Suomen Luonto
English summaries 8/2003

An assembly of red-throated divers
Text Mika Honkalinna, photos Asko Hämäläinen

Pages 4–11

A pair of red-throated divers and their offspring nesting on a wilderness pool are suddenly disturbed on a late summer evening by other members of the species from various parts of the Repovesi wilderness having the effrontery to land on their pool. These new arrivals are energetically repulsed. All night long the tranquillity of the pool is interrupted by the awesome cries of the assembled birds. The call of the red-throated diver begins as a low moan, before becoming a blood-chilling wail that increases and decreases in volume.

With the rising of the sun, more and more divers begin to fly in. Now the pond ‘owners’ accept these visitors, so that finally there are around 15 of the birds swimming about on the surface. They move about singly or in pairs and may form larger groups, giving vent the whole time to a variety of calls ranging from grumbling and cackling to hair-raising howls. Suddenly two or three of the birds start running in parallel across the water surface, bills pointing obliquely upwards. This act ends with general comments from every bird present.

Black-throated divers hold similar assemblies but they cause far less of a commotion than their red-throated cousins. What is the purpose of these gatherings? The birds cannot, at any rate, be said to congregate in order to catch fish, because there are very few such prey in a small wilderness pool.

The kestrel returns to the fields
By Anne Kärkkäinen

Pages 12–13

Previously common, the kestrel all but disappeared from Finland due to environmental toxins and changes in the structure of agriculture some 30 years ago. Now the bird has returned, the breeding population being currently estimated as around 10,000 pairs. Most kestrels are now nesting in boxes put up for them on hay barn walls. Such nest boxes provide the birds with a far safer haven than would normally be the case, for kestrels usually occupy old crows’ nests.

In 2002 a total of 5,669 young kestrels were ringed and this year the number is approximately the same. However, problems are discernible. Today’s agriculture does not make use of hay barns, which consequently are left to rot and collapse. Intensive agriculture does not encourage large vole populations. Consequently, kestrels have difficulty in finding enough food for themselves and their offspring.

Lauha – "mountain of the great plains"
By Markku Lappalainen

Pages 18–21

Southern Ostrobothnia is one of Finland’s most renowned flatlands, the country’s "great plains". Yet western Finland’s highest hill, Lauhanvuori, rises unnoticed up out of an otherwise level terrain. Although it is called a mountain in Finnish, one has to admit to a bit of exaggeration here, for there are no vertical walls, rocky summits or exposed granite on Lauhanvuori. For all that, its peak stands at 231 metres, making the hill only one metre lower than the famous Puijo and as much as 28 metres higher than Ounasvaara, in the Rovaniemi region.

Lauhanvuori is of great geological interest. Lower down there is ancient bedrock and this is topped by sandstone composed of quartzitic sand formed by the disintegration of the bedrock some 600 millions years ago. On top of the sandstone there is a thick moraine deposit from the latest ice age. At the end of the latter, Lauhanvuori formed an island about a square kilometre in extent in the ice cold sea occupying the area that is now the Baltic. Consequently, nutrients were not leached out of the moraine, enabling today’s luxuriant forest to thrive along the summit. The sea has washed away the nutrients from the lower slopes which are thus now clothed in barren pine forest characterised by ground lichens. The ancient shores remain visible as water-worn aggregations of rock known in Finland as "devil’s fields". The largest of these measures almost a kilometre in length.

Springs and mires occur commonly on the lower slopes. These have formed due to Lauhanvuori being much higher than the surrounding land and thus subject to a higher rainfall. Water trickles down through the moraine and sandstone to form groundwater which rises to the surface in several places lower down. In 1982 the Lauhanvuori area became a national park 5,100 hectares in extent. There is a small visitor centre and exhibition, as well as nature trails and waymarked trails.

Grubs as pets
Text Aura Koivisto, photos Risto Sauso

Pages 36–39

Children are generally interested in everything and move about closer to the ground than adults. Besides they are very open-minded. This explains why our kids find caterpillars more easily than we adults do. It is true, of course, that some adults as well may be interested in grubs or caterpillars. The author’s spouse is one of them.

The rhinoceros beetle is a large coleopteron but its larva is even bigger, growing up to 60 mm long and weighing 12 grams. It resembles a fatty white sausage with small feet totally incapable of supporting such a load. Rhinoceros beetle grubs live in sawdust. The authors provided a compost heap in their yard containing a mixture of sawdust and horse manure. The larvae took two years to develop in this outdoor "incubator".

Many insects spend most of their life cycle as larvae. This is the growth stage, when a privet hawkmoth caterpillar increases 9000 times in weight, and a goat moth larva 72,000 times its original weight on hatching from the egg. Most larvae never reach adulthood. To improve their chances, a lot of species have evolved camouflage, threatening postures, unpleasant smells, toxins, and irritating hairs and chemicals. Numerous others make webs to hide in.

Judicious fish population management halts eutrophication
By Antti Koli

Pages 62–65

When a lake receives too many nutrients from the river that supplies it, or from the surrounding habitation, industry or fields and forests, it becomes over-rich in them, i.e. eutrophication occurs. The increased nutrient concentration means a rise in primary production by the phytoplankton and aquatic higher plants, more zooplankton, and extensive nutrient accumulation in the bottom ooze.

The first priority for rectifying this situation is a severe reduction in the external loading. In other words, it is essential to limit the amount of nutrients reaching the lake. Otherwise no form of habitat restoration is going to have any lasting effect at all. Once the nutrient loading has been brought under control, a start can be made on restoration by attacking the lake’s natural food chains.

Feeding by fish affects the concentration of nutrients in the water and through this the density of algae and plants. The more fish there are in the lake which consume zooplankton, the more the phytoplankton is able to reproduce in the absence of its own consumers. Thus, reducing the number of fish consuming zooplankton decreases the amount of phytoplankton.

A large population of cyprinid fishes (belonging to the carp family), including roach, rudd, bleak, zope, and silver bream, increases eutrophication. Feeding off both benthal animals and zooplankton, the fish have to defecate in the water. Cyprinids therefore tend to appreciably increase the lake’s internal loading.

A new approach to managing lakes on an ecological basis entails vastly reducing the cyprinids. Fish are caught using trawls, seines and fyke nets. In many lakes 200-400 kilos per hectare have been harvested in this way, resulting in a radical, and visible, improvement in the condition of the habitat. Any predatory pike, perch and pike-perch caught are returned to the water. It is best to combine the fishing with the cutting of reeds and rushes, the plant material removed being destroyed by burning or composting.

Major lake restoration projects of this kind have been implemented in Lake Vesijärvi, in Lahti, some 100 km north of Helsinki, and in Lake Tuusulanjärvi, near Helsinki. The shores of both water bodies support urban populations and are used extensively by large numbers of people. The results of restoration by managing cyprinid fish populations have been good.

Teksti: Leigh Plester