Whooper swans don’t out-graze wigeons

A few decades ago the whoopers swan (Cygnus cygnus) was an endangered and rare species in Finland. It only bred in remote lakes and people rarely saw them. The population increase of whooper swans after protection is one of the success stories in Finnish nature conservation. Nowadays the swans can be heard gaggling all around Finland. The whooper swan is a large bird, and it thus consumes a lot of vegetation. Water horsetail (Equisetum fluviatile) is one of its favourites.

The whooper swan population has increased greatly, and their gaggling can be heard widely in Finland.

Certain other species also prefer water horsetails. For example, wigeon (Mareca penelope) broods forage within the horsetail growths searching for emerging invertebrates. A study published earlier this year showed that the water horsetail is disappearing from Finnish and Swedish lakes. The reasons for this pattern are unknown, but one possible explanation could be increased grazing pressure. Whooper swans effectively utilize horsetails, and swan grazing was therefore suspected to be influencing the disappearance of the horsetail. Wigeon populations have concurrently shown a worrying decrease.

A recently published study conducted of 60 Finnish and Swedish lakes utilized vegetation and waterbird data gathered in the early 1990s and in 2016. The study area widely covers the boreal, reaching from southern Sweden to Finnish Lapland. The whooper swan population increased strongly during the study period. Researchers studied whether whooper swans’ grazing on water horsetail is causing the negative trend in the wigeon population. Pair counts were used to indicate waterbird communities, and thus any changes caused during the brood time were not shown.

Whooper swans are grazers that have to consume a great deal of vegetation to survive.

The study showed that whooper swans strongly preferred lakes with horsetails during the 1990s, but this connections is not seen anymore. While the number of swan-occupied lakes has increased, the number of horsetail lakes has decreased dramatically. However, it appears that swans and disappearing horsetails do not associate, because the horsetail has also been from lakes where swans don’t occur. The horsetail has increased in some swan-occupied lakes.

The number of lakes used by wigeon has decreased, but swans are apparently not causing this. Wigeon loss has not been stronger on lakes occupied by swans. Quite the opposite, as wigeons and swans appear to positively correlate. Even though wigeons prefer horsetail lakes, their disappearance is not associated with the horsetail loss occurring in the study lakes, which suggests that wigeons can also utilize other lake types. On the other hand, the researchers note that this study  did not considered the critical brood time, when the foraging opportunities among the horsetail growths are especially important. Thus it may still be possible that wigeons are affected by horsetail loss, but this effect only appears during the brood time.

Read more:

Pöysä et al. 2017. Recovering Whooper Swans do not cause a decline in Eurasian Wigeon via their grazing impact on habitat. Journal of Ornithology.

Pöysä et al. 2017. Habitat associations and habitat change: seeking explanation for population decline in breeding Eurasian wigeon Anas penelope. Hydrobiologia.

Blog text: Vanishing wigeons and fading horsetails


Curious Finnish fireman rings 16 000 goldeneyes and Danish farmer rings 12 000 starlings – the most amazing examples of citizen science


Pentti Runko ringing a small goldeneye duckling.

While scientist struggle with short-term funding periods, the curiosity for nature that the general public shows, can unearth mechanisms that can only be found with long-term datasets. The persistent and systematic observations made by nature enthusts enables research about climate change or life history traits over several generations. Both are issues that require long-term research – and a lot of time and effort. Below are some examples of remarkable work done by citizen scientists curious about nature.

16 000 ringed goldeneyes have passed through the hands of a Finnish fireman

Finnish fireman Pentti Runko has collected systematic data of goldeneyes for several scientific studies. After starting his work in 1984, by 2017 Runko has ringed an amazing 16 000 goldeneyes and checked several hundreds of nest boxes every year.

In a recently published study, the authors utilized data concerning 14 000 of these goldeneyes ringed by Runko between the years 1984-2014. Among these goldeneyes were 141 females that were ringed as ducklings and recaptured later in the area. Based on these data it was possible to follow the recruit females’ lives from hatching to breeding. Thus the early life circumstances of these females are known, and the circumstances can be used to study their effects later on in life. In some cases early life circumstances have severe results on subsequent life, for example on breeding performance (duckling video).

Goldeneyes lay eggs in the nest boxes (video), which Runko checks for eggs several time during the season, to evaluate the hatching dates (video), to catch females and to ring ducklings.

The study was able to show deviations between individuals during the first breeding years and how circumstances during early life affected the breeding statistics of these females. Most females began breeding at the age of 2, but 44% delayed the start of breeding. Winter severity of the first two years affected the timing of breeding, but did not affect which year the females began breeding. As a conclusion, it appears that certain traits buffer the effects that the severity of the first weeks have, so the breeding parameters of females are not affected.  The research also showed that first-time breeders tend to begin breeding later than the yearly specific averages.

After ringing ducklings get back to the nest box.

The authors of another study used a set of 405 females and their offspring’s ringed by Runko, and found that the females’ condition matters when it comes to breeding success. Older, early-nesting females with good body condition and larger broods were able to produce more female recruits for the local population. The later the females bred, the less recruits they produced. The study also showed that females tend to adjust their breeding according to the ice-out dates of lakes. However, differences were observed between the flexibility of the females. Because early-breeding goldeneyes succeed better, the authors conclude that selection favours early-breeding individuals.

The lives and breeding habits of goldeneye females are closely followed at Maaninka (video).

Climate change effects can also be observed from goldeneye phenology. Runko showed that during the last 30 years goldeneyes have advanced their egg-laying dates by 12 days.

45 years of starling surveys in a farmer’s backyard reveal climate warming

Starlings are becoming scarce in Europe.

The Danish Ornithological Society Journal recently published a study that utilized data gathered by a Danish farmer, who ringed starlings for 45 years. Dairy farmer Peder V. Thellesen ringed ca. 12 000 starlings nesting in 27 nest boxes, and measured their phenology systematically. The data showed that during the study period starlings advanced their egg-laying dates by more than 9 days. This advance was observed in both first and second clutches. The result reflects the increase in April temperatures. Another important observation was that while no change was observed in clutch size and hatching rate, nest box occupancy has fallen dramatically in recent years. Starlings used to be common in Europe, but now they have decreased widely in Europe, also in Denmark. Changes in agricultural land use, especially decreased cattle grazing, are suspected as one example affecting starling populations. Loss of cattle-grazed land means less insect-rich foraging lands for the birds.


Read more:

Fox, T. and Heldbjerg, H. 2017. Ornithology: Danish dairy farmer delivers data coup. Nature.

Pöysä, H., Clark, R. G., Paasivaara, A. and Runko, P. 2017. Do environmental conditions experienced in early life affect recruitment age and performance at first breeding in common goldeneye females? Journal of Avian Biology.

Clark, R. G., Pöysä, H., Runko, P. and Paasivaara, A. 2014. Spring phenology and timing of breeding in short-distance migrant birds: phenotypic responses and offspring recruitment patterns in common goldeneyes. Journal of Avian Biology.

Kari S. Maattinen Youtube videos about goldeneyes

Thellesen, P.V. Common Starling Sturnus vulgaris clutch size, brood size and timing of breeding during 1971-2015 in Southwest Jutland, Denmark. The Danish Ornithological Society Journal.

YLE 2016: Lintuharrastaja on uhrannut kevätlomansa telkänpoikasille jo 30 vuoden ajan – “Se voisi olla Suomen kansallislintu”. In Finnish.

YLE 2013: Linnut pesivät nyt viikkoja aikaisemmin kuin 1980-luvulla


Four reasons why beaver wetlands are paradise for pin lichens

Beaver activity enhances the occurrence and diversity of pin lichens (Caliciales). Both the number of species and individuals is much higher in beaver-created wetlands than in other types of boreal forest landscapes. There are four reasons behind this:

1. High amounts of deadwood. Pin lichens grow on both living trees and deadwood. Decorticated deadwood in particular is preferred by pin lichens. Beaver-induced flooding kills trees in the riparian zone and produces high amounts of decorticated snags.

Pin lichen on decorticated stump. © Mia Vehkaoja

2. Diversity of deadwood types. Beaver activity produces snags, logs and stumps. Snags are created by the flood, whereas logs and stumps are also produced by beaver gnawing. The diversity of deadwood tree species is also wide, containing both deciduous and coniferous tree species. The diversity of deadwood types maintains a high diversity of pin lichen species.

3. High humidity conditions. High humidity conditions are favorable for many pin lichen species. Old-growth forests are usually the only places in the boreal forest belt that contain high humidity conditions. There the shading of trees creates a beneficial microclimate for pin lichens. Lighting, on the other hand, becomes a limiting factor for pin lichens in old-growth forests. Most snags in beaver wetlands stand in water, where steady and continuously humid conditions are maintained on the deadwood surface.

Snags produced by a beaver flood in Evo (southern Finland). © Mia Vehkaoja

4. Sufficient lighting conditions. Because most of the deadwood in beaver wetlands stands in water, it is concurrently in a very open and sunny environment. Many boreal pin lichens are believed to be cheimophotophytic (cheimoon=winter), meaning that they are able to maintain photosynthesis also during winter at very low temperatures. The algae member of pin lichens requires enough light for photosynthesis. Open beaver wetlands make photosynthesis possible for pin lichens during both summer and winter. Snow also enhances light availability during winter.

More information: Vehkaoja, M., Nummi, P., Rikkinen, J. 2016: Beavers promote calicioid diversity in boreal forest landscapes. Biodiversity and Conservation. 26 (3): 579-591.


Vanishing wigeons and fading horsetails

Over 20 years ago Finnish and Swedish duck researchers began the “Northern Project” and conducted vegetation measurements on 60 Finnish and Swedish lakes while also counting their duck populations. The study lakes were located from southern Sweden and Finland to Lapland in both countries. Researchers found that the water horsetail (Equisetum fluviatile) grew abundantly on many of the study lakes. Breeding Eurasian wigeons (Anas penelope) were also abundant according to the study.

The water horsetail prefers eutrophic lakes and wetlands. Horsetails are an ancient plant group that has existed for over 100 million years. They are thus living fossils.

Wigeons also utilize eutrophic lakes during the breeding season. Adults are vegetarians, but wigeon ducklings also consume invertebrates, a common trait in young birds.

Wigeon brood foraging within water horsetails at Lofoten. © Sari Holopainen

Wigeon brood foraging within water horsetails at Lofoten. © Sari Holopainen

The vegetation mappings and duck surveys connected to the Northern Project were repeated in 2013–2014. The researchers wished to find reasons for the deep decline in breeding wigeon numbers. They observed that wigeons had disappeared from several lakes where they were found on 20 years ago. When the habitat use of wigeon pairs was studied, the pairs were observed to particularly prefer lakes with water horsetails. In Evo, southern Finland, the feeding habitats of wigeon broods were followed over a period of 20 years. Broods were found to forage significantly more often within water horsetails than in other vegetation.

Wigeons therefore prefer lakes with water horsetail present throughout their breeding season. However, the long-term research by the Northern Project has shown that water horsetail has declined and even disappeared from many lakes in Sweden and Finland: this is a large-scale phenomenon. The wigeon is suspected to suffer due to vanishing water horsetail populations. Also, Finnish pair surveys in addition to reproduction monitoring show negative trends for the wigeon.

Health water horsetail at Lofoten © Sari Holopainen

Health water horsetail at Lofoten © Sari Holopainen

The reasons behind diminishing water horsetail numbers are not known. Impact from alien species can be suspected locally. Glyceria maxima, an alien species in Finland, appears to be growing in areas were water horsetail has traditionally grown. Grazing by the muskrat (Ondatra zibethicus) could also be a reason, but the species does not occur in southern Sweden. The whooper swan (Cygnus cygnus) could be another potential grazer, and the species’ populations have rapidly increased during the last decades. But these species can only have local effects, which do no not apply to the whole study area. Researchers cannot exclude other possible explanations, for example diseases or changes in water ecosystems. Despite water horsetail having commonly existed in boreal lakes, their influence in the water ecosystem is poorly understood. This study suggests that the water horsetail has an important role, and its disappearance will be reflected in the food web.


Read more: Pöysä, H., Elmberg, J., Gunnarsson, G., Holopainen, S., Nummi, P. & Sjöberg, K. Habitat associations and habitat change: seeking explanation for population decline in breeding wigeon Anas penelope. Hydrobiologia.  


The beaver – our wetland rescuer

The beavers (Castor canadensis and Castor fiber) have recovered from near extinction, and come to the rescue of wetland biodiversity. Two major processes drive boreal wetland loss: the near extinction of beavers, and extensive draining (if we exclude the effects of the ever-expanding human population). Beaver dams have produced over 500 square kilometers of wetlands in Europe during the past 70 years.


The wetland creation of beavers begins with the flood. As floodwaters rise into the surrounding forest, soil and vegetation are washed into the water system. The amount of organic carbon increases in the wetland during the first three impoundment years, after which they gradually begin reverting back to initial levels. The increase in organic carbon facilitates the entire wetland food web in stages, beginning with plankton and invertebrates, and ending in frogs, birds and mammals.

The previous shoreline is very evident from an aerial photograph. Also the beaver flooded area shows clearly. © Antti Nykänen

The previous shoreline is very evident from an aerial photograph. Also the beaver flooded area shows clearly. © Antti Nykänen

Beaver-created wetlands truly become frog paradises. The wide shallow water area creates suitable spawning and rearing places. The shallow water warms up rapidly, and accelerates hatching and tadpole development. Beaver-created wetlands also ensure ample nutrition. The organic carbon increase raises the amounts of tadpole nutrition (plankton and protozoans) in the wetland, along with the nutriment of adult frogs (invertebrates). Furthermore, the abundant vegetation creates hiding places against predators for both tadpoles and adult frogs.

Beaver-created wetlands are perfect rearing places for frogs. The warm water accelerates hatching and the abundant aquatic vegetation gives cover against predators. © Mia Vehkaoja

Beaver-created wetlands are perfect rearing places for frogs. The warm water accelerates hatching and the abundant aquatic vegetation gives cover against predators. © Mia Vehkaoja

The flood and beaver foraging kill trees in the riparian zone. Deadwood is currently considered a vanishing resource. Finnish forests have an average 10 cubic meters of deadwood per hectare, whereas beavers produce over seven times more of the substrate into a landscape. Beaver-produced deadwood is additionally very versatile. Wind, fire and other natural disturbances mainly create two types of deadwood: coarse snags and downed logs. Beavers, on the other hand, produce both snags and downed logs of varying width, along with moderately rare deciduous deadwood. The more diverse the deadwood assortment is, the richer the deadwood-dependent species composition that develops in the landscape.

Beaver-created wetlands produce  especially standing deadwood. © Mia Vehkaoja

Beaver-created wetlands produce especially standing deadwood. © Mia Vehkaoja

Deadwood-dependent species are one of the most endangered species groups in the world. The group includes e.g. lichens, beetles and fungi. Currently there are 400 000 to a million deadwood-dependent species in the world. Over 7000 of these inhabit Finland. Pin lichens are lichens that often prefer snags as their living environment. Beaver actions produce large amounts of snags, which lead to diverse pin lichen communities. Snags standing in water provide suitable living conditions for pin lichens; a constant supply of water is available from the moist wood, and the supply of light is additionally limitless in the open and sunny beaver wetlands.


The return of beavers has helped the survival of many wetland and deadwood-associated species in Finland, Europe and North America. Only 1000 beavers inhabited Europe at the beginning of the 20th century. Now over a million beavers live in Europe. I argue that this increase has been a crucial factor benefitting the survival and recovery of wetland biodiversity. Finland and the other EU member states still have plenty of work to do to achieve the goals of the EU Water Framework Directive. Both the chemical conditions and the biodiversity of wetlands / inland waters affect the biological condition and quality of wetlands.


The whole research published here


Pin lichens — the tiny color blots on deadwood

Have you ever entered a forest and seen a person hugging a tree, peering up along the trunk? From this day onwards you can breathe freely again, because you have just encountered a pin lichen biologist at work, and not some bizarre tree-hugging ritual.

Pin lichen biologist peering up along the trunk. © Stella Thompson

Pin lichen biologist peering up along the trunk. © Stella Thompson

Pin lichens, or more formally known as Calicioids, are a diverse and monophyletic lichen group, which usually inhabits deadwood. As their name suggests, they resemble pins. They are tiny, approximately between one millimeter and five centimeters in size. The best way to observe them is to peer up along the trunk of a tree. The spores accumulate into a mazaedium (a cup-shaped part of the fungi), from which they can cling onto the hairs and feathers of animals, or passively disperse otherwise. The spores can be recognized as soot-like dust on your fingers.

Pin lichens growing on deadwood. This species Mycocalicium subtile can be identified with often paler infested area than the surrounding wood. © Mia Vehkaoja

Pin lichens growing on deadwood. This species Mycocalicium subtile can be identified with often paler infested area than the surrounding wood. © Mia Vehkaoja

Although it is relative easy to observe pin lichens with the bare eye, species identification is usually conducted using a loupe or microscope. Further observation opens an entire new world of colors. The algae parts of many pin lichen species are brightly colored in yellow, green, or red. On other species, the stalk of the fungal part forming the actual pin structure can also be quite colorful: white, green, yellow, or brown.

Rust-stained pin lichen (Chaenotheca ferruginea) thrives on conifers, and it is quite widely distributed in temperate to cool temperate areas of the Northern Hemisphere. © Mia Vehkaoja

Rust-stained pin lichen (Chaenotheca ferruginea) thrives on conifers, and it is quite widely distributed in temperate to cool temperate areas of the Northern Hemisphere. © Mia Vehkaoja

There are approximately 70 different pin lichen species in Finland, but unfortunately they are a very deficiently studied group. Some species are parasites. They sponge on e.g other pin lichen species or mosses. Even pin lichen fossils have been found within amber. Using these fossils we are able to model the tree structures of forests that grew over a million years ago. This tiny, yet fascinating, species group deserves to receive more attention. Furthermore, observing them is relatively easy, because they don’t move and make a run for it. All you need is a pair of sharp eyes.


4 reasons why vanishing deadwood is a great catastrophe

Deadwood amounts have dramatically declined all over the world. Here I present four reasons why deadwood is so important:

1. Deadwood remains in the forest for a long time
When wood decays, it transforms into carbon dioxide, water and minerals. These are exactly the materials that a living tree binds during photosynthesis. The complete degradation of a tree takes 50 to 100 years in northern regions. Deadwood therefore remains a part of the forest ecosystem for a long time, thus enabling the survival of species depending on deadwood as a substrate.

2. Deadwood is nutrition for fungi and invertebrates

Fungi are the main decomposers of deadwood, but bacteria and invertebrates also take part in the decaying processes. These organisms have special digestive compounds, enzymes, to cut the wooden structure into more easily digestible forms. This works in the same way as the enzymes in our own stomachs that cut the food we eat into more usable shape. Fungi can be divided into three main decomposer groups: white, brown and soft rot. White-rot fungi, e.g. Phellinus nigrolimitatus, lives mainly on deciduous wood, whereas brown-rot fungi, such as Coniophora olivacea, are mostly in charge of decomposing conifers. Beetles (Coleoptera), ants (Formicidae) and termites (Isoptera) are examples of invertebrates that use deadwood as a form of nutrition, but e.g. pin lichens (Calicioid) can also more or less decompose wood.

Pin lichens (Calicioids) grow on deadwood surface. © Mia Vehkaoja

Pin lichens (Calicioids) grow on deadwood surface. © Mia Vehkaoja

3. Deadwood is home for animal offspring
Deadwood is home for thousands of species. For some species deadwood can be an incubation place and a safe nest for newborn offspring. Several beetles and termites lay their eggs inside deadwood, where the hatching larvae are safe in their own chambers. As for Nematocera, Brachycera and Aculeata, the deadwood-decomposing fungi functions as a rearing place for larvae. In addition to invertebrates, birds, bats and flying squirrels (Pteromys volans) also use the holes in deadwood as nesting places. Furthermore woodpeckers (Picidae) as cavity nesters are a good indicator for deadwood abundance.

Several beetle species lay their eggs inside deadwood. © Mia Vehkaoja

Several beetle species lay their eggs inside deadwood. © Mia Vehkaoja

4. The disappearance of deadwood creates local extinctions at the very least
Nowadays deadwood is a dying natural resource. Forestry has decreased the amount of deadwood in Finnish forests by over 90%, concurrently causing the local extinctions of several species. Species that depend on deadwood throughout their entire lives are at greatest risk. Such species include the fungi Phellinus igniarius and the three-toed woodpecker (Picoides tridactylus).