Understanding refuelling performance at stopover sites is central to elucidating the migration strategies of passerines, particularly at Mediterranean landfall islands where birds arrive after crossing major ecological barriers. We investigated fuel deposition dynamics and potential flight range in five long‐distance migrant passerines (Great Reed Warbler, Sedge Warbler, Common Nightingale, Wood Warbler and Garden Warbler) using long‐term ringing data (2007–2024) from the Antikythera Bird Observatory, Greece. We quantified arrival fuel load, fuel deposition (FD) and flight range and applied generalized additive mixed models (GAMMs) to assess factors shaping refuelling performance. FD increased with stopover duration, with some levelling during longer stays, and was highest among birds arriving with low fuel loads. Seasonal timing also influenced refuelling, with later‐arriving individuals exhibiting higher FD, consistent with compensatory strategies during delayed migration. Species showed some variation in arrival condition and clearer differences in refuelling performance. Wood Warblers arrived with persistently low reserves and exhibited the lowest fuel deposition, while both Wood Warblers and Sedge Warblers showed comparatively limited increases in flight range during their stopover. Although individuals of both species gained fuel and improved their flight range, these gains were smaller than those observed in Garden Warblers and Common Nightingales. In contrast, Garden Warblers and Common Nightingales achieved substantially greater post‐stopover flight ranges, frequently exceeding 200 km after refuelling on Antikythera. Model‐predicted flight ranges closely matched observed values, confirming robust model performance. These findings highlight Antikythera as an important spring stopover site for migrants crossing the Sahara and Mediterranean barriers while revealing substantial interspecific differences in refuelling success.
Within intertidal ecosystems, the availability of foraging areas for shorebirds changes rapidly with the tidal cycle, imposing a strict regime of foraging opportunity. Several shorebird species have been reported to forage during both diurnal and nocturnal low‐tide periods, making the most of available foraging times, but detailed descriptions of behaviour at night are rare. We may expect shorebirds to engage in distinct spatial behaviours between day and night due to differences in risk landscape, or because moving between foraging sites and searching for indicators of profitable foraging patches may require different strategies. Comparing the diurnal and nocturnal behaviour of the same individuals on intertidal mudflats is a challenge and requires high temporal and spatial resolution data collected over several weeks so that low‐tide periods that fall mostly in the day or in the night can be compared. We used ATLAS—a high‐throughput radiotracking system—to collect high‐resolution tracking data from Red Knots Calidris canutus , between September and October (2018–2022) in the Dutch Wadden Sea. We found that the Red Knots stayed within patches longer at night and that patches were also slightly closer (~100 m) to the roost site at low tide, and covered a smaller area per tide. Red Knots were found to use 20% of their diurnal range at night, and 41% of their nocturnal range during the day. At night, Red Knots showed higher site fidelity across tides. We suggest that these differences in behaviour are probably due to a combination of navigational capacity, risk perception and/or prey conspicuousness.
Captive breeding and reintroduction programmes have been instrumental in preventing the extinction of critically endangered species. As these efforts advance towards recovering self‐sustaining wild populations, understanding how reintroduced animals use space is essential for long‐term success. Home‐range analyses provide insight into habitat use, behavioural flexibility and exposure to human‐related threats, which are key for adaptive management. We compared annual home‐ranges of 12 California Condors Gymnogyps californianus tracked from 2016 to 2020 at two ecologically distinct release sites: the fragmented, urban‐influenced landscapes of southern California and the more heterogeneous coastal habitats of central California. Annual autocorrelated kernel density estimation (AKDE) home‐range estimates were approximately 3.44 times as large in southern California Condors (c. 8444.93 km 2 ) as in central California Condors (c. 2246 km 2 ), suggesting regional differences in habitat fragmentation, resource distribution and topography. Although absolute variability was greater in southern California, central California Condors showed greater relative variability in space use, consistent with diverse foraging opportunities across inland and coastal environments. These findings demonstrate how regional landscape characteristics influence condor movement patterns and emphasize the importance of site‐specific management, including maintaining connectivity in southern California and monitoring inland and coastal resources in the central population.
Migratory bird species fascinate humanity but also contribute significantly to the ecosystems they visit in various ways (e.g. food web structures) and can thus be considered good environmental indicators. Although protected areas (PAs) should play an important role in the conservation of migratory species, this is not always achieved; for example, South Africa (of which the world‐renowned Kruger National Park is among the top five largest PAs across southern African countries) meets the minimum threshold of 17% PA coverage by 2020 for global migratory species, as set out by the Strategic Plan for Biodiversity 2011–2020, Target 11. Nonetheless, little is known about how bird communities and migratory functional groups across the park respond to seasonal variation and whether their phenology and abundances have shifted over time. We investigated whether bird diversity differed among seasons and whether intra‐African and Palearctic migratory bird community arrival and departure times, as well as abundances, changed over a 30‐year period in a large protected area, the Kruger National Park, South Africa. We used bird species occurrence data and subsequent reporting rates (a proxy of abundance) from the first and second Southern African Bird Atlas Projects (SABAP1 and SABAP2). We computed three diversity indices and used a non‐linear least squares modelling approach. Unsurprisingly, we found that species richness was significantly lower when the migrant birds were absent during the Austral winter; however, functional and phylogenetic diversity remained unchanged. We also found that no shifts in the arrival or departure months occurred over the last 30 years, but, more concerning, the abundances of specifically the intra‐African migrant populations were reduced by 20% overall, including abundant species such as Senegal Lapwing Vanellus lugubris for which a > 60% decrease in reporting rate occurred. The causes of these declines, however, remain uncertain because we have not tested for the effects of any (e.g. the El Niño‐Southern Oscillation), although unknown local (e.g. land cover change because of African Elephant Loxodonta africana impacts) and extra‐limital effects (e.g. anthropogenic habitat transformation) may have driven declines in the park. Our results show that identifying community‐wide declines in migrant bird functional groups can be a starting point towards more focused, single‐species conservation action that PA management and non‐government organizations should support.
The study of avian wing shape helps in understanding how birds can adapt to their habitats and respond to changing environmental conditions. An important challenge in this endeavour is obtaining estimates of wing shape that are truly independent of body size, particularly when there is an allometric relationship between them. Size‐constrained component analysis (SCCA) has been proposed as the most appropriate method for estimating wingtip shape from flight feather measurements. Its implementation, however, has been hindered by the lack of open, accessible and reproducible software, leading many researchers either to adopt alternative multivariate methods or to continue relying on traditional, simpler to obtain, indices (e.g. hand‐wing index). Using data from 24 Western Palaearctic passerine species, we demonstrated that SCCA‐derived wingtip shape indices outperform five alternative methods in predicting interspecies variation in migration distance, the most influential life‐history trait shaping wing morphology. Although the scores of the shape indices derived from alternative methods were positively correlated with those obtained using SCCA—indicating that they captured a substantial proportion of the variation—our results provide empirical support for the value of SCCA, particularly in comparison with methods based on ratios of morphological measurements. In light of these findings, we strongly advise adopting SCCA as the gold standard for size‐independent wingtip shape estimation. To facilitate the implementation of this best practice, we provide an open‐source R code for SCCA calculation.
