by Árni Einarsson, 1992

The bird life at M‡vatn is characterized by ducks. Densities of breeding ducks are exceptionally high and the species composition is unusual. Ducks comprise a group of species which at first glance seem to have similar habits. When examined more closely the various species turn out to be quite different in their way of life.

One character which the duck species share is the difference in plumage between the sexes. The drakes attain their colourful plumage in autumn before the birds pair and keep it until the following summer. In the middle of the summer the males moult their flight feathers and become flightless. The body plumage becomes dull and resembles that of the females - they get into eclipse. The females also become flightless in late summer but the colour of the plumage does not change.

Ducks lay more eggs than most other birds. Clutches of 8 or 9 eggs are normal. Quite often much larger clutches occur when more than one female has laid in the same nest.

Duck eggs are relatively large and the local farmers traditionally collect a lot of them for domestic use. Four or five eggs are left in each nest for the ducks to incubate. Roughly estimated about 10,000 eggs are collected each year. In 1910 almost 29,000 eggs were collected by people from three farms around the Ytrifloi basin. As a matter of fact that was the record for this century.

The species differ slightly in the timing of their breeding season. Most species lay their eggs in late May - early July. Dabbling ducks (e.g. Teal and Mallard) are early breeders but the Red-breasted Merganser is the latest one. The female lays about one egg per day but does not start incubating until all the eggs have been laid. This ensures that all the young hatch at the same time. The duck incubates for a month without any aid from the other sex. When the females are about halfway through the incubation the pair bonds break up and the males gather in moulting flocks and are joined by non-breeding females. Males of certain species leave the area during the moulting period. The Harlequin and the Common Scoter for instance go to the sea. Other species stay and may even be joined by birds from other districts. This is the case with the Barrow's Goldeneye, Wigeon and the Scaup. Breeding females do not moult until they have left their young.

The males do not assist in brood rearing and the female has to manage singlehandedly. The young feed themselves but the mother locates the best feeding areas and leads the brood there. She occasionally takes the young to the bank and broods them. The broods of diving ducks frequently amalgamate. In some species, for instance the Barrow's Goldeneye and the Red-breasted Merganser, only one female stays with the mixed brood. In other species (e.g. Tufted duck and Scaup) more than one female may attend the group.

Most of the ducks are migratory. The mainstream goes to the British Isles. The ice-free areas on M‡vatn and Lax provide wintering opportunities for Barrow's Goldeneyes, Mallards and Goosanders.

The ducks can be grouped in three categories as to their feeding habits. Dabbling ducks feed mainly on vegetable matter, except the young and the laying females which prefer insects. The dabbling ducks do not dive for food but feed from the water surface or in the waters edge. They also upend for reaching submerged plants or invertebrates in shallow water. The Wigeon can often be seen gathering around swans and diving ducks to collect food stirred up from the lake bottom. Fish-eating ducks are highly specialized as fish consumers and have a sawtoothed slender bill with a hooked tip.

The third group consists of other diving ducks. They dive down to the bottom of the lake or the river. Their bill is designed like a sieve and they can filter the mud on the bottom in search of midge larvae, water fleas or snails. The tracks made by the ducks in the mud can often be seen in the clear water along the eastern lake shore. The bottom-feeding ducks mostly dive in relatively shallow water. In M‡vatn they seem to prefer water less than 3 m deep. When midges are emerging from the lake the ducks simply pick the flies from the water surface and save their underwater trips.

All Icelandic species of ducks can be found nesting at M‡vatn and Lax. These include populations which rely entirely upon the special life conditions in this area. What then are the conditions which make M‡vatn and Lax a Mecca for waterfowl? At M‡vatn and Lax there is a rare combination of factors which contribute to this. The fertility of the water and rich food has been described and some of the reasons for this discussed. This is not enough. Another main reason is how shallow the lake is.  M‡vatn is about 40 km2 and most of the bottom areal is accessible as feeding ground for diving ducks. The mining area in the Ytrifloi basin is an exception. It has become unsuitable for ducks.

Iceland is situated on biogeographical crossroads. Here we have birds originating from both the Old and New world and from the Arctic and more southerly latitudes. This is reflected in the species composition of ducks at M‡vatn and Lax and nowhere else in the world can the same mixture of species be found. The Barrow's Goldeneye and the Harlequin Duck have their origin in America. The Long-tailed Duck, Scaup and the Common Scoter are examples of arctic and subarctic species.

The diverse habitat contributes to the diversity of ducks. All the species have conditions which meet their special requirements. Nesting habitats are varied. Holes for hole-nesting ducks like the Barrow's Goldeneye are abundant. The bottom of the lake also varies from place to place. Even though some areas lack food in one year there are always areas where food is abundant. Finally it seems possible that moderate fluctuations in the environment may play a role in keeping the diversity high. These fluctuations apparently keep the duck populations in a constant state of succession and may prevent some few species from taking over.

The Barrow's Goldeneye Bucephala islandica is the species which is most dependent upon the special life conditions provided by the M‡vatn-Lax ecosystem. This is one of the bigger species but the sexes differ much in size. The drakes are about 50% heavier than the females. This is not without reason. The drakes are highly territorial and aggressive so they need to be big and strong. The females nest in holes and small size is therefore of advantage to them.

Barrow's Goldeneyes are resident in the area because the openings in the ice are large enough to foster most of the population through the winter. More than 200 birds leave the area, however, and head for other lakes, especially in southern Iceland. The total population is only about 2000 birds. Drakes form the majority, numbering about 1200 individuals. During the moulting period all the males in the Icelandic population gather in a few flocks on M‡vatn and the uppermost part of Lax. The male part of the population is steadily declining. The reason for the decline is unknown.

The Barrow's Goldeneye has some peculiar nesting habits. In late winter the pairs start defending a piece of water. The aggressive displays are mostly performed by the drakes. It looks as if invisible boundaries have been drawn on the water surface. Almost all other waterfowl are driven away if they trespass. The most popular areas are in the bays around Hfdi and the uppermost part of Lax. Where food is abundant the territories may be as small as 500 m2 but in less preferred areas up to 80 times larger (4 ha).

Barrow's Goldeneye drakes employ various strategies when defending their territories. Often it is sufficient to lay down flat on the surface and stretch the neck towards the intruder. If that does not work the territory owner swims towards the other bird in this threatening posture. A stubborn intruder will be attacked underwater. Sometimes this escalates into a direct fight.

The territory provides a safe food resource for the female which is devoting herself completely to the task of breeding. The territory is normally inshore and not far from the nesting site. The nest may, however, be as far as 2-3 km from the territory.

In April the females start prospecting for nest sites. Early in the morning they fly in small groups low over the lava fields, craters and buildings where potential nesting holes are abundant. They vocalize a lot and crawl in and out of every hole they come across. It is not uncommon to see them sitting on rooftops or peeping into chimneys. Accidentally they may fall into the chimneys and get themselves killed. Some birds find suitable nesting sites in the stonewalls or roofs of old sheephouses or barns.The Icelandic name "hsnd" or house-duck is without doubt derived from this habit. In the fifties farmers started erecting nest boxes for the Barrow's Goldeneye inside barns and other outhouses. It has been estimated that 10% of the nests now are in nestboxes. Other nests are in holes and crevices in the surrounding lavafields.

The females not only lay in their own nests but quite often visit other nests and lay eggs there. It seems likely that in this way the female lowers the risk of loosing all her eggs if her own nest would be destroyed.

The young hatch in early July. At this time of the year blackfly larvae abound in Lax. The largest larvae are in the outlet and females bring their broods there, even from nests on the other side of the lake. The females keep territories for their broods and a lot of fighting takes place before a new bird settles in the brood rearing area. During these disputes the broods may mix and many females leave the river after loosing their young to other females. Sometimes females with more than 100 young can be seen in the best feeding areas. Quite a few young may get killed by aggressive females. In August when most of the blackfly larvae have emerged as flies and disappeared from the river the broods move to the lake.

The Barrow's Goldeneye has a rather strange distribution. It is common in western North America and nests in tree holes. Flocks of this species occur in Labrador but breeding has not been proven. The small Icelandic population is the easternmost outpost of the species and the Barrow's Goldeneye is one of the few bird species in Iceland which originates from America.

The Tufted Duck Aythya fuligula invaded Iceland and started breeding at M‡vatn shortly before the turn of the century. Its population has grown rapidly and around 1970 it outnumbered the Scaup and became the most numerous duck at M‡vatn. Between 2000 and 6000 males are seen in the M‡vatn district in spring. The number of pairs is lower because there is an excess of males. Tufted Ducks tend to be in scattered flocks on the lake, but in the spring large numbers are seen on the ice edges and along the edges of the ponds in the marshes where they nest later on. The Tufted Duck is among the first arriving migrants in spring getting there as soon as the ice starts to retreat. Like other diving ducks it feeds mostly on midge larvae, but takes also molluscs and benthic waterfleas (Eurycercus). In years when sticklebacks abound Tufted Ducks may be seen in small but dense flocks feeding on them. The nests are mostly in colonies together with Scaup nests. Map of wintering area.

The Scaup Aythya marila has been present at M‡vatn for centuries and was the most abundant species until about 1970. Between 1400 and 2600 males occur in spring. During the moulting period they are joined by conspecifics from other districts nearby. The largest moulting concentrations are on the western half of the Sydrifloi basin and a small flock is usually on the pond Stakholstjrn by Skutustadir. The young tend to form loose flocks led by a few adult females. Often female Scaup are seen followed by a mixed brood of both Scaup and Tufted duck young. Same holds true for Tufted duck females. The food is similar to that of the Tufted Duck but with more emphasis on crustaceans (Eurycercus) and less preference for snails. Map of wintering area.

The Common Scoter Melanitta nigra is one of the species which is common at M‡vatn but rare elsewhere in Iceland. Between 200 and 500 males occur in spring but there is an excess of males. The species is most often seen on the western part of Sydrifloi but only occasionally on Ytrifloi. The food consists mostly of midge larvae and benthic crustaceans. The latter are clearly preferred and are especially important for the ducklings. The males leave M‡vatn in the middle of the summer and moult on the sea. Nonbreeding females leave at the same time but breeding females stay until August. The last to leave are the young which have to get to the wintering grounds in Europe on their own.

The Long-tailed Duck (Oldsquaw) Clangula hyemalis is an arctic species, one of the character birds of the tundra and Iceland is on the southern boundary of its range. It is quite prominent at M‡vatn in spite of the fact that the males number only 100-300. This is due to the conspicuous and musical territorial displays performed by the males in spring. The Long-tailed Duck overwinters on sea but arrives at M‡vatn as soon as the lake ice starts retreating in spring. It seem to prefer crustaceans, especially the cladoceran Eurycercus lamellatus and the tadpole shrimp Lepidurus arcticus. Long-tailed Ducks are most often seen on the western and southern parts of Sydrifloi. They are also common on ponds west and south of M‡vatn and on Lake Grnavatn. This species is first among the diving ducks to start breeding. Most of the males leave M‡vatn before moulting.

The Harlequin Duck Histrionicus histrionicus is a river specialist and is only to be found on the rivers. The species occurs on rivers all over Iceland but the highest density is at Lax. In winter the Harlequins stay on sea, mostly on exposed coasts. The first birds arrive in the Myvatn district in April but most of them come in early May. The uppermost part of the river, i.e. before it flows into the Laxrdalur valley, holds about 250 males. The pairs often sit for long periods on the banks or on rocks in the river. Frequently lone males accompany the pairs. The colourful plumage of the male is in fact an excellent camouflage on the river. The ability of the ducks to feed in the rapids is admirable. They dive into the strongest current without hesitation. Their effort is rewarded because the rapids hold the richest patches of their staple food, the blackfly larvae. The Harlequin Duck is very tame. In the middle of June the males leave the area and return to the sea where they moult. In August flocks of females are seen on Laxa. These are probably non-breeders and failed breeders. When the blackfly population is doing well over 100 young survive on the uppermost part of the river. In years with low production of blackflies only a few young survive. Harlequin Ducks do not breed elsewhere in Europe. Their breeding range elsewhere includes eastern Siberia and western North America.

The Red-breasted Merganser Mergus serrator is the commoner of the two merganser species at M‡vatn. Between 280 and 540 males are seen in spring but their numbers increase in mid summer. In years with high densities of Three-spined Sticklebacks, their principal food, over 700 birds may be seen in one flock out on the middle of Sydrifloi. The Red-breasted Merganser nests in holes and crevices in the lavafields. Newly hatched young are taken to the Ytrifloi where large creches are formed each one normally accompanied by one female.

The Goosander Mergus merganser is uncommon on M‡vatn. Only 2-3 pairs nest there. On Lax the Goosander is quite common, 6-10 pairs occur down to the hydropower station at Brar. Males disappear before moulting begins to an unknown moulting ground. During the winter, however, tens or hundreds of Goosanders gather at M‡vatn, probably depending on the stock size of Arctic Char and Brown Trout in the lake.

The Wigeon Anas penelope is the most common among the dabbling ducks at M‡vatn. Between 500 and 1900 pairs arrive in spring. First they graze on the hayfields but as soon as the midges begin to emerge they move out on the lake to pick up the flies as they come to the surface. On windy days flocks of Wigeon feed on material drifting ashore. In July more birds arrive to moult on the lake and large concentrations can be seen on Neslandavik and Ytrifloi. The ducks frequently gather around Whooper Swans and diving ducks to feed on material torn or stirred up by their feeding activity. Moulting Wigeon hide in the sedges and are normally not seen unless disturbed. The Wigeon winters mostly in the British Isles, but some of the young winter in eastern North America. Map of wintering area.

The Gadwall Anas strepera is one of the characteristic birds of the M‡vatn district. It is rare outside the M‡vatn-Lax system. Between 40 and 120 pairs are found around M‡vatn and about 45 on Lax. The birds stay on open water close to the shore but do not hide in the vegetation as most other dabbling ducks. They do not usually gather in flocks except when moulting. Then small flocks occur in Neslandavik and around the larger islands in Sydrifloi.

The Mallard Anas platyrhynchos is quite common in summer and it winters in some numbers too. They are mostly confined to the marshy areas except in early spring when they are common on temporary pools in the hayfields. Mallards are common on Lax and sometimes they dive into the river for food.

The Pintail Anas acuta is not uncommon in the marshy areas around the lake, especially the extensive Framengjar South of M‡vatn. Like most other dabbling ducks they are most active at dusk.

The Teal Anas crecca is common around M‡vatn. It is most conspicuous in spring before the sedges grow and the birds can hide in them. This smallest of Icelandic ducks is then frequently seen on small streams and at the waters edge.

The Shoveler Anas clypeata is without doubt the rarest of the nesting ducks at M‡vatn. A few birds are seen each spring suggesting that they nest regularly. The Shoveler is a rare bird in Iceland. It is believed to have started breeding in Iceland early this century and not until the thirties in the M‡vatn district.

A few species occur regularly on M‡vatn without breeding. The Common Goldeneye (Bucephala clangula) is not infrequent. Three to ten males are normally seen on the lake all the year round but females are rare. One or two American Wigeon (Anas americana) males occur every summer and Pochard (Aythya ferina) males also. Pochards were proven to breed on several occasions in the fifties but this seems happen more rarely nowadays. Other almost annual visitors include the Smew (Mergus albellus), Ring-necked Duck (Aythya collaris) and Ruddy Duck (Oxyura jamaicensis). Rare vagrants include Bufflehead (Bucephala albeola), Green winged Teal (Anas crecca carolinensis), Black duck (Anas rubripes), Garganey (Anas querquedula), Surf Scoter (Melanitta perspicillata) and Steller's Eider (Polysticta stelleri).