The value of enrichment to reintroduction success- Reading et al. 2013
Introduction:
Environmental enrichment is defined as an animal husbandry principle that enhances the quality of captive animal care by identifying and providing the environmental stimuli needed for optimal psychological and physiological well being. Animals that are raised for release need to a wide range of behavioural skills and cognitive abilities that normally depend on the conditions in which they were reared. Animals designated for release may require enrichment in the form of stressful stimuli since in nature these stressors would hone an animal’s adaptive behavioural response. It is important to note that distress is different from stress, distress can come from a new stimulus that the animal has no adaptive response to, for example like being locked in a cage without ample space can cause chronic distress which then leads to abnormal behaviours like pacing because the animals don’t have a behavioural outlet for the issue. It should also be noted that natural stresses is needed for normal psychological and behavioural development. A second reason to include natural stressors while in captivity for animals meant for release is that we should raise the animals to have a good quality of life after release which means getting them ready for the stressors they will encounter in the wild. This is why most reintroductions done in the past have failed, as the animals were not raised for encountering negative stimuli but the success rate of releases have increased with time. (check paper for specific examples). By exposing animals to natural type stressors they can increase survival by improving physical conditioning, behavioural expression and other skills.
Factors influencing reintroduction success:
Numerous factors affect reintroduction success such as genetics, demography, disease, habitat requirements and behaviour. Important behavioural traits that influence reintroduction included locomotion skills (for example like moving through a complex environment, constructing nests), predator avoidance (recognition and evasion of predator stimuli), foraging (including finding food, handling time), interacting socially (courtship, mating, raising young), habitat selection and avoiding conflicts with humans. Animals that are released without learning these end up with high mortality rates and mitigating these issues can be quite time consuming and expensive. These behaviours should be observed and used as a measure to identify successful reintroduction individuals: 1) foraging ability, 2) acquires food, 3) avoids predation, 4) reproduces, 5) parents, 6) communicates, 7) selects habitats, 8) locomotes, 9) how it moves daily and seasonally, 10) social organization and 11) territoriality.
Wild vs captive source animals
Reintroducing animals that were wild-born tend to do better than individuals born in captivity. This is because captive born animals tend to habituate to human caretakers and can increase animal-human interactions after release. Therefore including a training regiment that develops human avoidance skills can be crucial to released individuals. Using enrichment in captivity to develop the right expression of critical behaviours requires 1) an appropriate environment to learn, 2) sufficient opportunities to express the behaviours, 3) the correct social setting, this is more the case for animals that would need a skilled parent present to show them the behaviour, 4) understanding the role of developmental factors may play in the timing of stimuli, for example like imprinting when the correct stimulus must occur at the right time in development for it to be learned. For example captive born northern water snakes showed less surface movement and abnormal habitat use resulting in higher mortality rates than wild-born snakes that were translocated.
The value of enrichment to reintroduction:
Using enrichment can be costly thus conducting rigorous testing of enrichment protocols is necessary to ensure they will help the animals after release. Monitoring the animals after release is also a key part of this as this will tell us if the enrichment protocols are indeed working and where it needs to be strengthened for future releases. A simple but expensive manner in which to use enrichment is to create an environment that mimics their release sites as closely as possible. These types of environments would allow the animals to practice locomotor, foraging and social skills while also enhancing physical fitness and encourages the animals to not disperse once released. A way to do this is by setting up pens at the release sites so that the animals cannot leave or by creating environments close to or in the facility that mimic the environments. One study reintroducing black footed ferrets brought in large amounts of soil into warehouses and created a similar environment (check paper for other examples). They also found doing this decreased fecal corticosteroid levels. Providing enrichment early is key as an animal learns very early in life and some species have imprinting periods where exposure to proper stimuli is needed for survival, this is normally the case for food. For example black footed ferrets were exposed to prairie dog scents early in life to ensure that once they started to hunt they would have a preference for this natural prey item. This type of olfactory imprinting was crucial to proper neural development. An example of this imprinting going wrong is with golden lion tamarins that were allowed to free-range prior to release had performed no better in the wild than tamarins that weren’t allowed to free range because the exposure happened too late in their development.
Locomotion:
Learning the proper locomotory skills is crucial for animals that are destined to be in complex environments after release, for example if the animal is arboreal or semi-fossorial. These types of skills are learned very young in nature and should also be incorporated as early as possible for release animals so as not to miss the imprinting period or period of time where they learn best. Animals that are unable to move efficiently end up moving too little once released as they are unfamiliar with escape routes, identifying safe patches of food and end up producing large amounts of waste and odours that can attract predators. Providing acclimation pens on reintroduction sites can mitigate this problem.
Predator Avoidance:
Predation is a big issue with captive raised animals as they normally find predators to be novel and may not recognize an animal as being predatory in turn may not react appropriately. As a result many reintroductions now include a predator avoidance component to their regiment in the form of presenting animals with models of predators and delivering an aversive experience to individuals prior to release. This can be done by presenting the animal with a model of the predator and the aversive experience can be in the form of chasing by people or dogs to increase predator avoidance, this strategy was used for greater rheas. Predator avoidance training needs to be done in a few trials with large amounts of time in between to ensure the animals do not become habituated to the predator model. Therefore few trials done periodically starting from a young age would be optimal. As humans are seen as large potential predators, it can be difficult to instill this in animals as they are normally raised by humans in captivity, therefore limiting human interaction as much as possible is necessary to avoid habituation.
Foraging Skills:
Animals meant for release must be able to identify proper food, acquire it in a timely manner such as through hunting or foraging leafy matter, handle the food in the correct way such as constricting for snakes or shelling nuts for primates. Hunting takes a substantial amount of skill to do that captive animals rarely acquire. For example 2 captive raised fishers that were able to kill prey when they were exposed to it in captivity ended up starving to death in the wild cause they didn’t know how to effectively locate prey. Enrichment can mitigate this, for example black footed ferrets that were placed in pens with live prairie dog colonies showed higher predator abilities than cage reared ferrets. For predators providing them with live prey may be ethically wrong but will provide them with the best opportunity to learn and practice skills that will be needed later in life. For example polecats took 20min to kill their prey when first exposed but by their 3rd experience they reduced killing time to 5min. Also animals that do not eat regularly should also be fasted for irregular amounts of time to prepare them for conditions once released.
Social Interactions:
Learning social interactions is crucial for success after release, especially for animals that live in groups, but its still important for solitary animals as they need to communicate their presence, level of dominance, sex, and state of sexual receptivity of neighbours. One strategy to prep them for this type of interaction is to provide opportunities for antagonistic interactions with conspecifics so they can hone their skills on how to react appropriately, this may include over clumping food resources or access to mates. Group living species need a lot more social integration and training prior to release since a lot of animals learn calls from their parents and need to be capable of complex social interactions. Reintroduction of more colonial animals like prairie dogs may require having to translocate entire social groups to increase survival rate. Reintroducing naive animals with more experienced conspecifics may also benefit the survival rate of juveniles when released.
Physical Fitness:
Physical enrichment is crucial to reintroduction as it allows for animals to improve in physical fitness that is required in nature. This can aid in fending off other conspecifics for example captive raised bison were regularly dominated by ranch born bison until they became physically fit after a period of time. Most mortalities occur immediately after release as the individuals are at their weakest. Additionally when released they are exposed to a new array of microorganisms and parasites thus healthy physically fit individuals would do better during release.
Selecting individuals for release
The factors that should be observed for individuals meant for release are hunting, killing, predator avoidance, imprinting, reproduction, locomotion, daily and seasonal movements, timing of reintroduction, method of release and site fidelity. Temperament also plays a critical role in survival rate as bolder individuals are more likely to disperse from the released site as well as come into contact with hazardous situations. For example based on swift foxes that were released, bolder individuals had higher mortality rates as they would come into contact with predators more often. However on the other side, releasing a large genetically diverse group of animals is preferred as this would limit founders effects and inbreeding depression which can cause reintroduced populations to struggle.
Assessing the effectiveness of enrichment techniques:
Where possible it is recommended that running reintroduction programs as experiments is beneficial to iron out the details prior to mass reintroduction. Therefore the first step is to enrich half and not enrich the other half and release both types of individuals and monitor their success to identify whether the enrichment works. Traits that could be monitored short term after release are observing behavioural variables such as activity patterns, dispersal rates and social interactions. While in captivity researchers should try to use enrichment that will target the most vital behaviours needed for survival after release. If we find that targeting these numerous vital behaviours indeed does increase survival rate then we can begin to break down the components of which specific enrichments are the most valuable so that we can rank which enrichments should be done most and which could be left till later if time or money is a constraint. For even finding that a specific type of enrichment is ineffective is a valuable piece of knowledge to have like in the case of the golden tamarins and the free ranging enrichment that was provided too late.
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