THE RIVER THAMES - ITS NATURAL HISTORY continued

BIRDS

The Mute Swan (Cygnus olor) is one of the commonest birds to be seen on the River Thames. A mute swan gliding by so elegantly with wings raised and neck curved is a sight worth seeing. The cob (male) and the pen (female) generally mate for life. The cob has the larger black knob on its bill. A clutch of eggs can number between 3 and 10. It is advisable not to approach too closely when adults are caring for their cygnets. They can become very aggressive if alarmed. The brown plumage of the young changes to white as they mature. The mute swans feed in shallow water, upending themselves so that their tail feathers point skywards. Flying involves running along the surface of the water, with a great flapping of wings, before the swan becomes airborne.

Mute Swan


The Canada Goose (Branta canadensis) is not a native species but has flourished so much that large flocks can be seen all along the non-tidal Thames. The V-shaped formation of a flock flying passed is a familiar sight; their honking call a familiar sound. Both male and female look alike with greyish-brown plumage, black neck and white cheeks. The geese feed much in shallow water but also on pasture and arable fields.

Canada Goose


The Mallard Duck (Anas platyrhynchos) is another common species found on the River Thames. The drake (male) has a distinctive green head with a white neckband and curled feathers in its tail. It has a yellow bill and orange legs. After breeding it moults and looses its vivid plumage. The less colourful female is mainly brown with dark bars on its wings. Mallard feed by up-ending or by skimming the water surface with their bills.

Mallard Ducks


The Greylag Goose (Anser anser) is the ancestor of the domestic goose. Although the most widespread goose in Europe, it is not as numerous on the Thames as the Canada goose. The male and female are alike in appearence. Greylags usually graze for food but may be seen up-ending in shallow water.

Greylag Goose

The Great Crested Grebe (Podiceps cristasus) is an accomplished diving bird. It has short legs placed far back which aid this ability. Its summer plumage is very distinctive; the head has a black crown with a double crest and reddish facial feathers and black frills. It feeds on small fish and water insects, diving underwater for quite a long time as it catches its food. The courting ritual of a pair of grebes is a fascinating display with much vigorous head shaking and synchronised movement. Today the number of grebes are increasing. They suffered a decline because of the popularity of their feathers in fashion during the Victorian age. Now great crested grebes are fairly numerous, though rather shy; they will dive down into the water if approached too closely.

Great Crested Grebe


The Coot (Fulica atra) can be recognised by its dark body, large lobed feet and white bill with frontal shield. It swims with a vigorous action of its head, frequently diving underwater. It can fly but to do so it needs to run along the water surface before taking off. Coots are very aggressive birds and often can be seen chasing after other water birds as they defend their territory. The young chicks have red markings on their heads which fade as they mature.

Coot


The Grey Heron (Ardea cinerea) will often be seen standing absolutely still on the riverbank or flying through the air with a wingspan of about 180cms and its long sticklike legs stretched out behind . Its plumage is grey, white and black. It has a white head with a long pointed beak and a broad black streak running from the eye to the tip of the crest. One of the pleasures of bird watching on the river is to watch the patient heron as it stands motionless in preparation to strike at a passing fish. Although usually seen alone, the grey heron breed in colonies, preparing their old nests up in the trees during January ready for the breeding season which could be from February to early June. The nests are built of sticks and lined with grass. The eggs are plain green and are incubated by the female for about three weeks. Grey herons eat a mixed diet of fish, eels, frogs, small mammal or even large insects. They will even raid a garden pond and empty it of its goldfish.

Grey Heron


The Moorhen (Gallinula chloropus), with its red frontal shield and yellow tipped beak is one of our best known waterbirds, often confused with the larger Coot. It is generally a shy bird and will soon scurry into the vegetation if disturbed. Being about 33cm in height,it has dark plumage with a white flank line and undertail and greenish-yellow legs and long toes. It runs, walks, swims and dives effortlessly but flying is rather laboured. A moorhen has a mixed diet of leaves, seeds, berries, worms, snails and small fish. Breeding usually starts in late March and a moorhen may produce 3 clutches in a season with 3-10 eggs in each clutch. The eggs will take about 20 days to incubate.

Moorhen

MAMMALS

The Water Vole (Arvicola terrestris), with a weight of between 150 - 300g and body length of between 140 - 220mm, is the largest British vole. It has a round body covered with chestnut brown fur, short round ears and a blunt nose. It can be distinguished from a rat by its hairy tail. It dives and swims effortlessly, eating grasses and waterside vegetation. Water voles dig out tunnels into the river banks, creating sleeping/nesting chambers in the drier higher sections whilst making a lower entrance/exit below the water level. If the weather is mild a water vole will produce several litters between April and September. Usually there are five young in a litter. Born blind and hairless they grow quickly, are weaned by two weeks and leave the nest after about three weeks. Sadly most will not survive as they become prey for minks, and stoats as well as herons. In the 1990s there was a serious decline in water vole numbers along the Thames. There are several causes , escaped American mink being a major factor, but also destruction of their habitat and water pollution contributed to the decline. Fortunately in recent years there have been encouraging signs that the water vole is returning to the Thames.

Water Vole


The Otter (Lutra lutra), has brown fur, which is frequently pale on the underside, a long slender body, small ears, a long thick tail and webbed feet. They measure up to 120cms in length with a tail of about 40cms. An otter is a shy animal and as it is nocturnal is not often spotted, though the keen-eyed may spot the cigar shaped droppings (spraints) deposited at regular intervals on the river bank which serve as territory markers. They are excellent swimmers. The short powerful limbs propel it through the water whilst the thick tail acts as a rudder. The long upper hair repels water and keeps the under fur dry. Its main food is fish. Otter cubs are usually born in litters of two or three in a holt ( under a tree root or in a hole in a bank ). They venture out of the holt after about 10 weeks. Otters virtually disappeared from the Thames for a number of reasons but due to the efforts of the Berks, Bucks and Oxon Wildlife Trust and the Environment Agency to improve riverside habitats, there have been an increase in the number of confirmed sightings, which is great news.

Otter

The American Mink (Mustela Vison) is a member of the weasel family so is a relative of stoats, otters, polecats and badgers. As its name suggests it is not a native to the British Isles. The mink that are found in the wild are escapees from fur farms and can now be found along the Thames as well as other waterways of Britain. As they have no natural predators they have adapted very successfully to their new homeland, with dire consequences to indigenous species. These aggressive animals weigh about 1.2kg and measure about 60cm in overall length and are usually dark in colour. They swim and climb with ease. They eat a mixed diet of small mammals, fish, birds and invertebrates. The females gives birth to one litter of 5 to 6 young in underground dens. the kits will be weaned at 7 weeks.

American Mink

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