Monday, November 29, 2010
Zoo Post: Manatee
The manatee (Trichechus manatus) also know as the sea cow is a large herbivorous aquatic mammal, and the largest surviving member of the aquatic mammal order Sirenia (which also includes the Dugong and the extinct Steller's Sea Cow). The weights of these creatures can range from 880lbs to 1200lbs and are usually between 9 and 10 feet long. They can max out at almost 12 feet and 4000 lbs! They have a large flexible prehensile upper lip that acts in many ways like a shortened trunk, somewhat similar to an elephant's. They use the lip to gather food and eat, as well as using it for social interactions and communications. Their eyes are small and widely spaced, and are covered by eyelids that close in a circular manner. The adults have no incisor or canine teeth, just a set of cheek teeth, which are not clearly differentiated into molars and premolars. Uniquely among mammals, these teeth are continuously replaced throughout life, with new teeth growing at the rear as older teeth fall out from farther forward in the mouth (like sharks). At any given time, a manatee typically has no more than six teeth in each jaw of its mouth. Like horses, they have a simple stomach, but a large cecum, in which they can digest tough plant matter. In general, their intestines are unusually long for animals of their size.
The manatee spends most of its time either sleeping, or grazing in shallow waters. They usually surface for air close to every 20 mins, and have been know to live close to 60 years. Their average speed is around 5 mph but can reach a top speed of 20 mph, but only short bursts. Manatees are capable of understanding discrimination tasks, and show signs of complex associated learning and advanced long term memory. They demonstrate complex discrimination and task-learning similar to dolphins and pinnipeds in acoustic and visual studies. They enjoy warmer waters and are known to congregate in shallow waters, and frequently migrate through brackish water estuaries to freshwater springs. Manatees cannot survive below 15°C. Their natural source for warmth during winter is warm-spring fed rivers.
Current research on this mammal is mainly geared toward studying social interactions and behaviors. The sea cow is dieing more and more each day due to habitat loss and human interactions. Colder water temperatures are killing these creatures, and many are found with large cuts and gashes on their backs from boat engines. Since they feed in shallow water they are easy hit by propeller blades. They study I looked at watched the behavior of captive manatees in Mexico, They studied 2 adults, 1 sub adult, and 1 calf. The behavioural strategies of the manatees included (1) during the day, mainly foraging, feeding, and remaining inactive, and (2) evening activities were divided among social interaction, environment exploration, and resting activities. All the behaviour patterns of the captive manatees seemed to be influenced by the feeding schedule during the day. The number of contacts between manatees increased strongly at night, each individual having a preferred partner for social interaction. The cow-calf dyad showed the highest intensity of contacts, whereas subadults showed the lowest.
Hénaut, Yann. "Activities and social interactions in captive Antillean manatees in Mexico." Mammalia. 74.2 (2010): 141-146.