We measured food provisioning to broods of Common Kingfishers Alcedo atthis. We collected regurgitated undigested fish remains from artificial nests. Using artificial nests ensured that fish remains originated from the current nesting period and were not a result of multiple use of a nest within one breeding season or between seasons. In total, 4722 specimens of 24 fish species were identified in six nests; the remains were used to estimate the mass of individual fish prey. Chicks were fed with fish weighing between 0.01 and 16.2 g (average: 3.0 g, median: 2.6 g). Provisioning rate significantly increased with increasing brood size from 1498 g (505 fishes for four nestlings) to 2968 g (894 fishes for eight nestlings). During the fledging period each chick consumed on average 334 g of fish, which resulted in an estimated daily food intake of 37% of the chick's body mass (average over the entire nestling period). The average daily energy intake was 73.5 kJ per chick, which was lower than expected for birds of equivalent size. It seems that the relatively low energy requirement of chicks, in conjunction with selecting for large and energy-rich prey, are the key factors enabling Common Kingfishers to have large and multiple broods during one breeding season. In the temperate zone of continental Europe, this reproductive strategy enables the species to compensate for the mortality caused by periodically severe winters.

From 1950, spring temperatures in The Netherlands increased. Previous research suggested that advances in first egg dates of Lapwings Vanellus vanellus best correlate with climatic factors rather than with changes in farming practices. In an area constantly and uniformly managed especially for breeding meadow birds (the reserve Giethoorn-Wanneperveen), nesting phenology of Lapwings was monitored over almost three decades (1988–2014). During this period local average air temperatures across early spring (1 February – 31 March) showed no change. Although first laying dates of the initial clutches (varying between 7 and 30 March) did not change either, the median laying date of the first egg of all the clutches (varying between 21 March and 8 April) advanced by ten days (from 4 April to 25 March). Interestingly, laying dates were associated with temperatures, in that egg laying usually followed an increase in temperature in the previous weeks. As a consequence, whereas first laying dates of initial clutches correlated with temperatures in the 21 February – 31 March interval, they did not with temperatures in the previous 1–20 February interval. Likewise, median laying dates of the first egg of all the clutches did not correlate with the temperatures in February and early March, but the two variables were strongly correlated in the overlapping 11 March – 10 April interval. We found no associations with precipitation. That median laying dates (but not first laying dates) advanced without changes in the overall average spring temperature nor in habitat management, can only partly be explained by the finding that hatching success steadily increased during the study (note that the more frequent replacement clutches would have delayed the measured median laying date in the earlier years). As hatching success of earlier clutches is higher than that of later clutches, there may now be selection for earlier laying.

Black-headed Bunting Emberiza melanocephala and Red-headed Bunting Emberiza bruniceps are closely related passerine species that were reported to meet in a hybrid zone southeast of the Caspian Sea, Iran, over 70 years ago. In this study, we revisited the hybrid zone in the northern parts of Iran to compare its present extension and position with previous reports and to determine the relative importance of intrinsic and extrinsic factors in defining range limits of these bunting species in the contact zone. Species Distribution Models (SDMs) were constructed to characterize the factors affecting the current location of the zone. Our results show that the hybrid zone has expanded westwards approximately 170 km in recent decades and that the Black-headed Bunting is being replaced by the Red-headed Bunting in a westward movement. The Blackheaded Bunting has retreated a little from its eastern range in north Iran in recent decades. The hybrid zone has expanded westward rather than shifted. Model outputs show that climatically suitable habitats for both species extend far beyond the hybrid zone. This mismatch between the potential and realized distribution for the two species suggests that intrinsic factors play a major role in shaping range limits of these hybridizing bunting species.

In this descriptive study we performed an acoustic comparison of mimetic and non-mimetic song in a highly conspicuous mimic, the Northern Mockingbird Mimus polyglottos. Using automated acoustic software we measured 13 acoustic features from the mimetic and non-mimetic song of 13, free-living, male mockingbirds recorded during the breeding season. We found that when mockingbirds mimic they extend the maximum frequency of their song by over 600 Hz, which increases the frequency bandwidth by 42%. These differences might reflect female preference for the acoustic features present in mimetic song, or they might represent an artefact of which particular acoustic models are imitated by mockingbirds when developing a mimetic repertoire.

Avian breeding populations have been shown to be regulated by territorial behaviour, often creating a surplus of non-breeding individuals. However, most evidence is of a male non-breeder surplus, whereas for a surplus to actually buffer a population both non-breeding males and females should be present. Here, we provide descriptive and experimental evidence for the existence of a population buffer consisting of mostly male and potentially also female Pied Flycatchers using nest box areas. First we show that local recruits often do not breed in their first year, with 23% of all recruiting males observed breeding in their first year, and 51% of females. When accounting for mortality in the years prior to observed first breeding, we estimate that only 9% of all first-year males breed locally, and 29% of first-year females. Similar percentages of first-year flycatchers skipping breeding have been observed in other study populations. We show that in the year of new establishment of our nest box plots, most known-aged flycatchers were first-year birds (77%), whereas after establishment, recruiting immigrants from the same source population were mostly older (28% first-year birds). An experimental removal of paired flycatchers from one study plot in two years (19 and 58 individuals removed) resulted in complete replacement by males and females. Male but not female replacements were younger than removed individuals. These results imply that a non-breeding surplus is present in Pied Flycatcher populations. The average later age at first-breeding in males compared to females, suggests that this non-breeding surplus is strongly male-biased. Skipping breeding in the first year(s) is not just caused by shortage of suitable nesting sites, as we observed on average 12% of males defending a nest box without pairing up with a female. Using stable isotopes ratios, we show that non-breeding first-year individuals do not stay at their African wintering grounds. Competition for nest sites is one cause for refraining from breeding, as shown by our experiments, but cannot be the sole cause, as many nest boxes remain unused in a season, and up to 20% of territorial males defend a nest box without pairing up with a female. We hypothesize that many young flycatchers arrive too late for breeding and are therefore not seen in their first year. Indeed first-year Pied Flycatchers that do breed/defend a nest box arrive on average later at the breeding grounds, and we argue that the non-observed group arrives even later. The causes of their later arrival could be the need for learning, lower quality wintering sites resulting in later departure, and/or a trade-off between low breeding success and the costs of early arrival. These could be general factors in long-distance migrants, and this pleads for a better understanding of how migration develops during ontogeny.

In managed forests, birds that create their own breeding holes in trees have limited access to substrates in which they can excavate. Therefore, nest site use in these forests possibly reflects availability of substrates more than species preferences. We analysed data on nest sites of Great Spotted Woodpeckers Dendrocopos major collected during 1987–2013 in the strictly protected part of Białowieża National Park in East Poland. The woodpeckers excavated breeding holes in 11 tree species, but species used in individual habitats varied greatly: Alder Alnus glutinosa was almost the only species used in the riverine forest; Aspen Populus tremula, Hornbeam Carpinus betulus and Pedunculate Oak Quercus robur were used most often in oak-lime-hornbeam forest, whereas Scots Pine Pinus sylvestris and P. tremula were used most in coniferous habitat. In oak-lime-hornbeam habitat, the birds strongly preferred to excavate in P. tremula and Q. robur, in the coniferous habitat the birds preferred P. sylvestris and P. tremula, and in all habitats Norway Spruce Picea abies and Small-leaved Lime Tilia cordata were clearly avoided. The woodpeckers generally excavated in large trees (median diameter at breast height: 50 cm), high above the ground (median 11 m), mostly in the trunks (83%) of living trees (67%). Overall, 21.7% of entrance holes were facing downwards. This pattern of hole placement is similar to that reported from other mature forests in Europe. We stress that despite very high plasticity in this species, it seems to use a distinct set of criteria for nest site selection that is related to predation risk, microclimate and mechanical damage of the place of excavation.

We describe the finding of an urban roost of wintering Barn Swallows Hirundo rustica in Aveiro, Portugal, which remained stable with c.150 individuals from at least early December to mid-January 2015/16. The stability in numbers and the occurrence of freshly-shed primary feathers below the roost strongly indicate that these were indeed wintering birds that completed their annual moult and suffered a relatively low mortality during this period. The number of roosting Barn Swallows steeply declined in late January, coinciding with the appearance of singing males in the area and the arrival of numerous migrants from Africa to Portugal. The site characteristics and roosting behaviour are described, and the potential advantages of urban roosting discussed. Although this particular winter was unusually mild, observations indicate that this roost may have been present in previous years, and others may occur elsewhere in the Iberian Peninsula.

This research deals with two insectivorous reedbed-nesting songbirds: the Savi's Warbler Locustella luscinioides and the Great Reed Warbler Acrocephalus arundinaceus, breeding at the Marjal de Pego-Oliva (Valencia-Alicante, Spain). We studied the diet and prey selection of the two species and assessed the dietary differences between them. Diet composition was assessed by examining samples of regurgitated food obtained using apomorphine as an emetic. Prey availability was estimated through standardized invertebrate sampling. The diet of the two warblers was significantly different and included arthropods belonging to the orders Araneida, Coleoptera, Hymenoptera, Hemiptera, Diptera, Mantodea and Orthoptera. The most frequently found prey were Araneida and Coleoptera in the diet of Savi's Warblers, and Hymenoptera and Coleoptera in the diet of Great Reed Warblers. Both species positively selected Araneida and Coleoptera and avoided Diptera, while for other arthropod taxa prey selection differed between the two warbler species.