Black Woodpecker Dryocopus Martius (L., 1758) Distribution, Abundance, Habitat Use and Breeding Performance in a Recently Colonized Region in SW Europe. Olano, M., Aierbe, T., Beñaran, H., Hurtado, R., Ugarte, J., Urruzola, A., Vázquez, J., Ansorregi, F., Galdos, A., Gracianteparaluceta, A., & Fernández-Garć\ia, J. M. Munibe Ciencias Naturales, 2015.
abstract   bibtex   
At the southwestern edge of its global distribution, the Pyrenean population of the black woodpecker Dryocopus martius has increased its range during the last three decades, colonizing new areas where the species was previously unknown. This is the case for Gipuzkoa, where a systematic survey was performed in the breeding season of 2013 aimed at describing the species distribution, abundance, habitat use and reproductive performance. Potential locations were identified using forest inventories and were visited since January until March. Locations were considered occupied when nests or pairs were found, or single individuals were detected during three consecutive visits. Breeding performance in active nests was monitored during May and June. We found 21 breeding home ranges, mainly distributed across the Eastern and Southern fringes of the study area. The environmental variables positively related to the presence of breeding home ranges were higher proportions of canopy cover, mature structure of the stand, cover of beech Fagus sylvatica, mixed deciduous and black pine Pinus nigra stands, and unfragmented forest patches. Monterey pine P. radiata plantations and low tree heights were negatively selected. Preferred foraging areas comprised proportions of American oak Quercus rubra and black pine plantations. Thirteen active nests were found. All nests but two were excavated in beech trees. Breeding success was high (92%) but fledging success (1.8) was below the average reported in Europe, suggesting intrinsic limitations associated to a peripheral population. [Excerpt: Discussion] [::The colonizing process] The absence of paleozoological records for the black woodpecker in Europe west and south of the Alps might suggest that the species is a historic colonizer of the Atlantic section of the continent (Arribas, 2004; Holm & Svenning, 2014). During the 20th century, considerable range expansions have been described in The Netherlands, Belgium, France and Italy, with birds invading lowland, reforested regions (Cuisin, 1985; Mikusinski, 1995; Cuisin, 1998; Ceccarelli et al., 2008). In Northern Iberia, at the south-western edge of the global distribution, the black woodpecker has also increased its breeding range, colonizing formerly vacant areas over the last 30 years (Mart́ınez-Vidal, 2004; Camprodon et al., 2007). In Gipuzkoa, the first report of the black woodpecker dates back to the 1960's (Noval, 1967), but until the 2000's the species was extremely rare and irregular (Gainzarain, 1998; Aierbe et al., 2001). In 2011, the first successful reproduction was confirmed (Ruiz de Azua, 2012), though, without doubt, the Black Woodpecker was already breeding a few years before (T. Aierbe, com. pers.). [\n] This particular colonizing event is part of the wider range expansion across the Basque Mountains, which is currently filling the intermediate gap between the Pyrenean and the Cantabrian populations (Gainzarain & Fernández-Garćıa, 2013). The geographic origin of this recent population is unknown so far. There is not genetic or ringing information to support a Cantabrian or Pyrenean origin, which are the closest source areas. However, based on the favourable population trend of the neighbouring Pyrenean population (Mart́ınez-Vidal, 2004), opposite to the Cantabrian one (Simal & Herrero, 2003; Garćıa, 2008; Sánchez et al., 2009), it is plausible to speculate about a Pyrenean origin. [\n] The black woodpecker fulfills several biological features that Mikusinski (2006) related to decline-prone woodpecker species in transformed landscapes, like large body size and extensive home-ranges, therefore needing a network of vast forest tracts to maintain viable populations. But, on the the other hand, this species maintains a huge distribution indicating adaptability (Croci et al., 2007), is relatively tolerant to forestry practices (Cárcamo, 2006) which associates to rapid occupation of vacant habitats (Villard & Taylor, 1994), and has good dispersal abilities, in turn related to the velocity of expansion (Lensink, 1997). Although there are hardly any studies in Europe reporting on emigration and immigration rates (Passinelli, 2006), recoveries of ringed birds show a noticeable proportion of long post-juvenile movements (Gorman, 2011) and high average natal dispersal distance (16.25 km in Denmark; Christensen, 2002). Both this kind of life-history traits and tolerance to disturbance are fair predictors of colonizer birds (Shigesada & Kawasaki, 2002) and may explain the black woodpecker capability to expand its distribution, as shown from our study area. [\n] At the continental scale, the expansion of the black woodpeckers' range has been attributed to extensive coniferous reforestation (Mikusinski, 1995), but at the regional scale more emphasis is placed on forest maturation, due to a decline in timber exploitation (Gil- Tena et al., 2010). The occupancy of patches in Gipuzkoa did not seem to be influenced by distance to population sources, which was not unexpected given the comparatively small scale of our study area. In the Eastern Pyrenees, about three times larger, the pattern of colonization by the black woodpecker was mediated by connectivity among forest patches, depending in turn on distance to source and forest structure (i. e. basal area; Gil- Tena et al., 2013). The availability of a network of stepping stones is crucial to explain the progressive spread of the population (Saura et al., 2014). Such spatially explicit models could be improved if indicators of foraging quality, such as availability of dead wood, are taken into account (see below). Foraging quality enhances breeding performance and the production of a surplus of individuals than can disperse to non-occupied patches (Newton, 1998). [::Plantations and the black woodpecker] The black woodpecker inhabits several different types of Palearctic boreal and temperate forests, including coniferous plantations (Mikusinski, 1995; Gorman, 2011). In boreal and hemiboreal forests, the species is tolerant to plantation managing, provided that thick trunks (diameter $>$40 cm) for excavating nests remain, and decaying trees are also left as foraging substrates (Angelstam & Mikusinski, 1994). In the framework of worldwide afforestation and reforestation activities for commercial purposes, intense debates focus on the effect of plantation forestry on biodiversity (Bremer & Farley, 2010). As for birds, metaanalyses in Europe have shown that landscape history and spatial structure (patch size, matrix pattern) are probably more informative in explaining species richness than management at the stand scale (Paillet et al., 2009). [\n] Extensive Monterey pine plantations in Northern Spain have contributed to the restoration of forest bird communities (Carrascal & Telleŕıa, 1990), but for the black woodpecker in particular our study has found a number of limitations. Plantations of this pine species in the Basque region are a novel habitat for the black woodpecker across its entire range (Mead, 2013). The species' selection for nesting habitats is rather demanding, both for cavity- trees and cavity-tree plots (Mart́ınez-Vidal, 2001; Camprodon et al., 2007; Pirovano & Zecca, 2014). Preference for beech as nesting substrate has been demonstrated over much of Western Europe (Gorman, 2011; Zahner et al., 2012), and our own data supports this view. Beech trees provide less accessible nests: high holes and smooth bark are associated to lower predation pressure (Zahner & Bauer, 2014). But pine trees (i.e. black pine, Scots pine) are also used in some mountain regions, like the Pyrenees and the Alps, in similar proportion to their availability on the landscape (Mart́ınez-Vidal, 2001; Bocca et al., 2007). In Gipuzkoa, the avoidance of Monterey pine patches deserves further research, but the reason may lie on the combined absence of suitable (i.e thick, tall and debranched) nesting trees and the scarcity of foraging resources in dense, shaded stands (see below). On the contrary, stands of mixed deciduous trees were favoured because they probably supply hole-trees (beech and American oak, even though these two species do not dominate such stands). Because of the forest history of the study area, mixed deciduous stands appear scattered at lower altitudes, surrounded by the matrix of Monterey pine plantations. Similarly, Bocca et al. (2007) found a negative selection for the mountain pine Pinus uncinata in the Alps -in spite of accounting for half of the surface of their study area- attributed to the unsuitable tree conformation and the dense structure of this kind of forest. [::The role of habitat fragmentation] An interesting outcome was the influence of the spatial structure of the habitat on the presence of black woodpecker BHR. Fragmentation of suitable forest patches embedded in a matrix dominated by intensively managed plantations largely determines the composition of bird assemblages (Estades & Temple, 1999) but in a species-specific-way (Mönkkonen et al., 2014). Woodpeckers are thought to be relatively tolerant to fragmentation because, as primary cavity-nesters, they avoid the increasing effect of predation while decreasing patch size. This seems to be the case for the black woodpecker, whose density and breeding performance was not influenced by fragmentation in Sweden (Tjernber et al. 1993) or landscape structure in Finland (Brotons et al., 2003). [\n] But more detailed analyses have shown differences referred to patch size and density of edges in another generalist species, the great spotted woodpecker Dendrocopos major (Mazgajski & Rejt, 2006; Barbaro et al., 2007). Reduced clutch size, low number of fledglings and delayed breeding phenology were observed in smaller woodlots. Therefore even generalist woodpeckers can be sensitive to fragmentation processes, and this could also apply to the black woodpecker (Mikusinski, 1995). The preference for larger, less complex forest patches in our study area, as opposed to the pattern over much of the species range (Rueda et al., 2013), might indicate that the spatial structure plays an increasing role as departing from the range core. This idea is also supported by the fact that such a preference has also been described in other peripheral areas, namely Northern Scandinavia and the Pyrenees (Tjernberg et al., 1993; Garmendia et al., 2006), regardless of their varying degree of forest fragmentation at the European landscape level (Estreguil et al., 2013). [::Is breeding performance limited by habitat or demography?] A high percentage of the monitored nests produced fledglings. The review of Passinelli (2006) reported a median breeding success of 80.2\,% (55-96\,% in 12 studies from France, Germany, Denmark, Sweden and Finland); the figure in our study area was close to the highest section of that range. This might be an artifact because precision of nest success estimates depends on sample size (Pacĺık et al., 2009) and breeding failures at the stages of nesting and incubation are more difficult to detect, but the same could be applied to the mentioned studies, and the intensity of our field effort suggests that the breeding success was indeed relatively high. On the contrary, the number of fledglings per successful nest was low, if compared to the average 3.3 given over of the above referred studies (Passinelli, 2006). Our figure is based on a one-year monitoring, but additional data from previous years were in accordance with this (Ruiz de Azua, 2012; T. Aierbe, pers. com.). [\n] Although clutch size has been reported to be influenced by latitude in many bird species, other breeding parameters such as the number of fledglings per successful nest probably depend less on geographical determinants (Sanz, 1998). Reproductive performance in the black woodpecker is influenced by territory quality (Rolstad et al., 2000) and, possibly, by age, experience, duration of bond and kinship between the pair members, although these latter aspects have seldom been investigated in European woodpeckers (Christensen & Kampp, 2003; Passinelli, 2006). Regarding our study area, we do not have data to exclude any of these hypotheses. As for the first, the high proportion of exotic tree stands in black woodpecker territories may limit the availability of invertebrates as foraging resources, and drive higher chick mortality, as has been suggested for forest passerines in Monterey pine plantations (De la Hera et al., 2013). Epigeal ant and beetle abundances are very impoverished in Monterey pine plantations from Australia and South America, where this tree is also aloctonous (Gunther & New, 2003; Sinclair & New, 2004; Corley et al., 2006; Paritsis & Aitzen, 2008). [\n] In our study area, Alberdi et al. (2012) measured a lower frequency of occurrence of ground-dwelling ant (Lasius spp., Formica spp.) mounds on Monterey pine plots (11\,%, N=392), beech (7 %, N=157), black pine (7 %, N=54) and larch, Douglas fir and Lawson cypress (9 %, N=118), as opposed to oak and mixed deciduous plots (19 %, N=209). This data does not explain the foraging use by the black woodpecker, possibly because the abundance of ground-dwelling ants is not a reliable indicator of foraging habitat quality in our study area. Although these ants are known to be a part of the black woodpecker's diet, arboreal carpenter ants (Camponotus spp.) are the staple food in Europe (Rolstad et al., 1998; Gorman, 2011). The abundance of carpenter ants and saproxylophagous prey is primarily related to the shading and canopy cover (Dolek et al., 2009; Lemperiere & Marage, 2010). In Gipuzkoa, black pine stands are more sun-exposed than Monterey pine and beech stands, as deduced by the average herbaceous covers (28.5, 18.6 and 12.1 % respectively). In the Pyrenees, unmanaged patches of black pine are known to be good foraging sites (Camprodon et al., 2007). [\n] Overall, these differences may account for the foraging habitat use of the black woodpecker, even acknowledging the need for in-site field data to counteract the presumed high variability in determinants of foraging habitat quality (González & Villate, 2003; Pirovano & Zecca, 2014). Being a '' generalist-forager'' species, the black woodpecker is able to exploit several forest development phases (Begehold et al., 2015) in search of the most available prey types, thriving on dead wood (arboreal ants, saproxylophagous beetles) or on alternative substrates (ground-dwelling ants). Its dependence on dead wood volume seems not to be as intense as in other European woodpeckers (Garmendia et al., 2006; Lohmus et al., 2010; Camprodon, 2013). [\n] As for the second hypothesis, poor reproduction may be associated to demographic issues. For instance, if a greater proportion of young, dispersing birds from the core range was present in this area of recent colonization, lower breeding output could be expected (Karvonen et al., 2012). Peripheral populations may experience continual gene flow from central parts of the range, slowing the rate of adaptation to local conditions (Kawecki, 2008; Martin & Liebl, 2014). This kind of population can turn into demographic sinks, the persistence of which is favoured by dispersers from core areas with higher survival and reproduction (Newton, 2003). We do not have data to support or dismiss this hypothesis, but it deserves future study, because understanding demographic and spatial dynamics across central and marginal range sectors is key to determine the conservation status and perspectives of populations (Passinelli, 2006). [\n] [...]
@article{olanoBlackWoodpeckerDryocopus2015,
  title = {Black Woodpecker {{Dryocopus}} Martius ({{L}}., 1758) Distribution, Abundance, Habitat Use and Breeding Performance in a Recently Colonized Region in {{SW Europe}}},
  author = {Olano, Mikel and Aierbe, Tomas and Be{\~n}aran, Haritz and Hurtado, Rober and Ugarte, Jon and Urruzola, Aitzol and V{\'a}zquez, Jabier and Ansorregi, Fermin and Galdos, Aitor and Gracianteparaluceta, Ana and {Fern{\'a}ndez-Gar{\'c}{\i}a}, Jos{\'e} M.},
  year = {2015},
  volume = {63},
  issn = {2172-4547},
  abstract = {At the southwestern edge of its global distribution, the Pyrenean population of the black woodpecker Dryocopus martius has increased its range during the last three decades, colonizing new areas where the species was previously unknown. This is the case for Gipuzkoa, where a systematic survey was performed in the breeding season of 2013 aimed at describing the species distribution, abundance, habitat use and reproductive performance. Potential locations were identified using forest inventories and were visited since January until March. Locations were considered occupied when nests or pairs were found, or single individuals were detected during three consecutive visits. Breeding performance in active nests was monitored during May and June. We found 21 breeding home ranges, mainly distributed across the Eastern and Southern fringes of the study area. The environmental variables positively related to the presence of breeding home ranges were higher proportions of canopy cover, mature structure of the stand, cover of beech Fagus sylvatica, mixed deciduous and black pine Pinus nigra stands, and unfragmented forest patches. Monterey pine P. radiata plantations and low tree heights were negatively selected. Preferred foraging areas comprised proportions of American oak Quercus rubra and black pine plantations. Thirteen active nests were found. All nests but two were excavated in beech trees. Breeding success was high (92\%) but fledging success (1.8) was below the average reported in Europe, suggesting intrinsic limitations associated to a peripheral population.

[Excerpt: Discussion]

[::The colonizing process] The absence of paleozoological records for the black woodpecker in Europe west and south of the Alps might suggest that the species is a historic colonizer of the Atlantic section of the continent (Arribas, 2004; Holm \& Svenning, 2014). During the 20th century, considerable range expansions have been described in The Netherlands, Belgium, France and Italy, with birds invading lowland, reforested regions (Cuisin, 1985; Mikusinski, 1995; Cuisin, 1998; Ceccarelli et al., 2008). In Northern Iberia, at the south-western edge of the global distribution, the black woodpecker has also increased its breeding range, colonizing formerly vacant areas over the last 30 years (Mar{\'t}\i nez-Vidal, 2004; Camprodon et al., 2007). In Gipuzkoa, the first report of the black woodpecker dates back to the 1960's (Noval, 1967), but until the 2000's the species was extremely rare and irregular (Gainzarain, 1998; Aierbe et al., 2001). In 2011, the first successful reproduction was confirmed (Ruiz de Azua, 2012), though, without doubt, the Black Woodpecker was already breeding a few years before (T. Aierbe, com. pers.).

[\textbackslash n] This particular colonizing event is part of the wider range expansion across the Basque Mountains, which is currently filling the intermediate gap between the Pyrenean and the Cantabrian populations (Gainzarain \& Fern\'andez-Gar\'c\i a, 2013). The geographic origin of this recent population is unknown so far. There is not genetic or ringing information to support a Cantabrian or Pyrenean origin, which are the closest source areas. However, based on the favourable population trend of the neighbouring Pyrenean population (Mar{\'t}\i nez-Vidal, 2004), opposite to the Cantabrian one (Simal \& Herrero, 2003; Gar\'c\i a, 2008; S\'anchez et al., 2009), it is plausible to speculate about a Pyrenean origin.

[\textbackslash n] The black woodpecker fulfills several biological features that Mikusinski (2006) related to decline-prone woodpecker species in transformed landscapes, like large body size and extensive home-ranges, therefore needing a network of vast forest tracts to maintain viable populations. But, on the the other hand, this species maintains a huge distribution indicating adaptability (Croci et al., 2007), is relatively tolerant to forestry practices (C\'arcamo, 2006) which associates to rapid occupation of vacant habitats (Villard \& Taylor, 1994), and has good dispersal abilities, in turn related to the velocity of expansion (Lensink, 1997). Although there are hardly any studies in Europe reporting on emigration and immigration rates (Passinelli, 2006), recoveries of ringed birds show a noticeable proportion of long post-juvenile movements (Gorman, 2011) and high average natal dispersal distance (16.25 km in Denmark; Christensen, 2002). Both this kind of life-history traits and tolerance to disturbance are fair predictors of colonizer birds (Shigesada \& Kawasaki, 2002) and may explain the black woodpecker capability to expand its distribution, as shown from our study area.

[\textbackslash n] At the continental scale, the expansion of the black woodpeckers' range has been attributed to extensive coniferous reforestation (Mikusinski, 1995), but at the regional scale more emphasis is placed on forest maturation, due to a decline in timber exploitation (Gil- Tena et al., 2010). The occupancy of patches in Gipuzkoa did not seem to be influenced by distance to population sources, which was not unexpected given the comparatively small scale of our study area. In the Eastern Pyrenees, about three times larger, the pattern of colonization by the black woodpecker was mediated by connectivity among forest patches, depending in turn on distance to source and forest structure (i. e. basal area; Gil- Tena et al., 2013). The availability of a network of stepping stones is crucial to explain the progressive spread of the population (Saura et al., 2014). Such spatially explicit models could be improved if indicators of foraging quality, such as availability of dead wood, are taken into account (see below). Foraging quality enhances breeding performance and the production of a surplus of individuals than can disperse to non-occupied patches (Newton, 1998).

[::Plantations and the black woodpecker] The black woodpecker inhabits several different types of Palearctic boreal and temperate forests, including coniferous plantations (Mikusinski, 1995; Gorman, 2011). In boreal and hemiboreal forests, the species is tolerant to plantation managing, provided that thick trunks (diameter {$>$}40 cm) for excavating nests remain, and decaying trees are also left as foraging substrates (Angelstam \& Mikusinski, 1994). In the framework of worldwide afforestation and reforestation activities for commercial purposes, intense debates focus on the effect of plantation forestry on biodiversity (Bremer \& Farley, 2010). As for birds, metaanalyses in Europe have shown that landscape history and spatial structure (patch size, matrix pattern) are probably more informative in explaining species richness than management at the stand scale (Paillet et al., 2009).

[\textbackslash n] Extensive Monterey pine plantations in Northern Spain have contributed to the restoration of forest bird communities (Carrascal \& Telle\'r\i a, 1990), but for the black woodpecker in particular our study has found a number of limitations. Plantations of this pine species in the Basque region are a novel habitat for the black woodpecker across its entire range (Mead, 2013). The species' selection for nesting habitats is rather demanding, both for cavity- trees and cavity-tree plots (Mar{\'t}\i nez-Vidal, 2001; Camprodon et al., 2007; Pirovano \& Zecca, 2014). Preference for beech as nesting substrate has been demonstrated over much of Western Europe (Gorman, 2011; Zahner et al., 2012), and our own data supports this view. Beech trees provide less accessible nests: high holes and smooth bark are associated to lower predation pressure (Zahner \& Bauer, 2014). But pine trees (i.e. black pine, Scots pine) are also used in some mountain regions, like the Pyrenees and the Alps, in similar proportion to their availability on the landscape (Mar{\'t}\i nez-Vidal, 2001; Bocca et al., 2007). In Gipuzkoa, the avoidance of Monterey pine patches deserves further research, but the reason may lie on the combined absence of suitable (i.e thick, tall and debranched) nesting trees and the scarcity of foraging resources in dense, shaded stands (see below). On the contrary, stands of mixed deciduous trees were favoured because they probably supply hole-trees (beech and American oak, even though these two species do not dominate such stands). Because of the forest history of the study area, mixed deciduous stands appear scattered at lower altitudes, surrounded by the matrix of Monterey pine plantations. Similarly, Bocca et al. (2007) found a negative selection for the mountain pine Pinus uncinata in the Alps -in spite of accounting for half of the surface of their study area- attributed to the unsuitable tree conformation and the dense structure of this kind of forest.

[::The role of habitat fragmentation] An interesting outcome was the influence of the spatial structure of the habitat on the presence of black woodpecker BHR. Fragmentation of suitable forest patches embedded in a matrix dominated by intensively managed plantations largely determines the composition of bird assemblages (Estades \& Temple, 1999) but in a species-specific-way (M\"onkkonen et al., 2014). Woodpeckers are thought to be relatively tolerant to fragmentation because, as primary cavity-nesters, they avoid the increasing effect of predation while decreasing patch size. This seems to be the case for the black woodpecker, whose density and breeding performance was not influenced by fragmentation in Sweden (Tjernber et al. 1993) or landscape structure in Finland (Brotons et al., 2003).

[\textbackslash n] But more detailed analyses have shown differences referred to patch size and density of edges in another generalist species, the great spotted woodpecker Dendrocopos major (Mazgajski \& Rejt, 2006; Barbaro et al., 2007). Reduced clutch size, low number of fledglings and delayed breeding phenology were observed in smaller woodlots. Therefore even generalist woodpeckers can be sensitive to fragmentation processes, and this could also apply to the black woodpecker (Mikusinski, 1995). The preference for larger, less complex forest patches in our study area, as opposed to the pattern over much of the species range (Rueda et al., 2013), might indicate that the spatial structure plays an increasing role as departing from the range core. This idea is also supported by the fact that such a preference has also been described in other peripheral areas, namely Northern Scandinavia and the Pyrenees (Tjernberg et al., 1993; Garmendia et al., 2006), regardless of their varying degree of forest fragmentation at the European landscape level (Estreguil et al., 2013).

[::Is breeding performance limited by habitat or demography?] A high percentage of the monitored nests produced fledglings. The review of Passinelli (2006) reported a median breeding success of 80.2\,\% (55-96\,\% in 12 studies from France, Germany, Denmark, Sweden and Finland); the figure in our study area was close to the highest section of that range. This might be an artifact because precision of nest success estimates depends on sample size (Pac\'l\i k et al., 2009) and breeding failures at the stages of nesting and incubation are more difficult to detect, but the same could be applied to the mentioned studies, and the intensity of our field effort suggests that the breeding success was indeed relatively high. On the contrary, the number of fledglings per successful nest was low, if compared to the average 3.3 given over of the above referred studies (Passinelli, 2006). Our figure is based on a one-year monitoring, but additional data from previous years were in accordance with this (Ruiz de Azua, 2012; T. Aierbe, pers. com.).

[\textbackslash n] Although clutch size has been reported to be influenced by latitude in many bird species, other breeding parameters such as the number of fledglings per successful nest probably depend less on geographical determinants (Sanz, 1998). Reproductive performance in the black woodpecker is influenced by territory quality (Rolstad et al., 2000) and, possibly, by age, experience, duration of bond and kinship between the pair members, although these latter aspects have seldom been investigated in European woodpeckers (Christensen \& Kampp, 2003; Passinelli, 2006). Regarding our study area, we do not have data to exclude any of these hypotheses. As for the first, the high proportion of exotic tree stands in black woodpecker territories may limit the availability of invertebrates as foraging resources, and drive higher chick mortality, as has been suggested for forest passerines in Monterey pine plantations (De la Hera et al., 2013). Epigeal ant and beetle abundances are very impoverished in Monterey pine plantations from Australia and South America, where this tree is also aloctonous (Gunther \& New, 2003; Sinclair \& New, 2004; Corley et al., 2006; Paritsis \& Aitzen, 2008).

[\textbackslash n] In our study area, Alberdi et al. (2012) measured a lower frequency of occurrence of ground-dwelling ant (Lasius spp., Formica spp.) mounds on Monterey pine plots (11\,\%, N=392), beech (7 \%, N=157), black pine (7 \%, N=54) and larch, Douglas fir and Lawson cypress (9 \%, N=118), as opposed to oak and mixed deciduous plots (19 \%, N=209). This data does not explain the foraging use by the black woodpecker, possibly because the abundance of ground-dwelling ants is not a reliable indicator of foraging habitat quality in our study area. Although these ants are known to be a part of the black woodpecker's diet, arboreal carpenter ants (Camponotus spp.) are the staple food in Europe (Rolstad et al., 1998; Gorman, 2011). The abundance of carpenter ants and saproxylophagous prey is primarily related to the shading and canopy cover (Dolek et al., 2009; Lemperiere \& Marage, 2010). In Gipuzkoa, black pine stands are more sun-exposed than Monterey pine and beech stands, as deduced by the average herbaceous covers (28.5, 18.6 and 12.1 \% respectively). In the Pyrenees, unmanaged patches of black pine are known to be good foraging sites (Camprodon et al., 2007).

[\textbackslash n] Overall, these differences may account for the foraging habitat use of the black woodpecker, even acknowledging the need for in-site field data to counteract the presumed high variability in determinants of foraging habitat quality (Gonz\'alez \& Villate, 2003; Pirovano \& Zecca, 2014). Being a '' generalist-forager'' species, the black woodpecker is able to exploit several forest development phases (Begehold et al., 2015) in search of the most available prey types, thriving on dead wood (arboreal ants, saproxylophagous beetles) or on alternative substrates (ground-dwelling ants). Its dependence on dead wood volume seems not to be as intense as in other European woodpeckers (Garmendia et al., 2006; Lohmus et al., 2010; Camprodon, 2013).

[\textbackslash n] As for the second hypothesis, poor reproduction may be associated to demographic issues. For instance, if a greater proportion of young, dispersing birds from the core range was present in this area of recent colonization, lower breeding output could be expected (Karvonen et al., 2012). Peripheral populations may experience continual gene flow from central parts of the range, slowing the rate of adaptation to local conditions (Kawecki, 2008; Martin \& Liebl, 2014). This kind of population can turn into demographic sinks, the persistence of which is favoured by dispersers from core areas with higher survival and reproduction (Newton, 2003). We do not have data to support or dismiss this hypothesis, but it deserves future study, because understanding demographic and spatial dynamics across central and marginal range sectors is key to determine the conservation status and perspectives of populations (Passinelli, 2006).

[\textbackslash n] [...]},
  journal = {Munibe Ciencias Naturales},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13911737,biodiversity,bird-conservation,conservation,dryocopus-martius,ecology,ecosystem,fagus-sylvatica,forest-resources,pinus-nigra,pinus-radiata,pyrenees-region,quercus-rubra},
  lccn = {INRMM-MiD:c-13911737}
}
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