Alejandro Martínez-Abraín

We used data from two major continental fragment islands (Mallorca and Menorca) and from the nearby mainland (Catalonia) to test the avian density compensation hypothesis (i.e. abnormally high density of species inhabiting islands with species-poor biotas with a large data set. Our data sets covered 22 years in Catalonia, 10 years in Mallorca and 19 years in Menorca. We calculated island-mainland density ratios and their hierarchically bootstrapped confidence intervals for 87 species x habitat crossings, and then fitted logistic regression models to analyse whether island/mainland ratios were > 1 as a function of diet, habitat and taxonomic Order. Additionally, we compared densities of the three most common breeding raptors on the islands. Average avian densities were 2.8 times higher in Mallorca and 2.2 times in Menorca. From all species x habitat crossings analysed density ratios were > 1 in 73% of cases for Mallorca and 83% for Menorca. Some island top ten species x habitat crossings showed densities more than 20 times higher than those on the mainland. Raptors density ratios were 20–60 times higher in the islands. Most cases of higher island density were well explained by competitive release within guilds. Since under high densities birds are known to become more tolerant with conspecifics, we suggest a new explanation for island raptor sedentarism. When considering all diurnal breeding raptors as a test, the mainland/island density ratio was > 1, which rules out the possibility that large island densities could be the cause of island species impoverishment rather than the consequence.

El objetivo de este estudio fue analizar los cambios a largo plazo (2002-2023) en el origen geográfico de los migrantes o en la proporción de migrantes-residentes de una comunidad de aves paseriformes invernantes en un hábitat de carrizal en el estuario del río Anllóns (A Coruña, NO de España) a partir de datos de anillamiento. Aplicando la regla de Bergmann, utilizamos la biometría de las aves como indicador del cambio de origen dentro de las especies. A priori, esperábamos detectar una menor representación de aves de latitudes más altas, en el contexto del actual escenario de calentamiento global, manifestándose como una tendencia hacia las aves de menor tamaño. Para ello, se seleccionaron las cinco especies invernantes con más datos disponibles y se estudió la variación temporal de la longitud media de la cuerda alar, el tarso y un índice de alometría alar. Los resultados revelaron una notable estabilidad biométrica en la mayoría de las especies, lo que sugiere una resiliencia en los patrones de invernada o un desajuste ecológico frente al calentamiento en las últimas dos décadas. La única excepción notable fue el escribano palustre Emberiza schoeniclus, que mostró un incremento estadísticamente significativo y biológicamente relevante en la longitud del tarso (8,73% en machos; 6,28% en hembras). Este aumento contradice la hipótesis de una reducción del tamaño debido al calentamiento. Más bien, parece reflejar un cambio en la composición poblacional con declive de los escribanos residentes de menor tamaño y un aumento proporcional de los invernantes del norte de Europa, de mayor tamaño. Concluimos que, contrariamente a lo esperado, la comunidad invernante estudiada ha cambiado poco en cuanto a su origen geográfico durante los 22 años de estudio, a pesar del calentamiento del clima.—Iglesias-Manteiga, R., Maestro Saavedra, M. y Martínez-Abraín, A. (2026). No se detectan cambios relevantes a largo plazo en el origen de los paseriformes invernantes de carrizal presaharianos en el noroeste de España durante las últimas dos décadas, empleando la biometría como proxy. Ardeola, 73: 205-219.

Permanent population collapse has been long known to be caused by the interaction of at least two orthogonal factors. Fisheries collapses adjust to that pattern by the interaction of global and local factors. We focused on the study of this pattern on the collapse of eel fisheries. Specifically, we analysed a long time series of eel landing data (1951–2022) from a coastal wetland in the western Mediterranean (Albufera de Valencia). Landings peaked in 1958 but a strong regime shift was detected in 1968 by means of Rodionov’s sequential t test analysis, with captures dropping by 86% in ten years (1967–1977). Declining landings (1956–1976) showed a strong positive association ( r = 0.94; r ² = 0.88) with the 5-year moving average of the Atlantic Multidecadal Oscillation (AMO). However, both time series completely decoupled from 1976 on as AMO moved towards a warm phase favourable to eels but eel landings remained at low levels until present. We explain this decoupling as a result of the anthropogenic alteration of the wetland since the end of the 1960s. The eel fishery collapse occurred almost a decade earlier than in other western Mediterranean wetlands, likely because of the differential timing of eutrophication of these sites. Some urgent management actions are suggested.

En este estudio demostramos por primera vez que las predicciones sobre el futuro de la fauna vertebrada amenazada realizadas en los inicios de las políticas de conservación en España (años 70 del siglo XX) tuvieron una probabilidad baja de acierto (0.29 [0.15-0.45] IC 95 %), y por lo tanto peor de lo esperable por puro azar (0.5). Las predicciones fueron especialmente pobres en el caso de las aves y de los depredadores, en contraste con mamíferos y no depredadores. En concreto, las predicciones de futuros declives, identificadas por nosotros en una búsqueda de literatura faunística de los años 70, acertaron mucho menos (0.20 [0.07-0.38]) que las predicciones de recuperación (0.62 [0.25-0.91]). Discutimos estos resultados dentro del marco de la conservación de especies y de espacios, pero también de los cambios socioeconómicos experimentados por el país en los últimos 50 años, poniendo especial énfasis en las inesperadas consecuencias directas (disminución de la persecución directa) e indirectas (cambios en el uso del suelo) del éxodo rural. Si tenemos en cuenta sólo las predicciones de declive, sugerimos que el abandono del medio rural estuvo detrás del fallo de predicción en un 53.1 % de los casos, frente al 46.9 % atribuible a la conservación. Además, se repasaron los distintos catálogos nacionales de fauna amenazada desde el primer Listado promovido por Blas Aritio en 1973, concluyéndose que en general no han reflejado bien la mejora del estatus de las antiguas especies amenazadas.

Material Suplementario de Ecosistemas, 35(1), 3151 (https://doi.org/10.7818/ECOS.3151): Fuentes consultadas y Bibliografía relacionada con la conservación de la fauna vertebrada amenazada en España, publicada entre los años 1970 y 1979, identificando predicciones realizadas acerca de la situación esperada para las especies en el futuro.

The intense human persecution of wildlife in the past forced many animal populations to look for refuge in human‐inaccessible habitats. With the decline of direct persecution, and the changes in the attitude of modern urban societies towards wildlife during the last few decades, an ecological process of abandonment of refuge habitats has become pervasive, and many species make habitat choices deemed surprising presently, such as colonizing sites that are more accessible to humans. We tested this process in the yellow‐legged gull Larus michahellis by analysing long‐term time series (1976–2022) of breeding pairs in seven colonies in southern Europe. Overall, yellow‐legged gull numbers showed a strong pattern of decrease during the study period, due to the recent closure of open‐air garbage dumps. However, while the number of pairs in colonies located in human‐inaccessible sites (islets with cliffs) declined rapidly, new colonization together with a monotonic linear population growth was detected in human‐accessible sites, coinciding in time with the departure from refuges. Moreover, we found that the new small yellow‐legged gull colonies acted as cores for the formation of multispecies waterbird colonies likely by heterospecific attraction, that provides an added unexpected conservation value to yellow‐legged gulls traditionally considered a pest species.

Estimating hatching success of egg clutches is essential for quantifying reproductive success in sea turtles. Thus, proper reporting is necessary to provide meaningful information for knowledge acquisition and management. Here we review how hatching success has been reported in the scientific literature and use our own multi-annual multi-species datasets to explore the best ways for describing hatching success data. Despite non normality, the central tendency of hatching success data was most often described using arithmetic means. Only 17 out of 203 (8%) studies reported the median, compared to 192 (95%) that reported the mean (6 studies reported both). In 24% of studies, a dispersion metric was not provided. In our comparison, the arithmetic mean was only a good predictor of central tendency in leatherback turtles (Dermochelys coriacea), with the median (0.45) being only slightly above the mean (0.43). In leatherbacks, hatching success was characterized by high variability, and not by a consistently low hatching success, as indicated by the low skewness and large spread of data. On the contrary, hatching success data were strongly skewed and skewed toward high values in green turtles (Chelonia mydas) (25% and 75% percentiles: 0.88 and 0.98) and olive ridley turtles (Lepidochelys olivacea) (25% and 75% percentiles: 0.75 and 0.97) respectively, with presence of outliers in both cases. Basic statistics, appropriate for characterizing non-normal distributions such as the median, skewness or kurtosis, together with boxplots, provided accurate description of hatching success data. Using these straightforward statistics would greatly improve the ecological understanding of hatching success in sea turtles.

This study targeted prey type and prey size selection by a small but expanding population of the Eurasian oystercatcher (Haematopus ostralegus) at the southernmost range of its European distribution (Galicia, NW Spain). We compared consumption and availability of prey items delivered to chicks. Consumption was studied through piles of discarded shells and availability was sampled in the foraging grounds located around nesting sites on three different islets. The only two prey types present in shell piles were mussels (Mytillus galloprovincialis) and limpets (Patella sp.). Our chi-square analyses did not detect any prey type selection by oystercatchers, but the use of the Savage index with Manly’s method identified negative selection of limpets at one of the study sites. As a rule, the birds consumed limpets and mussels in proportion to their availability in their foraging grounds. At one of the study sites periwinkles (Littorina sp.) were present but not consumed. Regarding prey size, oystercatchers selected (1) mussels that were either similar to or larger than those available, and (2) limpets that were larger than those available. However, at one site out of three, the oystercatchers positively selected limpets of smaller size than those available. Hence, our results showed some heterogeneity among sites regarding prey type selection, but quite a consistent pattern of selection of larger prey. We suggest that oystercatcher foraging ecology is not explained solely by considering the balance between energy uptake and costs, but importantly by introducing additional variables such as the risk of chick predation, and current nesting as refugees on islets with no access to mainland beaches and sand dunes for breeding, where both adult and chick diet could be substantially different.

Identifying and quantifying the main factors that are jeopardizing amphibian communities worldwide is essential for planning effective amphibian conservation. We collected data on the presence/absence of salamanders and newts (Caudata) and frogs and toads (Anura) in >3600 water points from a large region (30,000 km²) in NW Spain during a 10‐year period (2004–2013). We contrasted a large set of hypotheses explaining presence/absence as a function of anthropogenic factors across the regional elevation gradient (1–2036 m). Logistic regression modeling revealed that salamanders and newts were mainly influenced by pollution and by land use changes, and that the effect of these factors changed with elevation. However, frogs and toads were affected by a larger set of factors acting synergistically, although not including land use changes, and their effect operated at all elevation ranges, except in the case of biological factors (invasive species and wild boar abundance) with higher effects at low elevation. Changes in land use was the most common factor at any elevation and included the abandonment of rural areas, which favors shrub and tree encroachment on former open land, and loss of water points. The most resilient species at any elevation were two frogs, Pelophylax perezi and Rana parvipalmata. The least resilient species were two salamanders, Chioglossa lusitanica and Lissotriton helveticus, followed closely by two toads, Alytes obstetricans and Pelobates cultripes. Unoccupied sites had higher frequencies of biological effects and of changes in land use in the first 5 years of study and lower frequencies of direct human influence factors in the second period. Overall, our results showed that the studied amphibian metacommunity was negatively influenced both by direct and indirect anthropogenic factors, but also that many amphibian species were not only capable of occupying sites which had been altered by human action, but were even favored by land uses generating open habitat, a habitat type that is increasingly uncommon in the region, in the entire Iberian Peninsula and in Europe.