Agricultural ecosystems have faced dramatic changes during past decades, resulting in a dramatic loss of farmland biodiversity. The Corn Bunting Emberiza calandra is considered a suitable indicator for the conservation value of farmland habitats, and has recently suffered strong declines throughout much of its European range. As a basis for targeted conservation measures, we investigated the habitat preferences of this species in north-eastern Germany by comparing the composition of male territories with randomly chosen control sites. A territory was defined as the area within a radius of 150 meters around the assumed centre of the territory, as the majority of nests is found within this radius. To assess food availability for nestlings, arthropod abundance within the most abundant land use types i.e. crop fields, fallows, grassland as well as within unploughed strips was investigated. In total we found 102 male Corn Bunting territories, which were mainly composed of crop fields (50%), grassland (28%), and fallows (12%). Territories compared with control sites were characterized by a lower proportion of crop fields, a higher proportion of fallows, more diverse land use types, more abundant field boundaries, unploughed strips, and tracks, and a higher availability of song posts. However, neither the number of larger (≥ 1 cm), smaller (< 1 cm) or all arthropods differed significantly among analysed land use types i.e. crop fields, fallows, grassland, unploughed strips. Our study confirms the significance of habitat heterogeneity and especially of sites with sparse vegetation (fallows > 10%) and song posts (> 70 m ‘linear song posts’ or > 1 solitary post per ha) for the habitat selection of male Corn Buntings. We conclude that measures to halt population declines of Corn Buntings seem to be relatively easy to implement, provided that farmers are granted a fair compensation.

We investigated the winter social organisation of a population of British Marsh Tits, using radio-tracking, colour-ringing, and analysis of spatial and social relationships. The observed social structure was defined by adults and juveniles occupying individual but partially-overlapping home-ranges, with typical groups of 2–3 birds (maximum of 9 birds) having a changeable composition. There was no evidence of exclusive territoriality among individuals or groups during the winter, and no evidence of stable social groups with a consistent membership. Instead, the major social units detected were male-female pairs, with mostly casual associations between other individuals. Individual home-ranges averaged 31 ha (10-63 ha, n = 9) and their core areas overlapped with each other by an average 14% (0-65%), indicating that Marsh Tits in this population had very large spatial habitat requirements during winter. Our results have relevance for Marsh Tit conservation, and also the understanding of the drivers and plasticity of social organisation in the family Paridae; we discuss our findings in the context of the discrete and basic flock system exhibited by other species within this group.

Hummingbird vocalizations are usually displayed in two contexts. When foraging or defending territories, males and females usually display relative simple calls as territorial advertisement, while during courtship males perform individually elaborate songs to mate attraction or through singing assemblies (leks). About 15% of all described hummingbird species form leks or singing assemblies during the breeding season. However, the vocal repertoire displayed by males in these arenas has been rarely described. Here we studied the songs of Green Violetear Colibri thalassinus in a temperate forest from central Tlaxcala, Mexico, to document structure and variation within and between singing assemblies established over 3 years. We found 41 well differentiated and structurally complex syllable types across eleven recorded singing groups of Green Violetears (≈12 syllable types per singing group). The songs of most birds were repeats of the same 3–4 syllables, but the syllables types emitted can vary. Birds from the same lek tend to have similar song. Comparison of syllable sharing within-groups showed a Jaccard'similarity coefficient averaging 0.51 ± 0.09 (mean ± SD), and 0.24 ± 0.01 for among groups comparisons. These differences were corroborated by bootstrapping tests finding no significant similarity among males from different leks. However, significant similarity in syllable sharing was found between males from the same lek. No significant correlation was found between song similarity and geographic distances between leks. We have documented that static songs of lekking Green Violetears are more complex than had previously suggested. The variation of vocal repertoire among leks indicates the apparent presence of “vocal dialects” that are variable across time and space. The song variation in the context of discrimination ability in vocal neighborhoods requires further research.

We studied a sympatric and crossbreeding population of the Lesser and the Greater Spotted Eagle in the Biebrza Valley, NE Poland. In order to follow the dynamics of hybridisation and its possible causes we monitored these two species between 1996 and 2012, using visual and genetic species identification. Individuals in up to 51 territories annually were determined as one of the two species or as a hybrid according to plumage characteristics. Feathers from adults and chicks from 114 broods were collected and genotyped using 30 nuclear markers. Hybridisation was observed with both methods already at the beginning of the study, and showed a significantly increasing trend. The proportion of broods producing hybrids of the Greater and the Lesser Spotted Eagle increased during the study by over 30%. The percentage of territories occupied by pure Greater Spotted Eagle pairs declined to 50% at the end of the study. The increasing number of mixed pairs highly significantly correlated with the decreasing number of pairs of the rare Greater Spotted Eagle, but weakly with the numbers of the more common Lesser Spotted Eagle. Mate replacement was frequently recorded and favoured the Lesser Spotted Eagle or hybrids. Adult males were the most often replaced sex (71%), possibly due to their higher mortality. Sex ratio at the nestling stage did not diverge from 1:1. Overall, 13 cases of within-pair species composition change were recorded, leading mostly to hybridisation (61%), but sometimes also to re-establishment of pure A. clanga pairs (23%). Alteration of habitat towards that preferred by the Lesser Spotted Eagle and differential sex-mortality are discussed as the most possible causes of the increasing crossbreeding rate.

Feeding wild bird is popular in domestic gardens across the world, with around half of households in the UK, North America and Australia doing so. Nevertheless, there is surprisingly little empirical information on many aspects of the activity. We sought to characterise garden bird feeding in a large UK urban area in two ways. First, we conducted face-to-face questionnaires with a representative cross-section of residents. Just over half fed birds, the majority doing so year-round and at least weekly. Second, a 2-year, longitudinal study recorded all foodstuffs put out by households on every provisioning occasion. In this way, we obtained the first year-round quantitative records of the amounts and types of wild bird food provided in individual gardens. A median of 127 g, equivalent to 628 kcal, was given daily per household (typically consisting of several food types). We estimated the daily cost of this provisioning level to be UK£0.35 per household based on the relative proportions of each food type. Provisioning level was not significantly influenced by weather or season. Comparisons between the data sets revealed significantly less frequent feeding amongst the feeders in the longitudinal study (assumed to be ‘keen’ feeders owing to their participation in this longterm study and numbers of food types provided) than the face-to-face questionnaire respondents, suggesting that questionnaires relying upon participants' estimates rather than records of provisioning may overestimate actual provisioning frequency. Assuming 100% uptake, the median provisioning level equates to sufficient supplementary resources across the UK to fully support 196 million individuals of a hypothetical average garden-feeding bird species (based on 10 common UK garden-feeding birds' energy requirements). This compares with an estimated total of 71 million breeding individuals of these 10 species in the UK (non-breeding numbers unknown). Taking the lowest provisioning level recorded (101 kcal/day) as a conservative measure, 31 million of these average individuals could theoretically be supported.

The Skylark populations are declining in most European agricultural landscapes. Changing crop compositions and seasonal vegetation dynamics have been suggested to influence the breeding success of Skylarks in arable fields. We quantified the breeding performance of Skylarks by means of continuous video surveillance in maize fields (n = 83 nests) and in a pooled sample of other crops, mostly sugar beet, opium poppy and cereals (n = 89 nests), in the Czech Republic, from 2009 to 2011. Skylarks colonized the bare ground of maize fields immediately after sowing and continued to breed there until the end of the breeding season in late July. The vegetation height at the time of laying did not exceed 100 cm, but late broods left nests under maize reaching up to 210 cm. In spite of similar clutch sizes, a lower number of chicks fledged per successful nest in maize fields compared to other crops, as a consequence of the lower hatchability and higher partial nestling mortality. Nest success (based on daily survival rates) was very low ranging from 8% (raw estimate) to 12% (model estimate), while the difference between crops was less than 1%. The nest productivity was less than 0.4 chicks produced per nesting attempt in both crops. At least 84% (maize) and 65% (other crops) of primary nest losses were caused by predation. After controlling for vegetation height, there was little difference in nest survival between crops during the egg stage, but nest survival was marginally lower in maize during the nestling stage. Results of the study suggest that the recent increasing area of energy cropping fields represented mainly by maize provide an attractive, yet risky, nesting habitat for Skylarks, especially late in the season when autumn-sown crops are too dense. The main factor responsible for the low nesting success is the high rate of nest predation, regardless of vegetation height, as a consequence of shift from mainly avian to mammalian predation towards the end of breeding season.

The Baillon's Crake Zapornia (Porzana) pusilla is considered as one of the least known Rallidae species of the Palaearctic. Very little information exists about its ecological requirements and knowledge on diet refers to very few observations. Based on the analysis of faecal samples (N = 59) from two study sites in Djoudj National Park (NW Senegal), we describe the major diet components and examine how seasonal and environmental factors influence its dietary composition. All faeces contained remains of invertebrates. Coleopterans were the most frequent prey items with an occurrence in 95% of the samples. Other important food items were: Odonata (82%), Aranaea (78%), Nematocera (59%), and Brachycera (44%). Remains of gecko skin were the only evidence for vertebrate prey. 75% of the faeces contained plant matter, especially seeds of Eleocharis mutata which constituted in some individuals > 90% of the sample content. Generalized linear models (GLMs) were used to assess whether occurrence of prey items was an effect of selection or environmental variation, considering both consumed items as well as prey availability. Sweep netting was used to provide an estimate of relative abundance of potential invertebrate prey.

Despite pronounced seasonal changes in temperature and humidity, models revealed a lower influence of meteorological variables on prey composition and availabilty. Rather we found water level, date and site having the highest impact in the models. In contrast to decreasing diversity of available food items in the course of the season, diversity in the faeces remained constant indicating Baillon's Crakes prey less selectively when resources diminish. Furthermore, diversity of Baillon's Crakes' diet was lower at higher water levels, suggesting stronger selectivity when prey abundances are high as implied by positive relationships of several invertebrate groups with water level. Despite the rapidly declining water levels and decreasing abundances of e.g. Nematocera, Odonata and Mollusca in the course of the season, we found no clear shift from aquatic to a more terrestrial dominated composition of taxa in the birds' diet. This might be due to the selection of profitable prey such as araneans or molluscs but could also be explained by better accessibility due to physical changes in the habitats e.g in the case of consumed Odonata and Saltatoria. High disintegration of invertebrates in the faeces rendered quantification of prey items impossible. Biomass estimates could support the assessment of specialization of the Baillon's Crakes as well as the detection of seasonal succession of the wetlands' biotic communities.

Sequentially laid eggs of small songbirds are built from the current income of resources and therefore can be subject to different environmental influences on the short-term and long-term time scales. In this paper we study variation in egg length, breadth, volume and shape in Pied Flycatchers Ficedula hypoleuca in Łódź, central Poland, during 2002–2012, in relation to climatic and habitat-related factors. We found a significant decreasing trend in egg length, breadth and volume across the study years and a slight tendency for eggs to be a little more elongated in a forest site than in an urban parkland site. Even though mean monthly temperature in May is known to have increased since the 1970s in the area of Łódź, the average ambient temperature during the time of formation of eggs in particular clutches tended to decrease, with increasing variability at the same time, in 2002–2012. Egg size traits showed a positive association with average temperature and a negative relation with variability in temperature during egg formation. In spite of a general trend for spring temperature to increase, mean clutch-specific temperature during egg formation decreased and variation in this temperature increased over the years of this study, which explains the overall decreasing trend in egg sizes. We also found that fledging success was positively correlated with egg length, but not any other trait. Therefore, a decrease in egg sizes resulting from climate changes may influence nestling performance, with potentially negative consequences for the Pied Flycatcher population.

We documented the composition and structure of the breeding bird assemblage in the primeval temperate forest of the Białowieża National Park (BNP), during 2010–2014, and used 40 years of data to assess patterns of its diversity. We applied an improved version of the mapping technique (a combined mapping method) for forest birds in seven plots located in three old-growth forest types: ash-alder riverine, oak-hornbeam, and mixed coniferous. The composition of the breeding avifauna and species richness remained basically unchanged. Jointly 67 (79% of 40-year total) breeding species were recorded in 2010–2014. Overall 49 (57%) of all species bred in the study plots in more than 35 years, they formed c. 97% of the pairs in the breeding assemblage. The composition of the group of dominants changed slightly; Phylloscopus sibilatrix became much less numerous in comparison to the earlier periods. Anthus trivialis ceased to breed — possibly due to disappearance of its habitat. The numbers of Sylvia atricapilla reached the highest ever level, and those of Columba palumbus and Dendrocopos medius equalled the maxima observed during 40 years. The overall breeding densities did not change significantly but they were substantially lower than in the peak year (2001). Crown insectivores, crown nesters and short-distance migrants remained the most numerous foraging, nesting and migratory groups, respectively. The earlier observed density gradient across habitats — highest in the riverine, lowest in the coniferous stands — was retained. Overall composition of the breeding avifauna did not change during 40 years, and no colonization of forest areas by a new species, nor extinction of a formerly widespread species, except A. trivialis, were observed. Some local changes of species richness occurred, however. Large-scale changes in coniferous habitats due to die-back of Picea abies and appearance of canopy gaps were followed by the increase in species richness there, while disappearance of former sharp forest edges reduced the number of species breeding in the “edge” plots. We suggest that the high constancy of species composition of the breeding bird assemblage in BNP results largely from the interplay of two factors: 1) long-term stability of the forest habitats, causing places suitable in one year to remain so over many seasons, and 2) cross-generational reproducibility of the selection criteria used by the birds in their settlement decisions.

Four species of songbird, Great Tits Parus major, Blue Tits Cyanistes caeruleus, Pied Flycatchers Ficedula hypoleuca and Wood Warblers Phylloscopus sibilatrix, have nests that have similar insulatory properties, but are made of widely differing materials. This study used a novel technique to investigate the role of air-gaps between component materials of the nest wall on the insulatory properties of the whole nest. Nests of four passerine species were investigated by measuring the rate of warming of a temperature logger within the wall materials before and after vacuum-packing, which removed the air and compressed the nest. After vaccum-packing nest volume was estimated to have decreased by 90% and the measured insulatory values decreased by an average of 20% irrespective of the nest materials. Nest maintenance behaviors that may serve to ensure that air-gaps are maintained within the nest wall, which perhaps maximises its insulatory properties, are discussed.