MI7 Mire birds

>> Background information

Development

The mire bird indicator is based on the monitoring data of 12 species since 1979. During the past three decades, mire birds have declined by almost 40%. Mire birds populations have demonstrated strong annual fluctuations, but, on the whole, the declining trend is uniform and clear. The decline of mire birds has continued also during the 2000s. It remains to be seen whether the increase in 2007 and 2008 represent a turning trend or fits merely within natural fluctuation.

The large-scale draining of mires has decreased the area of suitable breeding habitat especially in southern Finland (MI1). The decline of mire species might thus get explained by diminishing breeding grounds. However, this explanation is complicated by the fact that all of the birds included in the indicator are migrating species, most even long-distance migrants that over-winter in Sub-Saharan Africa. For these species, Finnish mires may be regarded as short-duration breeding centres. Little is known about the factors affecting mire birds during winter.

According to the combined data on open habitat birds, the residents and short-distance migrants have declined almost as steeply as long-distance migrants. Judging by this comparison there must be other factors than those related to migrating routes and wintering grounds behind the decline of mire birds. For example, the only resident mire bird, Willow Grouse, has nearly entirely disappeared from southern Finland since the 1970s. The data on open-habitat species include also farmland birds.

The production of offspring of mire birds relies largely on the short-duration peak of biomass production of non-biting midges (Chironomidae) on flarks and other open water pools. The abundance of midges increases towards the north. Approximately 75% and 90% of the flark fens that are especially important for mire birds remain pristine in southern and northern Finland, respectively. Some species particularly valuable in terms of conservation are missing, for the time being, from the indicator due to lack of monitoring data. If these species ? including Spotted Redshank, Jack Snipe, Broad-billed Sandpiper and Red-necked Phalarope ? have also declined, the development of mire birds appears particularly worrisome.

Mire birds

The majority of the 12 species included in the indicator breed in open mires or semi-open pine mires. The two exceptions are Rustic Bunting, which prefers wooded spruce-mires and edges of pine mires, and Reed Bunting, which lives in a number of different wet-floored habitats. In addition to mires, several mire birds can be found in other open habitats. The dominating species of fens and pine mires ? Meadow Pipit and Yellow Wagtail ? breed also in shore meadows and arable fields, yet the majority of their populations breed in mire habitats. The distribution of Common Snipe and Reed Bunting is centered in mires in northern Finland, but in the southern parts of the country are associated more clearly with other wetlands.

Off all mire birds, Ruff has declined most steeply. Its populations fell on average by 5.3% per year during 1981?2006. The species has practically disappeared from the southern half of the country and no Ruffs were observed there in transect counts in 2007. The population of Wood Sandpiper has also declined steeply. The decline of these species is most likely due to the draining of mires. Whereas Wood Sandpiper migrates to sub-Saharan Africa, Ruff over-winters mainly in southern Europe and North Africa.

In addition to Wood Sandpiper, the list of declining long-distance migrants includes Yellow Wagtail and Rustic Bunting. Especially Rustic Bunting, one of the few Finnish species migrating to southeastern Asia, has declined steeply, approximately 3.5% per year.

Of the species included in the mire bird indicator Meadow Pipit, Golden Plover and Whimbrell can also be found on alpine heaths. The populations of these species have fluctuated greatly without any clear trend. The breeding population of Lapland Bunting is concentrated in alpine mires and moist alpine heaths to the extent that the species should be included among alpine birds if there was enough data of alpine birds to base an indicator on.

Only one species included in the indicator has become clearly more abundant. The breeding population of Common Crane more than doubled during the past two decades. Common Crane over-winters in the wetland and deltas of southern Europe. The increase of the species may be explained by reduced winter mortality. On the other hand, the large-scale feeding with cereals during spring migrartion in southern Sweden and the species colonisation of other habitats than mires may also count for the growing population.