Ann. Zool. Fennici 43: 86–95 ISSN 0003-455X Helsinki 28 April 2006 © Finnish Zoological and Botanical Publishing Board 2006 Woodpeckers: distribution, conservation, and research in a global perspective Grzegorz Mikusiński Grimsö Wildlife Research Station, Department of Conservation Biology, Swedish University of Agricultural Sciences, SE-730 91 Riddarhyttan, Sweden (e-mail: [email protected]) Received 7 Oct. 2005, revised version received 6 Mar. 2006, accepted 6 Feb. 2006 Mikusiński, G. 2006: Woodpeckers: distribution, conservation, and research in a global perspec- tive. — Ann. Zool. Fennici 43: 86–95. The main aim of this paper is to examine and discuss the global pattern of woodpecker diversity from a conservation perspective. In addition, I review ecological traits and the conservation status of the entire family Picidae, and relate these factors to the human driven change in their habitats. Finally, I present a global overview of the research on woodpeckers in order to identify the major gaps in our knowledge which render the management of populations of these species difficult. The hotspots of woodpecker spe- cies richness identified by GIS were found in tropical and subtropical forests of South- East Asia, South and Central America, and equatorial Africa. Most of these hotspots were located in developing countries. However, almost 90% of articles published in 1985–2004 encompassed studies performed in North America and Europe, that is, in geographic areas harbouring only 17% of the global number of Picidae species. Introduction their drilling for phloem sap and thus their activ- ities can influence entire community structures The family Picidae, which encompasses wood- (Blendinger 1999, Schlatter & Vergara 2005). peckers, wrynecks, and piculets contains ca. 216 Through wood excavation activities, including closely related species, all with strong ties to nest construction and foraging, woodpeckers forest environments. Trees, snags and logs are play a role in wood decomposition processes primary substrates providing nesting sites, shel- (Farris et al. 2004). It has also been suggested ter, and food for the majority of woodpeckers that woodpeckers function as dispersal vectors (Winkler et al. 1995). One striking feature of for wood-living fungi (Jackson & Jackson 2004). woodpeckers is their ability to excavate cavi- It is quite apparent from these relationships that ties in living and dead trees (Winkler & Christie this avian family plays a significant ecological 2002). Due to this “engineering activity”, wood- role in forest environments and communities. peckers have been proposed as key-stone spe- Woodpeckers occur in all types of forest cies in several communities with large numbers and woodland and are found on all continents of secondary cavity nesters (Daily et al. 1993, except of Australia and Antarctica (Winkler et Jones et al. 1995, Conner et al. 2004, Martin al. 2005). Woodpeckers are virtually absent from et al. 2004, Ojeda 2004). Moreover, facultative treeless landscapes such as desert, tundra and sap-consuming species are also benefited by alpine areas. In addition, most isolated islands ANN. ZOOL. FENNICI Vol. 43 • Woodpeckers: distribution, conservation and research 87 lack woodpeckers. Most woodpeckers are sed- other threatened organisms — is habitat loss. entary birds and are generally considered to be Logging of vast areas of woodland as well as relatively poor dispersers (e.g. Higuchi & Koike their conversion to farmland has been the major 1978). Blackburn et al. (1998) conducted a global cause of range contractions, regional extinctions, analysis and found that body mass of woodpeck- and population declines both now and histori- ers was rather weakly correlated with the size of cally (Winkler & Christie 2002). Dependence of their geographic ranges. Blackburn et al. (1998) woodpeckers on certain forest characteristics found that woodpecker geographic range sizes typical for unmanaged forest (i.e. presence of decreased with increased woodpecker species large and old trees, high structural diversity, richness and that species living in high latitudes and presence of large quantities of dead wood) tended to be more widely distributed. Interest- makes them particularly susceptible to forestry ingly, the best predictor of species richness for practices. Short-rotation schemes, selection of woodpeckers was the area of a given geographic few most productive tree species, even-age struc- region; smaller regions had more woodpecker ture, removal of dead wood, active fire suppres- species and more endemics. sion, and replacement of native tree species with Several species of woodpeckers have expe- fast-growing exotics apparently degrade habi- rienced dramatic population declines and range tat for woodpeckers (Angelstam & Mikusiński contractions due to habitat loss and degradation 1994). Alternatively, in areas with traditional, through various human activities (Winkler & low-intensity agricultural practices as is the case Christie 2002). This applies to large, area-sen- in several regions of Europe, woodpeckers may sitive species such as the ivory-billed wood- be relatively abundant in sparsely forested land- pecker (Campephilus principalis) or imperial scapes that contain elements of forest structure woodpecker (C. imperialis) that depend upon such as large, older trees (Mikusiński & Angel- vast areas of unmanaged forest as well as small stam 1997, 1998). In these areas, the clearance but highly specialised species such as the red- and intensified use of such semi-open landscapes cockaded woodpecker (Picoides borealis) or poses the main threat for woodpecker species South American piculets with small geographic (Tucker & Evans 1997). ranges. The effects of human activities on wood- The strong association that woodpeckers dis- pecker assemblages have been observed at dif- play with forest environments and their sensi- ferent scales. In a country-by-country analy- tivity to structural and compositional changes sis, Mikusiński and Angelstam (1997, 1998), in their habitats caused by human action has reported negative population trends for most been a reason for utilizing woodpeckers in forest European woodpeckers and related species rich- and landscape management (e.g. Angelstam & ness to the degree of anthropogenic change for Mikusiński 1994, Diaz 1997, Hutto 1988, Jans- this group of species. In a study from north-east- son 1998, Nilsson et al. 2001, Hess & King 2002, ern Poland, species richness for woodpeckers Lammertink 2004, Uliczka et al. 2004). Wood- was positively correlated with the availability of peckers may fit different concepts that recom- dead wood and large deciduous trees (Angelstam mend use of surrogate species in practical con- et al. 2002) — factors which are closely associ- servation. Woodpeckers have been suggested as ated with the level of naturalness of forest stands. indicators for forest biodiversity (Mikusiński & Strong negative correlation between woodpecker Angelstam 1998, Nilsson et al. 2001). It has been biomass and density with logging intensity has argued that since several woodpecker species been found on Borneo (Lammertink 2004) and display a highly specialised selection of resources the Malaysian peninsula (Styring & Ickes 2001). that are typical of naturally dynamic forests (e.g. Conner et al. (1975) reported higher diversity of dead wood, big and old trees) that their pres- woodpecker species in uncut versus cut wood- ence may indicate high overall biodiversity. The lands in Virginia. empirical evidence supporting this hypothesis is Human impact on woodpecker populations growing. Mikusiński et al. (2001) demonstrated encompasses several factors. The most obvi- a strong positive relationship between the number ous factor for woodpeckers — as well as many of woodpecker species and overall forest bird 88 Mikusiński • ANN. ZOOL. FENNICI Vol. 43 species richness at the landscape scale in Poland. conservation perspective. I also review some The lesser spotted woodpecker (Dendrocopos ecological traits and the conservation status of minor) has been found to be a reliable indicator of the entire family Picidae and relate them to the the occurrence of avian deciduous forest special- human driven change in their habitats. Finally, ists in northern Europe (Jansson 1998, Roberge & I present a global overview of the research on Angelstam 2006). Also tree species diversity was woodpeckers in order to identify the major gaps found to be positively correlated with the number in our knowledge. of woodpecker species observed in one study performed in south-central Sweden (Angelstam 1990). Martikainen et al. (1998) found high num- Material and methods bers of threatened wood-species beetles in areas with white-backed woodpeckers (Dendrocopos Analyses in this study were performed at the leucotos) in Finland and Russian Karelia. global scale. I created a spatially-explicit Geo- Woodpeckers have also been proposed as graphic Information System (GIS) database on indicators of structural diversity and ecological the distribution of the breeding ranges of 216 quality of forest habitats and as umbrella/focal Picidae species, including woodpeckers, wry- species for forest and landscape management necks and piculets. The source of information on (McClelland & McClelland 1999, Derleth et al. geographic ranges of species was taken from dis- 2000, Angelstam et al. 2002, Pakkala et al. 2002, tribution maps published in Winkler and Christie Lammertink 2004). Hess and King (2002) used (2002). Spatial