There are good reasons to listen out for drumming in our boreal and temperate forests, because the number of woodpeckers tells us something about the health of forest ecosystems.
One February day, over 30 years ago, I saw a white-backed woodpecker in real life for the first, and so far only time. It was perched high up in a tree. Its rapid, drum-like call lasted up to two seconds. Every now and then it pecked at the trunk. If it had been in Norway or the Baltic States, it might not have seemed so remarkable. But this was in Sweden, where forestry, with its clear-cutting and spruce plantations, had hit the species hard. There weren’t many white-backed woodpeckers left.
Naturally I had heard drumming in the forest and pecking from trees before, usually from the great spotted woodpecker, a relative of the white-backed. Drumming and pecking sounds are intimately associated with woodpeckers and can be heard in many parts of the world. There are around 240 species in the woodpecker family, Picidae, of which around 210 are in the subfamily Picinae – the true woodpeckers. Tropical forests harbour most species, but woodpeckers are found all the way up in the northern taiga. They have strong beaks that are used for drumming, pecking out nest holes and foraging. Many species peck holes in tree trunks and then use their long tongues to extract insects and larvae. Drumming is the “call” that woodpeckers use to mark their territory and attract a nesting partner.
There are good reasons to listen out for drumming in our boreal and temperate forests. Not just for the sake of woodpeckers, but because the number of woodpeckers tells us something about the health of other species. This is because many woodpeckers are sensitive to changes in the environment, especially because they depend on trees, often dead or dying trees. Woodpeckers are known as the construction workers of the forest. They create nests for other species and are therefore keystone species. These species have a disproportionate impact on an ecosystem in relation to their abundance or biomass.
Ecosystem engineers are keystone species that create or influence the habitats of other species. Woodpeckers peck out their own nests and thus act as ecosystem engineers. Once they have finished nesting and abandoned their holes, other species move in or use them for roosting. In northern Europe, for example, the black woodpecker’s nest hole can be reused by goosander, smew, goldeneye, stock dove, owls, jackdaw, starling, pine marten, red squirrel and bats (1). In the coniferous forests of western North America, 20 to 30 similar bird and mammal species have been reported to use nest holes or other cavities made by the pileated woodpecker (2). Examples include several owl species, the American marten, fisher bat and silver-haired bat.
Woodpeckers build fewer holes in intensively managed forests. This has been shown by a study based on inventories carried out over a period of 37 years (1986–2022) in 56 forest stands in southern Finland (3). The spruce-dominated forests consisted of coniferous and mixed forests. The nests were made by six species of woodpecker and two species of tit. The woodpecker species were black woodpecker (Dryocopus martius), great spotted woodpecker (Dendrocopos major), lesser spotted woodpecker (D. minor), white-backed woodpecker (D. leucotos), three-toed woodpecker (Picoides tridactylus) and grey-headed woodpecker (Picus canus).
The forest was divided into three groups: managed forest (based on clear-cutting, planting and repeated thinning), natural forest (largely protected forest with no signs of having been clear-cut and basically unmanaged since the early 1950s) and semi-natural forest (where there was some diversity and some natural values).
The annual median number of new nest holes made by all woodpecker species per square kilometre was 5.7 in natural forests, 4.3 in semi-natural forests and only 1.5 in managed forests. According to the researchers involved in the study, the fact that the value was also fairly high in the semi-natural forest indicates that nest hole production recovers relatively quickly when the intensity of forestry is reduced.
The great spotted woodpecker accounted for 72–78 percent of nest holes in the three forest types. According to the researchers this is because it is both the most common woodpecker species in Eurasian boreal forests and so efficient at creating nest holes, making nests in both coniferous and deciduous trees and in healthy, weakened and dead trees. However, this species also created significantly fewer nests per square kilometre in managed forests than in natural forests.
Several previous studies have shown that the great spotted woodpecker often makes holes in living but weakened trees, and in dead or damaged parts of otherwise healthy trees. There are probably fewer of these trees in intensively managed forests. In addition, there are probably more insects to feed on in natural forests, which could be equally as significant as the presence of suitable cavity trees.
The black woodpecker also usually chose living, but weakened or damaged, trees for its nests. The nests of the other four species, which were less common, were mainly in dead or dying trees.
The study also showed that woodpeckers created holes in deciduous trees more often than in conifers. It is already known that aspen (Populus tremula) is an important hole tree for woodpeckers in boreal forests. This was also confirmed in this study, as 45–55 percent of new holes in the three forest types were in aspens.
As constructors of nest holes, woodpeckers are thus keystone species. This is a well-established concept used in species conservation. Woodpeckers fit into several such concepts. They can be bioindicators (indicator species), umbrella species and flagship species. The concepts overlap to some extent, but used correctly they can facilitate conservation work.
Flagship species are popular or well-known species that are used to generate public opinion or raise funds for conservation work. Many people recognise and admire both woodpeckers and their drumming.
Bioindicators are species whose condition reflects the state of a particular environment. Woodpeckers can be indicators of deciduous forest environments with high biodiversity. For example, the white-backed woodpecker is an indicator species for forest environments with abundant dead hardwood.
Umbrella species are species with particularly demanding habitat requirements. Protecting umbrella species also helps to protect other species with similar requirements. The white-backed woodpecker is the specialist among specialists. Its diet consists largely of insects that live in hardwood and bark, especially beetle larvae. This is why it needs a plentiful and continuous supply of insect-infested, dead or dying deciduous trees. Because such environments are important for several threatened species, the white-backed is also an umbrella species. In a couple of the historically well-recognised nesting areas of white-backed woodpecker in Sweden, about 200 red-listed species have been found (4).
The reason I saw a white-backed woodpecker in the early 1990s was because I was writing an article about a new project to conserve the species: the White-backed Woodpecker Project, managed by the Swedish Society for Nature Conservation along with several other organisations. I had been invited to accompany project members to the most recently discovered site in the country. The year before, a nest had been found there, but now only the drumming of this single female was heard. That was a bad sign.
Today, the species is mainly found in three regions of Sweden, and the area where I saw the white-backed is not one of them.
White-backed woodpeckers are found in a belt from Scandinavia and Eastern Europe in the west, to Japan and the Kamchatka Peninsula in the east. In much of Europe, only small, scattered populations remain. Viable populations are found in eastern Poland, the Baltic States, western Norway and Belarus.
In the 1990s the white-backed was just as endangered in Finland as it was in Sweden, with perhaps 10 pairs in the whole country. But in the latest Finnish Red List, published in 2019, the species has jumped up two categories, from critically endangered to vulnerable. It is now estimated that there are more than 300 breeding pairs in the country. The recovery is due to active measures, such as protecting forests, removing spruce and ensuring that there is dead hardwood in areas where the white-backed woodpeckers live.
However, according to the Finnish Forest Agency, which manages state-owned land in Finland, even more forests need to be protected to secure enough suitable nesting sites (5).
In Sweden, the species is still red-listed as critically endangered. In 2023, some 60 white-backed woodpeckers, including 20 pairs and 11 confirmed nests, were observed in the country (6). The figures are described as both encouraging and worrying. On one hand, this is the best result in the three-decade history of the White-backed Woodpecker Project, but on the other, it is a long way from the 250 individuals which, according to the project, set the lower limit for a viable population.
In addition to protecting and restoring the species’ habitats, the project now also works on releasing young birds raised for breeding. Influencing forest policy is also a priority. This is not an easy task.
For example, Sweden, which has a large forest industry that has strong lobbying power, made concerted efforts to block the EU Nature Restoration Law and voted against it when it was finally approved by the Environment Council on 17 June 2024.
Clear-cutting of deciduous forests, thinning and other felling of deciduous trees is a constant threat to the white-backed woodpecker. Lack of regeneration of deciduous forests, especially aspen and goat willow (Salix caprea), in the areas where the white-backed woodpecker is found is also a major problem. Spruce is taking over and the numerous deer and moose graze on deciduous saplings.
If the species is to survive in the long term, larger and better connected areas with a high proportion of deciduous trees and dead wood are ultimately needed.
Karin Bergqvist
(Karin Berqvist is a science writer/journalist from Sweden)
References
1. SLU Artdatabanken. https://artfakta.se/taxa/Dryocopus-martius-100049/information
2 Aubry KB, et al. (2002) The Pileated Woodpecker as a Keystone Habitat Modifier in the Pacific Northwest. USDA Forest Service, PNW Research Station, Olympia, WA. https://www.fs.fed.us/psw/publications/documents/gtr-181/023_AubryRaley.pdf
3 Pakkala T, et al. The intensity of forest management affects the nest cavity production of woodpeckers and tits in mature boreal forests. Eur. J. Forest Res. 143, 617–634 (2024). https://doi.org/10.1007/s10342-023-01645-x
4. Action programme for the white-backed woodpecker 2017–2021. Swedish Environmental Protection Agency Report 6770; May 2017. https://www.naturvardsverket.se/4a6920/globalassets/media/publikationer-...
5. Metsähallitus. https://www.metsa.fi/sv/natur-och-kulturarv/skydd-av-arter/vitryggig-hac...
6. Swedish Society for Nature Conservation. https://www.naturskyddsforeningen.se/artiklar/projekt-vitryggig-hackspett/
