Juan Arizaga

Aranzadi Science Society · Department of Ornithology

The food available in open-air landfills, one of the most common predictable anthropogenic food subsidies (PAFS), can have a profound impact on animal biodiversity. Understanding how and to what extent PAFS affect wildlife is crucial for a sustainable management of resources. Most large gulls behave as opportunistic foragers and constitute a good a...

The dynamics of migratory populations at wintering quarters can inform on population state and size because these areas act as demographic funnels, assembling birds from different origins. Previous evidence on survival probability of woodcock Scolopax rusticola wintering in northern Spain suggested a high harvesting pressure, but whether this press...

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 Medi-terranean and Cantabrian-Atlantic Iberian colonies as previous studies...

En 2019 se diseñó una red de muestreo basada en puntos fijos de censo para monitorizar poblaciones de pequeñas aves riparias en Gipuzkoa. El objetivo de este programa es obtener estimas robustas sobre la probabilidad de ocupación (presencia; ψ), detectabilidad (p), tasa de colonización (γ) y tasa de extinción (ε) de especies como la lavandera casca...

Several bird species benefit from anthropogenic food subsidies, such as landfills and fishing discards, that are being reduced owing to introduced legislation. For instance, since 2019, Europe has passed legislation to reduce dramatically the amount of fisheries discards through the Landing Obligation (LO), which states that all fish species under...

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 p...

Compared to other animal movements, prospecting by adult individuals for a future breeding site is commonly overlooked. Prospecting influences the decision of where to breed and has consequences on fitness and lifetime reproductive success. By analysing movements of 31 satellite-and GPS-tracked gull and tern populations belonging to 14 species in E...

Capsule Barn Owls Tyto alba and Red-billed Choughs Pyrrhocorax pyrrhocorax show differential breeding outputs as a consequence of sharing nest boxes. Aims To describe for the first time a commensal relationship between the Red-billed Chough and the Barn Owl during the breeding period. Methods During systematic monitoring of 90 nest boxes installe...

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. T...

En 2017, al amparo del Comité Ornitológico de Euskadi (COE), se puso en marcha el Comité de Rarezas de Euskadi (CRE), un grupo de trabajo cuyo fin es compilar, estudiar y publicar todas las citas de especies o subespecies de aves cuya presencia en Euskadi es accidental o irregular. Desde su creación, el CRE ha evaluado un total de 681 citas. De tod...

A través de este documento, el Comité de Rarezas de Euskadi (CRE) recopila la homologación de citas de aves raras en 2021 en el territorio de Euskadi (Comunidad Autónoma Vasca). Este Comité, creado al amparo del Comité Ornitológico de Euskadi (COE), ejerce su actividad para recopilar, estudiar y publicar todas las citas de especies o subespecies cu...

Artificial food subsidies like landfills generate very strong impacts on animal ecology and spatial behavior. Landfills indeed have been considered to be one of the most influential factors explaining the very fast recovery of many colonial waterbird populations worldwide, as documented for the white stork Ciconia ciconia. More recently, the increa...

Volunteer-based (i.e., citizen science) monitoring schemes constitute a basic piece for the long-term monitoring of bird populations. This work aims to determine whether we can reduce the sampling effort, in terms of number of sampling journeys per yearly campaign, of a long-term breeding bird monitoring ringing scheme in Spain. With that goal, we...

The aims of the present article were to (1) estimate population trends for breeding aquatic birds in the Basque Country during the period 2005-2017, (2) estimate the importance of different wetlands according to their relevance for aquatic birds and (3) evaluate the methodology of the programme in order to detect potential biases or shortcomings an...

The food available in open-air landfills, one of the most common Predictable Anthropogenic Food Subsidies (PAFS), can have a profound impact on animal biodiversity. Understanding how and to what extent PAFS affect wildlife is crucial for a sustainable management of resources. Most large gulls behave as opportunistic foragers and constitute a good a...

The increase of the tourism and urbanization of vast areas of dunes and beaches has been accompanied by an increase in the level of disturbances to many shorebirds, especially on those species which depend on such habitats to breed. The European Kentish plover (Charadrius alexandrinus) population is declining, also in the Canarian archipelago, one...

A lo largo de lo que va de siglo se viene observando en Gipuzkoa un posible aumento de la población nidificante de milano real Milvus milvus. Si bien parcialmente esta realidad se ha asociado a un incremento en el esfuerzo de muestreo, el proceso de colonización y aumento poblacional de la especie en la provincia parece evidente. Así, de la ausenci...

Censos recientes revelan un declive poblacional acusado de la gaviota patiamarilla Larus michahellis en buena parte de su área de distribución. Ya a mediados de la década de 2010 se registró en la costa vasca un declive cercano al 50% respecto al censo de 2007. Tras repetir el censo en 2021, el objetivo de este artículo es (1) actualizar el tamaño...

El atlas de aves nidificantes de San Sebastián es un proyecto colaborativo en el que han participado más de 60 personas con el fin de detectar todas las especies de aves que se reproducen en el municipio. Se trata de un trabajo exhaustivo y detallado, sin precedentes, que muestra por primera vez la distribución espacial y estima del tamaño de la po...

The dynamics of wild populations are governed by demographic rates which vary spatially and/or temporally in response to environmental conditions. Conservation actions for widespread but declining populations could potentially exploit this variation to target locations (or years) in which rates are low, but only if consistent spatial or temporal va...

The Bay of Biscay is an important non-breeding area for some Palaearctic gull species and populations. The aim of this work is to describe the spatial and temporal distributions of non-breeding gulls in the Bay of Biscay, and to identify their major areas of origin. With that goal, we analysed 6773 live sightings of colour-ringed gulls within the s...

A través de este documento, el Comité de Rarezas de Euskadi (CRE) recopila la homologación de citas de aves raras en 2020 en el territorio de Euskadi (Comunidad Autónoma Vasca). Este Comité, creado al amparo del Comité Ornitológico de Euskadi (COE), ejerce su actividad para recopilar, estudiar y publicar todas las citas de especies o subespecies cu...

Determining the age of specimens is of great help in wildlife management, especially for rare or threatened species in which each individual has a high value. In birds, differences in moulting pattern between juveniles and adults may in some cases allow determination of a bird’s age from the examination of its plumage. In the present study, we anal...

Natural habitats are being altered and destroyed worldwide due to urbanization, leading to a decrease in species abundance and richness. Nevertheless, some species, including tawny owls, have successfully colonized this novel habitat. Consequences at the population level have not been described; thus, our main objective was to describe the effects...

Carotenoid staining has been repeatedly shown to serve as a sexually selected individual quality signal. In different species, individuals that show brighter carotenoid-based signals have been found to have superior feeding abilities, recover faster from disease, and generally enjoy better body condition. In the common crossbill (Loxia curvirostra)...

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...

Las cajas-nido constituyen una herramienta muy útil para el desarrollo de diversos estudios en aves, pues permiten el diseño experimental y la comparación de muestras sometidas a distintos tratamientos o localizaciones. Igualmente, son útiles para la conservación de aves en hábitats con muy poco arbolado maduro, como ocurre en muchos parques urbano...

The growth pattern of an organism is influenced by multiple factors, such as its sex, parental investment, food abundance and sibling competition. For species showing sexual size dimorphism, the sex of siblings is expected to affect the growth of nestlings through differences in competitive hierarchies mediated by an asymmetry in body size. This st...

Background Philopatry rate is one of the main factors shaping population dynamics in colonial seabirds. Low rates of philopatry are linked to populations with high dispersal, while high rates are linked to populations with a very high spatial structure pattern (i.e., metapopulations). The Cantabrian Yellow-legged Gull ( Larus michahellis ) populati...

The management of mixed municipal waste can have an impact on wildlife and ecosystems. Previous studies have investigated how opportunistic species like gulls can react very fast to new landfills; however, the impact of landfill closure on bird populations is less investigated. Yet, there is a need to understand how fast and to what extent, animal...

Wildlife conservation policies directed at common and widespread, but declining, species are difficult to design and implement effectively, as multiple environmental changes are likely to contribute to population declines. Conservation actions ultimately aim to influence demographic rates, but targeting actions towards feasible improvements in thes...

The white stork Ciconia ciconia is one of the most emblematic birds in rural habitats of Europe. Its populations showed a drastic decline during the 20th century, followed by a rapid recovery in the last decades. The population increase has led to a relaxation in the specie’s monitoring effort, the last Spanish national official census having been...

Variación de la abundancia del zorzal en invierno durante la temporada de caza en el sur de Europa: la importancia de las reservas Analizamos las variaciones de la abundancia del zorzal común (Turdus philomelos) y el mirlo (T. merula) durante la temporada de caza en reservas y en zonas de caza. Una vez controlado el efecto del hábitat, la abundanci...

Presencia marginal de plástico en nidos de gaviotas patiamarillas (Larus michahellis) en el sureste del golfo de Vizcaya El enredo en nidos y el consumo de plástico pueden ser algunas de las causas de mortalidad en los pollos de varias especies de aves marinas. Los desechos de plástico se eligen como material para la construcción de los nidos y, se...

Human disturbances can have a severe impact on avian conservation, decreasing diversity and carrying capacity of ecosystems. Coastal wetlands are hotspots for the conservation of biodiversity but they commonly suffer the impact of human activity because they are usually priority areas for socio–economic development. The aim of this study was to det...

Background The dynamics and structure of many bird communities are changing due to the global warming and changes in the land use and management. The Ebro Valley constitutes one of the chief wintering areas for several passerine species in Iberia, and the reed beds spread across this Valley concentrate huge numbers of birds that use them to roost,...

Las plantaciones de eucalipto (género Eucalyptus) tienen una amplia distribución a escala global y causan preocupación por los efectos que pueden ocasionar sobre el medio ambiente. En este trabajo revisamos la evolución de la superficie cubierta por los eucaliptos en Euskadi y evaluamos sus efectos ambientales a partir de la bibliografía científica...

El Grup Au d’Ornitología se adhirió al proyecto Piccole Isole (PI) en 1994, con la realización de campañas de anillamiento en el archipiélago de Columbretes y, particularmente, en Illa Grossa (Columbrete Grande). Desde entonces, se ha anillado de manera ininterrumpida durante el periodo de paso migratorio prenupcial, principalmente entre los meses...

La costa vasca constituye un área de paso e invernada de gaviotas en el Golfo de Vizcaya y éste a su vez en el Paleártico sudoccidental. Este trabajo se establece con el fin de determinar la importancia relativa de las especies que frecuentan la región en invierno, estimar su abundancia, identificar las zonas más importantes y evaluar hasta qué pun...

Capsule: Linear censusing and occupancy models based on fixed sampling points are alternative widely used techniques to determine bird densities in riparian ecosystems, although it cannot be always properly executed. Aims: The aim is to assess the survey efficiency for river birds using occupancy models in contexts of impaired visibility owing to d...

El objetivo de este trabajo es estimar la tendencia de la población de carricero común Acrocephalus scirpaceus Herman, 1804 en la costa vasca. Para ello, se han utilizado los datos que se obtienen en el Programa de Estaciones de anillamiento para la Monitorización de Aves Nidificantes, entre los meses de mayo y agosto durante el periodo 2010-2019,...

Studying the individual or population response of species to variations in weather is gaining impetus due to increased interest in quantifying the effect of global change on biodiversity. Our goal here was to test the role of meteorological conditions (particularly extreme weather) on the activity budget of a generalist seabird species during its b...

El objetivo de este artículo es describir la morfología de la lavandera cascadeña Motacilla cinerea L., 1758 (y en particular su variación según sexos y clases de edad) en Gipuzkoa. Además, y dado que en las aves de primer año no es posible conocer el sexo a partir de la coloración, se realiza un Análisis Discriminante (AD) con el fin de ofrecer un...

Methylmercury (MeHg) is the most bioavailable and toxic form of the globally distributed pollutant Hg. Organisms of higher trophic levels living in aquatic ecosystems have potentially higher concentrations of MeHg. In this work, we analysed both MeHg and inorganic Mercury (Hg(II)) concentrations from dorsal feathers of chicks from ten colonies of Y...

Crossbills (Loxia spp) provide a classical avian model of ecological specialization on food resources. Previous studies have suggested that morphometric, genetic and vocal diversification among Common Crossbill L. curvirostra populations is better explained by ecological distance (use of different conifers) than by geographical distance, indicating...

The carotenoid-based colouration that many birds present may honestly reflect the quality of the bearer, as carotenoids have to be obtained through diet. These pigments are important for many physiological functions and individuals could find a trade-off between the allocation of carotenoids for these uses and their accumulation for secondary-sexua...

The University of the Azores, in collaboration with the Spanish Foundation Aranzadi has been developing a project to colour ring YLG chicks on different islands of the Azores since 2017 to discover some aspects of the biology of this species that remain unknown.

The availability of food subsidies of anthropogenic origin has strong consequences on the trophic ecology and population dynamics of several opportunistic species. However, evidence suggests that the use of certain feeding sources is very local, and hence, potentially important food subsidies may have a relatively small area of influence, resulting...

Measures of species co-occurrence, as a proxy of biotic interactions, may be as important as environmental factors when explaining the distribution of many species. We assessed the relative effect of both species co-occurrence and environmental factors in predicting the occurrence (presence/absence) of woodpeckers and passerines in mature forests o...

El seguimiento de poblaciones, y particularmente la monitorización de sus tendencias demográficas, es esencial en el ámbito de la conservación. Este estudio analiza la estructura del ensamblado de aves capturadas en la estación de anillamiento de Loza (Navarra), adscrita al Programa de Estaciones para la Monitorización de Aves Nidificantes (EMAN),...

Transients can have a severe impact on demographic parameter estimates. For instance, the use of visual counts or number of captures at a ringing station to assess indices of abundance may result in biased over-estimates due to the presence of transients. With the aim of contributing to understand transient dynamics within the Eurasian breeding pas...

The structure of a species assemblage at given sites constitutes a key ecological parameter to understand the dynamics of bird assemblages. The aim of this paper is to (1) quantify how variable is a passerine assemblage associated with an inter-tidal reedbed area at a main stopover site in the Atlantic flyway in northern Iberia and to explore poten...

Este es el segundo informe del Comité de Rarezas de Euskadi (CRE), relativo a la homologación de citas de aves raras en 2018 en el territorio de Euskadi (Comunidad Autónoma Vasca). Este Comité, creado al amparo del Comité Ornitológico de Euskadi (COE), ejerce su actividad para recopilar, estudiar y publicar todas las citas de especies o subespecies...

The development of long-term monitoring programmes is essential to determine the con- servation status of populations and species. The white-throated dipper, Cinclus cinclus L., 1758 is included in several lists of threatened species and is, consequently, an interesting species from the point of view of conservation and management of our natural he...

The migration strategies of smaller, south European, Mediterranean birds are less well known than those of northern and central European birds. We used geolocators to map individual spatio-temporal migration schedules of three species breeding in the Iberian Peninsula: the White-rumped Swift Apus caffer, rufous-tailed Scrub-robin Cercotrichas galac...

The region of Gipuzkoa is used on a permanent basis by the bearded vulture Gypaetus barbatus L., 1758, but the colonization process is slow, apparently due to the difficulty of finding a permanent mate. This article aims to contribute to evaluating the role of Gipuzkoa, which forms the western border of the Pyrenean population of bearded vulture, i...

Additional supporting information. Table S1. Individual and mean migration parameters of southern and northern species, respectively. Table S2. Mean and standard deviation (SD) of migration parameters in southern and northern species. Table S3. Wilcoxon-Mann-Whitney test results comparing different migration parameters of individual southern and no...

The management of game species relies on robust estimates of hunting-related mortality. A relative measure of this mortality can be obtained by comparing survival estimates of animals across similar areas with different hunting pressures. We conducted live recapture-dead recovery analyses on wintering Eurasian Woodcocks Scolopax rusticola (hereinaf...

During the chick-rearing period, strategies of prey provisioning can have a decisive impact on several reproductive aspects.Adults can maximise their foraging effort by increasing the number of fish-prey brought to the nest per unit time and/or by catching more JMLC energetic prey, i.e. larger prey or prey with relatively higher caloric values. The...

The ecology of opportunistic foragers can be highly dependent on anthropogenic food sources, such as landfills, resulting in changes in several ecological and demographic aspects. The total closure of several landfill sites and the use of deterrence systems to prevent access to the remaining open landfill sites in a region in the northern Iberian P...

The migratory behaviour of European Song Thrush (Turdus philomelos) populations ranges from resident in the south and west to partly or totally migratory in northern, central and eastern Europe. This varied migratory behaviour could be reflected in morphological adaptations, with migrants having a proportionally longer wing, lower tail:wing ratio,...

Este es el primer informe, sobre aves raras en Euskadi, del Comité de Rarezas de Euskadi (CRE), relativo a la homologación de citas de rarezas en 2017 en el territorio de Euskadi (Comunidad Autónoma Vasca). Este Comité, creado al amparo del Comité Ornitológico de Euskadi (COE), se pone en marcha en 2017 y nace con el fin de compilar, estudiar y pub...

Capsule: Northern Gannet Morus bassanus counts obtained from a coastal monitoring network in northern Spain were highly determined by wind conditions. Aims: To determine how external factors including weather conditions affect seabird counts in a land-based seabird monitoring project (Red de observación de Aves y Mamíferos marinos, RAM project; Sea...

During migration, birds often need to gain large fuel loads, especially if they must cross large geographic barriers with poor or absent fuelling opportunities. The Willow Warbler is a songbird associated with woodland that also opportunistically exploits other habitat types, such as reed beds, allowing it to fuel quickly. Reed beds along the coast...

Capsule: Nocturnal passerine migration patterns were studied by a network of weather radars within the East-Atlantic flyway providing large-scale information on the effect of a geographical barrier. Aims: The aim of this study was to obtain a large-scale spatial overview of the effects of a sea barrier on migratory flyways in northern Spain/western...