NOT many years ago, the crayfish was common in many of our local rivers.

Those in limestone districts were vital to this crustacean as they needed the lime because their exoskeletons are made of this substance.

At one time they were eaten and were called “freshwater lobsters”.

How things have changed.

The decline has been due to two reasons. Pollution seems to have been a problem, but the main worry seems to be that there is now a fatal disease affecting crayfish.

Added to this is that the much larger Amercian Red Clawed, or Signal Crayfish, has escaped from restaurants.

It is much more aggressive and larger than our native crayfish, and it is not affected by the disease which is fatal to our native species.

Work is going on around Malham Tarn field centre, and in other areas, but, as yet, a satisfactory solution seems to be a long way off. Here then is another of our native species under severe threat.

A dab hand at ducking and diving

ALTHOUGH the dabchick is not uncommon, it is so elusive that it is thought to be rare.

The species, also known as the little grebe, dives whenever danger threatens and can swim long distances under water.

It can fly, but usually chooses not to. It is less than 30cms (12inches) and it has distinct winter and summer plumages.

In summer, it has a dark body, brown neck and cheeks, and a prominent yellow spot at the base of the bill.

In winter, there is more white on the rump and the yellow bill patch is less obvious. There is a prominent white throat, with a black head, neck and back.

The dabchick dives for its food, which consists of insects, molluscs, and small fish.

It is common along our canals and reservoirs, and the harder you look, the more often you will see it.

Bird watching should be just that – watching. Those with the most patience will be ones who see most!

'Thirsty' tree thrives in damp

THE alder is one of the most underrated trees in our countryside.

It grows up to 40feet (12 metres) and is found along streams, rivers, and areas where the soil is damp.

Its roots reach out beneath the ground in search of running water and, since it is a “thirsty” tree, it has small pink rootlets which actually project into the water.

If these are looked at under a microscope, large numbers of swellings, or root nodules, can be seen. These contain bacteria which provide nitrates.

This means that the alder can thrive in areas with few nutrients in the soil.

The alder bears male and female catkins on the same tree. The female catkins are round, and the male catkins hang down like lambs’ tails and can be confused with those of the hazel.

The timber has been used to produce clogs, and also for the supports of bridges and buildings. Because they grow well in water, the timber from the trees does not rot, and lasts for centuries.

At one time the alder was important to the dyeing industry. A yellow dye was made from the shoots, red from the bark, green from the female catkins, and pink from the wood chippings.

The alder thrives well in East Lancashire, and is one of our most common trees.