Natural life in the racing torrents and waterfalls

Posted in Animals, Birds, Fish, Nature, Wildlife on Monday, 24 February 2014

Click on any image for details about licensing for commercial or personal use.

This edited article about wildlife first appeared in Look and Learn issue number 563 published on 28 October 1972.

Salmon leaping falls,

Salmon leaping torrents and waterfalls

In the hilly and mountainous parts of the country the streams are torrents which come tumbling downhill, splashing over rocks and pouring over waterfalls. The movement of the water is eye-catching in what is often an otherwise desolate scene. Over the years, the streams have carved gullies and ravines in the hillsides for small trees and bushes to find shelter from the wind. Waterfalls are especially spectacular, where a wall of foaming water crashes in to a pool at the bottom.

These streams and waterfalls may look pretty but they do not appear at first sight to be good places for animals to live. A paddle in the water shows up the disadvantages. The water is icy cold and quickly numbs the feet, while the current is often strong enough to make standing difficult. In the fiercest mountain streams the boulders may be dislodged and hurled down-stream.

Yet, as in other inhospitable places, from hot volcanic springs to the ocean bed, there are certain animals which make a living in torrents. There are some advantages for small animals. The foaming water is full of oxygen for breathing and the water carries food which only needs to be picked up as it goes past. Two things are needed, however. Torrent animals must be able to withstand cold and they must be able to cling tightly to the rocks by means of claws or suckers so that they do not get swept away.

In the British Isles there are several small animals which live in fast-flowing streams. They are mostly the larvae of insects. The adults do not live in the streams but they come there to lay their eggs.

Mayflies are common insects which can be seen flying near water. They lay their eggs in the water and these hatch into larvae called nymphs. The nymphs have three “tails” at the tip of the abdomen, as do the adults, and there are two rows of feathery gills on the sides of the body. Mayfly nymphs can be found in many ponds and streams. Some burrow in mud near the bank, others creep amongst the water weed, but a few can be seen in fast streams. Nymphs of the mayfly called Ecdyonurus have broad, flat bodies and cling to stones so that the water rushes past them. The legs are also flattened and are held at an angle so that the force of the water pushes them against the stone. A relative of Ecdyonurus, called Rhithrogena, has turned one of its pairs of gills into a sucker to help it cling to stones.

Another common kind of water insect is the caddis fly. Its nymphs are famous for building tubular houses, or cases, from tiny pebbles and pieces of plants. Caddis nymphs of fast streams live under stones. Some build cases of pebbles but others live in the open or in silken tubes. The tubes are used as nets for catching small animals which are being swept along in the water.

Along the sides of waterfalls there is often a thick carpet of plants, mainly mosses and liverworts, with clumps of ferns here and there. The carpet is soaking wet with spray or with water trickling out of crevices. Similar carpets can be seen under bridges or on the walls of canal locks. The plants form a sheltered home for many small insects. As in the main stream, there is plenty of oxygen, but the water does not flow very fast.

This is a good place for fly larvae. Midge larvae cling to vertical rocks by suckers. Others are held against the rockface by the thin film of water running over it or have spines and hooks on their bodies which become entangled in the mosses.

The insects living in or alongside torrential streams form the food of several kinds of animals. In Britain, as well as in other parts of the world, hillside streams are the home of the dipper. This is a small brown bird with a white “bib.” It can swim underwater, using its wings. The dipper’s food is mainly insect larvae, but it also catches small fishes. It nests under banks or among tree roots. The nests are often in danger of flooding if the water level rises. In Africa, the red-winged starling is a bird of waterfalls. It feeds on the insects that live among the vegetation close to the water and builds its nest behind waterfalls.

There are two kinds of ducks which can live in much worse places than dippers do. The torrent duck lives in the raging streams that descend on each side of the Andes and the blue duck lives in the same sort of place in New Zealand. No one is quite sure how the torrent ducks survive in these conditions. They seem to be able to swim in very fast currents and usually fly only when they have to get up waterfalls.

In the northwestern corner of the United States the tailed frog lays its eggs in mountain streams. Unlike most frogs it thrives in cold water. The eggs are laid under rocks and the tadpoles cling to the rocks by a special organ on their heads.

Fish, too, can survive in mountain torrents. They usually cling to rocks with suckers, but the humpback sucker is a fish of the United States that has a special shape so that the force of the water pushes it against the rocks. In the hillstream fishes of southern Asia, the two front fins form a sucker like the rubber suckers used for attaching nooks to walls in kitchens or bathrooms. Rubber suckers are made to stick by squeezing them to drive out air and so forming a partial vacuum. Hillstream fishes make a vacuum by pushing their fins against the rock surface. With these suckers the fishes can hold their position without effort while they eat the weed on the rocks.

Comments are closed.