According to the structural‐function hypothesis, the eggshell pigment protoporphyrin, deposited at weak spots, can strengthen the shell structure when calcium is lacking in avian species. However, this hypothesis has not been tested in species that produce pigmented eggs of uniform ground colour without spotting patterns. We tested the structural‐function hypothesis using 435 eggs produced on seven calcium diets (0.2–4.5%) given to Common Pheasants Phasianus colchicus, a species that produces a large number of eggs on a low‐calcium diet with unspotted eggshells composed of a uniform ground colour of mainly protoporphyrin. We found that pheasants on the lowest calcium diet (0.2%), which had thinner eggshells, produced eggs containing more protoporphyrin‐based coloration than four of six other diets, suggesting this species employs pigmentation as ground colour to strengthen eggshells when available calcium is low. Our results provide the first, at least partial support for a structural function for eggshell pigments producing ground colour without spotting in a species that is often calcium‐limited. This pattern may be more widespread in other ground‐nesting taxa that also produce large numbers of eggs with protoporphyrin‐based ground colour and are potentially limited by calcium during breeding.

SCO44850 (Scotland

Elongated tails are elaborate plumage traits possessed by a variety of bird species. Sexual selection has long been the dominant hypothesis for explaining why certain species possess such long tails. During the past three decades, however, alternative hypotheses have been proposed and tested. Here, we review evidence, and the lack thereof, for four hypothesised functions of elongated tails in birds: sexual selection, aerodynamic enhancement, anti‐predation signalling and perch balancing. Sexual selection has received the most attention, though with inconsistent support. The other three hypothesised functions, in contrast, have gained less attention, with perch balancing remaining largely speculative. After reviewing and synthesizing information about these functions, we show that our current knowledge of avian elongated tails is not comprehensive. To advance our understanding of this topic, we suggest (1) devising a uniform definition of elongated tails that can be applied to a wide variety of bird species, (2) further investigation of less‐studied functions of such tails, (3) conducting meta‐analyses to discover the origins and trait correlates of elongated tails, (4) considering the possibility that elongated tails serve multiple functions simultaneously, and (5) testing unexplored functions of elongated tails.

Bird song is a culturally transmitted behavioural trait strongly tied to territory defence and mate attraction in oscine passerines. Divergent song variations can appear in different populations of the same species as a consequence of multiple factors generating geographically distinct songs also termed dialects. Most studies show that males react more strongly towards local dialects, potentially as a by‐product of evolutionary divergence between populations, although other hypotheses have been suggested. In addition, females are hypothesized to show stronger responses to local songs as this may lead to greater reproductive success. In this context, song may become a prezygotic barrier for reproduction. The Yellow CardinalGubernatrix cristatais an endangered species of the South American thorny shrubland that has suffered from population fragmentation due to habitat destruction and its capture for the illegal wildlife trade. Genetically different groups that sing their own dialect have been studied in the context of a conservation programme that intends to restore and preserve natural populations by releasing individuals that are recovered from the illegal pet market back into their area of origin. Although dialects have been identified, it remains unknown whether there is vocal recognition between the populations. In this study, we performed playback experiments in two populations and found that male Yellow Cardinals reacted more strongly to the local dialect, although the foreign dialect was still recognized. This information is important as it is not always possible to genetically assign an individual to its geographical origin before release, which could contribute to a secondary contact scenario where dialects play a critical role for settlement and reproduction.

Interbreeding of related forms following anthropogenic activity can lead to genomic homogenization, contributing to decreasing biodiversity. Assessing spatiotemporal variation in the extent of introgression is important for conservation but can be expensive and logistically complex. The Rock DoveColumba liviais threatened by interbreeding with its feral conspecific and it is difficult to identify wild birds when wild, feral and mixed populations exist. Here, using British and Irish populations, I assess whether the proportion of birds with wild type plumage corresponds to distinctive head morphotypes differing between Rock Doves and feral pigeons, and whether plumage can be used to identify Rock Dove flocks and infer the extent of hybridization. I also determine whether plumage proportions have changed since a prior study was carried out in the 1960s. I show that flocks in which > 75% of individuals have wild type plumage consist of Rock Doves, as determined by head morphotype. Plumage proportions vary geographically, corroborating known genomic assessments of Scottish and Irish Rock Doves. Finally, the number of birds with aberrant plumages has increased since the 1960s, even in regions where no such birds were identified previously. This highlights the value of the Rock Dove as a current case study with which to explore the process of extinction by hybridization.

Birds exhibit flexible movement responses to environmental variation across the annual cycle, and those responses can provide insight into potential impacts that environmental changes may have on these species. To understand year‐round variation in space use by Ferruginous Hawks Buteo regalis, we tracked 12 birds breeding in southwestern Idaho, USA, using GPS telemetry collected over 207 bird‐months. Home‐range sizes of territorial adult hawks showed strong intra‐annual variation, being smallest from April to June and largest from July to October. In contrast, juvenile birds (< 2 years old) did not appear to hold territories and showed no detectable intra‐annual variation in ranging behaviour. Association with land‐cover types by territorial birds varied between breeding and non‐breeding months and was linked to home‐range size. Home‐range sizes of non‐territorial birds were larger than those of territorial birds, and that size did not vary across the year. Association with anthropogenic habitats (irrigated cropland habitats that can provide high rodent densities and increased foraging opportunities) was negatively associated with home‐range size in months of the non‐breeding season. Unexpectedly, the opposite was true in the months of the breeding season, such that use of croplands resulted in larger home‐ranges. Patterns in home‐range size were probably linked to intrinsic factors such as the timing of breeding and migratory behaviour, and to extrinsic factors such as prey availability associated with specific land‐cover types. These results have implications for our understanding of the response of Ferruginous Hawks and other similar species to predicted changes in land cover, and they suggest unexpected relationships between human activity and wildlife behaviour. Furthermore, because the birds we tracked used a large portion of western North America, they are probably relevant far beyond the small area where these individuals were trapped.

Geographical isolation is a key factor in allopatric speciation although divergence with gene flow has been detected in an increasing number of studies, even in island systems. To understand the divergence in island taxa, it is necessary to examine historical gene flow with mainland sister groups, which largely differ due to the various geological and ecological characteristics of each region. The Izu Islands are a chain of young and active volcanic islands in a warm‐temperate climate zone that branch off from the middle of the Japanese mainland. Despite the chain's relatively limited isolation, given its proximity to the mainland, the Izu Islands feature endemic bird species and subspecies. The Japanese Robin Larvivora akahige is an endemic breeder on East Asian islands, and there is also a subspecies on the Izu Islands that is different in feather coloration and ecological traits. The population genetic structure of this robin was investigated using nine nuclear microsatellite markers and mitochondrial cytochrome b region sequences. Distinct and recent differentiation between the groups from the Izu Islands and mainland was detected from nuclear loci, although the genetic structure within the mainland group was unclear over the 1900‐km habitat chain. The mitochondrial haplotypes were divided into two distant clades, one dominated throughout the robin's range and the other coexisting only on the Izu Islands as a minor type. Those clades were inferred to have diverged independent of the recent differentiation of the two nuclear clusters, although their origins and the mechanism underlying their distribution remain unclear. The geographical characteristics of the Izu Islands may have formed a moderate but long‐lasting barrier for gene flow and promoted speciation, as well as serving as refugia for the preservation of relict lineages, particularly for migratory species, which usually move along the mainland chain.

While automated recorders are becoming a favourable tool to monitor birds, methods to analyse the large amount of data generated and their reliability for estimating population size are still limited. In this study, I compared Little Penguins Eudyptula minor call detection between a trained researcher, amateur volunteers and an automated software, assessed which environmental factors affect call variability and detectability and determined the feasibility of automated recorders to estimate population sizes. I found that (1) the number of calls detected by the trained researcher was significantly higher than those detected by the amateur volunteers and automated software, (2) neither wind speed nor moon illumination affected call variability and detectability, and (3) six automated recorders estimated between 3% (large colony) and 14–26% (small colony) of the population. This study contributes to our understanding of the efficacy of automated recorders for avian monitoring.

Automated recognition software is paramount for effective passive acoustic monitoring. BirdNET is a free and recently developed bird sound recognizer. I performed a literature review to evaluate the current applications and performance of BirdNET, which is growing in popularity but has been subject to few assessments, and to provide recommendations for future studies using BirdNET. Prior research has employed BirdNET for a wide range of purposes but few studies have linked BirdNET detections to ecological processes or real‐world monitoring schemes. Among evaluated studies, average precision (% detections correctly identified) usually ranged around 72–85%, and recall rate (% target species vocalizations detected) ranged around 33–84%. Some studies did not assess BirdNET performance, which hampers the interpretation of the ecological results and may provide poorly informed decisions. Recommendations on how to evaluate BirdNET efficiency are provided. The impact of the confidence score threshold, a user‐selected parameter as the minimum score for detections reported, on BirdNET output although variable among species is consistent. The use of high confidence score thresholds increases the percentage of detections correctly classified but lowers the proportion of calls and bird species detected. The selection of an optimal score may depend on the priorities of the user and research goals. BirdNET is a great tool for automated bird monitoring but it should be used with caution due to inherent challenges for automated bird identification. The continued refinement of BirdNET suggests further improvements in the coming years.