The Significance of Woodpeckers in Forest Ecosystems

Ann. Zool. Fennici 43: 82–85 ISSN 0003-455X Helsinki 28 April 2006 © Finnish Zoological and Botanical Publishing Board 2006

Why study woodpeckers? The significance of woodpeckers in forest ecosystems

Raimo Virkkala

Finnish Environment Institute, Research Department, Research Programme for Biodiversity, P.O. Box 140, FI-00251 Helsinki, Finland

On the basis of an opening address given at the 6th International Woodpecker Sympo- sium in Mekrijärvi, Finland, on 27–30 August 2005, and papers presented there, a brief introductory review on population biology and habitat requirements of woodpeck- ers, woodpeckers in changing environments, and woodpeckers as indicators of forest diversity is presented.

There are over 210 woodpecker species (Dick- wood for foraging and excavating cavities, and inson 2003). The hotspots of woodpecker spe- many woodpecker species prefer specific forest cies richness are in south-east Asia, in South habitats. By excluding dead wood and habitats and Central America, and in equatorial Africa preferred by woodpeckers, modern forestry cre- (Mikusiński 2006), but woodpeckers also play ates unsuitable habitats for many woodpecker essential roles in bird communities in northern species and thus causes their decline (Virkkala et latitudes. al. 1993, Angelstam & Mikusiński 1994, Czeszc- Studying the ecological impact of wood- zewik & Walankiewicz 2006). For example, in peckers is important for several reasons. It is Finland there are seven breeding woodpecker well-known that woodpeckers provide cavities species, five of which are threatened (red-listed) for secondary cavity-nesters. Cavity nesters form due, in large part, to forestry practices (Rassi et cavity-webs (Martin & Eadie 1999, Martin et al. al. 2001). 2004), which consist of primary cavity-nesting Because of their susceptibility to habitat species, weak cavity nesters, secondary cavity changes, woodpeckers can be used as general nesters, and bark nesters. Certain woodpeckers indicators of forest biodiversity and specific indi- within the nest-web can be regarded as key- cators of forest birds (Mikusiński et al. 2001). stone species, such as the black woodpecker For example, the white-backed woodpecker (Dryocopus martius) that provides the largest (Dendrocopos leucotos) is regarded in Finland cavities in Europe (Johnsson 1993), and both as an umbrella species associated with several the northern flicker (Colaptes auratus) and great threatened beetle species, because both prefer spotted (Dendrocopos major) woodpeckers that a similar resource — decaying wood in mature provide the majority of cavities for secondary deciduous forest (Martikainen et al. 1998). In cavity nesters in NW North America (Martin et general, woodpeckers are bio-indicators of natu- al. 2004) and Europe, respectively. ral forests and can be used, for example, in Woodpeckers are highly susceptible to habi- forest restoration operations. Most woodpecker tat changes. One important reason for this is that species are resident, with adults showing high most woodpecker species are dependent on dead nest-site fidelity (for the three-toed woodpecker ANN. ZOOL. FENNICI Vol. 43 • Why study woodpeckers? 83

Picoides tridactylus, see Pechacek 2006), which mate change, which may cause a further decline also make woodpeckers accurate indicators of of this species. The three-toed woodpecker has forest quality. a northeasterly distribution in Europe, and it In addition to providing cavities for second- prefers old-growth forests with plenty of dead ary cavity nesters, woodpeckers interact with coniferous wood. Breeding individuals may not other bird species. The increase of the great be able to adjust their breeding date to the local spotted woodpecker in Britain is, at least partly, food supply in particularly warm springs when connected to the decrease of the starling (Sturnus their preferred prey (cerambycid beetle larvae) vulgaris). The great spotted woodpecker used to develops earlier than normal (Fayt 2006). suffer from nest-site interference by starlings, but A recent review of regulation of spruce bark its breeding success has clearly increased after the beetles by woodpeckers shows that prey mortal- decrease of the starling (Smith 2006). In a south- ity caused by woodpeckers can reach 98% (Fayt ern Finnish forest landscape the occurrence of the et al. 2005). Accordingly bark beetle populations goshawk (Accipiter gentilis) was positively, and may be regulated by woodpeckers, such as the that of the great spotted woodpecker, negatively three-toed woodpecker, during an epidemic. Pre- associated with the density and breeding suc- dation by woodpeckers also shows that wood- cess of the three-toed woodpecker (Pakkala et al. peckers may decrease bark beetle damage in 2006). The impact of the goshawk may have to managed boreal forest stands. This brings forth do with a decrease in mammalian predation on an interesting conclusion: to protect managed three-toed woodpecker nests. forest from pests, old-growth forests preferred Woodpeckers also interact with many other by, for example three-toed woodpeckers, should organisms, such as wood-rotting fungi. The suc- be preserved in sufficient quantities. Thus, there cess of woodpeckers in excavating nests or roost may not be a conflict between logging and con- sites depends on fungi having rotted the wood. servation of forests: to grow timber, natural for- Interestingly, it is possible that wood-rotting ests should also be preserved. fungi, such as polyporous fungi, may depend Even within natural forests, several wood- on woodpeckers as vectors (Jackson & Jackson pecker species are habitat specialists. Conse- 2004). Accordingly, all data suggest that wood- quently, resources and habitat characteristics peckers are disproportionately important to their used by the woodpeckers can be quantified and ecosystems. the significance of habitat analysed in a reason- As such, woodpeckers are important model able way. Such a habitat study includes the species in conservation biology. The red-cock- availability and use of a specific woodpecker’s aded woodpecker (Picoides borealis), which is preferred food, dead wood, tree species, habi- an endangered species in southeastern North tat patches, etc. (Hartwig et al. 2006, Huot & America, is commonly used in population via- Ibarzabal 2006, Ibarzabal & Desmeules 2006, bility analyses (e.g. Walters et al. 2002). The Kosiński 2006). significance of critical thresholds was studied Unfortunately, small habitat patches are not on the basis of habitat quantity and quality sufficient even for the most abundant European (Angelstam et al. 2003). Thresholds are values woodpecker, the great spotted woodpecker: off- of habitat quantity or quality below which a spe- spring production was lower in small as com- cies does not occur even when its preferred habi- pared with large forest patches in Poland (Maz- tat or resource still exists in small amounts. The gajski & Rejt 2006). This means that fragmenta- critical threshold for the proportion of suitable tion of forests had a negative effect on the most habitat needed by the white-backed woodpecker abundant and probably also least sensitive wood- in Europe was analysed by Carlson (2000). Dead pecker species in European managed forests (see wood thresholds were presented for the three- also Virkkala et al. 1994). toed woodpecker in Sweden and Switzerland Although the ecology of woodpeckers, (Bütler et al. 2004). such as habitat use and foraging patterns, have Fayt (2006) showed that the cold-adapted been studied, population data are much scarcer three-toed woodpecker may be susceptible to cli- (Pasinelli 2006, Wiebe 2006). Demographic data 84 Virkkala • ANN. ZOOL. FENNICI Vol. 43 on woodpeckers are currently accumulating, structure and variability of white-backed woodpecker (Dendrocopos leucotos) populations in northern Europe. however, partly resulting from the development — Hereditas 130: 291–299. of novel methods (e.g. Ibarzabal & Trembley Fayt, P. 2006: Reproductive decisions of boreal three-toed 2006). Genetic variability of woodpecker popu- woodpeckers (Picoides tridactylus) in a warming world: lations and genetic relationships among popula- from local responses to global population dynamics. tions are also being investigated using microsat- — Ann. Zool. Fennici 43: 118–130. ellite genetic markers (Ellegren et al. 1999). The Fayt, P., Machmer, M. M. & Steeger, C. 2005: Regulation of spruce bark beetles by woodpeckers — a literature development of new techniques, and their wide- review. — For. Ecol. Manage. 206: 1–14. spread use, is very important to complete our Fitzpatrick, J. W., Lammertink, M., Luneau, M. D. Jr., Gal- understanding of woodpeckers and their place in lagher, T. W., Harrison, B. R., Sparling, G. M., Rosen- the ecosystem. berg, K. V., Rohrbaugh, R. W., Swarthout, E. C. H., Woodpeckers are a common favorite amongst Wrege, P. H., Swarthout, S. B., Danzker, M. S., Charif, R. A., Barksdale, T. R., Remsen, J. V. Jr., Simon, S. D. the interested public, particularly when conser- & Zollner, D. 2005: Ivory-billed woodpecker (Campe- vation issues are raised. This point was well philus principalis) persists in continental North America. made by the international publicity received by — Science 308: 1460–1462. the rediscovery of the ivory-billed woodpecker Hartwig, C. L., Eastman, D. S. & Harestad, A. S. 2006: Char- (Campephilus principalis) in USA (Fitzpatrick acteristics of foraging sites and the use of structural ele- ments by the pileated woodpecker (Dryocopus pileatus) et al. 2005). Unfortunately, even though several on southeastern Vancouver Island, British Columbia, woodpeckers are regarded as charismatic species, Canada. — Ann. Zool. Fennici 43: 186–197. many of them are red-listed. While conservation Huot, M. & Ibarzabal, J. 2006: A comparison of the age-class is often of primary importance, the reasons for structure of black-backed woodpeckers found in recently studying woodpeckers go beyond this. Indeed, burned and unburned boreal coniferous forests in eastern Canada. — Ann. Zool. Fennici 43: 131–136. reasons for studying these animals include the Ibarzabal, J. & Desmeules, P. 2006: Black-backed wood- generation of basic scientific information, the pecker (Picoides arcticus) detectability in unburned and development of techniques extendible to other recently burned mature conifer forests in north-eastern systems, and possibly into the realm of bio-con- North America. — Ann. Zool. Fennici 43: 228–234. trol, with an associated economic benefit. Ibarzabal, J. & Tremblay, J. A. 2006: The hole saw method for accessing woodpecker nestlings during developmen- tal studies. — Ann. Zool. Fennici 43: 235–238. Jackson, J. A. & Jackson, B. J. S. 2004: Ecological rela- References tionships between fungi and woodpecker cavity sites. — Condor 106: 37–49. 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