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Posted by EdK on April 20, 2003 at 10:09:07:
In Reply to: Rodent vs Amphibians - My perspective [up dated] posted by mike z on April 19, 2003 at 23:28:18:
":Taken in the bigger picture, there does seem to be ample anecdotal info supporting the claim that dietary specialists can live and thrive on substituted diets. This is probably mostly true ONLY when absolute best husbandry is provided including dietary supplements and a stress free environment. It is also probably only true with certain individuals of any given species."
The problem with anecdotal information is that it needs to be kept in context and used with a grain of salt. The amount of anecdotal information often does not have any bearing on the validity of the information, for excellant examples of this please review all of the information available on bigfoot, UFOs, and the Loch Ness Monster. All of the data provided on in these cases are anecdotal. Does this make it true that there is a real animal/phenomenon in these examples?
"If the animals have so much trouble with these things in captivity, how the heck have they been able to survive in nature these past million years or more? "
Animals that were maladapted to deal with these issues die. There is no coddling in the wild to get them over a weak period. There are reasons that most offspring fail to reach reproductive age in wild populations and not all of them are due to predation.
You have to keep in mind that animals in thier "native" enviroments can do things like move to escape stress (example high traffic areas), more easily esacape inappropriate temperatures/humidity by moving to a different location (or even just vertically) that they are prevented from accomplishing in captivity. These items can stress an animal to the point that the immune system becomes depressed and the animal succombs to an infection (whether its parasitic, bacterial, viral, protozoal).
":This is where I have to come in on the side of the frog faction. It seems utterly illogical and kinda silly to be lectured and preached to about the evils of feeding an animal something that hundreds of thousands of years of Natural Selection has caused it to become a specialist in. Hognose don't eat toads because they can't catch mice! There's got to be SOME good reason they became specialists. If parasites were such a big problem for amphibian specialists, they would have changed their diet or gone extinct a very long time ago. Yet look how many amphibian specialist there are in the animal kingdom. Everything from birds to bats and lotsa snakes!"
Prey specialization comes around through niche partioning. Usually dietary specialization occurs because a prey item is very abundant throughout the animals range and there is some adaptation that allows the animal to predate upon that species more efficiently. Unless there is some requirement that the prey animal contains that the predator is unable to obtain in another way then the predator can be fed an alternative diet. If this were the case then Zoos would be unable to exhibit giant anteaters, aardwolves, or echidnas as these are ant and/or termite specialists but are kept and bred through multiple generations on artificial diets that do not contain any ants or termites. I am unaware of any birds that feed solely on amphibians, the ones I am aware of are opportunists and feed upon any approriate sized prey item. I also believe that the bats you are referring to (hammer headed,ect) also feed upon other prey items including other bats and are not true dietary specialists).
":When we talk about stress levels, we have to acknowledge that captivity for a wild animal is ALWAYS stressful to some extent. The poster below from the zoo made a very good point about acclimating an animal until a strong captive feeding response is developed. Here too I must cast my vote with the amphibian crowd. In order to help an animal adapt to captivity, what better way than to provide its natural diet?"
An animal in nature is also under some stress, the trick and the goal is to minimize the stress so the animal can be acclimated and stabilized. A good example of a time to possibly feed amphibians is if you have an animal that is not feeding and has lost 10% of its body weight. At this point you need to make a decision to either force feed or to offer a more natural prey item to see if the animal will eat. If you wait too long to make this choice the animal may have insufficent reserves to deal with the food item or to handle the stress of being force fed. The best reason to offer rodents if possible is that you can control the quality of the food item offered the snake. You cannot achieve this with any other wild collected food item. There are too many subtle cofactors that need to be dealt with from wild caught food items such as low levels of pesticide/herbicide residue that can act as a immunosupressent or interfere with reproductive activity. As the snake is a higher level trophic predator than the amphibians any snake fed contaminated amphibians will bioaccumulate the contaminants. (I can give you a good reference once I get home, if interested e-mail me off list).
Just some thoughts on your comments