Flight can be highly-energy demanding, but its efficiency depends largely on flight style, wing shape and loading, and a range of morphological and lifestyle adaptations that can modify the cost of sustained flight. Such behavioural and morphological adaptations can also influence the physiological costs associated with migration. For instance, during intense flight and catabolism of reserves, lipid damage induced by pro-oxidants increases, and to keep oxidative physiological homeostasis under control, the antioxidant machinery is upregulated. Studies on the oxidative physiology of endurance flight have produced contradictory results, making generalization difficult, especially because multispecies studies are missing. Therefore, to explore the oxidative cost of flight and migration, we explored the association between three measures of the antioxidant capacity (total antioxidant status, uric acid and glutathione concentration) and one measure of oxidative damage of lipids (malondialdehyde) with variables reflecting flight energetics (year-round or specifically during migration) across 113 European bird species using a phylogenetic framework. We found that none of the traits predicting year-round flight energy expenditure, including flight style, wing morphology and flight muscle morphology explained any measures of oxidative state measured during the energy demanding breeding period, suggesting that birds endure their everyday exercise without or low oxidative cost. However, oxidative damage to lipids and one component of the endogenous antioxidant system (uric acid), measured after the end of spring migration on breeding adult birds, increased with migration distance. Our results suggest that migration might have oxidative consequences that are carried over to subsequent life history stages (breeding).

I aimed to better understand the community ecology of sympatric birdlife in subtropical South East Queensland, Australia using patterns of temporal species co-occurrence and principles from network theory. In line with expectation, a hierarchical clustering analysis showed that dates that were successive were joined by the shortest branch lengths because of similar patterns of observed bird species. The only date sampled in the Southern hemisphere Autumn was awarded its own branch in the tree, indicating these observations were relatively distinct. Estimates of total observed bird biomass were substantively higher in the Autumn sample. Ranking each species on its average pairwise correlation to the other 87 species in the set shows that, unsurprisingly, raptors (such as Whistling Kites, Haliastur splenurus) tend to be the most negatively correlated (hypergeometric enrichment statistic P = 0.00029) indicating their presence is inhibitory to other avian species. On the other hand, Silvereyes (Zosterops lateralis) possess the highest number of total connections, the highest radiality (or ‘network influence’) metric within the inferred co-occurrence network and have the second highest average positive correlation to all other bird species in the set (+0.32). Collectively, this means Silvereyes can be seen as an indicators whose presence indicates an enhanced likelihood of observing a diversity of other bird species. Network clustering analysis detects a large module of positively connected bird species within the overall structure (dominated by non-threatening diminutive species as Z. lateralis, Little Friarbirds Philomon citreogularis and Red Backed Fairy Wrens Malurus melanocephalus), whereas all but one of the raptors sit on the periphery. The use of the PCIT network reconstruction algorithm is demonstrated for the first time in community ecology.

Most birds are characterized by a seasonal phenology closely adapted to local climatic conditions, even in tropical habitats where climatic seasonality is slight. In order to better understand the phenologies of resident tropical birds, and how phenology may differ among species at the same site, we used ~70,000 hours of audio recordings collected continuously for two years at four recording stations in Singapore and nine custom-made machine learning classifiers to determine the vocal phenology of a panel of nine resident bird species. We detected distinct seasonality in vocal activity in some species but not others. Native forest species sang seasonally. In contrast, species which have only had breeding populations in Singapore for the last few decades exhibited seemingly aseasonal or unpredictable song activity throughout the year. Urbanization and habitat modification over the last 200 years have altered the composition of species in Singapore, which appears to have influenced phenological dynamics in the avian community. It is unclear what is driving the differences in phenology between these two groups of species, but it may be due to either differences in seasonal availability of preferred foods, or newly established populations may require decades to adjust to the local phenology. Our results highlight the ways that anthropogenic habitat modification may disrupt phenological cycles in tropical regions in addition to altering the species community.

The Andean and Atlantic forests are separated by the open vegetation corridor, which acts as a geographic barrier. However, these forests experimented cycles of connection and isolation in the past which shaped the phylogeographic patterns of their biotas. We analyzed the evolutionary history of the Rufous-capped Antshrike (Thamnophilus ruficapillus), a species with a disjunct distribution in the Atlantic and Andean forests and therefore an appropriate model to study the effect of the open vegetation corridor and the Andes on the diversification of the Neotropical avifauna. We performed a phylogenetic/phylogeographic analysis including the five subspecies, using mitochondrial and nuclear genomic DNA, and also studied their differences in vocalizations and plumage coloration. Both the mitochondrial and nuclear DNA evidenced a marked phylogeographic structure with three differentiated lineages that diverged without gene flow in the Pleistocene (1.0-1.7 million years ago): one in the Atlantic Forest and two in the Andean forest. However, the two Andean lineages do not coincide with the two disjunct areas of distribution of the species in the Andes. Vocalizations were significantly different between most subspecies, but their pattern of differentiation was discordant with that of the nuclear and mitochondrial DNA. In fact, there is no song differentiation between the subspecies of the Atlantic Forest and that of the northwestern Bolivian Andes, even though they differ genetically and belong to different lineages. Consistently, no differences were found in plumage coloration between the subspecies of the Atlantic Forest and that of the southern Andes. Our results suggest a complex evolutionary history in this species, which differentiated both due to dispersion across the open vegetation corridor, likely during a period of connection between the Andean and Atlantic forests, and as a consequence of a geographic barrier in northern Bolivia. In both cases Pleistocene climatic oscillations appear to have influenced the species diversification.

Many subcomponents of human language can be found within the vocal communication systems of other species, most notably songbirds. One of the most prominent of these subcomponents is syntax. While studies of syntax are abundant, a lack of consensus on the definition of syntax has led to much debate. The goal of this review paper is to solidify the definitions of syntax and to explore the mechanisms that shape syntax formation in songbirds and other species, with a specific focus on neurobiology, genetics, dopamine, and chunking organization.

Understanding population dynamics requires estimation of demographic parameters like mortality and productivity. Because obtaining the necessary data for such parameters can be labour-intensive in the field, alternative approaches that estimate demographic parameters from existing data can be useful. High-resolution biologging data are now frequently available for large-bodied bird species, and can be used to estimate survival and productivity. We build on existing approaches to develop a new tool (‘NestTool’) that uses GPS tracking data at hourly resolution to estimate important productivity parameters such as territory acquisition, breeding propensity and breeding success. We developed NestTool with data from 258 individual red kites (Milvus milvus) from Switzerland tracked for up to 7 years. NestTool first extracts 42 movement metrics such as time within a user-specified radius, number of revisits, home range size, and distances between most frequently used day and night locations from the raw tracking data for each individual breeding season. These variables are then used in three successive random forest models to predict whether individuals exhibited home range behaviour, initiated a nesting attempt, and successfully raised fledglings. The models achieved > 95% accurate classification of home range and nesting behaviour in cross-validation data, but slightly lower (> 80%) accuracy in classifying the outcome of nesting attempts, because some individuals frequently returned to nests despite having failed. NestTool provides a graphical user interface to manually annotate those individual seasons for which model predictions fall below a user-defined threshold of certainty. When applied to tracking data from different red kite populations in Germany, NestTool yielded accurate predictions with > 80% accuracy in all parameters. NestTool is available as R package at https://github.com/Vogelwarte/NestTool and we encourage ornithologists to adapt it for different populations and species. NestTool will facilitate the more widespread estimation of demographic parameters from tracking data to inform population assessments

The study of the diet of extreme specialist species can help to understand the selective pressures that modulate the trophic strategies of raptors. This article provides insight into the trophic strategy of a little-known top predator and allows for a better understanding of the selective pressures that shape its diet. We studied the diet of European honey-buzzards, a raptor specialized in the consumption of social wasp brood. The ratio of predator to prey biomasses is one of the highest among raptors. We studied some factors that affect the energy demand of pairs which influence the diet composition and the daily rate of prey delivery to the nest. We explore hypotheses about the role of native and exotic vespids in the diet and the influence of the number and age of nestlings on diet composition, daily rate of prey delivery, and size of combs delivered. We installed trail cameras in 24 honey-buzzards nests in north-western Spain in 2018-2021. We estimated the proportion and daily rate of delivery of native common-wasps (Vespula vulgaris), invasive Asian-hornets (Vespa velutina), reptiles, and birds and the honey-buzzard´s preferences for vespid species. We performed LMMs, GLMMs, and MLRMs to analyse relationships between response variables and predictors. We identified 4611 prey. Honey-buzzards mainly consumed vespids (82% of prey). Common-wasps and Asian- hornets were almost the only two vespids consumed. The invasive hornet was the second most important prey consumed, but common-wasps were preferred. Vespids were more important as the age and number of nestlings increased. Our results suggest that the honey-buzzard´s diet is the adaptive result of the conflict between being a median-sized insect-eating migratory nidicolous raptor and collecting enough morsels for the growth of its nestlings, supporting the prey size and ingestion rate hypothesis. We discuss implications of our findings for the management of the invasive wasp

Urbanization reflects a major form of environmental change impacting wild birds globally. Whereas urban habitats may provide increased availability of water, some food items, and reduced predation levels compared to rural, they can also present novel stressors including increased light at night, ambient noise, and reduced nutrient availability. Urbanization can also alter levels of brood parasitism, with some host species experiencing elevated levels of brood parasitism in urban areas compared to rural areas. Though the demographic and behavioral consequences of urbanization and brood parasitism have received considerable attention, their consequences for cellular-level processes are less understood. Telomeres provide an opportunity to understand the cellular consequences of different environments as they are a well-established metric of biological state that can be associated with residual lifespan, disease risk, and behaviour, and are known to be sensitive to environmental conditions. Here we examine the relationships between urbanization, brood parasitism, and blood telomere lengths in adult and nestling song sparrows (Melospiza melodia). Song sparrows are a North American songbird found in both urban and rural habitats that experience high rates of brood parasitism by brown-headed cowbirds (Molothrus ater) in the urban, but not the rural, sites in our study system. Among adults and nestlings from non-parasitized nests, we found no differences in relative telomere lengths between urban and rural habitats. However, among urban nestlings, the presence of a brood parasite in the nest was associated with significantly shorter relative telomere lengths compared to when a brood parasite was absent. Our results suggest a novel, indirect, impact of urbanization on nestling songbirds through the physiological impacts of brood parasitism.

Parasites may alter host physiology, which may promote behavioural adaptations to counteract their effect. Adaptive feeding may help individuals to cope with infection, especially during physiologically highly demanding life stages. For instance, migrating birds need to fuel long-distance flights and repair oxidative damage caused by intense aerobic exercise, and parasites may influence on how individuals balance these needs. Infected birds may face increased oxidative challenges, which could induce them to favour antioxidant defences over other needs, such as fattening. We tested whether migrating birds can adaptively choose food according to their needs, favouring dietary antioxidants to cope with oxidative stress caused by blood parasites during migration. During autumn migration, we mist-netted young male European blackcaps (Sylvia atricapilla) stopping over in central Spain. We placed the birds in cages where they were offered fat and anthocyanin-enriched food alternatives. We measured preference for each food offer. We tested their infections by haemosporidian parasites with PCR techniques and their parasitaemia with blood smear inspection. We also measured physiological variables that account for nutritional and oxidative status in red blood cells and plasma. We found that birds with multiple infections favoured anthocyanin-enriched food controlling for an effect of body mass on food preference (lean blackcaps preferred anthocyanins, likely because they are urged to repair oxidative damage upon arrival on stopover with depleted energy reserves). Infected birds had a lower antioxidant capacity of plasma, and individuals with more oxidative damage preferred anthocyanin-enriched food. Our results suggest that parasite infections may increase individuals’ antioxidant needs, which could affect migration performance if the urge to find dietary antioxidants reduces fuel consumption rate.

Bio-logging has revealed much about high-latitude seabird migratory strategies, but tropical species are comparatively understudied. Here we use geolocators to study the year-round movement behaviour of adult red-footed boobies (Sula sula rubripes) from the Chagos Archipelago, tropical Indian Ocean. Light levels suggest that red-footed boobies are resident in the archipelago year-round, although there are large latitudinal errors this close to the equator. However, immersion data revealed tracked birds returned to land year-round, with no extended at-sea periods, further indicating this population is non-migratory. Our findings have important implications for seabird conservation and phylogenetics, as well as for assessing the impact of seabird nutrients on coral reef ecosystems.