Using GPS telemetry, field observations, and dropping analysis, the study reveals a marked day–night contrast in habitat use and diet of Red Knots (Calidris canutus) in the bay of Saint-Brieuc (Brittany, France). While Red Knots traditionally forage on intertidal soft-bottom sediments rich in bivalves, several tagged individuals were observed using offshore rocky islands located up to 15 km from their usual feeding grounds. The use of rocky habitats occurred exclusively during daytime and only at the end of winter, from early March until departure for pre-breeding migration. In contrast, night-time activity at the same period remained concentrated on soft-bottom sediments. This behaviour was recorded during two consecutive winters, suggesting that it might not be anecdotal but could be part of a broader seasonal strategy. Dropping analysis highlighted dietary shifts associated with these habitat changes. On the rocky island, they ate the green algae Prasiola stipitata and mussel spat. The use of these rocky islands by Red Knots provides them with access to alternative foraging resources in the context of declining bivalve populations in the southern soft-bottom sediments of the Bay of Saint-Brieuc.
For many bird species, migration is crucial for reproduction and survival, and environmental conditions such as weather influence birds’ migratory timing. However, the specific weather cues used are poorly understood. The limited research on endocrine factors affecting migration suggests that the glucocorticoid hormone corticosterone, which can be elevated during the migratory season, affects migratory behaviour through its stimulatory effect on locomotion. Thus, we investigated the possible interaction between weather cues, migratory behaviour, and corticosterone levels by testing the effect of experimental changes in temperature and barometric pressure on White-throated Sparrows’ (Zonotrichia albicollis) nocturnal migratory and diurnal behaviour, and corticosterone levels during a spring migration. Using a hypobaric climatic wind tunnel we exposed sparrows to simulated low pressure warm fronts or high pressure cold fronts. We recorded behaviour during the weather manipulation and following lights out, and collected faecal samples the next morning. During the weather manipulations, sparrows showed reduced movement in the experimental conditions as lights out was approaching, and they ate more in the cold front treatment. Following lights off, sparrows showed an increase in migratory restlessness in both experimental conditions compared to no change in weather cues, with the most restlessness occurring shortly after lights went out. Faecal corticosterone levels were highest following the cold front treatment. Furthermore, the degree of migratory restlessness per night and corticosterone levels were positively correlated. These experimental results demonstrate that White-throated Sparrows adjust their migratory behaviour and experience endocrine regulation in response to changes in temperature and barometric pressure.
Alpine grasslands are shrinking as shrubs and forests colonize higher elevations due to changes in climate and land use. Accordingly, many alpine bird species are advancing their distributions upslope. Under spatial constraints, species can either persist by adapting to new conditions or experience trailing edge distribution contractions. In relatively low mountains where grasslands already occupy the highest elevations, shrub encroachment may significantly impact open-habitat species, yet community-level studies of habitat use in these areas are lacking. To address this gap, we conducted bird surveys during the breeding season on a grassland plateau in the Southern Carpathians, with point counts ranging from the shrub ecotone to the regional elevation peak. We encountered 18 species and selected the six most common to analyse habitat use at landscape and microhabitat scales. An additional landscape analysis was done for abundant guilds. Results showed that while Water Pipits (Anthus spinoletta), Black Redstarts (Phoenicurus ochruros) and Northern Wheatears (Oenanthe oenanthe) were tolerant of shrubs within the landscape, Horned Larks (Eremophila alpestris) and Eurasian Skylarks (Alauda arvensis) strictly used open grasslands. Shrub-tolerant species were more abundant on north-facing slopes that may provide thermal buffering. These landscape associations contrast with species’ preferences in high mountains where elevational space is currently available for upslope redistribution. At a finer scale, Water Pipits and Dunnocks (Prunella modularis) actively used shrubs, while Northern Wheatear and Black Redstart selected rock microhabitats. The overall pattern suggests that, under limited elevational space, certain species show greater flexibility towards shrubs within the landscape, which could be beneficial with ongoing vegetation advancement, although microhabitat needs will be limiting for several of them. Conversely, species that are tied to open grasslands may be more sensitive to changes in habitat availability and might suffer trailing edge distribution contractions, with potential negative effects on their populations in the Southern Carpathians.
Migratory birds employ different strategies for using climatic conditions throughout the annual cycle, including niche tracking, niche switching, and mixed patterns that combine elements of both. Distinguishing between them is fundamental for understanding the evolution of migration and its conservation implications. However, little is known about the climatic strategy of the Rufous Hummingbird (Selasphorus rufus), a near-threatened, long-distance migrant. We quantified and compared the climatic conditions used by the species across seasons, including simulated non-migratory scenarios, to evaluate its seasonal niche dynamics and determine how climate shapes its spatio-temporal distribution. We combined ordination-based analyses and ellipsoid niche models to quantify overlap, equivalency, similarity, and clustering among seasonal niches, as well as their geographic overlap and interprediction. Our results revealed that climate conditions used by S. rufus vary markedly among seasons and that breeding and overwintering conditions do not co-occur within a single region. Seasonal niche comparisons also revealed very low climatic overlap (Schoener’s D < 0.2) and significant differences in niche centroid distances among stages, but also moderate overlap among seasonal ellipsoids (IJ = 0.30–0.63), indicating partial climatic continuity rather than complete niche replacement. These findings indicate that S. rufus exhibits a mixed seasonal climatic strategy, in which substantial seasonal differentiation coexists with partial climatic continuity. This study highlights the role of climate in shaping the spatio-temporal distribution of S. rufus and shows that incorporating all migratory stages provides a more complete understanding of the species’ climatic strategy and enhances our ability to anticipate responses to ongoing climate change.
Passive acoustic monitoring (PAM), combined with automated classifiers such as BirdNET, has transformed biodiversity assessment by enabling large-scale, standardized species detection. However, while evaluation typically emphasizes false positives and false negatives, the structure and nature of classification errors remain underexplored, particularly in acoustically complex urban environments. We analyzed BirdNET detection outputs from 4,339 recordings collected in Turin and Florence (Italy) between May and June 2024. For each species, we manually reviewed up to 500 randomly selected audio clips, first classifying detections as correct or incorrect, and subsequently categorizing misclassifications as biophonies, anthropophonies, or geophonies. From these classified errors, we then selected a subset of salient and recurrent misclassifications for open-source sharing. Error rate was greater in more specialist species. Biophonies accounted for most errors (70.4
