Saturday, 11 December 2010

Miscellaneous Mammals 5: The Yellow Armadillo

Yellow Armadillo
 A common sight in the southern United States is remains of the Nine Banded Armadillo, Dasypus novemcinctus, generally flattened on roads. As armadillos are so widespread, and with a few exceptions mostly not under serious threat, there are not many to be seen in the world’s zoos. This I feel is a great pity, as they are fascinating animals with numerous peculiarities. We are lucky here at Bristol to have a breeding pair of Yellow or Six-banded Armadillos, Euphractus sexcinctus, plus a tame individual which we have in our animal displays in the summer. ISIS lists a total of 68 individuals worldwide in WAZA zoos.

As with the sloths last week, armadillos belong to an almost entirely South American group of mammals called the Xenarthra. The name comes from a peculiarity of the articulation of the vertebrae – why is not at all clear. As a group, Xenarthrans tend to have rather slow metabolisms and rather variable body temperatures. This last has meant that armadillos are one of the few animals capable of incubating the Leprosy bacterium, and have been used experimentally as a result. An additional feature of their biology is that many species produce multiple identical births, facilitating experimental research. Yellow armadillos do not seem to do this however, with young of both genders in a single litter of 1-3 infants.

Nine-banded Armadillo
The armadillos of today are mostly medium sized animals, with the largest, the scarce Giant Armadillo, reaching 30kg. Yellow armadillos are also among the larger species, but they are usually around 4kg, although obese captives have reached 11kg. Animals with slow metabolisms typically suffer from obesity in captivity and need to be kept on a carefully controlled diet to avoid problems.

Giant Armadillo
A diet for armadillos is not hard to provide, as with the exception of some specialists like the sand-swimming Fairy Armadillos, almost all species are omnivorous, with a high percentage of plant material in the diet. Captive Yellow armadillos have been known to kill rats, although they are very inefficient predators unless the potential prey is sick, injured, or otherwise defenceless. They probably take a high percentage of the eggs and nestlings of ground nesting birds in the wild during the nesting season.

Fairy Armadillo
Until we got them at Bristol I was under the impression that armadillos were slow-moving animals – mammalian tortoises if you like – but seeing ours run around the enclosure hunting for food or snails which have got in from outside (our pair lives in the inside quarters for our Black Howler monkeys) shows they are at least as fast as a rodent of similar size such as an agouti. They do not have good eyesight however, relying on a keen sense of smell to locate food. Many armadillo species are nocturnal, but yellow armadillos are active by day, at least after midday, and continue their activity cycle into the early part of the night.

The armadillos in the US are fairly new arrivals in the last century from Mexico. Originally there were two populations, one in Florida deriving from escaped animals, while a second population moved north naturally through Texas, The two populations have now merged, and the main limit to moving northward is their susceptibility to cold weather. In some respects they are filling an ecological gap left by their extinct relative, the much larger (to 1m long) Beautiful Armadillo Dasypus bellus, which became extinct at the end of the last glaciation. Why so many species of the Americas dies out then is not at all clear – humans have been implicated but it might also have been caused indirectly by diseases contracted from human commensals such as the domestic dog. Several other species of armadillo, mostly the larger forms (plus their car-sized relatives the Glyptodonts) died out at the same time.

Today the main threat to most species is hunting for food. Armadillos are hard to study in the wild however, so some species, especially those with a limited range, might be in more danger than is currently thought.

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