A reasonably-complete bird inventory is the crucial starting point for the analysis of the bird community. We evaluated the efficiency of point counts in detecting forest birds and verified how many sampling points or occasions are needed to adequately characterize the bird community. We sampled birds in 5 forest stands (conifer and beech forests) from northern to southern Italy in 2012. Sampling (through aural and visual clues) lasted 5 minutes, during which species were recorded. Data were analysed in relation to both the number of sampling points and the number of sampling occasions. Then, estimates of species richness were compared to random resampling of subsets of the original data. Results showed that after 3.8 sampling occasions (out of 19–24 sampling points) or 10.4 sampling points (given points are sampled 5 times), the species coverage of each community approached, or exceeded, the 90% threshold. Also, no difference in the mean values emerged with the subset estimates, but the latter appeared less precise. Our results suggest that the density of 1 sampling point per every 5 ha, each repeated at least 3 times, can represent an adequate optimization of the sampling effort. We provided useful methodological information for planning bird inventories in forest environments (applicable at least for Mediterranean and south-European mountain forests) when personnel and financial resources are limited, leading to a thoughtful fund management whilst providing a method to evaluate the reliability of species coverage for bird surveys.

Birds' eggs exhibit a small amount of interspecific diversity in terms of their colors and patterning but considerable variation occurs at the intraspecific level. Here, we examined the contributions of habitat geology, first egg dates, clutch sizes and year in determining intraspecific variation in the intensity of speckling patterns on the eggs of Blue Tits Cyanistes caeruleus and Great Tits Parus major breeding in deciduous woodlands with underlying calcium-rich limestone and calcium-poor gritstone rock types in northwest England. Eggshell speckling patterns varied significantly in relation to habitat geology, with both species laying more heavily speckled eggs in woodlands with gritstone rock types than in woodlands with limestone rock types, even though the weights of laying females and the availability of aerial invertebrates never differed between the two habitat geology types. Meanwhile, there was no variation in eggshell speckling patterns in both species in relation to first egg dates, clutch sizes or year. The eggs of both species were probably more speckled in the calcium-poor gritstone woodland because laying females were compensating for reduced eggshell strength in those woodland areas where there was low calcium availability by depositing more protoporphyrin-based pigments, that constitute the darker speckles and form at locations on the egg where the shell is thinnest, than conspecifics laying eggs in the calcium-rich limestone woodland. We thus conclude that micro-geographic heterogeneity in habitat geology types significantly influence the eggshell patterning of birds' eggs and more broadly our study confirms that environmental factors strongly influence intraspecific variation in avian eggshell patterning.

The incubation stage in avian reproduction could be as costly as the nestling rearing stage. This is particularly true in the case of uniparental incubation, during which both current and future breeding attempts may be compromised. Therefore, the knowledge of the proximate effects that condition the incubation behaviour in free-living bird populations is of great importance in understanding the evolution of avian life history. In this two-year study, we assessed the incubation behaviours of Blue Cyanistes caeruleus and Great Tits Parus major inhabiting the same Mediterranean area in central Spain through the usage of iButton data loggers. It showed that the incubating behaviour of our tit populations resembles that reported in previous studies, but with peculiarities related to living at lower latitudes, i.e. with a relatively low attentiveness and a shorter active day. Both tit species showed very different incubation strategies, with Blue Tits leaving more frequently the nest (Mean ± SE number of off-bouts, Blue Tit = 27.14 ± 0.63, Great Tit = 16.95 ± 0.58) but for shorter periods than Great Tits (off-bout duration, Blue Tit = 8.76 ± 0.22 min, Great Tit = 14.04 ± 0.56 min; on-bout duration, Blue Tit = 22.63 ± 0.60 min, Great Tit = 36.86 ± 0.86 min). Nonetheless, both species provided a similar nest attentiveness, percentage of time of the active day during which the females were actively incubating (Blue Tit = 70.87 ± 0.57%, Great Tit = 70.75 ± 0.83%). Presumably, differences in the cooling rate of clutches, estimated with the iButtons, could be behind the differences in incubation behaviour between species and the greater capacity of Great Tits to adjust their incubation behaviour.

We report on nocturnal hunting by Eleonora's Falcons in their breeding range in the Mediterranean region and in their non-breeding range in Madagascar. Hunting activity of Eleonora's Falcons near floodlights during the breeding season in western Morocco peaked 30–60 min after sunset, but continued into the early morning. Hunting activity and prey capture rates near floodlights were highest during nights with little moonlight or overcast conditions. Fifty-one percent of 73 group capture attempts were successful. Of the migratory prey species identified at the Moroccan study site (26 species), 73% belonged to species mainly migrating at night, whereas 57% of all migratory bird prey species of Eleonora's Falcon reported to date (122 species) migrate predominantly at night; suggesting that hunting near artificial light may increase the proportion of nocturnal migrant species in the diet of falcons. Sylvia and Acrocephalus were the most commonly recorded genera among prey caught after dark. Our direct observations and analysis of satellite transmitter data indicated that Eleonora's Falcons also hunted away from artificial light in Morocco, Italy, and frequently so in Madagascar. Flight activity was detected in 18% of 342 night-time locations of seven satellitetagged Eleonora's Falcons in Madagascar, at an average moon illumination of 60%. We conclude that nocturnal hunting by Eleonora's Falcons is more common than previously assumed and occurs preferably, but not exclusively, at above-average moon illumination on wintering grounds or near artificial lights during the breeding period.

Bay-capped Wren-Spinetail Spartonoica maluroides (Furnariidae) nests very close to the ground in dense clumps of grasses or sedges and builds both open and enclosed nest. We describe a proportion and characteristics of both types of nests and evaluate some causes that could force the construction of one nest architecture or another. In order to study the causes of this variation, we assessed the variability of nest types (architecture and size) and vegetation structure, and examined their consequences for breeding parameters in a population of Bay-capped Wren-Spinetail breeding in Spartina densiflora saltmarshes located at a coastal lagoon on Atlantic coast in east Argentina. We found that Bay-capped Wren-Spinetail builds nests enclosed and open with similar frequency within the same population and vegetation type. All nests were built with stems and grass leaves of S. densiflora. We found that open nests were built in sites with denser vegetation than enclosed nests. Nesting success and nest survival were not affected by nest architecture and size. The ability to adjust nest structure according to the vegetation density may be a strategy aimed at increasing nest concealment to reduce the temperature inside the nest or to avoid nest depredation. A flexible nest architecture strategy in Bay-capped Wren-spinetail is a possible adaptation to living in simple, yet structurally variable environments such as saltmarshes.

Birds have specific habitat requirements during the breeding period. The Blue Tit Cyanistes caeruleus is a species evolutionarily associated with forest areas that prefers deciduous and mixed forests, whilst its breeding in urban areas is a relatively recent phenomenon. Long-term data (2002–2015) on reproductive performance (number of hatchlings, hatching success, number of fledglings and fledging success (fledging success as the number of fledglings in relation to the number of hatchlings)) were quantified for two Blue Tit populations in two, floristically and structurally contrasting areas (a mature deciduous forest and an urban parkland) in central Poland. The principal aim of this study is to see whether the habitat type, year or the food availability affect the breeding success of Blue Tits. Forest Blue Tits produced significantly more hatchlings (9.82 ± 2.64 (SD) in the forest vs.9.17 ± 2.16 in the parkland) and fledglings (9.18 ± 2.84 in the forest vs. 8.14 ± 2.68 in the parkland) than urban Blue Tits. The number of fledglings was positively correlated with the number of hatchlings in both study areas. Both forest and urban Blue Tits shared a similar hatching success (85.9 % in the parkland and 85.5 % in the forest), while the fledging success was significantly higher in the forest (83.4 % in the parkland and 86.1 % in the forest). The amount of caterpillar frassfall was also studied (caterpillars are the optimal food for nestlings) at both study areas and it suggested that caterpillars were more abundant in the forest than in the parkland (the maximum amount of frassfall, averaged 0.21 ± 0.11 g frass/m²/day in the urban parkland and 0.59 ± 0.50 g frass/m²/day in the forest in 2003–2015). In the forest area, the mean number of fledglings tended to be related to the amount of frassfall but in the parkland, this relation was non-significant. The long-term dynamics of fledging success in our study sites seems to be mutually independent. Thus low fledging success in the forest site does not mean similarly low fledging success in the urban parkland site and vice versa. We suggest that food availability is one of key drivers of differences in the tits breeding success between both studied habitats.

Riparian ecosystems are critical in maintaining biodiversity on a regional scale, which is particularly important for open agroforestry systems. We evaluated bird species richness and abundance in three different distances from the stream (0, 125 and 250 m) in Cork and Holm Oak forest systems (Montado) in southern Portugal. We used 5-minute point-counts to survey birds in two daily periods (morning and afternoon) of three different seasons (breeding season, summer-autumn migration and winter), to describe seasonal and daily variations in the use of riparian galleries and adjacent areas by birds. To assess whether birds move actively from the surrounding matrix into the riparian gallery, we installed mist-nets in mid-summer, autumn migration and winter periods, in two sites adjacent to streams, and recorded flight direction of all passerines trapped in the mist-nets. Both species richness and bird abundance were significantly higher in the riparian gallery than in the adjacent matrix. Species richness was significantly higher during the summer-autumn migration period, and bird abundance significantly lower during the breeding season. Apart from the Short-toed Treecreeper Certhia brachydactyla, Nuthatch Sitta europaea and Chaffinch Fringilla coelebs, all other species (e.g. Blackbird Turdus merula and Sardinian Warbler Sylvia melanocephala) were generally more abundant closer to the stream than at 250 m away. A significantly higher percentage of birds moved from the surrounding matrix into the riparian gallery in mid-summer, but not during the autumn migration and winter, which suggests that microclimatic conditions are important to explain observed seasonal differences. This study shows the importance of considering seasonal variation for the management of passerine bird populations in riparian galleries of Mediterranean areas. A well conserved riparian gallery appears to be a keystone structure exerting a strong influence on the number of bird species associated with surrounding agro-forestry systems such as the Montado.

Understanding foraging strategies remains a central question in behavioural ecology, but studies investigating how foraging of sexes is affected by other individual characteristics, like body size, are still scarce. We investigated how foraging behaviour during chick rearing varies in males and females with brood size, offspring age and individual body mass of parents, in a sexually size-dimorphic waterbird, the Whiskered Tern Chlidonias hybrida. Our study took place at the carp fish ponds in southern Poland, where both invertebrates (dragonflies, a typical prey of females — caught by picking) and small vertebrates (fish, tadpoles, frogs, males typical prey — caught by plunge-diving) are plentiful and available for both sexes during chick-rearing period. In total, 1680 attacks of 29 uniquely marked birds (16 males and 13 females) were observed during chick-rearing period. Foraging techniques were affected by sex of the parent and offspring age, interacting with body mass, and brood size. Males foraged mainly by plunge diving, but avoided this foraging technique if their broods were small and when offspring were young, probably because the chicks were too small to consume vertebrate prey caught by diving. In contrast, females foraged mostly by picking prey from the air, water surface or floating leaves, for most of chick-rearing period, but increased frequency of plunge diving as offspring age increased. A significant interaction between body mass and offspring age suggests that birds differing in body mass foraged differently as their offspring grew. We conclude that despite sex-specific differences in foraging behaviour (and prey type delivered to the chicks), both sexes in the Whiskered Tern alter foraging behaviour in response to both brood and individual birds' attributes.

Of the many negative effects roads have on wildlife, vehicle-caused mortality is important, killing several hundred million birds on an annual basis worldwide. Mortality is often the result of sitting on the road and failing to avoid an approaching vehicle, or being hit by a car while flying across the road at too low height. Therefore, one would expect that in areas with very high traffic density, birds would stay away from the road and roadside, and that birds flying over the road would do so at an elevation that minimizes the risk of collision. To test these hypotheses, I observed bird numbers along the roads at approximately 1000 car trips of at least 5 km in Iceland, Norway and the United States, and about 1800 flight heights of birds crossing a road before and after it was opened for car traffic. The bird abundance on roads was significantly lower at higher traffic densities. After start of traffic in a new road situation, birds crossed that road at significantly higher elevations than before. As an example, nearly 40% of Hooded Crows Corvus cornix and 70% of Western Jackdaws Corvus monedula were observed in the high-risk collision zone 0–5 m height before the road was opened; this was reduced to about 20% and 5% respectively for the two species after the road was opened. Heavy bird species flew higher than small birds. The behavioural adaptations shown here together with other publications provide the foundation of a hypothesis that the relationship between traffic density and the number of bird roadkills is non-linear, with a maximum number of roadkills occurring at a certain traffic density. This implies that fewer roads with high traffic density could reduce the number of roadkilled birds compared to many less trafficked roads.

Composition of Marsh Tit Poecile palustris nestling food was studied in the Białowieża National Park (E Poland). The birds relied exclusively on natural food sources. Repeated visual observations of food brought to young in over 500 broods, during 14 seasons (1993–2007), showed that Marsh Tit used a highly specialised diet in rearing young. Soft-bodied, folivorous caterpillars typically composed > 80% of the nestling diet both in riverine and oak-hornbeam habitat. Spiders formed the second most important prey type (c. 12%). Diet composition fluctuated across years but the proportion of caterpillars in the diet remained high (70–90%) despite more than hundredfold variation in the caterpillars' supply across years. Within years, diet composition changed with nestling age and the broods' synchronisation with the seasonal peak of caterpillars availability. Young that were fed within 15 days before and 10 days after the peak received a high (> 80%) proportion of caterpillars, independent of their age. The share of caterpillars in the diet dropped only outside of that period. In most seasons, Marsh Tit young appeared in nests more than two weeks before the caterpillar peak; consequently, the share of caterpillars fed to small young in the earliest broods was lowest (c. 62% on average). Marsh Tits strove to collect caterpillars even when they were scarce, rather than switch to alternative food types. Spiders were brought in highest numbers (up to 20%) to the youngest (1–7 days old) nestlings. This suggests that spiders contained specific nutritional ingredients required by the small young.

Numerous bird species depend on the availability of tree cavities, and most non-excavators fill their cavities with considerable amounts of nest material. If not removed, this material can accumulate and render cavities unusable, as recorded in some nest-box studies. Data from earlier studies of tree cavities, however, showed that nest material can decrease mostly due to in situ decomposition, but the relative difference between nest decomposition in tree holes and nest-boxes is still unknown. We undertook parallel studies of decay in tree holes and nest-boxes used by European Starlings Sturnus vulgaris in oak-hornbeam stands (SW Poland). We inserted into its tree holes and nest-boxes litter-bags filled with cellulose and wool. After 7.5 months of exposure we detected much greater decomposition in tree holes than in nest-boxes. In tree holes a median 75% of cellulose and 26% of wool disappeared, whilst in nest-boxes a median of only 2% of cellulose and 14% of wool. These results are the first to document the relative difference between natural and artificial breeding cavities in the extent of nest decomposition. We also discuss the effect of nest material accumulation in tree holes and nest-boxes on the different nesting conditions available for hole-nesting birds. Taken together with: microclimate, nest safety, competition with social insects and presence of ectoparasites, the physical accumulation of nest material appear to be distinctive feature that differentiates the natural and artificial sites of tree-hole-nesting birds.