BIOLOGISTS have developed a very interesting theory which has become known as the Ecological Niche.

This means that no two similar organisms can live in the same environment and eat the same food. When two organisms are too similar one will out-compete the other and the less dominant species will become extinct.

While bird watching last week in an area around Entwistle, between Blackburn and Bolton, I saw two species of duck which are very very similar. These are the tufted duck and the scaup. Both are small diving ducks and there are only minor physical differences between them.

The male tufted duck is black and white and as its name implies it has a small crest on its head. The male scaup lacks the crest and has a grey back. The females are quite difficult to distinguish and this suggests that the two species are in direct competition.

This is where the theory of the Ecological Niche comes in. The tufted duck is very common in fresh water habitats and it is very rare to see one in salt water areas.

In contrast, the scaup is a species which prefers a salt water environment and my sighting of one male bird at Entwistle reservoir is unusual. Thus the tufted duck and the scaup each has its own environmental niche which prevents competition.

The scaup as a species is likely to have a few problems in the next few years. In the past scaup have gathered during the winter around coastal sewage outflows. The sewage has acted like a fertiliser and marine plants have grown and these have been fed upon by invertebrates. These in turn have been the food of the scaup. In 2001, the sea water quality has improved because new sewage works have been built. The discharge of sewage directly into the sea is now a thing of the past. The scaup numbers have started to decline.

Water companies, including our own United Utilities, are continuing to spend millions of pounds and the water quality is improving all the time. What we need now is to count scaup regularly to see if they are declining in numbers or merely changing the location of its feeding grounds.

Studies like these are vital if we are all to help in conserving our wildlife. We must continue to strive for better quality water (both fresh and sea) and to link all these improvements with studies of living organisms.