Monday, 26 July 2010
Rodents of Bristol 6: Praire Dogs
Unlike the other species, the Black-Tailed does not hibernate, probably because it is usually found in warmer and wetter climates than the others, and its staple diet of grasses is therefore available all year round. In the autumn, broadleaf plants become more important as green grass is less available. In winter, any available green vegetation is consumed. In the spring and summer, each prairie dog consumes up to two pounds of vegetation per week.
Black-tailed prairie dogs live in complex communities, called "towns" or "colonies." The colony is an underground tunnel system leading to various chambers which are bedded with dry leaves and grass. At one time, the typical town covered 100 acres (404,700 m²) or more, but the largest ever recorded covered 64,000 km2 (25,000 sq mi) and included 400,000,000 individuals!
The towns are divided into territorial neighborhoods or "wards," which are comprised of coteries. Coteries are family groups made up of one male, one to four females, and their young up to 2 years of age. The burrow system is quite complex, but entrances are usually very visible as mounds of earth, which are created and maintained by the burrow owners, especially after rain when the ground is soft, by alternately digging and pressing down earth with the snout. I have observed that at Bristol at least, grasses are incorporated into the earth of the entrance mound, possibly as reinforcement.
The complicated tunnel system provides homes to many other creatures. Burrowing owls use the burrows for nesting and the entrance mounds for look out points, and foxes and the endangered black-footed ferret use the burrows (and prey on the burrows’ creators). Bullsnakes and rattlesnakes also take young prairie dogs but generally not adults. The main enemy however is the American Badger (which is not closely related to the European Badger and has a far more solitary and predatory lifestyle).
Being a highly social creature, prairie dogs have a complex set of behaviours which govern relations between coterie members, and between the coterie and the outside world. How complex the communication system is however has only recently been discovered. Dr Constantine Slobodchikoff of Northern Arizona University has conducted research on the alarm calls of prairie dogs that show that they are far more than simple screams. Subtle harmonics, only detectable to humans after computer analysis of the calls, shows that the alarm call can also convey information about the type of threat, being able to distinguish between different types of bird of prey, different ground predators (foxes and badgers hunt differently and require different avoidance strategies), and even create new calls for new situations.
Studies on zoo prairie dogs for example show that their alarms are simple generalisations – they do not need to distinguish different threats and so do not create distinctions. I would be interested however to learn if that is true for all captive animals – we have had to protect our exhibit from predatory Black-backed and herring gulls, which take pups, and Bristol also has a high Red Fox population which has been known to enter the zoo grounds.
In captivity, Prairie Dogs are easy to look after. Ours are in a fairly large enclosure (originally grassed), in which they have dug their tunnels and aside from being fed supplementary food look after themselves. I am not sure if it still there, but at one time there was a feral colony on the Isle if Wight in a farmers field, probably founded by escapees digging their way out (we have to check the perimeter of the enclosure when the young are dispersing as ours have been known to turn up in the shrubberies).
Unfortunately, because they are disliked by ranchers, prairie dogs have been much persecuted, and roads and urbanisation has fragmented their habitat. The Utah and Mexican prairie dogs are currently listed under the Endangered Species Act as threatened and endangered respectively. Additionally, black-tailed prairie dogs are remarkably susceptible to sylvatic plague. In 2006, 8 of 8 appearances of plague in black-tailed prairie dog colonies resulted in total colony extinction.
(Images from wikipedia)