Pregled bibliografske jedinice broj: 207218
Why not to re-introduce "rehabilitated" brown bears to the wild?
Why not to re-introduce "rehabilitated" brown bears to the wild? // Rehabilitation and release of bears / Kolter, Lydia ; Dijk, Jiska van (ur.).
Köln: Zoologischer Garten Köln, 2005. str. 28-34
Why not to re-introduce "rehabilitated" brown bears to the wild?
Vrsta, podvrsta i kategorija rada
Poglavlja u knjigama, pregledni
Rehabilitation and release of bears
Kolter, Lydia ; Dijk, Jiska van
Zoologischer Garten Köln
brown bear, ursus arctos, rehabilitation, reintroduction
Why not to re-introduce "rehabilitated" brown bears to the wild? Biological background Brown bears are very unique animals: as the largest terrestrial carnivores they feed predominantly on vegetation. They are very demanding towards the habitat they live in and they need complex inherited and acquired skills. Bears need large unfragmented areas with good vegetation cover, enough diversity and low disturbance (Huber and Roth 1993). Depending on geographical latitude and general habitat quality an individual bear may roam over some 100 km2 up to 100.000 km2. Bear walks in search for food, daily and winter shelter, sexual partners and to avoid other bears of the same sex. Food finding strategy Vegetation in bear habitat must comprise of various plant species that provide food in different seasons. With the typical carnivore digestive system bears are poorly decomposing plant cells and absorbing nutrients. This means that they have to find the optimal plant species and the edible parts of those plants in the right time and at the right spot. They also have to eat large quantities of those plants, while such food sources are rarely found in sufficient quantities at one spot. Bears need up to 10% of proteins in their diet and most of that they do satisfy by insects and other invertebrates and eventual carrion (Cicnjak et al. 1987). When other carnivores kill a sizeable prey they often can stay at a spot and eat for up to a week. Contrary to other carnivores, bears typically have to move their whole body for almost each tiny bite. Food for bears may be hidden almost everywhere: bears will turn-over many rocks, pluck rotten logs, dig at promising spots to find tubers, invertebrates and their larvae or eggs, food cashes of other animals, to catch a mouse or other small mammal. All this requires: 1. regarding to their habitat , vast and diverse area ; 2. regarding to the bears themselves , much intelligence, curiosity, determination, skills, memory, and endurance (Morić and Huber 1989, Roth and Huber 1986)… Cover vegetation for rest and denning Vegetation and topography in bear habitat must provide hiding cover which bear needs daily to prepare a day-bed ; a resting place for most of the daytime(Kusak and Huber 1998). Day beds are on spots where the horizontal visibility is lower than in other, average parts of the habitat. Specially demanding is the site for a winter den. The winter den is always on a spot difficult to access. Preferable are rocky areas with natural spaces where the den can be dug out and/or arranged (Huber and Roth 1997). The potential spots for digging are between the roots of large trees or at places with special structures like anthills in some areas. The den itself must fulfil several requirements: it should be big enough to accommodate a bear and eventual a litter, it should be small enough to maintain the bear's body heat together with favorable air temperature, it should be strong enough to be safe and not to collapse while the bear is in the den, and it should be waterproof. Above all it is important that the bear will not be found and disurbed during hibernation. Therefore a bear must have extremely large and diverse habitat that holds appropriate spots for dens. A bear must know its habitat very well to be able to find a good spot for a den. A bear must know and be skilful enough to dig the den, collect the nesting material and to make a nest where it can safely spend the winter. Social and reproductive requirements Bears live alone but maintain complex communication with other bears. Marks on trees and various scent marks make the presence of one bear known to the others. The success in the game of finding and avoiding other bear decides if a bear can stay in one area or not. The error might result in a death of a weaker one. Finding a sexual partner during the mating season is specially demanding. Males roam over vast areas trying to fertilize as many females as possible. They must be capable of detecting the olfactory signals sent by females in heat and, at the same time have the control of other males to be able to accurately decide where to fight and where to retreat. A female with cubs is the only bond within the species that lasts for at least a year and half (Frković et al. 2001). During that time a female has to skilfully avoid big males that may try to kill her cubs in order to mate with that particular female and to spread their own genes. Hence, social and reproductive requirements in bears also ask for a large habitat, excellent knowledge of this habitat, and skilful behavior. Process of learning The share of learned skills compared to the inherited ones in bears is much larger than in other carnivores, not to speak of other nonprimate mammals, and other nonmammal vertebrates or invertebrates. Most of the skills required for survival under the conditions of continuous search for what is needed and in avoidance of trouble, are learnt during the first two years of their life in nature while accompanied with their mother. Each bear develops his own behavioral strategy exhibiting individualism rarely seen in animal kingdom (Huber et al. 1994). The only common component may be the opportunistic behaviorm ; a bear quickly learns to go for an easier way whenever possible. In natural situation this optimizes the use of potential benefits of each situation. When this concerns the relation to man, the opportunistic behavior is typically not a safe way of life. It is for instance much easier for a bear to eat large quantities of food at a garbage dump than to search for the same amount over many kilometres. Through the mechanisms of natural selection, however, many mothers fail to successfully raise their offspring: cubs may be killed by an adult male, may die in an accident or simply starve. The fittest mothers raise most cubs and their genes do get spread into the population. There are also cases in which the mother dies while nursing. Chances for survival of orphaned cubs are directly proportional with the length of time they spent with the mother. The ones that become orphaned while still in the den, i.e. during the first 3 months of their life, will surely die (Huber et al. 1993). If orphaned later in spring, summer or fall cubs are faced to the cruel game of survival. They may survive only with enough luck not to be killed by other bears or other predators and to find sufficient food if the seasonal crop was good and the cub finds it. Due to opportunistic behavior orphaned cubs occasionally survive by searching food from human sources. They become habituated to people and as nuisance individuals never last long ; either have to be killed or do die in traffic or other accidents. Relation to man Process of habituation Especially for brown bears centuries of killing by humans resulted into a strong selective force towards shy bears (Frković et al. 1987). Only the ones that learned that man and everything related to man is dangerous survived and reproduced successfully. The gradual increase of human population and development of sophisticated weapons they used gave the opportunity for bears to adapt. Exception is North America where the white man arrived with already efficient guns facing naive brown bears that were wiped from most of their territory within only one century. Bears in Europe are recently facing opposite challenge. In the last decades the smells and other signs of man are occasionally related to some food attractions for bears. External and internal factors work together to increase the likelihood for an individual bear to start behaving unnaturally. In the group of external factors belong all described bears demands towards the habitat. Any deficiency of habitat (usually provoked by man) may easily trigger the bear's internal factors to change behavior. Each of described peculiar bear features like intelligence, individualism and opportunism carry the seed of habituation. Man-made food sources will attract bears even regardless to general food availability in habitat (Huber and Frković 1993). Bear will find, remember and repeatedly use any concentration of food. If the food sources are domestic animals, crops in field or orchards, or any storage, the use of these sources by a bear is seen treated as damage. When a bear makes a damage it is a multiple problem: cost for the owner of the food source, cost for the organization that is responsible for compensations, and cost for protecting food sources for further damage. It also implies danger for human casualties when trying to protect their property, but most of all it implies a loss of public acceptance of bears. If the food is an open garbage dump in bear habitat the problem is very serious too: the bear may get himself in a trouble searching the garbage and eating potentially poisonous and infectious items (Madić et al. 1993 ; Modrić and Huber 1993, Huber et al. 1997). At any man-made food source bear may learn and adopt the undesirable behavior: the loss of fear from man. The bear that does not run away from man is a nuisance bear. Man-made obstacles for bear movements, like highways, may force a bear to try to satisfy some of its basic needs on one side of such obstacle. This may lead a bear closer to humans. At this point the chance increases for a bear to be killed in hunting, poaching, or by traffic (Huber et al. 1998 ; Kusak et al. 2000). Also the chance for lossing litter in a disturbed den, for cubs to become orphaned , for the damage on human property or on man himself increases. The handicapped bear like the one that was orphaned or that for any reason did not grow up with its mother in the natural environment has a disproportionate greater chance to become habituated in the described situations. Habituated bears are unacceptable A habituated bear is a nuisance bear although it is typically not spontaneously aggressive towards man. At the first instance a bear that does not run away may be an attraction. A small alone bear may be given food by some people and get increasingly habituated. There are cases when the same people that attracted and fed a cub in front of their home, call the bear managers to remove the bear when it grew bigger and became a threat for their children. In another scenarios the bear that does not escape at the first instance may: 1. attract an enthusiastic photographer to get too close, 2. prompt the hunter or poacher to shoot at him with a inappropriate weapon and the wounded animal grabs him, or 3. create a false impression of bear "invasion". The latter happens when somebody does see a bear near the village almost daily. People frequently fail to recognize the individual animal and the local community start believing that there are many bears around. Usually they call the hunters to reduce the "overpopulation". Acceptance of bears as part of our natural environment directly depends on how much they effect the living of local human population. The bears that cause considerable damage or even threat human lives are highly unacceptable. It is the individual bear behavior that makes most of the difference, although the bad things done by a single bear are typically blamed to the entire bear population. Any situation that stimulates creation of problem bears should be avoided as the matter of the first priority. The bear that behaves differently than other natural wild bears creates the problem for their population as well. An individual that does not follow the complex rules over different seasons, range marking, reproduction phases and food finding strategies will most likely be lost in the competition, but may occasionally influence some "normal" bears to start behaving "abnormally". Conclusion It is nearly impossible, or extremely unlikely, to hand raise orphaned wild or captive born bears in the way that will develop all skills necessary for their life in nature and to behave properly in relation to man and to other bears. The problems of releasing "rehabilitated" bears are different in areas with low human population and healthy bear population compared to the human dominated surrounding with small endangered bear population. In the first case the main question is the survival and eventual successful reproduction of released bear in the wild. That could and should be measured by intensive radio telemetry tracking. However, the strict measures against possible gene pollution by mixing foreign populations have to be implemented (Taberlet et al. 1992, Randi et al. 1994). The problem of behavioral "pollution" is hard to mitigate. Each eventually successfully reintroduced cub can be welcomed as a merely ethical achievement. Biologically this addition to viable population is negligible. On the other hand bear populations that are critically low and typically in a human dominated surrounding can not afford the risk of adding a bear with potentially unacceptable behavior. Even for reintroductions from other wild populations extreme care has to be taken to decrease the risk of bringing the misbehaving individuals. In conclusion I propose the investments in efforts to prevent the situations where wild born bears become orphaned and to prevent the birth of unwanted captive bears. The existing captive population should be given the best possible care and used as ambassadors to raise public awareness about situation of free-living conspecifics .
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Köln: Zoologischer Garten Köln, 2005. str. 28-34