All cavities are not equal

Come spring (late winter), the forests are bustling. Cavity-dwelling animals search for tree crevices and holes in which to lay their eggs and raise their offspring. Tree cavities provide a stable environment for successful nesting.

Wetland_Ecology_Group_University of Helsinki_tree cavity

Natural cavities are usually found in old wide trees, where the inner temperature of such cavities remains more stable than outside temperatures.

Only one problem remains. Cavities usually form in old or, at the least, decomposing trees, but forestry practices simplify forest cover composition. Fewer trees surpass forestry practice recommendation ages, so our forests have less large aging trees in which fungi can spread. More tree cavities are desperately needed. Nest boxes are our solution to this problem. The idea is simple: anyone can build a nest box and hang it on their own land (or somebody else’s with permission). This has helped boost the populations of certain cavity-nesters such as pied flycatchers (Ficedula hypoleuca) and great tits (Parus major).

It would be nice to think that we have solved the cavity problem, or that the problem will be solved if we raise the number of nest boxes to sufficient levels. But it’s not that simple. Several researchers have studied the functionality of nest boxes over the years. The microhabitats of tree cavities and nest boxes differ from each other in relation to temperature and moisture. Wroclaw University researchers were the most recent group to prove this distinction, but they also demonstrated that these functional differences drive the marsh tit (Poecile palustris) to choose natural cavities over nest boxes. Their study was conducted in two forests; the other had an unlimited number of tree cavities, while nest boxes were the only nesting option in the other forest. The marsh tits preferred natural cavities with thick walls buffering the holes from outside temperatures. And birds are not the only species that have been shown to prefer natural cavities, for example certain bats and the common brushtail possum (Trichosurus vulpecula) will settle in natural cavities due to their more stable microclimates.

Wetland-Ecology-Group_University of Helsinki_brushtail possum

The common brushtail possum is an Australian mammal that nests in tree cavities. Picture: Wikimedia Commons. https://upload.wikimedia.org/wikipedia/commons/b/b4/Brush_tail_possum_4-colour_corr.jpg. By user:benjamint444 modified by Tony Wills [GFDL]

Nest box temperatures in the Wroclaw study fluctuated significantly more than the inner temperatures of tree cavities. Nest box temperature also changed at the same rate as outside temperatures. Nest box temperatures can therefore rise to dangerous levels during the summer, to where chicks are at higher risk of dying from excessive heat compared to broods in tree cavities. During the winter, nest box temperatures drop to lower levels than cavity temperatures, decreasing the shelter effect that many small birds utilize to survive the harsh cold.

Nest boxes also average lower air moisture levels compared to natural cavities. This may hinder mold from growing in the nest boxes, but concurrently lower moisture may encourage wasps (Vespidae) and tree bumblebees (Bombus hypnorum) to settle in nest boxes, making them inaccessible for birds. Fleas (Siphonaptera) may also increase in dry and warm conditions, so the number of competitors and ectoparasites may increase.

Wetland_Ecology_Group_University of Helsinki_birch dead wood

Woodpeckers excavate cavities in decomposing trees and standing dead wood

To cap, nest boxes and natural cavities do not replace each other from a structural point of view and not all species will nest in boxes. The majority of nest boxes are so-called standard models, i.e. they are copies of each other in terms of dimensions and flight hole diameter. In real life, a standard model nest box is only accepted by a limited number of cavity dwellers. It is therefore imperative to conserve aging and decomposing trees, as their cavities are never of standard shape or size. If nothing else, decomposing trees in our yards should be conserved; trees can always be cut to a height that ensures they are of no danger to nearby buildings or people. Such standing dead wood is very rare in current heavily managed forests. With a standing birch dead wood tree it is even possible to attract the picky willow tit (Poecile montanus) to your yard.

The next best alternative is to ensure the structural heterogeneity of nest boxes, i.e. build boxes that are also suitable for species such as the common redstart (Phoenicurus phoenicurus), owls (Strigidae), treecreepers (Certhiasp.), and even certain mammals such as flying squirrels (Pteromys volans). This may require a little more trial and error, but it is the only way of maximizing the nesting alternatives in managed forests. Ideas for nest box designs abound online, Pinterest for example has a huge selection of box models. However, it is important to follow nest box construction instructions issued e.g. by the BTO and Audubon Society or these general safety instructions, to make sure that the boxes are as safe as possible for birds. Nest box positioning is also important; foliage has a protective effect, and the microhabitat of nest boxes positioned under foliage therefore remains more stable than in sun-exposed areas.

Wetland_Ecology_Group_Vehkaoja_Mia_blue tit and nest box

Blue tits often utilize nest boxes.

Adding insulating materials to nest boxes is one way of adding to the inventiveness of nest box construction. To mimic the microclimates of natural cavities, a team of Australian researchers recently compared nest boxes that had been fitted with three types of insulating or heat-reflecting materials. Nest box temperatures remained most stable around the clock in nest boxes insulated with polystyrene foam. The inner temperature of one polystyrene-fitted nest box was nearly six degrees Celsius less than outside temperatures. Nighttime inner temperatures were also higher in the polystyrene nest boxes compared to non-insulated boxes when a heat-producing pillow was placed in the insulated and non-insulated nest boxes, to mimic the effect of birds spending the night in the boxes. The Australian study showed insulation had a more significant effect on nest box temperatures than nest box placement in a shady or sunny location. However, for the environment and breathability, it is probably better to use some type of natural fiber insulation in nest boxes. Also, insulated nest boxes are not enough to fill the void created by the disappearance of natural tree cavities, as the study showed that the temperature fluctuation of even the polystyrene-fitted nest boxes was greater that of natural cavities.

P.S. It is currently trendy to set up cool or “beautiful” nest boxes without thinking about their safety at all. Not a good idea! For example, ceramic bird boxes are much worse insulators than wooden ones, and painted boxes should use lead-free paint. https://www.telegraph.co.uk/news/earth/wildlife/12165505/Novelty-nest-boxes-putting-garden-birds-at-risk-warns-RSPB.html

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The secret wildlife of golf courses

The cool morning air has strewn the lawn with small dewdrops. The green is bathed in flickering mist and shining dewdrops. Soon the green is filled with the sibilant sound of golf balls and walking golfers, but for a while, the course still belongs to someone else.

Water hazards of Hiekkaharju Golf in Vantaa (in the Helsinki metropolis area) provide suitable habitats for diverse species. Picture borrowed from http://www.hieg.fi

Keimola Golf, located in Vantaa (in the Helsinki metropolis area in Finland), is a true paradise for birds and amphibians. Whooper swan (Cygnus cygnus), common goldeneye (Bucephala clangula), and horned grebe (Podiceps auritus) pairs nest in the largest water hazard. In addition, the black woodpecker (Dryocopus martius) nests nearby. The number of horned grebes has declined worldwide, and the species is considered vulnerable in Finland. The Finnish population has decreased from 3000 to 6000 nesting pairs in the 1980s to the present 1200–1700 nesting pairs.

On the other hand, all Finnish amphibian species, except one, can be found living in one of the smallest water hazards of Keimola Golf. Only the Northern crested newt (Triturus cristatus) does not occur there. The Northern crested newt is critically endangered in Finland, and can only be found in a few places in eastern Finland. In spring, the common frog (Rana temporaria), the moor frog (Rana arvalis), and the common toad (Bufo bufo) croak vigorously. The smooth newt (Lissotriton vulgaris) does not croak, but mating males bring tropical colors into an otherwise brownish landscape.

Mating smooth newt males are springtime color spots in a wetland. ©Mia Vehkaoja

By Midsummer, golf courses are swarming. On dry land, golfers enjoy their sport in warm summer weather, while hatched ducklings and tadpoles are concurrently going through growth spurts around the water hazards. Golf courses provide lots of nutrition for ducklings and tadpoles. Water hazards, as most wetlands, are habitats for several invertebrates, such as mosquito (Culicidae), nematocera (Nematocera), and trichoptera larvae, as well as for phyto- and zooplankton. Amphibians prefer open and sunny wetlands because higher temperatures escalate tadpole development. Ducklings, on the other hand, prefer wetlands with luxuriant shoreline vegetation (for example club rushes and sedges). Vegetation provides cover against predation.

Luxuriant shoreline vegetation provides cover for ducklings against predation, whereas openness increases water temperature and escalates tadpole development. ©Mia Vehkaoja

Golf courses are oases for wetland-associated species, especially in urban environments, where most wetlands are isolated from each other. For numerous species, water hazards and golf greens offer nearly free access between wetlands and other habitats. Golf courses are currently not planned to consider nature and its needs. What if nature were taken into account during planning, with at least a 10% effort? Keimola Golf’s extraordinary biodiversity has arisen through chance. Waterfowl diversity is due to an island left in the middle of the largest water hazard. The island has some ten trees and bushes. The whooper swan and common goldeneye nest on this island.

Both national and international designers have planned Finnish golf courses. Keimola Golf was planned in Great Britain. More and more, architects plan golf courses by initially outlining the routes, after which the planning is continued on-site concurrently while the course is being constructed. This method enables taking nature into account during the planning process.

Architects could pay attention to small things that benefit animal and plant species when planning water hazards and groves. For example, bushes and shoreline vegetation could be left next to the shoreline that is not close to the green. This has been done at Keimola Golf. Paying attention to such small details does not even cause additional costs. Furthermore, most golfers enjoy the sport because they can be outside and “enjoy” nature. If nature were actually taken into account during planning, golfers could actually play their sport “in the wild”.

What do ducklings eat?

Ducklings grow rapidly. In just a couple of months, an egg becomes a bird with feathers that enable flying thousands of kilometres. Growing feathers requires a lot of protein. Where do ducklings get the protein?

Ducklings can reach their food using different methods.

If you have ever visited a wetland, you may have noticed a lot of invertebrates, for example mosquitoes and dragonflies. Many invertebrates flying around the wetlands actually lay their eggs in water. The larvae will develop in the water and emerge when ready to fly. Often these flying invertebrates rest on wetland vegetation. Swimming and flying invertebrates are duck food.

Mosquito larvae in various phases of their development. Larvae develop in water and emerge as flying invertebrates.

Wetlands are occupied by many kinds of aquatic invertebrates from small zooplankton to large beetles. They are all duck food, but ducks also help them disperse from one pond to another: invertebrates and their propagules can be carried over long distances in duck feathers or intestines.

What type of food a duck consumes depends on the duck species. Ducks are specialised to eat various types of nutrition, and for example the size of the lamellar (teeth like structures used for filtering or straining food) in the bills differs between species. Diving and dabbling ducks have diverging ways of reaching their food. Diving ducks, even their small ducklings, dive under water and can utilise swimming and benthic aquatic invertebrates.

Duck bill lamellar (tooth-like structure on the sides of a bill) density differs between species. Lamellar are used to sieve food.

 

Females should find good foraging spots for their broods. Broods can move long distances from the nesting site to find proper food patches. Most European ducks breed in the boreal zone, but many lakes lack enough invertebrate food for ducklings. Thus many of the lakes are empty of duck broods.

The common goldeneye (Bucephala clangula), a diving duck, is associated with boreal lakes with large numbers of free-swimming aquatic invertebrates (e.g. dytiscidae) and large emerging invertebrates (caddisflies and mayflies). Of these, mayfly larva live in the bottom of the wetlands.

Dytiscidae are diving beetles.

Of the dabbling ducks, the mallard (Anas platyrhynchos), common teal (A. crecca) and Eurasian wigeon (Mareca penelope) are sympatric species with a shared niche. However, the habitat use of their broods differ. While mallard broods prefer lakes with luxuriant vegetation and large emerging invertebrates, teal broods utilise lakes with smaller emerging invertebrates, such as flies (diptera). Flies are abundant especially in newly created wetlands and flowages, and teals are considered pioneering species.

Productive wetlands can be full of small invertebrates such as copepodas, cladocerans and isopodas.

Adult wigeons are vegetarians, and also appear to prefer lakes with luxuriant vegetation during the brood stage, but small flies are also important for them. Beavers are important for mallards and wigeons in the boreal landscape: lakes that typically lack luxuriant vegetation can establish large and shallow well-vegetated areas during the beaver flood. Thus beavers can provide habitat enhancement. Without them less lakes would be available in the boreal landscape for wigeons and mallards.

 

Read more:

Nummi, Paasivaara, Suhonen & Pöysä 2013: Wetland use by brood-rearing female ducks in a boreal forest landscape: the importance of food and habitat

Nummi & Holopainen 2014: Whole-community facilitation by beaver: ecosystem engineer increases waterbird diversity

Do ducks have teeth?

Beavers facilitate Teals at different scales

Wetland ecology group_University of Helsinki_Teal

Teal broods utilize beaver ponds.

Blog text by Petri Nummi, Eeva-Maria Suontakanen, Sari Holopainen and Veli-Matti Väänänen “Beavers facilitate Teals at different scales” is now available on the Ibis website.

There and back again – a mire’s tale

In a remote country lived a rich mire species community. But that was once upon a time, when Finland was a land of mires. Nowadays, only fragmented pieces are left in the southern region, while large natural mires can still be found in Lapland. Nevertheless, only one third of historical levels remain. Most mireswere dried due to farming and forestry. Ditches were dug to gather water from ca. 6 million hectares of mires. This affected the hydrology and further the ecology of these wet ecosystems. Several plant and animal species are adapted to mires, and have thus suffered from habitat loss and fragmentation. For example, forest grouse and bean geese (Anser fabalis) utilize mires during their breeding period. Due to ditching, mires stop producing their ecosystem services, because berry production and game bird populations (these are cultural and provisioning ecosystem services), decrease, and thus the recreational values of the areas lessen.

Wetland ecology group_University of Helsinki_Mire_Cloudberry

Cloudberry (Rubus chamaemorus) grows on mires and benefits from restoration activities.

Finland has about 10 million hectares of dried mires, more than half of which have been utilized by forestry. However, about a fifth of this area does not produce wood well enough for it to be profitable. After several centuries of mire destruction,  a change is now in the air. Finnish mires are being restored with increasing effort. For example, in 2017 Metsähallitus (the Park and Forest Service) began an EU-funded project called Hydrology LIFE. The project aims to safeguard not just mires, but also small water bodies and important bird lakes in 103 Natura 2000 areas. The project restores and protects mires.

Wetland ecology group_University of Helsinki_duck_mire_restoration_hydrology

Mire hydrology can be restored by blocking ditches.

Hydrology is the most important issue to consider when restoring a mire. Blocking ditches leads to changes in water balance, and eventually to active peat formation, which is basically the definition of a mire. After the ditches are blocked, water levels normally rise rapidly to correspond with the natural situation. However, actual peatland processes return at a much slower speed. Forest vegetation is slowly replaced by mire vegetation, starting from the ditches. The processes take a long time, so whether or not the original mire ecosystem returns is yet to be seen. It is also possible that we are actually just creating new mire types.

Wetland ecology group_University of Helsinki_Elimyssalo_mire_peatland_forest reindeer

Elimyssalo nature conservation area in Eastern Finland consists of various peatland types. The area is an important calving place for wild forest reindeer (Rangifer tarandus fennicus).

Helping forest grouse

Wetland ecology group_University of Helsinki_hazel grouse

Forest grouse utilize peatland-forest ecotones. The hazel grouse (Tetrastes bonasia) population in Finland has suffered from peatland loss.

Peatland-forest ecotones are key environments for forest grouse, but unfortunately these areas are becoming very rare. The willow ptarmigan (Lagopus lagopus) has suffered from mire fragmentation in Finland. Ptarmigan habitats are fragmented especially in Southern Finland, and thus there are small populations living far from each other. Luckily, local people are usually interested in peatland restoration that helps species such as the willow ptarmigan. Several good examples exist of how ptarmigans have accepted restored peatlands. The Finnish Association for Nature Conservation has a project “SuoMaa”, which began in 2016, and targets protecting and restoring taiga nature. One of the aims is to restore peatlands to support and enlarge a ptarmigan breeding peatland network and create connections between strong and threatened populations.

 

Read more

Hydrologia-Life

Suomen metsäkanalintukantojen hoitosuunnitelma

Restoration of peatlands, Luke

 

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

Increased geese populations occupy pastures and city lawns in Fennoscandia

Many geese populations in Fennoscandia are increasing rapidly, and geese have become more visible in human-inhabited landscapes. Currently geese utilize agricultural lands and even urban lawns. High geese brood densities have a significant impact on their environments due to increasing grazing pressure.

Greylag geese graze on pastures and hay lands, preferring short vegetation to high ones. Geese grazing also keeps vegetation short. Geese trimming a lawn in Reykjavik, the capital of Iceland.

Geese broods prefer pastures near shores

A newly published Swedish study revealed that greylag geese broods are rather picky when selecting farmland fields for grazing. The most used fields were pasturelands near water. Goslings preferred shorter vegetation, assumingly due to its higher quality and the open landscape views in case of predators. Grazing geese also keep the vegetation short.

Broods tend to prefer grazing areas near shores, from where they can easily reach the safety of water when threatened. Grazing geese broods are suggested to pose a fairly small risk of agricultural conflicts due to their preference for near-shore pastures (instead of crop fields for example). However, extremely high grazing pressure by geese can reduce plant biomass, thus affecting livestock grazing. In arctic areas, such as Greenland and Svalbard, geese grazing is observed to be the reason for decreased hay and decreased seed counts in soil.

In contrast to broods that prefer near-shore areas, non-breeding geese can cause conflicts with agriculture, due to their grazing in crop fields. Non-breeding birds that are able to fly can utilize areas further from water, and according to a Swedish study, they also graze also on crop and vegetable fields in addition to pastures. Large flocks preferred typically open and flat with no or few trees or shrubs.

The two differing patterns shown by broods and adults means that geese managers should consider the two behavioural strategies when planning geese management.

Barnacle geese grazing among Helsinki University research cattle. Breeding geese flocks have e.g. destroyed some the university’s research fields and caused high expenses.

City geese have found Helsinki’s shore lawns

The barnacle goose is a fairly new species in Helsinki. The species tends to breed in remote arctic areas, but after geese were released from the local zoo in the late 1980s, geese began breeding on the islands and islets of the Helsinki archipelago. The released geese are assumed to have returned to breed, and brought their offspring and other geese with them. Since then the goose population has been growing and occupying shore areas from the islands and mainland. Grazing geese are nowadays a visible element in the city of Helsinki, competing over space with citizens.

Geese densities are rather high on Helsinki shore lawns, where non-flying broods gather to graze. In August juvenile birds can move further from the shoreline to feed. The best seashore lawns tempt dozens of broods. In urban areas lawns are usually a nice buffet table for the geese: they typically prefer plant species used in lawns, and mowing sustains fresh vegetation. Compared to natural lawns, urban lawns can be better for broods.

This geese enclosure has very limited plant diversity, but Potentilla species not preferred by geese are flourishing.

 

However, geese grazing is affecting plant diversity by decreasing it. Few plant species tend to dominate in the grazed areas, while  the diversity and coverage of species is more balanced in areas with no geese grazing. Good quality lawns benefit broods, because they don’t need to move long distances while grazing. Geese population growth in the Helsinki area has been refracting after reaching ca. 1300 breeding pairs, and one reason is thought to be the limitation of good feeding habitats for broods. Geese already use almost all possible lawns in Helsinki. During dry summers with poor lawn growth geese may be greatly food-limited, which is reflected in the population size. Thus it seems that the barnacle goose population in Helsinki has reached its carrying capacity.

In the Helsinki archipelago barnacle geese nest commonly on rocky islands and islets, where food availability is highly limited. Well-managed city lawns are thus tempting for the broods.

Methods for preventing geese grazing were measured in Helsinki. One possibility is to use plant species that geese don’t prefer, instead of the current species mix that seems to be especially tempting for geese. Another possibility is to fence off areas were geese are not welcome. Goslings cannot fly, and thus cannot reach fenced areas, and they also avoid areas where they have limited visual contact to water.

 

Read more:

Olsson et al. 2017: Field preference of Greylag geese Anser anser during the breeding season. European Journal of Wildlife Research

Barnacle goose population declined in the Helsinki Metropolitan Area. 2016. Environment.fi

Barnacle goose population remains unchanged despite a good breeding year. 2013. Environment.fi

Niemi et al. 2007: Valkoposkihanhi pääkaupunkiseudulla. Suomen Ympäristö.

Valkoposkihanhien seuranta. 2016. Ymparisto.fi.