Releasing animals "into the wild"

Hi SD,

I understand it’s impossible to know exactly where a creature lives, and the authorities do the best they can to release captured animals in an environment they are familiar with. And I also understand that animals are adapted to survive as best they can in whatever environment. Say Bear A and Bear B are two identical bears, both captured by local authorities for straying in the neighborhood. Bear A is released in an unfamiliar location. Bear B is released in an area it knows well (i.e. its den). Assume the bears live the rest of their lives in their released locations. Also assume that each location has equally accessible shelter, food, and water for the bear. Can an outside observer presume Bear A will have a shorter lifespan that Bear B? Do the natural survival skills of animals mitigate any detectable differences between a creature’s “home” and areas unfamiliar to them?

What about humans? Does a nomadic lifestyle mean a shorter lifespan, assuming hypothetically that all necessities can be equally met both through a nomadic lifestyle and a sedentary one?

I hope this question makes sense. Thanks.


Bear A is presumed to be undergoing a restocking, while B is a temporary absence. B will almost certainly take to its wild surroundings better. I’m saying this only because I know that restocking is usually a continuing effort until the numbers return to old levels.

It’s not necessarily a restocking. The bear’s den is probably too close to civilization. Or perhaps civilization moved too close to the bear. Chances are they have no idea where the bear’s den is anyway, except that it’s so close that the bear is likely to return. So they move it much further away.

The real problem with this kind of relocation (and not just for bears) is that they’re probably putting it into another animal’s (of the same species) territory. That leads to problems. One of the two animals is probably not going to survive.

An animal released in an area it is unfamiliar with will almost certainly have a lower probability of survival than one released in its own home range. It won’t know the best places to find food or where to find shelter, and as has been mentioned it will likely come into conflict with other animals of the same species that already have territories there (or at least, know the area better).

When problem animals are released far from their home territories, it is usually because those released close by will just return to their old territory, and do the same thing that got them into trouble in the first place. Some animals will return from quite far away (suggesting how important a home range is in the first place).

It’s impossible to compare the lifespan benefits of a nomadic vs a sedentary life style without knowing more about the environments and food collecting strategies employed. Are these nomads tropical hunter-gatherers, or are they desert pastoralists? Are the sedentary people temperate zone agriculturalists, or coastal fishermen? Nomads may undergo more risk, but be healthier overall because of better diet and exercise.

In any case, the life-styles we characterize as “nomadic” are usually more seasonal migrations than aimless wandering. Hunter-gatherers may migrate to the mountains to collect nuts and berries in the autumn, and to the coast in winter for fish and shellfish. Pastoralists migrate between summer and winter pastures. They know their home ranges very well, they just don’t make permanent dwellings.

It’s going to depend a bit on the kind of animal - for bears, being plunged into a new territory is indeed probably negative on survival probability, but for some other animals (esp smaller ones with simpler requirements), it might not make a difference - and for some, it will be an advantage because the new location could be short of their specific predators.

A study was done in Germany on stone martins being released only a mile or so away from their home territory. It was a virtual death sentence for about 80% of them if I remember right. Urban raccoon’s also struggle to reestablish themselves in many areas.

Said another way, releasing wild animals far away from home is simply a way to kill and dispose of them without creating a political backlash from local activists.

If it’s to a random new site, I think it’s going to be bad for animals irrespective of size. In fact, it will probably be worse for small animals, since they need more food proportional to size and have many more predators. Of course if you relocate them to a better site with fewer predators or more food, then they could do better, but that’s not really the question at hand.

I had a raccoon that lived under my eve for several years. The eve was protected by some jasmine that she had created a nest out of. When I removed all the jasmine I watched her struggle for the next month or so and then she was finaly hit by a car and died. She lost a lot of weight before she died and all we did was remover her nest.

What about for animals that are nomadic, such as opossums? Does their lifestyle make them better able to cope with being relocated?

Opossums are not territorial but do have a home range (although that range may shift over time). They have several dens that they use on different days. They may be more opportunistic than other mammals but still would be at a disadvantage if moved suddenly.