formation. That this procedure is connected with enormous pain — even over long time periods — is well documented. For example, foals often showed pain symptoms lasting weeks and were behaviourally impaired (18). In wildlife research hot-branding is used with different seal species. Among Steller sea lions (Eumetopias jubatus) behavioural changes were observed in the first three days after branding. In harbour seal pups (Phoca vitulina) the wound did not heal after 9-10 weeks, and in southern elephant seals (Mirounga leonina) healing took up to a year (19).

2.3. Tags

A common method of identification is attaching plastic or metal tags with an individual number. Typical body parts where tags are placed are ears, wings and fins. Capturing and immobilization of the animals is a prerequisite. When attaching the tag a piece of tissue is often punched out, which is associated with corresponding pain. The subsequent impairments range from injuries of the marked body parts, altered behaviour, reduced food intake up to increased mortality (20-25).

For example, vultures (Gyps coprotheres) fitted with wing tags flew slower, less often and covered shorter distances than leg-banded birds (20). Magnificent frigatebirds (Fregata magnificens) marked on the wings showed poorer breeding success (21). An analysis of prey remains of peregrine falcons (Falco peregrinus) found that unusually many Montagu’s harriers (Circus pygargus) and hen harriers (Circus cyaneus) fitted with wing tags were predated upon. The result suggests that tags may attract attention from predators, which leads to increased predation rate and thus increased mortality (22).

Especially for many aquatic living animals, a streamlined body shape is vital for survival. A tag attached by humans increases drag in the water and leads to impaired swimming. This in turn affects food intake and makes the animal easier prey for predators. For instance, tagged Magellanic penguins (Spheniscus magellanicus) had to swim longer distances for daily food intake than non-tagged animals during years with food scarcity and thus expended more energy (23). In tagged Adélie penguins (Pygoscelis adeliae) injuries of the wings and a reduced survival rate of 24% were observed (24). A computer simulation showed that a device mounted on the back of a grey seal (Halichoerus grypus) increased water drag by 12%, which suggests altered swimming behaviour (25).

Adélie penguins: wing marks increase drag and make swimming more difficult, thus hindering food intake. ©Katie Dugger, USGS

2.4. Transmitters

Animals have been transmitter-tracked for decades to follow their home range and migration movements.

There are three tracking techniques:

• Very-High-Frequency radio-tracking (VHF)
• Satellite tracking
• Global Positioning System (GPS).

VHF has been standard since the 1960s in wildlife research. A transmitter attached to the animal sends signals on a predefined radio frequency at regular intervals. With antenna and receiver, based on the signal frequency and the time between two signals the position of the animal can be determined.

Satellite tracking, used since the 1980s, sends signals from a transmitter on the animal to certain satellites, which in turn are received on earth.

GPS technology has been used in wildlife research since the early 1990s. Signals from at least three satellites are received, from which the position is calculated. Although GPS units are small and light, they present a disadvantage in that the data are stored in the GPS device. To read them out the animal must be captured a second time or even repeatedly. GPS and satellite technology may also be combined to continuously obtain data, but this increases the size and weight of the device (26).

Typically, batteries or small solar panels are used as power source. There is the possibility that the transmitter falls off the animal, e.g., after a predetermined time or when the battery is empty — thus avoiding another capture.

Eagle fitted with a transmitter-backpack. ©belizar AdobeStock_79454631

The transmitters are attached externally (via a collar or backpack) or glued on. Or they are implanted under the skin or into the abdominal cavity. For such an operation the animals must be anaesthetised. The duration of transmitter use may vary greatly depending on the research question – from a few days to many years.

The problems arising from transmitter use are manifold. One study from the USA reports that sparrows tangled body parts in the straps of the transmitter or became stuck in vegetation (27). Eastern phoebes (Sayornis phoebe) threw their chicks from the nest in an attempt to remove the transmitter from their young. In other sparrows (Ammospiza caudacuta) the parents abandoned their chicks or fed only the non-transmitter-fitted ones (27). In mantled howler monkeys (Alouatta palliata) serious skin and muscle injuries were found around the collar area (28).

The weight of a transmitter collar affects zebra behaviour while grazing. ©PACO COMO AdobeStock_134126186

The size and weight of the transmitter and the method of attachment play a role. Recommended weight ranges from 0.7% up to 9% of body weight, with an average under 5% (29). In zebras (Equus burchelli antiquorum) in Botswana it was observed that even a small weight difference had major behavioural impact: animals with a heavier GPS collar (1.8 kg) covered only half the distance when grazing compared to zebras with a lighter collar (1.2 kg), despite both collars being well below the lowest guideline threshold (0.4% vs 0.6% of body weight respectively) (29).

Especially dramatic can be the effects for animals into whose abdominal cavity transmitters are implanted. Among 305 dead or living Scandinavian brown bears fitted with VHF transmitters up to 13 years post-implantation, severe pathological changes such as inflammation and adhesions in the abdominal cavity were found. The batteries were in some cases corroded or leaked. Two bears died from a short-circuit of the batteries (30).

Serious pathological changes caused by a transmitter in a bear's abdominal cavity. Reference: Arnemo. Frontiers in Veterinary Science 2018; 5: 252

Severe immune reactions were also found in European beavers (Castor fiber) and channel catfish (Ictalurus punctatus) that had devices or temperature/heart monitors implanted into their abdominal cavity. The transmitters and monitoring devices were rejected by the body and expelled through the intestines or the operation wound (31).

Because of their body shape, for snakes surgical implantation of devices into the abdominal cavity is standard. However, a number of problems may occur, from anaesthesia risk and wound infections to negative effects on growth and reproduction (31). Increasingly external devices are used in snakes, e.g., glued with tape or sewn on. Negative effects included changed behaviour and movement patterns, skin and scale injuries, and even death (32).

3. Killing

For species identification and for museum collections animals were commonly killed in the past. In recent decades more non-lethal methods are used, yet there are still vehement defenders of killing animals for these purposes. Especially amphibians, birds and small rodents are commonly killed for DNA analysis (33). Also, insects, spiders, scorpions and other invertebrates fall victim to species identification. To identify species diversity on a meadow, for instance, all organisms in a certain area may be collected with a net and preserved in alcohol.

Collections containing countless animals preserved in alcohol are standard at many universities. © DAAE

Animal-experiment-free wildlife research

On the website “3R’s Principles in Wildlife Research” by Marina A. Zemanova a wealth of animal-experiment-free research methods sorted by research objective and animal class is presented (36). Researchers can inform themselves via numerous studies and instructional videos.

Unfortunately, the author limits herself to the 3R principle, which besides replacement also includes reduction and refinement of animal experiments. The concept developed in the 1950s positions the animal experiment as a method that is not questioned and wants only a modification of the existing system. Our association DAAE demands, however, the abolition of all animal experiments for ethical and scientific reasons (37). So, unfortunately, some studies on Zemanova’s website merely represent a refinement — for instance a swab from the mouth of caught fish (38). Also stomach-flushing of frogs and experimentally inducing stress in rabbits via fox scent to measure cortisol in faeces are listed as non-invasive methods here (39). Nevertheless, the website can serve as an extremely important resource for animal-experiment-free wildlife research.

1. Faecal samples

Faecal samples carry a lot of information. For example, species can be determined via DNA (40), physiological parameters such as sex and stress hormones (41), diet components (42), absorbed pollutants like heavy metals, toxins (43) or microplastics (44), as well as presence of parasites (45) and viruses (46) can be investigated.

2. Hair and other samples

Hair can be used for species identification via DNA analysis (47) or examined for heavy metals such as lead and mercury (48). To obtain hair samples hair-traps are used: sticky tapes near hamster burrows (49) or otter couches (50), power poles fitted with barbed wire where bears rub (51), or for territory marking by lynx favourite trees (47). Also moulted hairs of sea lions (48), hairs found in wildlife underpasses (52) or hairs of road-kill animals (53) can be analysed.

Likewise moulted feathers from birds can detect DNA (54) and heavy metals (55).

DNA analysis is now so advanced that a genetic profile can be determined not only from faeces, hairs and feathers but also from urine (56), eggshells (57), shed antlers (58), shed skin from lizards (59), collected skin pieces from whales (60), and placentas of seals (61). Even spider webs (62) and snail slime (63) contain sufficient DNA trace for species identification. For animals that move very slowly or not at all (e.g., mussels) swab samples may be used (64). Skin particles of manta rays can be sampled underwater with a toothbrush (65), and with a lice-comb on a telescopic pole skin parasites of sea lions can be collected (66).

3. Environmental examination

Animals leave traces in their environment. For example, the genetic code can be traced in water not only from aquatic animals such as fish (67) and whales (68), but also from land animals drinking water (69) or temporarily swimming in it (70). Earthworms leave DNA traces in soil (71), insects (72), nectar-drinking bats and hummingbirds (73) on the flowers they visit. Via a telescopic pole or drone the blow of whales and dolphins can be captured – this not only determines the genetic code (74) but also provides information about health by examining bacteria (75), pollutants such as chemicals (76), hormones (77) and the microbiome (78).

Bats leave DNA traces on the flowers they visit. ©FotoRequest_AdobeStock_598449622

Saliva on leftover food is also very useful. This can include fruit pecked by birds (79), leaves chewed by bonobos (80), salmon remains left behind by bears (81), or even tools made by chimpanzees for termite fishing (82).

Traces of the genetic profile can even be found in the air, for example at bat roosts (83), in footprints in the snow (84), and in scent markings used to define territories (85).

4. Photo-ID / Face recognition / AI

Instead of tagging or transmitter-fitting animals, modern computer-based recognition methods can be used – so-called Photo-ID – to identify individual animals. Even with animals that look very alike or whose way of life leaves little visible, individual assignment is possible. For example: whales can be recognised by their fluke or dorsal fin (86); crocodiles by the pattern of their tail-scales (87); manatees by their individual scar pattern (88); polar bears via their whisker pattern (89). For many animals fur colour and pattern is also individual. The photos required can be obtained via camera-traps, drones or unmanned aerial vehicles without disturbing the animals.

Whales can be identified by the individual shape of their fluke. © ÄgT

Photos can also provide information about diet composition (90), parasite load (91) and biometric body measurements (92).

The Photo-ID technique can also be used for foot, hoof or claw impressions (93) to track movement patterns of individual animals. Bears (94) and primates (95) can be identified via face-recognition software, using deep learning (a machine-learning method). Using deep learning even flying insects can be identified via their flight patterns (96).
In reef fish, AI-assisted high-resolution 3D-tracking was used to gain detailed insight into movement patterns and energy expenditure of the animals (97).

Modern photogrammetry and 3D-scanning with high-resolution cameras can help investigate the anatomy of animals (98). For species identification, the calls, sounds and noises animals make can also serve — e.g., cricket chirps (99), bees/hornets flight-sounds (100) or ultrasound from bats (101).

Does the end justify the means?

In wildlife research the protection of species and biodiversity is in the foreground. The welfare of the individual animal regularly recedes into the background. Only in this way is it possible to explain that for decades animals have been intentionally exposed to capture and various manipulations — often into the greatest suffering. Death of the animals is either planned or at least accepted. A rethink seems hardly to be making progress.

A survey among ecology researchers found that more than a quarter of them kill animals for research purposes; a further 18 % use exclusively invasive methods that can lead to damage to the animals; roughly a third use both invasive and non-invasive techniques; and only 22 % reported using only non-invasive methods. As hurdles for the use of non-invasive investigations, the most commonly cited were financial restrictions and lack of awareness (103).

Besides this alarming obvious indifference toward the suffering of the individual animal, the scientific relevance of the data obtained must also be questioned. If a difference of 600 g in the weight of a collar on a 320 kg zebra has massive behavioural impact (29) then one must ask whether even the lightest collar and the “gentlest treatment” do not cause behavioural change and thus miss the actual objective of the experiment.

The call for the abolition of all animal experiments rightly includes wildlife research. It exposes animals to suffering and death, although even in this field modern non-harmful research methods are available in large number. Animal experiments in wildlife research are unjustified and must — just like all other animal experiments — be abolished.

02/06/2025
Dr Corina Gericke DVM

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