Female birds are exceptionally consistent in laying rather uniform and individually specific eggs, so that variation in eggs of individual females is low, while variation among females is high. Repeatability is a population-level parameter used in quantitative genetics to quantify the level of intraindividual consistency in relation to interindividual variation in phenotypic traits, in this case, the egg traits. The statistical measure of repeatability is intraclass correlation of particular egg traits clustered in clutches. This study is based on a long-term dataset on repeatabilities of the length, breadth, volume and shape of eggs of Blue Tits Cyanistes caeruleus investigated in two ecologically varying sites (an urban parkland versus a mature deciduous forest) around the city of Łódź, central Poland in 1999–2013. Coefficients of repeatability of egg length, breadth, volume and shape in the study populations of Blue Tits showed some variation between years and study sites, but were generally very high, on average 0.7 or more, and did not significantly differ between the traits within years. The observed differences between repeatabilities do not seem to be strongly associated with year-specific weather indicators for the first half of April. Only coefficients of variation in mean daily temperature influenced repeatabilities of egg length and breadth, whereas effects of mean temperature were non-significant. Repeatability of egg length in the forest and breadth in both sites increased with increasing variation in daily temperature, whereas repeatability of egg length in the urban park site showed a reverse relation with variation in temperature. Year-site-specific mean laying dates, clutch sizes and egg volumes, considered as indicators of breeding conditions, tended to negatively affect the repeatabilities. However, in general, repeatabilities of different egg traits were not consistent in their variation between years and sites, which suggests an important role of stochastic factors in shaping this variation. External factors that are able to force females to diversify traits of eggs in a particular laying sequence do not seem to directly result from the environmental conditions prevailing during a spring period critical for laying eggs in a population in a given year (the first half of April), but seem to be linked to more subtle aspects of variation in the conditions for egg laying, as shown by links with the mean values of basic breeding parameters.

Avian incubation relies on maintenance of the appropriate temperature and humidity within the nest. Previous studies suggested that conductance of the nest wall to water vapour was relatively low, albeit greater than the conductance of the eggshell, but no empirical studies confirmed this. In this study hygrometer loggers were used to measure water vapour inside and outside nest cups to determine conductance of the nest wall. Average water vapour conductance values for nine species of passerine ranged from 479 mgH₂O·day^-1·Torr^-1 for Common Chaffinch Fringilla coelebs nests to 712 mgH₂O·d^-1·Torr^-1 for Eurasian Reed Warbler Acrocephalus scirpaceus nests. Generally, water vapour conductance values were two orders of magnitude higher than that of published values for the eggshell for these species, although humidity in the nest cup were comparable to published data for passerine nests. These results indicate that in the study species the nest wall was not an effective barrier to water vapour loss. Reconsideration of high values for nest wall conductance, nest attentiveness and sources of water to create humidity, have led to a new approach that deals with nest humidity as part of the water budget during the incubation period. Over time the amount of water vapour required to raise nest humidity far exceeds that released by the eggs. It is proposed that nest humidity is driven by cutaneous water loss from the incubating bird, rather than water vapour lost from the eggs, in order to counter loss of humidity through the nest wall and during incubation recesses.

Knowledge about migration strategy and availability of stop-over sites of globally threatened migratory birds is crucial for the implementation of efficient conservation plan. In this study, we investigated the refuelling strategy of the globally threatened Aquatic Warbler Acrocephalus paludicola at stop-over sites during the autumn migration in West Europe and Africa (40 and 72 sites, respectively, documented in published works about stop-over ecology and sites). Based on fuel reserves of captured birds we calculated potential maximal range of non-refuelling flight from stop-over sites located on the Atlantic flyway migration route. We tried to verify the hypothesis that Aquatic Warblers are able to cross the Sahara during one non-stop flight. We found that mean range of flights was affected significantly by the stopover geographic location but not by age of the birds and stop-over habitat. Individuals staging in France are able to cover smaller distances (mean 612.7 km) compared to individuals staging in Portugal and Spain (mean 857.5 km), i.e. closer to two important geographical barriers (the Gibraltar Strait and the Sahara desert). However, maximal ranges of the heaviest individuals were longer (2370 km in France and 1998 km in Portugal). Our study suggests that Aquatic Warblers are generally not able to cross the Sahara during one non-stop flight. Only some individuals with high fat loads starting from stop-overs in Portugal may be able to cross the Sahara without refuelling. However, due to diel air temperature pattern in the desert they need to stop at least once to rest and wait for nighttime drop in temperature to continue migration. Within the Sahara there are many small patches of suitable habitats which can facilitate resting and maybe even refuelling. Observed and predicted reduction of available area of stop-over habitats may have serious negative consequences for population dynamics of many land-bird species, including the globally threatened Aquatic Warbler.

Existing parentage analyses of large raptors have mostly used naturally shed feathers as a source of DNA. There is evidence that eagle nests are sometimes visited by conspecifics. Are these visitors involved in extra pair-paternity? More than 400 feather samples of nestlings and full-grown White-tailed Eagles were obtained in May at 13 nest sites in the Czech Republic, mainly during the years 2010–2016. The samples were genotyped at six microsatellite loci to determine the identity and number of individuals occurring at each nest site and to test genetic monogamy. In the end, 110 unique genotypes of possible parents were identified from moulted feathers found below nests and were used in a parentage analysis together with 86 offspring genotypes. Interestingly, more than two adult genotypes were sampled from shed feathers in one-third of 64 checks of 11 nests, but nest success was not affected by the number of genotypes. No case of extra-pair paternity was recorded. The results showed that feathers of individuals other than the parent pair can be found below nests of White-tailed Eagles during a single breeding season, and the identity of parents at individual nests can change even during seven years of study, which is inconsistent with the expected longevity, lifelong monogamy and presumed territoriality of White-tailed Eagles. We cannot recommend DNA sampling of nesting pairs on the basis of feathers found below eyries, because the most likely parent was recorded in the appropriate year only in 58% of cases with this method.

Upturned root systems are used by several species of birds as nesting sites. The primeval lowland temperate forests are the crucial the source of information with this respect. The aim of the study was to characterise the root plates as nesting sites in a forest covered by a reserve protection system for about 20 years. The research was conducted between 2016–2018 in south-eastern Poland. In the area examined, nests of the Eurasian Wren Troglodytes troglodytes and the European Robin Erithacus rubecula were found to occupy 19.9% and 2.1% of root plates in uprooted trees, respectively. Among root plates with wren nest, Scots Pine accounted 36.8%, subsequently Norway Spruce 28.9%, and Silver Birch 18.4%. Inclined root plate and root plate of large surface were often chosen by Wrens for building a nest. A week positive correlation was found between the height at which the nest was built and the height of the root plate.

Many woodpecker species rely on different forms of deadwood for nesting and foraging. However, the knowledge of the effect of enrichment of their habitat with different types on deadwood of this species group is lacking. Complex conservation-oriented management, including deadwood enrichment, was applied in a 20 ha even-aged oak-dominated woodland in Hungary. The foraging activities of woodpecker species were documented on selected treated trees over one, two and three years since these measures were implemented. The 109 individual oak trees examined represented five deadwood types: damaged-, girdled-, felled trees, and low- and tall stumps. We analysed the relationships between three variables (depth of foraging work, type of deadwood, and year) and foraging activity. Our results illustrated the prompt responses of woodpeckers to the treated trees. The woodpeckers used the five deadwood types in very different ways, and foraging activity was found to vary greatly in terms of depth of foraging and between years. More activity was carried out on both low- and tall stumps than on any other type one year after the treatment, whilst work on girdled trees and tall stumps predominated two and three years after the treatment. The utilisation of felled- and damaged trees by woodpeckers proceeded at a markedly slower pace than that of girdled trees and stumps, but the utilisation increased gradually. Most of the foraging activity was found to be on the outer bark, however, work on the inner bark and in the sapwood increased between the three years. The measures to conserve the woodpecker species should include the permanent creation and maintenance of various forms of deadwood to provide diverse and continuous foraging sites for woodpeckers.

The White-backed Woodpecker Dendrocopos leucotos is one the rarest and the most vulnerable woodpeckers in Europe. Intensive forest practices have caused a widespread decline of the species. In the Spanish Pyrenees, on the south-west limit of the species range, a population of the lilfordi subspecies (Lilford Woodpecker) is estimated at less than 200 individuals which are confined to a few relatively well-conserved beech forests. Despite being an endangered taxon, our knowledge about the size and shape of its home range is still incomplete. Conventional radio-tracking studies of the taxon have been limited due to the complex topography of forests, whereas miniaturized GPS devices have not been available for such a small bird (∼100 g bodyweight) until recently. Here, we evaluate for the first time the utility of modern lightweight GPS tags to characterize the home range of the White-backed Woodpecker. Using 3.4 g GPS-tags we tracked movements of 14 adult individuals during the breeding and post-breeding periods between years 2017–2019. On average, the failure rate (the percentage of failed fix attempts) was 30%, and 76% of successful fixes were accurate (error < 20 m). According to 95% kernel density estimator, the mean home range (∼300 ha) was several times larger than previously reported for the species, and it did not change over the post-breeding period. This finding challenges the utility of previous management recommendations for protecting small buffer areas around the nest or single forest stands. By modeling the home range size as a function of the number of fixes and errors, we found that males had significantly larger home ranges than females. Our results demonstrate that GPS telemetry is feasible in White-backed Woodpecker adults, and it can provide novel and accurate information about the home range of the species if potential sources of error are adequately addressed.

The sub-Himalayan dipterocarp forests of subtropical region in northwest India support 17 species of woodpecker. From a conservation perspective it is necessary to assess the ecological requirements of woodpeckers in these biologically diverse landscapes, which are experiencing habitat modification and decline in some woodpeckers. We studied the foraging niche differentiation among ten sympatric woodpeckers in the sub-Himalayan forests of northwest India: Dendrocopos canicapillus, D. macei, Picus chlorolophus, P. xanthopygaeus, P. canus, Dinopium shorii, D. benghalense, Chrysophlegma [Picus] flavinucha, Chrysocolaptes lucidus, and Mulleripicus pulverulentus. We examined the foraging site preferences of individual woodpecker species and explored the role of inter-specific differences in foraging behaviour as a possible mechanism for their coexistence. Observations on foraging woodpeckers were taken vis-a-vis the following niche dimensions: diameter of the foraging tree, height of the foraging bird, type of substrate on which it was foraging, vertical position with respect to canopy, condition of the forage tree and condition of the substrate. Distinct preferences were evident among species in their foraging tree diameters, foraging heights, vertical positions, and choice of substrate type, while preference for dead substrates was not an important distinguishing factor. Species that overlapped in one dimension generally segregated along other dimensions. Niche segregation in forage tree diameter was associated with body weight. Based on their overall niche overlaps species could broadly be differentiated into groups according to body size viz. small (3 species), medium (3 species), large (3 species), and very large (1 species). Our study demonstrates that differentiation in foraging may be a likely mechanism for coexistence of sympatric woodpeckers in this region. Given that larger species prefer larger substrates, removal of mature trees could affect their abundance, and homogenisation of stand structure could lead to impoverishment of woodpecker diversity.

The Atlantic Forest in southeastern South America is a biodiversity hotspot with high species richness and high forest loss. Three large to medium-sized woodpecker species (Robust Woodpecker Campephilus robustus, Lineated Woodpecker Dryocopus lineatus, and the globally threatened Helmeted Woodpecker Celeus galeatus) coexist in the south of the ecoregion, and show remarkable convergence in plumage patterns and colouration, possibly driven by interspecific interactions. We assessed differentiation in nest tree species, nest substrates, and timing of breeding and evaluated whether nesting ecology may be a factor explaining an association with mature forests in the Helmeted Woodpecker. Robust and Lineated Woodpeckers excavated cavities in nine and eight nest tree species, respectively, whereas Helmeted Woodpeckers specialized narrowly on laurel trees (88% of nest cavities in two species in genus Nectandra of 52 ± 14 cm DBH). Helmeted Woodpecker is further distinguished by a more frequent use of living, partially decayed trees and by more frequent re-use of nest cavities. When nesting in selectively logged forest (vs. old-growth), Robust and Lineated Woodpeckers used trees with smaller DBH and Robust Woodpeckers excavated lower in trees. Helmeted Woodpeckers selected nest trees with similar dimensions in both environments, indicating lesser flexibility. Helmeted Woodpeckers bred 20–23 days later in the year than Lineated and Robust Woodpeckers, potentially allowing them to avoid nesting near the two larger species. The narrow specialization of Helmeted Woodpecker on nesting in Nectandra trees of large sizes at the onset of decay is a possible factor in making it sensitive to selective logging effects. To stop declines of Helmeted Woodpecker we recommend (1) sparing large trees from selective logging (including Nectandra and tree species used for roosting), and (2) restoring more forested areas to mature forest conditions.

Studies dealing with the selection of tree species and characteristics for cavity-nesting birds are important to evaluate the abundance and quality of available resources in the environment. The aim of this study is to characterize the use of trees by woodpecker species in the subtropical piedmont forests of northwestern Argentina by using the analysis of niche selection, breadth and overlap in a total of five woodpecker species of different body size found in these subtropical forests: White-barred Piculet Picumnus cirratus (small woodpeckers), Golden-olive Woodpecker Colaptes rubiginosus, Golden-green Woodpecker Piculus chrysochloros, Dot-fronted Woodpecker Veniliornis frontalis (medium-sized woodpeckers), and Cream-backed Woodpecker Campephilus leucopogon (largest woodpeckers). From a total of 54 tree species, only 15 were used by these woodpecker species. Primary excavator species were moderate specialists in tree use (Levin's index), and they showed selection according to their availability (Ivlev's index) of four of the fifteen tree species (Calycophyllum multiflorum, Amburana cearensis, Cedrela balansae, Astronium urundeuva) and snags. There was a high overlap (Morisita's overlap index) in the use of tree species between Picumnus cirratus and medium-sized woodpeckers, while less overlap was found between Campephilus leucopogon and other woodpecker species. Both living trees and snags were used by the woodpeckers, although snags were more important for small and medium-sized woodpeckers, whereas living trees were more important for Campephilus leucopogon. Both snags and living trees had a large diameter at breast height (DBH) in > 50 cm. Results show the existence of different cavity-excavation niches for woodpecker species in subtropical forests of Argentina, and they allow us to identify the important relationships between these birds and the available tree species. Thus, the results of this work may be useful to develop sustainable forest management guidelines for this group of birds.

The Great Spotted Woodpecker Dendrocopos major in spite of its broad food niche may prefer some trees or places on them during foraging. Different preferences for foraging sites can also be found in males and females, which may minimize competition for food between them. The main goal of our study was to define sex-specific use of foraging sites of the Great Spotted Woodpecker, in the primeval oak-hornbeam-lime forest of the Białowieża National Park, E Poland. This forest has never been logged and is distinguished by the structure of great vertical and horizontal diversity, high amount of dead wood and trees which reach large dimensions. Therefore, there are a large number of potential foraging sites, and some trees, due to their species or condition, may be particularly preferred in this respect. Our study revealed that the foraging sessions of woodpeckers were longer on the dead parts of trees than on alive ones which were especially noticeable in the case of females. The longest foraging sessions were found on dead parts of Norway Spruce Picea abies for both sexes. The males foraged the longest at high altitudes (> 20 m above the ground) on thin parts of trees (diameter 5–10 cm) whereas females on sites above 15 m and on thicker parts of tree (diameter 10–20 cm). Moreover, the duration of foraging session of females increased with increasing of trunk diameter at breast height, which was not revealed in males.

The disputed occurrence of drumming in Middle Spotted Woodpecker Dendrocoptes medius is due to a lack of sufficient, substantive evidence. In order to obtain a more reliable resource for assessing possible use of drumming in this species, breeding pairs were observed close to potential nest holes in south west France over five years. Drumming was heard in two of the six territories identified and sound recordings were made over four breeding seasons. Analysis of the recorded files consisted of counting and measuring intervals between strikes in all instrumental signals consisting of or containing drumrolls. The results showed that a form of drumming was performed but that it was infrequently produced in a discrete roll. It was usually soft and lacked the regularity of pattern found in the territorial drumrolls of other European woodpeckers. There was also a marked lack of consistency in the amplitude of strikes. As an acoustic signal, this study suggests its principal function to be a communication between partners in relation to the location and construction of a nest site.