Wondrous Wildlife – December 2010

Wondrous Wildlife

By Vern and Lori Gieger

They Live Where?


water-opossumMexico has some amazing wildlife. Many species of mammals live near rivers and lakes. When we think of aquatic mammals we usually think of beavers, muskrats, or perhaps even raccoons but not this species. When most think of an opossum we think of the common opossum, or perhaps their cute tiny cousin the marmosa mexicana; but not an opossum that is aquatic. Mexico is home to the only living aquatic marsupial.

It is called the water opossum and is also the only living marsupial in which both sexes have a pouch. The water opossum has distinctive adaptations for its watery lifestyle. They have short, dense fur which is water-repellent much like that of an otter. Their broad hind feet are webbed like other aquatic animals, which give them great momentum through the water, moving with alternate strokes. They also have a long tail that assists in swimming and is used much like a rudder.

Their physical appearance is much different also, their fur is a marbled grey and black pattern while the muzzle, and head are all black; with the exception of a lighter colored band running across the forehead to the ears. The front feet are not webbed but rather used to feel for and grab prey as they swim. Unlike the common opossum which will eat almost anything, the water opossums hunt for fish, crustaceans and other small aquatic animals.

Being a marsupial and at the same time an aquatic animal poses some challenges but, the water opossum has evolved a way to protect its young while swimming. The pouch has a strong ring of muscles and the pouch opens to the rear, unlike the common opossum’s. One might think of their pouch as a bit like a ziplock baggie nice and watertight, so the babies remain dry, even when the mother is totally submerged in water.

The male also has a pouch although not as watertight as the female’s; and it serves a completely different purpose, he places his genitalia in it before swimming. It is believed that this protects the family jewels so to speak, and is helpful in streamlining the opossum as well.

Water opossums den near waterways and river banks; they tend to have permanent dens, unlike their cousins the common opossums which tend to be much more nomadic and follow the ever changing food source. About the only thing they seem to have in common besides both being opossums, is that they are both nocturnal; and they rear their young in much the same way, however the water opossums usually only have two to four young, whereas the common opossum may have up to 13.

The longevity of the water opossums is not known; in captivity the average lifespan is approximately three years. The water opossum is an anti-social loner. They are not listed as endangered. However, they are indeed rare, whether this is due to its nocturnal and mysterious way of living or their small pockets of populations. Even researchers can only guess. Their habitat range is from southern Mexico to Brazil in subtropical to tropical areas, near freshwater streams.

The weird, wondrous and extraordinary fauna we share this planet with certainly leaves one in awe. Speaking of awe, congrats to Lakeside Spay and Neuter / Ranch, on reaching their 10,000th spay / neuter.

Ojo Del Lago
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