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| Floating Loons |
| | Building artificial raft-nests can enhance the nesting opportunities and breeding success of red-throated divers (Gavia stellata), the rare wilderness waterbird found in boreal peatbog pools.
Status of Red-Throated Divers
The red-throated diver (Gavia stellata) is a water bird related to the loon, the population in Finland being about 1000 nesting pairs. It nests in small forest- and bog-lakes and open peatbog pools throughout the whole country. The population of red-throated divers collapsed in the 20th century to a fraction of its original size, although the decline seems to have stopped during the 1990s. Threats to the population include forest ditching, building of cottages at lake shores, fishnets, oil damage on hibernation areas, hunting, nesting site competition and predators. The two latter threats can be reduced using artificial small isles, or raft-nests.
The red-throated diver is long-lived and extremely faithful to its breeding ground, so it will not very easily populate new lakes. Pairs often nest in loose communities. A new lake will be occupied most often only within a few kilometres of an existing territory. Commonly only one pair nests on each lake. Raft-nests have increased the breeding success of red-throated divers in southern Finland, and some new pairs have also appeared.
Red-throated divers nest on small floating islands or quite close to the coastline. With floating islands, nesting success is at least one and a half times higher compared with shore nests. It is well worthwhile building raft-nests for this magnificent waterfowl to nest on, because the lack of good nesting places is perhaps the most limiting factor for the population of red-throated divers.
Building a Raft-Nest
First it is necessary to ask permission for the raft-nest from the water area’s owner.
There are three methods of construction of a raft-nest. The first two methods are suitable for lakes with floating shores, where at least some part of the shore floats on the water. The easiest method is to anchor an already separated block of peatbog, if there happens to be a suitable floating island in the lake of at least 1 m2 in size. There are often such free-floating islands, probably detached by ice.
Another way to build a raft-nest is to cut a piece of floating shore off to create a separate island. Some floating shores can be cut easily, but some shores cannot.
The third way to make a raft-nest is from wood, plastic bottles and moss. This type of raft needs lots of plastic liquid canisters or bottles, with a total of 50–70 litres in volume, and if using oil canisters they should be carefully cleaned of chemicals before being used for the raft-nest. First, build a wooden grating about 1 m2 in size. Then nail the grating onto edges made of board. Under the grating, bind the sealed liquid canisters or bottles. Above the grating, nail a thick wooden octagonal or circular frame, about 5 cm thick. The resulting low ‘box’ should be filled with peat or preferably moss. The moss mix should be a bit higher at the centre. It may be worth planting some bushes on the banks of the raft.
The nest-raft must then be anchored to a stone with rope, preferably in the middle of the lake or at least about 20 m from the shores. The anchor rope can be bound to the grating of wooden rafts easily from below. With peat rafts it is advisable to pierce the raft with a peg of fir or pine to keep the rope down in the peat in a hook grip, then bind the rope to the stick on the surface of the raft. Another alternative is to somehow thread rope through the raft and then bind the rope to a piece of wood inside the moss. The rope should be fairly thick at the upper end so that it will not cut into the peat and break it.
If you are interested in making a raft-nest for a diver, you do need to wait until the end of the summer or the autumn. This is because divers are usually on their lakes the very day the ice melts, so in spring time there is no time to make a raft-nest without disturbing the divers. In the winter the construction of a raft-nest is usually not succesful, as it can be hard to make a hole in the ice to get it into position.
Raft-Nests Make a Real Impact
In south-eastern Finland, in Kymenlaakso (Kymi Valley) and South Savo, located in the new Repovesi National Park, there is a good example of the impact of raft-nests on the breeding success of a population of red-throated divers. In this area raft-nests have been built since 1997. Only 15 years ago, there were about 10 pairs of divers and production of young was about 6–8 young per year. In the last seven summers the number of pairs has risen to 14 and the production of young has been about 16 per year.
Black-Throated Divers Need Help Too
In fact two species of divers nest in Finland. The another one is the loon or black-throated diver (Gavia arctica). The same type of raft-nest should work also for black-throated divers, which feel comfortable on larger lakes. In Finland there have been quite a few observations of black-throated diver’s nesting on raft-nests. In my opinion, this bigger diver is under greater threat than the red-throated diver. This is because although the black-throated diver is currently much more common than the red-throated diver, the habitat of the former is much more severely affected by the increasing recreational use of lakes and construction of buildings on shores.
Because knowledge is the basis of protection, diver conservation plans require long-term diver inventories. Developments that are the most damaging to Gavia species should be prevented at the regional planning phase.
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| | Contact
Mikko Heino, Finnish Nature League |
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