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The ecophysiology of the Norway spruce (Picea abies (L.) Karst.) trees that were used by three-toed woodpeckers (TTW) (Picoides tridactylus) for their sap-feeding activities were investigated. The pilot study was conducted in southern Finland (61°15′ N, 25°00′ E). During April–June 2015, three different tree categories of Norway spruce were selected for monitoring: trees that were frequently used by the TTWs for phloem sap-feeding for several previous years; trees that were only recently used by TTWs for sap-feeding; and control trees that were not used at all for sap-feeding. Phloem sap and phloem tissue samples were frequently extracted from tree trunks and analyzed for the content and composition of nonstructural carbohydrates, phloem sap osmolality, solute, and water content, as well as for the content and composition of secondary metabolites typical for defense reactions in the phloem. Simple crown characteristics were also measured, including tree height, diameter at breast height, and their ratio (slenderness index). According to our results, the TTWs preferred Norway spruce trees that showed advanced spring phenology to feed on, as evidenced especially by the lower ratio of raffinose (typically high during the winter months) to total soluble sugars of phloem tissues as compared to non-used control trees. The lower slenderness index of the trees chosen by the TTWs indicates low canopy competition pressure with good access to light (i.e., the sun heats the trunks well in spring). There were no differences in the phloem osmolality or solute content between the used or unused control trees. The trees used by the TTWs had significantly higher concentrations of antioxidant phenolic (+)-catechins and stilbene glycosides in phloem tissue, and the stilbene content was also higher in the extracted sap. The phenolics content of the phloem tissue had a clear seasonal trend, being the highest in the early spring and lower towards the onset of the cambial growth processes. The phloem sap is rich in antioxidants and soluble sugars that are potentially beneficial for the TTWs, but more quantitative research is needed to explore the importance of the sap properties to TTWs. [ABSTRACT FROM AUTHOR]

Cavities provide suitable microhabitats for various organisms. Therefore, cavity excavators are important species in forest environments. We observed large differences in both persistence and occupancy of the cavities of Grey-headed Woodpecker Picus canus monitored during the whole cavity lifespan in a 33-year study in southern Finland. Of a total of 80 cavities studied, the median persistence time was 17 years, but this varied from a median lifespan of 29 years for cavities in living trees to only 9 years for cavities in dead trees. The expected number of life-span nests of forest bird species per old cavity was 4.2 in living, and only 1.6 in dead trees. Ten bird species utilised the old cavities (most frequently Great Tit Parus major, Grey-headed Woodpecker and Pied Flycatcher Ficedula hypoleuca). The results show that both suitable living and dead trees should be available for cavity excavators such as the Grey-headed Woodpecker, and that living and dead trees may have different, but important ecological roles for cavity-nesting birds in boreal forests. [ABSTRACT FROM AUTHOR]

Woodpeckers are important species in forest ecosystems because they make tree cavities that are microhabitats for several other taxa. However, even in boreal areas where most tree cavities are made by woodpeckers, the properties of woodpeckers' nest trees and cavities are poorly known. We studied nest tree characteristics of the Grey-headed Woodpecker (Picus canus) in a 170-km2 forest-dominated area in southern Finland during 1987-2019. The data included 76 nest trees with 80 nest cavities in five different tree species. During the study period, 44% of all nesting attempts were in old cavities. Nestswere found in four forest types, but the proportions ofnest tree species differed between them. In all, aspen (Populus tremula) with 70% ofnest trees, and with 71% ofnest cavities was the dominant cavity tree species. Mostnesttrees (85%) were dead or decaying, and most cavities (70%) were excavatedat visible trunk injury spots. The mean diameterofanest tree atbreastheight(DBH)was 37.2 cm and the meanheightofacavityhole was 7.8 m; these were significantly positively correlated. The results highlight the importance of large aspens as nest cavity sites for the species. Conservation and retention of group s of large aspens in main habitats, including clear-cuts, are important for continuous availability of nest trees. This applies particularly to managed boreal forest landscapes where scarcity of suitable trees may be a limiting factor for the species. [ABSTRACT FROM AUTHOR]

Tree cavities, and especially cavities made by woodpeckers, are important microhabitats in forest ecosystems. However, the properties of woodpecker nest trees and cavities are poorly known even in boreal areas wheremost tree cavities aremade by woodpeckers. We studied the nest tree characteristics of the Lesser SpottedWoodpecker (Dendrocopos minor) in a 170-km² forest-dominated area in southern Finland during 1987-2018. The data included 97 nest trees with 106 nest cavities in five deciduous tree species. During the study period, more than one nest cavity (2-3) was excavated in 7% of all cavity trees. Nestswere found in three forest types, but the proportions of nest tree species differed between them. Birch (Betula spp.) was the most common nest tree species with 40% of nests. Nest trees were either dead (79%) or decaying (21%), and themajority (69%) had a broken top. Themean diameter at breast height (DBH) of a nest tree was 24.7 cmand the mean height of a cavity hole was 3.3m; size and height were significantly positively correlated. The mean ratio of cavity height in relation to the respective nest tree height was 0.49, and did not depend on the nest tree condition. The results highlight the importance of dead and decaying deciduous trees as nest cavity sites for this small woodpecker species. Provision of suitable cavity trees during forestmanagement is important tomaintain breeding and cavity building opportunities for theLesser SpottedWoodpecker inmanaged forests. [ABSTRACT FROM AUTHOR]

Primary cavity-producers such as woodpeckers produce nest sites for several other cavity-nesting animals and, thus, are often considered to be keystone species. However, the persistence and occupancy rates of cavities are rarely known and as such the real importance of primary cavity-producers also remains unclear. Cavities of the Lesser Spotted Woodpecker Dendrocopos minor were monitored during their whole lifespan. The data include the annual availability and occupancy history of 106 cavities in a 170-km2 area in southern Finland during 1987–2018. The median survival time of a cavity was six years, but there were differences between the various forest types (range six to eight years). The median time for cavity fall was six years, and five years for cavity damage. Six bird species used the old cavities for breeding, with the Pied Flycatcher Ficedula hypoleuca the dominant species accounting for 53% of all occupancies. The cavity reuse rate in the Lesser Spotted Woodpecker was 3.6%. The mean occupancy by secondary cavity-nesting birds in old cavities was 32%, with a range of 29–36% across the various forest types. There was a significant negative correlation between annual occupancy rates and the age of the cavity. The first two years of a cavity were found to be the most important for total occupancy and 90% of occupancies took place before the median age of the cavities. The expected mean number of lifespan occupancies by secondary cavity-nesters for a single cavity was 1.97. The results indicate that new, fresh cavities are continuously needed for the secondary cavity-nesters that use Lesser Spotted Woodpecker cavities in their territories. [ABSTRACT FROM AUTHOR]

The Three-toed Woodpecker Picoides tridactylus is a mature and old-growth forest specialist but how the species uses trees for nesting in its breeding sites and whether cavity trees are a critical habitat feature is poorly known. We studied the nest tree characteristics of the species in a 170-km2 area in southern Finland during 1987-2016. The data included 538 nest trees of eight different species and 665 nest cavities in 86 territory areas. Norway spruce Picea abies was the predominant nest tree comprising 71% of all nest trees. portionally, deciduous nest trees were more common in moist forests on mineral soils and conifer nest trees more common in spruce swamps. The majority of nest trees (85%) were dead or decaying trees; higher numbers of dead deciduous nest trees were recorded than dead conifer trees. The mean diameter of a nest tree at diameter at breast height (DBH) was 29.4 cm and the mean height of a cavity hole was 5.1m; size and height were signifi-cantly positively correlated. The proportion of deciduous nest trees was significantly higher (45%) in natural forests compared with other areas subjected to variable amounts of forest management, where the respective proportion was only 9-17%. In addition, cavity holes were significantly higher in natural forests than in managed ones. In general, the results highlight the substantial flexibility in nest tree use but also the importance of large dead and decaying trees (including deciduous trees) as nest cavity sites for the species. Spruce swamps can be considered as key nesting habitats in managed forest landscapes. [ABSTRACT FROM AUTHOR]

Abstract. Woodpeckers are important primary excavators that produce nest-sites that are also used by several other cavity-nesting animals. However, the value of nest sites produced by different woodpecker species for other cavity-nesters is not generally known. We studied old Three-toed Woodpecker Picoides tridactylus cavities to examine their importance for other cavity-nesting forest bird species. Over a 31-year period (1987–2017), we annually monitored the occupancy of 655 cavities excavated by the Three-toed Woodpecker in 86 territories of the species in a 170-km2 area in southern Finland. Eight bird species used old Three-toed Woodpecker cavities for breeding, and the occupancy of these cavities by all secondary users was 21.3%. The expected mean number of lifetime occupancies by secondary cavity-nesters for a single cavity was 2.03. This is equivalent to a mean of two cavities occupied per territory per year, if we assume that Three-toed Woodpeckers produce a new cavity every year. The actual numbers of annually occupied cavities by secondary cavity-nesters can be substantially lower especially in territories that are not constantly occupied by the Threetoed Woodpecker. Based on the use of old cavities and densities of secondary cavity-nesting bird species, we conclude that cavities made by Three-toed Woodpeckers are most significant for the species itself, which accounted for 23.3% of nests in old Three-toed Woodpecker cavities. When Three-toed Woodpeckers reused an old cavity rather than occupy a freshly excavated cavity, 93% of cavities selected were originally excavated by Three-toed Woodpeckers. In addition, old cavities are important for the Pygmy Owl Glaucidium passerinum — up to 26–31% of breeding attempts were in old Three-toed Woodpecker cavities. The importance of old cavities for other hole-nesting bird species like the Pied Flycatcher Ficedula hypoleuca or the Great Tit Parus major was rather minor considering their densities within woodpecker territories. [ABSTRACT FROM AUTHOR]

Primary cavity-producers like woodpeckers are often considered as keystone species, because they produce nest-sites also for several other cavity-nesting animals and, thus, maintain ecological webs of cavity-breeders. However, the detailed temporal dynamics of cavities and their lifetime occupancy rates and survival are not usually known which makes it difficult to assess the actual significance and full impact of primary cavity-breeders. In this study, we monitored cavities in a large forest landscape, covering the full lifetime of cavities. We focused on a mature and old-growth forest specialist cavity-breeder, the Three-toed Woodpecker Picoides tridactylus . The data include the annual occupancy history of 655 old cavities of the Three-toed Woodpecker in 86 territories in a 170-km 2 area in southern Finland during 1987–2017. The study area included both managed and natural forest types. The median survival time of a cavity was 10 years, but there were significant differences between forest area types with a range of 7–13 years. The occupancy in all cavities was 21.3%, and the cavities were available for secondary cavity-breeders each year. There was a significant negative correlation between the occupancy and the age of the cavity. The first five years of a cavity were important for the total occupancy, and 86% of occupancies took place before the median age of the cavities. In cavities older than 15 years the occupancy was only 7%. The pattern was similar in all types of forests. Our results show that cavities made by Three-toed Woodpeckers have rather long lifespan but also that their active use by other cavity-breeding species is restricted mostly to few years only. The result indicates that new, fresh cavities are needed continuously in a forest landscape, in order to maintain the role that Three-toed Woodpecker has as a keystone species. [ABSTRACT FROM AUTHOR]

Indicator species have been proposed to be used for revealing common status of ecosystems and their biodiversity. We studied breeding forest birds in southern Finland. Our aim was to find bird species combinations that would predict species richness of forest bird assemblages at several spatial scales. We evaluated statistical models that included 1-5 indicator candidate species, and ranked them according to the Bayesian information criterion. The red-breasted flycatcher Ficedula parva, the pygmy owl Glaucidium passerinum and the three-toed woodpecker Picoides tridactylus were found to be the best multiscale indicators. Models at smaller spatial scales, including several indicator species better explained the total variation in species richness. The indicators mostly revealed properties of the forest site rather than variation in species richness caused by species interactions. Our results show that a suitable set of indicator species may be a useful and quick method for the evaluation of bird diversity in forest environments. [ABSTRACT FROM AUTHOR]

• Cavities had a median persistence time of 10 years. • Persistence of a cavity depended on both tree- and stand-level factors. • Cavities persisted longest in the largest trees, except in European aspens. • Cavities persisted longer in healthy and weakened, living trees than in dead trees. • There was significant spatial variation in the risk of cavity persistence. Tree cavities are microhabitats used by multiple taxa and are considered indicators of forest biodiversity. The factors that affect cavity occurrence and its dynamics are poorly known. We studied tree- and stand-level factors that affect cavity persistence in boreal forests. Cavities of Eurasian Three-toed Woodpeckers (Picoides tridactylus) (n = 654) were surveyed in a 170 km2 area in southern Finland for 31 years during 1987–2017. In total, 447 cavities were lost during the study period: 329 to tree fall or breakage, 72 to cavity damage, and 46 to logging. With the Kaplan-Meier method and Cox proportional hazards models, we analysed which tree- and stand-level factors affected the risk of a cavity to be damaged or lost due to tree fall. The median lifespan of cavities was 10 years, and both tree- and stand-level factors affected the persistence of cavities. Cavities in managed forest areas with low territory occupancy rates were more at risk of tree fall and cavity damage than in other types of forest areas. In all nest tree species, with the exception of European aspen (Populus tremula), the risk of cavity loss to tree fall declined with increasing tree diameter. Moreover, the risk of cavity loss to tree fall was higher in dead trees than in healthy and weakened trees. Cavities in deciduous tree species other than aspen were more at risk of damage than in other tree species. Furthermore, the risk of cavity damage was greater in cavities located lower in a tree. This study showed that factors like the tree species, and size and condition of a tree modify the persistence of woodpecker-made cavities. Consequently, it is likely that these factors influence the value of cavities as microhabitats and how these cavities can be used as indicators of forest biodiversity. Understanding the dynamics of cavities in forest habitats appears critical for the use of cavities as general biodiversity indicators. [ABSTRACT FROM AUTHOR]