Search

Above all, bird ringing must be safe for birds, for ethical reasons but also to ensure that data collection is not biased by marking effects. Bird ringing schemes are responsible for determining the size of the rings used to mark birds individually. This paper critically reviews the recommended ring sizes in the Aranzadi Ringing Scheme and proposes an objective criterion for ringers. A morphological analysis of tarsus width (MTW) and the width of the tibia–tarsus articulation (MAW), over a sample of more than 4000 individuals of 74 species of both passerines and non-passerines captured in Spain, revealed that the mean difference between the internal diameter of the recommended ring (IDR) and MTW was 32% in relation to MTW (sd 15.8%, 95% confidence interval 28–35%). Experience demonstrates that this clearance is adequate, but recommendations for rings with clearances either too narrow (<6%) or too wide (>50–60%) should be reviewed and changed, if possible, to bring them closer to a 32% standard. [ABSTRACT FROM AUTHOR]

Tawny Owls in southern Europe were trapped and measured. Compared to males, the females were larger, heavier, and more greyish in colour, but there was a large biometric overlap. The variable with the highest Storer's dimorphism index (SDI) was weight, though our population had one of the smallest dimorphisms observed in Europe for weight. It has been proposed that differences in diet could lead to differing behaviour and, in consequence, the observed dimorphism degree (SDI) by natural selection. [ABSTRACT FROM AUTHOR]

Woodlands subjected to commercial exploitation can play an important role in the conservation of forest-dwelling birds, whether these species breed, forage, or spend all or part of their annual cycle in this habitat. Since 2016, the Administration of Gipuzkoa Province, Spain, has implemented a new protocol designed to preserve the nesting habitat of the Red Kite (Milvus milvus) population breeding within the region. This species is locally classified as endangered and therefore has conservation priority. The aim of our study was to evaluate the efficacy, demographic impact, and cost of this protocol. Over a period of 7 yr (2016–2022), implementation of the protocol preserved 23 nests (i.e., 15.2% of the total 151 nests). From these protected nests, 37 young fledged, which was 16% of all the young fledged within the region in this period. Relative to the financial cost of protecting nature in Gipuzkoa, implementation of this protocol was inexpensive, totalling <0.1% of the administration's budget for managing natural habitats within the province. Los bosques sometidos a explotación comercial pueden desempeñar un papel importante en la conservación de aves que habitan en ellos y se reproducen, forrajean o pasan todo o parte de su ciclo anual allí. Desde 2016, la Administración de la Provincia de Gipuzkoa, España, ha diseñado e implementado un nuevo protocolo con el fin de preservar el hábitat de nidificación de la población de Milvus milvus que se reproduce en la región, ya que esta especie está clasificada como localmente en peligro de extinción y, por lo tanto, tiene prioridad de conservación. El objetivo de nuestro estudio fue evaluar la eficacia, el impacto demográfico y el costo de este protocolo. Durante un período de siete años (2016–2022), la implementación del protocolo preservó 23 nidos (es decir, el 15.2% del total de 151 nidos). De estos nidos protegidos, 37 crías emplumaron, lo que representó el 16% de todas las crías emplumadas en la región en este período. En relación con el costo financiero de proteger la naturaleza en Gipuzkoa, la implementación de este protocolo fue económica, totalizando <0.1% del presupuesto del departamento para la gestión de hábitats naturales en la provincia. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

River systems are some of the habitats most drastically affected by climate change. Consequently, many riparian species are amongst the most threatened living organisms worldwide, making riparian areas a conservation priority. Demographic analyses destined to improve our comprehension of the population dynamics of riparian species are crucial in this context. The present work analyses the spatio-temporal demographic dynamics of a presumably well-preserved White-throated Dipper (Cinclus cinclus) population from northern Spain. Using multistate models where we considered the effects of factors such as mean water flow in winter, age, sex, hydrographical basin of origin and hatching date, we found that the population had a constant annual dispersal rate (ψ = 0.038; 95% CI: 0.022-0.065). The mean apparent survival of Dippers from first-order clutches was 0.18 (95% CI: 0.12-0.22), whereas for those hatched in second-order clutches was 0.07 (95% CI: 0.03-0.15). The mean annual apparent survival for adults was 0.64 (95% CI: 0.56-0.70). Although apparent survival varied from year to year, we found no effect of the average winter flow on this parameter. Recapture probability (p) varied among basins, probably reflecting a heterogeneous sampling effort. In conclusion, using multistate models were found that Dippers from three adjacent river basins in northern Spain had a very short-range natal dispersal rate, and a breeding dispersal close to zero, a trait that could be different from findings in other zones of Spain, where dispersal rates seem to be much higher. [ABSTRACT FROM AUTHOR]

Copyright of Ibis is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Environmental conditions in non-breeding areas cause differential winter distribution patterns between age classes in a Eurasian Woodcock Scolopax rusticola population wintering in northern Iberia. To determine the factors driving spatial distribution of first-winter and adult birds in the non-breeding period of a population of the Eurasian Woodcock, in order to make decisions for the management of the species. Using a data set of 10 consecutive winters (2009/10–2018/19), we tested for the effect of year, geographical and habitat-related variables on age ratio and body condition of Eurasian Woodcocks wintering in two nearby zones with different hunting regimes in northern Iberia. Our results suggest that the age ratio depended mainly on year, month, and altitude. As winters progressed, we observed a higher proportion of first-winter birds occurring at sites with lower altitude. First-winter birds were in poorer body condition than adults, and body condition was higher in mid-winter and spring. The effect of hunting on body condition was unclear. Variation in the population structure and body condition between age classes are discussed in the context of age-dependent wintering strategies, which to a large extent depend on survival thresholds that take into account foraging efficiency and the risk of predation. The lack of detectable effects of hunting on age structure and body condition precludes us from giving any management recommendations for northern Iberia. [ABSTRACT FROM AUTHOR]

During migration, landbirds normally need to stop-over in order to rest and/or acquire fuel stores that power their flight. Refuelling strategies become particularly evolutionarily relevant when birds must cross broad geographic barriers, where the chance to land and get food is nil, such as when crossing oceans. Our objective was to learn more about the use of the small islands located close to the mainland coast as stopover areas by small migratory birds that cross the Bay of Biscay. Using data collected in a constant-effort mist-netting programme conducted on Izaro Island (northern Spain) during autumn migration (years 2018 to 2021), we aimed to determine (1) which species land on the island and for how long they stay there, and (2) their fuel load and fuel deposition rate. Structurally, the assemblage was dominated by Willow Warblers Phylloscopus trochilus, which on average accounted for 84% of the abundance. Clustering analyses reveal that the assemblage was rather homogeneous across the four study years. Most birds probably stayed on the island for less than 24 hours, with fewer than 5% being recaptured one or more days after their first capture. The first-capture-event body mass of Willow Warblers captured only once (8.0g, 95%CI 7.8-8.4g) did not differ from the initial body mass of those captured two or more times within a season (8.0g, 95% CI 7.0-9.0g), and those stopping over on Izaro had a negative mean fuel deposition rate of –0.2g/day (SE = 0.1g/d). Overall, Izaro was used as an emergency stopover site during the course of this study, where exhausted birds landed after sea-crossings. From a conservation standpoint, and as compared to other stopover sites used as 'emergency' stopover sites, results suggest that Izaro is of little value for replenishing the fuel stores of these small birds during autumn migration.—Betanzos-Lejarraga, L., Guzmán, I., Escandell, R., Unamuno, E. & Arizaga, J. (2023). Stopover ecology of passerine birds on an islet in the Bay of Biscay in autumn reveals a pattern similar to their use of small Mediterranean islands in spring. Ardeola, 70: 241-255. Durante la migración, las aves terrestres normalmente necesitan detenerse para descansar o adquirir las reservas que después consumirán durante el vuelo. Las estrategias para ganar estas reservas se vuelven particularmente relevantes desde el punto de vista evolutivo cuando las aves han de cruzar grandes barreras geográficas en las que la posibilidad de aterrizar y alimentarse es nula, como ocurre al atravesar océanos. El objetivo de este artículo es profundizar en el uso de las pequeñas islas situadas cerca de la costa por las pequeñas aves migratorias que cruzan el golfo de Vizcaya. Utilizando los datos que fueron recolectados mediante un programa de anillamiento científico desarrollado en la isla de Izaro (norte de España) durante el periodo de paso posnupcial (años 2018 a 2021), se pretendió identificar (1) cuáles son las especies que usan la isla y cuánto tiempo permanecen allí, y (2) cuál es su cantidad y tasa de deposición de reservas. Estructuralmente, el ensamblado estuvo dominado por el mosquitero musical Phylloscopus trochilus, que en promedio representó el 84% de la abundancia. Los análisis de clusters revelaron un ensamblado muy homogéneo a lo largo de todo el periodo de estudio. En general el periodo de estancia en la isla fue de un día para la mayoría de los ejemplares capturados para anillamiento, y de ellos menos del 5% fueron recapturados uno o más días después de su primera captura. La masa corporal de la primera captura no varió entre mosquiteros musicales capturados una sola vez en la isla (8,0 g, IC 95 % 7,8-8,4 g) y capturados dos o más veces en la temporada (8,0 g, IC 95 % 7,0-9,0 g). La tasa de ganancia de reservas de los recapturados fue negativa (–0,2 g/d; SE = 0,1 g/d). En general, nuestros resultados sugieren que Izaro es usada como punto de parada migratoria de emergencia por las aves que, tras cruzar el Cantábrico, llegan exhaustas a la costa del norte de España. Desde el punto de vista de la conservación, y en comparación con otros sitios de parada migratoria utilizados, Izaro parece tener poco valor como punto de ganancia de reservas durante el periodo de paso posnupcial. —Betanzos-Lejarraga, L., Guzmán, I., Escandell, R., Unamuno, E. y Arizaga, J. (2023). La ecología de parada de descanso migratorio de las aves paseriformes en un islote del golfo de Vizcaya en otoño revela un patrón similar al uso de las pequeñas islas mediterráneas en primavera. Ardeola, 70: 241-255. [ABSTRACT FROM AUTHOR]

Variability in morphology and body size between populations of the same species is common and can be influenced by environmental conditions or differential migratory strategies. We focused on analysing body size differences between Yellow-legged gulls Larus michahellis from Mediterranean and Cantabrian-Atlantic Iberian colonies as previous studies have suggested that Cantabrian-Atlantic gulls are smaller than Mediterranean gulls. However, those analyses were based on small sample sizes or did not account for sexual dimorphism. Here we analyse an extensive biometric data set (> 1,500 adult individuals), separating males and females, from nine different sites in each region. Our results reveal a 7% (median) difference both between regions and sexes, for most morphometric variables, with Mediterranean gulls having longer legs (tarsi) and heads (cranium-bill) and thicker bills (bill-depth). This inter-regional difference was even larger for body mass, Mediterranean gulls being 11% (males) and 20% (females) heavier than Cantabrian-Atlantic gulls. In particular, we found that individuals from the Mediterranean populations were allometrically longer-winged than their northern counterparts. We suggest, after discarding other factors, that this wing allometry may be related to the sedentariness of the Cantabrian-Atlantic gulls, compared with the partially migratory strategy of Mediterranean gulls. We also suggest that the larger body size of Mediterranean gulls may help them compete better with resident gulls for food acquisition, once they coincide in the Cantabrian-Atlantic region. Finally, females from both populations were also found to be proportionately longer-winged than males. We hypothesise that this difference could allow smaller females to travel longer distances locally in search of food or to make use of different habitat types, avoiding foraging competition with the larger males.—Marcos Pacheco, M.L., Tavecchia, G., Igual, J.M., Alonso-Álvarez, C., Arizaga, J., Galarza, A., Oro, D. & Martínez-Abraín, A. (2023). Yellow-legged Gulls from the Mediterranean are not only larger but also allometrically longer-winged than those from the Cantabrian-Atlantic. Ardeola, 70: 225-240. La variabilidad en la morfología y el tamaño del cuerpo es común entre poblaciones de la misma especie y puede verse influenciada por las condiciones ambientales o por estrategias migratorias diferenciales. En este trabajo nos centramos en analizar las diferencias de tamaño corporal entre las gaviotas patiamarillas Larus michahellis del Mediterráneo y de las colonias ibéricas cántabro-atlánticas, ya que estudios previos sugirieron un tamaño más pequeño de las gaviotas del Cantábrico/Atlántico en comparación con las gaviotas mediterráneas. Sin embargo, esos análisis se realizaron empleando tamaños de muestra pequeños o no tuvieron en cuenta el gran dimorfismo sexual de la especie. Aquí, analizamos un extenso conjunto de datos biométricos (> 1,500 individuos adultos), separando machos y hembras, de nueve sitios diferentes en cada una de las dos regiones. Nuestros resultados revelaron una diferencia del 7% (mediana) tanto entre regiones como entre sexos, para la mayoría de las variables morfométricas, teniendo las gaviotas mediterráneas patas (tarsos) y cabezas (cráneo-pico) más largos y picos (altura de pico) más gruesos. Esta diferencia entre regiones fue aún mayor en el peso, siendo las gaviotas mediterráneas un 11% (machos) y un 20% (hembras) más pesadas que las gaviotas cántabro-atlánticas. Es importante destacar que los individuos de las poblaciones mediterráneas tuvieron alas alométricamente más largas que sus contrapartes del norte. Sugerimos que esta alometría alar puede estar relacionada con el sedentarismo de las gaviotas cantábrico-atlánticas, frente a la estrategia parcialmente migratoria de las gaviotas mediterráneas, tras descartar otros factores. También sugerimos que el mayor tamaño corporal de las gaviotas mediterráneas podría ayudarles a competir mejor con las gaviotas residentes por la adquisición de alimento, una vez coinciden en la región cántabro-atlántica. Finalmente, también se encontró que las hembras de ambas poblaciones tuvieron alas proporcionalmente más largas que los machos. Proponemos que esa diferencia podría permitir que las hembras (más pequeñas) viajen distancias más largas a nivel local en busca de alimento o hagan uso de diferentes tipos de hábitat, evitando la competencia de forrajeo con los machos más grandes.—Marcos Pacheco, M.L., Tavecchia, G., Igual, J.M., Alonso-Álvarez, C., Arizaga, J., Galarza, A., Oro, D. y Martínez-Abraín, A. (2023). Las gaviotas patiamarillas del Mediterráneo no sólo son más grandes que las cántabro-atlánticas sino que además tienen alas alométricamente más largas. Ardeola, 70: 225-240. [ABSTRACT FROM AUTHOR]

Simple Summary: Urban areas are constantly increasing, as well as human activities related to them. This can lead to an effect in bird populations due to the alterations caused in nature. According to the latest national censuses in Spain, House Sparrow and Eurasian Tree Sparrow populations are decreasing. In this study, we used ringing station data from Spain to assess the tendency of both populations over a two-decade period of time. We also tried to determine the relation of these two populations and their breeding success with the habitat composition. The data analysis confirmed the decreasing trend in both species. However, Eurasian Tree Sparrow showed signs of increasing presence in urban areas, contrary to our predictions. Furthermore, the productivity of both populations remained stable over the study years. Urban areas are constantly increasing, which can cause an effect in bird populations since human activities lead to nature alterations. Populations of House Sparrow (Passer domesticus) and Eurasian Tree Sparrow (Passer montanus) have been decreasing in Spain according to the latest national censuses in Spain. In this study, we tried to assess the population trend over more than two decades using ringing data from Spanish constant effort sites, as well as to determine the population and breeding success proxy in relation to habitat composition at landscape level. We analysed the data and confirmed the decreasing trend in the two species. However, Eurasian Tree Sparrow showed signs of increasing presence in urban areas. Furthermore, the productivity remained stable over sampling sites and years, meaning that the causes of the decreasing populations are affecting both adult and juvenile individuals. [ABSTRACT FROM AUTHOR]

Carotenoid-based ornaments are often considered reliable (honest) individual condition signals because their expression implies physiological costs unaffordable for low-quality animals (handicap signals). Recently, it has been suggested that efficient cell respiration is mandatory for producing red ketocarotenoids from dietary yellow carotenoids. This implies that red colorations should be entirely unfalsifiable and independent of expression costs (index signals). In a precedent study, male common crossbills, Loxia curvirostra, showing a red plumage reported higher apparent survival than those showing yellowish-orange colors. The plumage redness in this species is due to ketocarotenoid accumulation in feathers. Here, we correlated the male plumage redness (a 4-level visual score: yellow, patchy, orange, and red) and the body morphology in more than 1,000 adult crossbills captured in 3 Iberian localities to infer the mechanisms responsible for color evolution. A principal component analysis summarized morphometry of 10 variables (beak, wing, tarsus length, etc.). The overall body size (PC1) and the length of flight feathers regarding body size (PC3) showed significant positive relationships with plumage redness. Plumage redness was barely correlated with bill shape measures, suggesting no constraint in acquiring carotenoids from pine cones. However, large body sizes or proportionally long flying feathers could help carotenoid acquisition via social competition or increased foraging ranges. Proportionally longer flight feathers might also be associated with a specific cell respiration profile that would simultaneously favor flying capacities and enzymatic transformations needed for ketocarotenoid synthesis. Such a phenotypic profile would agree with the hypothesis of ketocarotenoid-based colors acting as individual quality index signals. [ABSTRACT FROM AUTHOR]

Urbanization constitutes one of the most intensive and fast spreading factors explaining biodiversity loss worldwide. The extension of urban areas and landscape configurations affects the ability of raptors to exploit urban patches. The Tawny Owl Strix aluco is a forest-dwelling nocturnal species with a wide distribution range that is well-adapted to urban environments. However, it remains unknown which habitat factors explain its presence in urban-associated landscapes. Our main objective is to determine the effect of urban landscapes on the probability of occurrence of Tawny Owls along an urban-rural gradient. It is expected that Tawny Owls will be able to use urban patches that have (1) at least 30% tree cover thanks to gardens/parks for hunting but (2) they will not use those with high noise levels (i.e., highways). Our research was carried out in the municipality of Donostia-San Sebastian in the Basque Country, Northern Spain. Data were obtained from a survey conducted in 2017. The municipality was divided into 329 square cells, of which 251 were surveyed. Tawny Owls were detected in 141 cells, and we found that nocturnal noise level and scrub cover contributed most to explaining the probability of Tawny Owl occurrence; with nocturnal noise having a significant negative effect on occurrence probability, and scrub cover a positive effect, probably because the species uses open or semi-open areas to hunt (but woodland to breed). Overall, it can be concluded that the very noisy and/or urbanized parts of the city comprised a non-optimal habitat for the species.—Pagaldai, N., Rodríguez-Pérez, J., Arnaiz, A. & Arizaga, J. (2023). Factors shaping occurrence probability of a generalist raptor species across an urban-rural gradient. Ardeola, 70: 75-88. La urbanización es una de las causas más intensivas y rápidas que explican la pérdida de biodiversidad a nivel mundial. La extensión de las áreas urbanas y la configuración del paisaje afectan la habilidad de las rapaces para explotar parches urbanos. El cárabo euroasiático Strix aluco es una especie forestal nocturna con una amplia distribución y bien adaptada a los ambientes urbanos. Sin embargo, siguen siendo desconocidos qué factores relacionados con el hábitat explican su presencia en ambientes urbanizados. Nuestro objetivo general es el de determinar el efecto que tienen los paisajes urbanos en la probabilidad de presencia del cárabo euroasiático a lo largo de un gradiente urbano-rural. Se espera que el cárabo sea capaz de usar los parches urbanos que tengan (1) un mínimo número de jardines/parques con árboles para cazar; y (2) un limitado nivel de ruido durante la noche (ej. autopistas). Nuestro estudio se llevó a cabo en Donostia-San Sebastián, en el País Vasco, norte de España. Los datos se obtuvieron mediante un censo realizado en 2017. El municipio se dividió en 329 cuadrículas y 251 de ellas fueron censadas. Se detectaron cárabos en 141 cuadrículas, y obtuvimos que el ruido nocturno y la cubierta de matorral fueron las variables que más contribuyeron a explicar la probabilidad de presencia; el ruido nocturno tuvo un significativo efecto negativo en la probabilidad de presencia, mientras que la cubierta de matorral tuvo un efecto positivo, probablemente porque la especie utiliza áreas abiertas o semiabiertas para cazar (pero bosques para criar). En general, se puede concluir que las zonas más ruidosas y urbanizadas de la ciudad componen un hábitat no óptimo para la especie.—Pagaldai, N., Rodríguez-Pérez, J., Arnaiz, A. y Arizaga, J. (2023). Factores que afectan a la probabilidad de presencia de una rapaz generalista a lo largo de un gradiente urbano-rural. Ardeola, 70: 75-88. [ABSTRACT FROM AUTHOR]

Crimean-Congo hemorrhagic fever virus (CCHFV), the causative agent of Crimean-Congo hemorrhagic fever (CCHV), is an arthropod-borne virus (arbovirus) with clinical relevance worldwide (1). CCHF causes sudden onset of signs and [...]

Barn Owls Tyto alba and Red-billed Choughs Pyrrhocorax pyrrhocorax show differential breeding outputs as a consequence of sharing nest boxes. To describe for the first time a commensal relationship between the Red-billed Chough and the Barn Owl during the breeding period. During systematic monitoring of 90 nest boxes installed for Barn Owls in Navarre, northern Spain, it was found that in some boxes, Barn Owls and Red-billed Choughs nested simultaneously (inside and on top of the box, respectively). The clutch size, breeding success, and the number of fledglings of each species were compared when nesting together versus separately during the breeding period of 2015 and 2017. About one-third of the nest boxes observed during the study were simultaneously used by both Barn Owls and Red-billed Choughs. No relationship was found between the composition of the habitat around the boxes and the degree of occupancy for either species. Nest box sharing had no significant effect on the breeding output of Barn Owls, but improved the breeding performance of Red-billed Choughs by increasing the number of fledglings in relation to clutch size. Barn Owls can provide benefits to Red-billed Choughs by controlling the populations of rodents, which could act as nest predators. Given that Barn Owls apparently do not obtain benefits nor incur any costs by the association with Red-billed Choughs, this interaction may be defined as commensalism. To our knowledge, this is the first documented nesting association between a corvid and an owl species. [ABSTRACT FROM AUTHOR]

The main goal of this study was to describe in detail the structure and phenology of flocks of the Common Linnet (Linaria cannabina) passing through eastern Spain. Data were compiled during the spring and autumn migrations of 2019 to 2021 (excluding spring 2020), by counting and by capture for ringing. We counted 6151 flocks, comprising 17 732 birds, of which 7638 individuals were captured. The size of flocks ranged from 1 to 30 Linnets (mean ± 95% CI, 2.8 ± 0.1), with a higher proportion of solitary migrants in spring (46.8%) than in autumn (33.8%). Passage in spring peaked during the third hour after dawn, whilst in autumn this peak was just after dawn. There were more females than males (56%), probably as an indicator of latitudinal differential migration. Juveniles were significantly more abundant (c. 80%) than adults. The phenological pattern of the passage was more variable in spring than in autumn, and such variation could be useful to explore potential impacts of climate change on the migration ecology of the species. [ABSTRACT FROM AUTHOR]

Aim: In temperate mountain ranges, sharp spatial variations in habitat heterogeneity and climate provide a perfect study setup to assess genetic and phenotypic differentiation in bird populations. In this paper, we analysed morphological divergence patterns across geographical and environmental gradients, in correlation with genetic differentiation and geographical isolation, in the breeding grounds of a long‐distance migratory passerine. Location: Northwestern Iberian mountains. Taxon: The Iberian bluethroat, Luscina svecica azuricollis. Methods: We collected a sample of 625 Iberian bluethroats across their whole breeding range to measure body weight and tarsus length, as well as wing length and pointedness. Morphological differentiation across geographical (latitude and elevation) and environmental (climate and vegetation) gradients was assessed using generalized linear mixed models. Additionally, the role of genetic distance and geographical isolation as drivers of morphological differentiation was evaluated with Mantel tests. Results: Bird morphology varied significantly with latitude and elevation, but not with climate or vegetation. In the case of latitude, morphological differences in body size were contrary to Bergmann's rule statements. All biometric and morphometric variables diverged among localities. A similar trend was found for genetic clusters, except for wing shape. Body weight and wing length were both correlated with geographic distance, while only the former varied with genetic differentiation. The greatest genetic and phenotypic differentiation was detected in the southernmost mountain range, that holds the most geographically isolated genetic group. Main conclusion: Evidence suggests that the strong morphological differentiation observed in the Iberian breeding bluethroat across geographical gradients results from the combination of unambiguous deterministic forces, such as ecological selection mechanisms, and other factors, such as geographical isolation, that can be either deterministic, stochastic or both, all acting at different scales. [ABSTRACT FROM AUTHOR]

We aimed to describe the morphologic and isotopic differences of European Goldfinches Carduelis carduelis according to their migratory behaviour or geographic origin. We compared morphologic and isotopic variables between birds caught in two different obligatory migratory pathways (eastern and western border of the Pyrenees) and throughout the post-breeding period (from late summer to winter). The isotopic and morphological traits varied across seasons (from autumn to winter), indicating that birds captured later in the season had traits typical of longer-distance migrants that come from regions situated further north. Moreover, our results suggest that Goldfinches caught in the eastern and western borders of the Pyrenees slightly differ in body size and in one of the two colour patch-associated traits, but not in their flight apparatus or isotopic values, these last being more strongly related to their areas of origin. Such observed regional differences, therefore, may be more strongly related to other selection pressures. [ABSTRACT FROM AUTHOR]