Siren squad. Why do species migrate from land back to the sea? Siren squad animal

It lives in the shallow waters of the Atlantic coast of North, Central and South America. The north of its range is limited to the southeastern states of the United States, where the American manatee winter time lives in the Florida region, and in the summer migrates north to Virginia and Louisiana. South of the US, the American manatee can be found near the islands Caribbean Sea, along the coast of Central and South America up to the northeastern part of Brazil - Manzanaras Bay. Found in shallow ocean waters, found in shallow rivers and canals. If there is an abundance of food, it leads a sedentary lifestyle; if there is a lack of vegetation, it wanders in search of it.

The average length of an adult American manatee is approximately 3 m, although some individuals can reach 4.5 m in length, including the tail. The weight of these animals varies on average between 200-600 kg; the largest specimens rarely reach one and a half tons. Females are usually longer and heavier than males. Newly born cubs are 1.2-1.4 m long and weigh approximately 30 kg.

The American manatee easily adapts to both salt and fresh water, and calmly moves from sea bays to river mouths and canals and back. Because they have very low speed metabolism, and there is no thick layer of fat, their distribution is limited to the waters of tropical and subtropical latitudes. The manatee can live peacefully in both clean and polluted water. Because of them large sizes they require at least 1-2 m of depth, but they calmly move at a depth of 3-5 m, and try not to dive below 6 m. If the depth is sufficiently large and the current speed does not exceed 5 km/h, manatees are able to swim far upstream of the river - for example, on the St. John River, manatees are found 200 km from the ocean.

American manatees live in areas where they lack natural enemies, and therefore they have not developed complex mechanisms of behavior in case of danger. In addition, in the latitudes of their habitat, seasonal temperatures change slightly, and the vegetation is very diverse. Having no need for group hunting or group protection, American manatees lead a mostly solitary lifestyle, sometimes gathering in free groups. They do not have their own territory and do not adhere to any social hierarchy. Most groups meet on a temporary basis, without division by gender; the only exceptions to this rule are packs of young males who have not reached sexual maturity, and the female's estrus period, when several males court her.

Manatees use their tail to forward movement in water, but are also able to somersault in the water, roll over and float on their back. They are active both day and night, resting only for a few hours at the surface or at the bottom. Resting at depth, they rise to the surface every few minutes to breathe air. Manatees use several techniques to communicate with each other. Males scratch themselves, thereby releasing an enzyme that is designed to let the nearby female know about his sexual maturity. Manatees have excellent hearing, and use their creaking trill to communicate between mother and calf. Manatees use vision to navigate in space.

The muzzle of American manatees is inclined even lower than that of other related species. This may be due to their diet. They mainly feed on grass vegetation growing on the bottom. One of them characteristic features This species is characterized by the presence of a flexible, forked upper lip, with which they capture food and send it into the mouth. Manatees are quite indiscriminate in plant food, and eat the leaves of almost all plants that they can grab with their upper lip. They are also able to dig up plant roots with their lips. Some manatees feed on invertebrates and fish, both in the wild and in captivity.

Although animals of this species lead a mostly solitary lifestyle, during the mating season they gather in groups consisting of a female pursued by up to 20 males. A hierarchy of subordination is established among the males for the right to possess the female, and the female tries to avoid the males.

Males reach sexual maturity at the age of 9-10 years, although they are able to conceive by the age of two. Females reach sexual maturity at 4-5 years of age, but most of them begin to bear calves only after 7-9 years. Pregnancy lasts 12-14 months, and the newborn cub depends on its mother for about two years. Typically, only one cub appears at a time, although two are occasionally reported. The period between pregnancies lasts 3-5 years, but in the event of the death of the baby it can be reduced. For the first 18 months, the female feeds the baby with her milk, although the baby has large and small molars from birth, and already about 3 weeks after birth, manatees are able to eat plant foods.

The mother-calf bond is the only stable and long-term union among American manatees. It is assumed that this connection remains for many years, when the cub has already grown up and does not require direct assistance from the mother.

Amazonian manatee
Amazonian Manatee
(Trichechus inunguis)

Lives exclusively in fresh waters Amazon and its tributaries; to life in salt water not suitable. Countries in South America where Amazonian manatees are currently found include Brazil, Eastern Peru, Southeast Colombia and Eastern Ecuador.

The largest Amazon manatee ever caught had a body length of 2.8 m and weighed less than 500 kg; overall, it is the smallest species of manatees.

Unlike other manatees, the Amazonian manatee is exclusively freshwater species. It prefers stagnant lakes, river backwaters, oxbow lakes and lagoons connected to large rivers and overgrown with abundant aquatic vegetation. Remains in water with a pH of 4.5-6.5 and a temperature of 22-30° C.

Amazonian manatees are herbivores that feed exclusively on succulent aquatic vegetation, including Vallisneria, Ceratophyllum, Myriophyllum, Sagittaria, Limnobium, Utricularia, Potomogeton, waterweed lettuce (Pisitia), pontederia (Pontederia) and water hyacinth (Eichhornia). They also eat palm fruits that have fallen into the water. In captivity, adult manatees eat 9-15 kg of plant food per day, that is, up to 8% of their body weight.

The manatee is active both day and night, and spends most of its life under water, above the surface of which, as a rule, only its nostrils protrude. Typically, a manatee emerges from the water 3-4 times a minute to breathe air; The recorded dive record for an Amazonian manatee was 14 minutes. Amazonian manatees are slow; According to observations, the manatee swims about 2.6 km per day.

Their life cycles tied to the alternation of dry and wet seasons. Cubs are usually born during the rainy season, when rivers are in flood. At the same time, manatees feed off, eating fresh vegetation growing in shallow water. Research has shown that Amazonian manatee populations (central Amazon basin) make their annual migration in July-August, when water levels begin to drop. Some return to the beds of large rivers, where during the dry season (September-March) they starve for several weeks. Others remain in the slowly drying lakes left in the place of the retreated river, keeping to the depths; they have no access to normal food resources until the water level rises several meters again. The latter populations are apparently capable of fasting for up to 7 months, rarely and irregularly feeding on vegetation debris. Accumulated fat reserves and an unusually slow metabolism (36% of normal) allow these animals to survive the dry season.

Most manatees observed in the wild are solitary animals or females with babies. However, in feeding areas they are able to gather in groups (herds), which currently, due to the general decline in the number of Amazonian manatees, rarely exceed 4-8 heads.

In some parts of their range, Amazonian manatees breed at any time of year (Ecuador). In others, reproduction is seasonal and is tied to fluctuations in water levels, so the vast majority of cubs are born from December to July, mainly from February to May, when the water is highest (the central parts of the Amazon basin). Pregnancy lasts about 1 year and usually ends with the birth of a single calf, 85-105 cm long and weighing 10-15 kg. The interval between births appears to be about 2 years.

The lifespan of the Amazonian manatee in the wild is unknown; two individuals lived for more than 12.5 years in captivity. Natural enemies of manatees are jaguars and crocodiles.

African manatee
African Manatee
(Trichechus senegalensis)

African manatees live in rivers, estuaries, shallow bays and coastal waters along the entire western coast of Africa; also found in lakes. The northern limit of their distribution is the Senegal River (Southern Mauritania, 16° N), the southern limit is the Kwanza River in Angola (18° S).

Adults weigh less than 500 kg with a body length of 3-4 m. The largest African manatee caught, with a length of 4.5 m, weighed about 360 kg.

African manatees are found both in shallow coastal waters and in fresh water bodies, moving freely between them. They prefer quiet waters rich in plant food, but avoid highly salty waters. sea ​​waters. Their favorite habitats are: coastal lagoons with abundant mangrove and herbaceous vegetation, estuaries of large rivers with mangroves (Rhizophora) at the mouth and herbaceous vegetation (mainly the genera Vossia and Echinochloa) upstream, coastal areas less than 3 m deep, bordered by mangroves or overgrown with marine plants (Ruppia, Halodule, Cymodocea).

Upstream rivers, manatees rise up to waterfalls and rapids, or as long as the water level allows. In some areas, during the dry season, manatees find refuge in permanent lakes and ponds, which, when the water rises during the rainy season, are connected to river beds. They also swim into flooded forests and swamps overgrown with reeds (Phragmites), barnyard grass (Echinochloa) and other cereals. In the sea they are found 75 km from the coast among mangroves and fresh water outlets of the Bijagos archipelago (Guinea-Bissau). Isolated populations, cut off from the sea, were found in the lake. Volta (Ghana) above the hydroelectric dam. Another population isolated by river rapids was found in upper reaches R. Niger, in the area of ​​Ségou (Mali), which constitutes a record for advance into the interior of the continent for this species - more than 2,000 km from the ocean. In Chad, the African manatee is found isolated in the rivers of the Lake Chad basin, Baningi, Logone and Chari.

The behavior of this species is still poorly studied. Apparently, their lifestyle is predominantly nocturnal, since manatees are most successfully harvested at this time of day. During the day, they usually rest in shallow (1-2 m deep) waters, hiding among vegetation or staying in the middle of the river bed. Previously, it was believed that manatees were able to go ashore in search of food, but this point of view is now recognized as erroneous. African manatees live alone or in variable groups of 2-6 individuals. The strongest and most stable social bonds unite a female and her cub.

African manatees feed on aquatic vegetation, mainly coastal ones. Estuarine populations feed in mangroves by stripping leaves from low-growing branches. Their diet includes Vossia species, Eichornia crassipes, Polygonum, Cymodocea nodosa, Ceratophyllum demersum, Azolla, Echinochloa, Lemna, Myriophyllum, Pistia stratioties, Rhizophora racemosa and Halodule. Considering that an adult consumes 12 to 18 kg of food per day, one manatee can apparently eat up to 8,000 kg of vegetation per year. In some areas of their range (Senegal, Sierra Leone), local fishermen accuse manatees of stealing fish from nets, but this is not a confirmed fact. It is also believed that manatees will destroy rice crops in flooded fields. In Senegal and Gambia, shellfish were also found in the stomachs of caught manatees.

The reproduction of African manatees is still poorly understood, and much of the speculation about their reproductive behavior is based on the species' close resemblance to the well-studied American manatee. They are able to reproduce all year round, but the peak of calving, as a rule, occurs in late spring - early summer. Females reach sexual maturity by 3 years. A female in estrus is accompanied by several males, with whom she apparently mates randomly. Pregnancy lasts about 13 months and ends with the birth of 1 cub, and occasionally twins. Childbirth occurs in shallow lagoons. Baby manatees are born tail first and are able to swim immediately after birth. The female feeds the offspring using paired mammary glands located on the chest. The cubs apparently remain with their mother until they are 2 years old.

Pygmy manatee
Dwarf Manatee
(Trichechus bernhardi)

Lives in the fresh waters of the Amazon basin. Where it prefers rivers and canals with fairly fast currents.

Body length is about 130 cm, with a weight of 60 kg.

Dugong
Dugong
(Dugong dugon)

The largest population of dugongs (more than 10,000 individuals) lives near the Bolshoi barrier reef and in the Torres Strait. Large populations off the coasts of Kenya and Mozambique declined greatly after the 1970s. Off the coast of Tanzania, the last dugong sighting was on January 22, 2003, after a 70-year hiatus. A small number of dugongs are found off Palau (Micronesia), off the island of Okinawa (Japan) and in the Strait of Johor between Malaysia and Singapore.

Body length is 2.5-4 m, weight reaches 600 kg.

Dugongs live in warm coastal waters, shallow bays and lagoons. Sometimes they go out to the open sea; enter river mouths and estuaries. They stay above depths of no more than 10-20 m. Most activity is feeding, associated with the alternation of ebbs and flows, and not with daylight hours. Dugongs swim to shallow waters to feed coral reefs and shallows, to a depth of 1-5 m. The basis of their diet is aquatic plants from the pondweed and water-red families, as well as seaweeds. Small crabs were also found in their stomachs. When feeding, 98% of the time is spent under water, where they “graze” for 1-3, maximum 10-15 minutes, then rise to the surface to breathe. They often “walk” along the bottom on their front fins. Vegetation is torn off using the muscular upper lip. Before eating a plant, the dugong usually rinses it in water, shaking its head from side to side. The dugong consumes up to 40 kg of vegetation per day.

They live alone, but gather in groups of 3-6 animals above feeding areas. In the past, herds of dugongs of up to several hundred animals have been recorded. They live predominantly sedentary; some populations undergo diurnal and seasonal movements depending on fluctuations in water level, water temperature and food availability, as well as anthropogenic pressure. According to the latest data, the length of migrations, if necessary, is hundreds and thousands of kilometers. The usual swimming speed is up to 10 km/h, but a frightened dugong can reach speeds of up to 18 km/h. Young dugongs swim primarily using pectoral fins, adults - tail.

Dugongs are usually silent. Only when excited and frightened do they make a sharp whistle. The cubs make bleating calls. Dugongs' vision is poorly developed, but their hearing is well developed. They tolerate captivity much worse than manatees.

Reproduction continues throughout the year, with peak times varying in different parts of its range. Male dugongs fight for females using their tusks. Pregnancy is expected to last a year. There is 1 cub in a litter, rarely 2. Births take place in shallow water; a newborn with a body length of 1-1.2 m weighs 20-35 kg and is quite mobile. During dives, the cubs cling to the mother's back; milk is sucked upside down. Grown-up cubs gather in schools in shallow water during the day. Males do not take part in raising offspring.

Milk feeding continues up to 12-18 months, although already at 3 months young dugongs begin to eat grass. Puberty occurs at 9-10 years of age, possibly later. Young dugongs are hunted large sharks. Life expectancy is up to 70 years.

Steller's sea cow †
Steller's Sea Cow
(Hydrodamalis gigas)

Marine mammal of the sirenian order. Length up to 10 meters, weighed up to 4 tons. Habitat: Commander Islands (however, there is evidence of habitat also off the coast of Kamchatka and the Northern Kuril Islands). This sedentary, toothless, dark brown animal, mostly 6-8 meters long with a forked tail, lived in small bays, practically did not know how to dive, and fed on algae.

The story of the disappearance of the sea cow represents perhaps the most tragic page in the destruction of one of the most remarkable animals in an amazingly short term. The commander's herd was literally eaten by man. Already 27 years after the discovery of the islands, in 1768, the last animal was killed on Bering Island, and on Medny Island even earlier - in 1754.