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Introduction
Pygmy rabbits (Brachylagus idahoensis) are an important
animal that we know
little about. They are a small North American rabbit that eats primarily sagebrush
(Artemisia tridentata). In the state of Washington, there is a population of pygmy rabbits
that are genetically different from the other populations of pygmy rabbits. These rabbits,
called the Columbia Basin pygmy rabbits, have become endangered due to habitat loss and
other reasons. Currently, the Columbia Basin pygmy rabbits are being bred in captivity to
build up a population for release into the wild. It is important for us to learn about the
behavior of these animals while they are in captivity, so that we can apply this knowledge
when they are released back into the wild and improve their chances of survival.
One thing that we need to know is what these rabbits eat and how they forage.
We know that a pygmy rabbit's diet is made up of more than 99% sagebrush in the winter and
their summer diet is mostly sagebrush and other available greens. Pygmy rabbits live and
forage in a patchy sagebrush habitat and forage out from their burrow. Pygmy rabbits are a
prey species to many animals such as coyotes and raptors, and they have a high risk of
predation while they are foraging. If pygmy rabbits live in a patchy, open environment and
have a high risk of predation, then how do they forage to reduce these risks? One theory
is that they are "central-place foragers".
Central-Place
Foraging
There are many definitions of central-place foraging, but it can generally be thought
of as an animal foraging out from a central location that they use as a refuge, and
bringing some food back to this refuge and consuming it there. This method of foraging is
very costly to the animal. Not only does the animal have to go out and find food, but they
have to drag the food back to their central location to consume it. This requires the
animal to expend a lot of extra time and energy. Pygmy rabbits seem to use the
central-place foraging method as their strategy for foraging. Pygmy rabbits have a burrow
as their central location, and they move out from this burrow to forage for food. They are
often seen dragging food items back to the entrance of their burrow and consuming it
there. If central-place foraging is so costly to the animal, then why would the pygmy
rabbits choose this foraging strategy? The answer can be found in the major benefit of
central-place foraging; a reduced risk of predation to the foraging animal. If the animal
consumes the food in a protected location, they spend less time avoiding predators out in
the open. This allows the animal using the central-place foraging strategy to devote less
time to vigilance while foraging. Since pygmy rabbits have a great risk of predation, it
would be greatly beneficial for them to choose this foraging strategy. It seems that the
reduced predation benefit the pygmy rabbits receive for using central-place foraging is
able to compensate for the high costs occurred from this foraging strategy.
Learned or Innate Behavior
We also need to know if central-place foraging is a learned or an innate behavior.
Because this strategy of foraging is a predator avoidance behavior, we might assume it is
an innate behavior, since behaviors that can have deadly consequences if done incorrectly
are often innate. Also, the pygmy rabbits are generally solitary animals and spend little
time with their mothers as young, so they would have little opportunity to learn the
central-place foraging behavior from another rabbit. However, central-place foraging is a
fairly involved behavior and may need to be perfected over time to perform it correctly.
This contradicts the idea that central-place foraging is an innate behavior, and indicates
the behavior might be learned. Actually, central-place foraging is probably a combination
of learned and innate behaviors. The general use of the behavior as a means to avoid
predators is most likely an innate behavior. However, because of its complexity, rabbits
probably individually learn over time how to perfect this foraging strategy to best suit
their needs. For example, the pygmy rabbit may instinctively know to run when it sees a
predator approaching, but may learn with time where optimal foraging places are, with
sufficient amounts of cover.
Management Implications
So now we know how pygmy rabbits forage and why they do so. How will this aid us in the
recovery of the endangered Columbia Basin pygmy rabbit? This knowledge of their foraging
strategy can help us to choose their release site when rabbits are reintroduced into the
wild. We can choose release sites that provide the rabbits with enough cover to evade
predators and enough food to satisfy their needs. This ideal release site will be around
soil that is easy for the rabbits to dig in and has abundant sagebrush for cover and food.
Choosing the ideal release sites for these rabbits upon their reintroduction, will aid the
rabbits in their survival, and provide them with a chance for a successful recovery.
Suggested Readings:
Orians, G.J. and N.E. Pearson. 1979. On the theory of central place foraging.
An Analysis of Ecological Systems: 155-177. Horn, D.J. and
R.D. Mitchell
(Eds.). Columbus: Ohio State University Press.
Elliott, P.F. 1988. Foraging behavior of a central-place forager: field tests of
Theoretical predictions. American Naturalist 131:59-174.
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