Birds and Newt

 

I am speaking of the salamander, not the politician once seeking the Republican nomination. In the valley and on the coasts of California the California Newt is pretty common in the moist springtime. Growing up to eight inches long and colored orange-yellow-brown, it is easy to find. Like a number of animals, its bright color serves as a warning to its potential predators.

Taricha torosa has glands in its skin that secrete a deadly neurotoxin called Tetrodotoxin, a poison hundreds of times more toxic than cyanide and is the same poison found in pufferfish. (In Japan where pufferfish are a delicacy, chefs have to be especially trained in the preparation of the fish so as not to poison their restaurant customers.) Bacteria actually synthesize the chemical and newts get it from eating the bacteria. If you were to handle a newt and then lick your fingers, you could ingest this poison, so be careful and wash your hands if you pick one up.

What does this have to do with birds? Well, some birds eat amphibians: Great Blue Herons, kingfishers, and shrikes, for example. So it would be nice, if you were an amphibian, to have some protection. Being poisonous is one way. But it’s not that simple. If a newt is eaten by a bird and the bird dies, nobody wins; the bird doesn’t learn and a newt is dead. So the toxin’s actual purpose is not to kill predators but to teach them that a newt is a bad meal. Even though birds do not have a good sense of taste, the toxin is strong enough to teach them not to eat any more newts. Other salamanders and many South American frogs are also toxic. Along with being poisonous, these animals are brightly colored – to advertise the fact that they are toxic.

The same trick works with Monarch Butterflies who eat milkweed as larvae and ingest cardiac glycosides which are very distasteful to birds. So the Monarch is protected from bird predation. The Viceroy Butterfly has evolved to look like a monarch but is not poisonous; it is also avoided by birds because birds can’t tell the difference between the bad-tasting Monarch and the edible Viceroy. (Viceroy at bottom of photo.)

But birds don’t totally avoid bad-tasting prey. Recent experiments have shown that European Starlings differentiate among individual prey animals that have different levels of toxin. The starlings ate non-toxic and mildly toxic mealworms and avoided the very toxic ones as the more toxic they were the more distasteful they were. There is no reason for birds to avoid toxins totally as the prey also contain useful nutrients, so the birds learn to discriminate.

Evolution has produced lots of bad tasting and toxic plants and animals in order to deter predators. Some predators have evolved ways around this. A classic example is that of birds being able to eat hot chili peppers. The chemical that burns our mouths when we eat them, capsaicin, does not set off birds’ taste buds.

 

 

 

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