Open landfills seem to be playing an increasing role as target feeding areas for several species, not only in their breeding areas or during the winter, but also during the migration period. Evaluating the extent to which landfill sites are used by migrants is crucial to understanding their role in driving stopover decisions during migration, and in the potential health risks linked to feeding on refuse. The aim of this study was to evaluate the role of two open landfills located just before (France) and after (Spain) the East-Atlantic flyway enters Iberia through the western Pyrenees as potentially important stopover sites for the White Stork populations moving along this route. Overall, we detected that these sites were used by storks that had been ringed from many western European breeding populations, mainly during the migration period, but also in winter. The mean distance between the stork breeding/ringing origin and the landfill sites increased from summer to winter, suggesting that storks breeding further away pass through Iberia later in the season, reflecting population-specific timing of migration. During the autumn migration period (August-September), the first encountered landfill in France was estimated to be used by c. 1200 storks, and the other in Spain by 4000 storks. Our study hence contributes to a better understanding of the current and potentially hazardous role played by landfill sites in White Stork ecology, which is essential in order to provide management recommendations, and to evaluate the consequences of proposed open landfill closures in Europe.During long-distance migration, most birds need to stopover to refuel so they can successfully undertake subsequent flight bouts. Sometimes, migrants depend on very specific target stopover locations for that purpose, and hence these sites are crucial for the success of migration, even of entire populations (Newton 2008). This can be the case for stopover sites close to bottlenecks which concentrate high numbers of migrants. Soaring birds, including storks or raptors, largely rely on thermal updrafts for assisted flight and normally avoid large fuel accumulations, as they have a relatively small energy consumption during migration (Alerstam 1993). However, even these species still need some refuelling along their migration routes, especially when crossing hazardous geographical obstacles such as seas, mountains or deserts, which might require additional energy investment (Yosef et al.

ResumenEn las últimas décadas, la población reproductora de cigüeña blanca Ciconia ciconia L., 1758 en Navarra ha aumentado exponencialmente. La abundancia de comida predecible en vertederos, que proporcionan uno de los recursos tróficos más utilizados por la especie, parece haber tenido influencia tanto a nivel demográfico como en la distribución espacio-temporal en el conjunto de la península ibérica. Con el objetivo de estudiar los patrones de dispersión, movimientos y usos del hábitat de la población de cigüeñas en Navarra, durante el periodo 2012-2015 se anillaron 243 pollos en 9 colonias de cría del sur de Navarra. De todos ellos, el 16% de los individuos (n = 37) fue observado con posterioridad, tanto vivos y en buen estado (i.e., avistamientos) como muertos (i.e., recuperaciones, en su mayoría por electrocución). Todos los avistamientos, excepto tres, se realizaron en vertederos (n = 64), en donde el esfuerzo de muestreo fue considerablemente mayor. Dos avistamientos correspondieron a cigüeñas observadas en humedales, así como otro ejemplar que se observó dos años después en la colonia donde nació (i.e., reclutamiento). La distancia promedio de avistamiento en relación a la colonia de anillamiento fue de 48 km (distancia máxima, 410 km). La mayoría de avistamientos/recuperaciones se realizó durante la primavera y verano, con independencia de la edad. Todas las aves que se hallaron muertas (n = 7) fueron jóvenes encontrados en la proximidad de sus colonias de nacimiento.Palabras clave: Colonias, dispersión, electrocución, hábitat, vertederos. AbstractIn recent decades, the breeding population of White Stork Ciconia ciconia L., 1758 in Navarre has increased exponentially. The abundance of predictable food in landfills, providing one of the most used food resources for the species, seems to have influenced both demographically and spatiotemporal distribution in the whole Iberian Peninsula. In order to study dispersal patterns, movements and habitat use of the White Stork population in Navarre, during the period 2012-2015, we ringed 243 chicks in 9 breeding colonies in southern Navarre. Of these, 16% of the individuals (n = 37) were observed afterwards both alive and in good condition (i.e., sightings) and dead (i.e., recoveries), mostly by electrocution. All the sightings, except three, were made in landfills (n = 61), where the sampling effort was considerably higher. Two sightings corresponded to storks observed in wetlands, and another individual was observed two years after at the colony where it was born (i.e., recruitment). The average sighting distance in relation to the colony was 48 km (maximum distance, 410 km). Most sightings/recoveries were obtained during the spring and summer, regardless of age. All dead birds (n = 7) were fledglings found in the vicinity of the colonies where they were born.Key words: Colonies, dispersion, electrocution, habitat, landfills. LaburpenaAzken hamarkadetan Nafarroako amiamoko zuri Ciconia ciconia L., 1758 populazio ugaltzaileak gora egin du modu esponentzialean. Z...

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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 conducted more than 15 years ago. In order to update this knowledge, this study shows the results of a breeding population census conducted in Navarre during the spring of 2018, describing the preferences in nest location, and comparing the current breeding population size with that described in the literature published since 1960. Our results show a breeding population of 739 pairs, which is the highest value ever recorded. However, this increase in the number of pairs has not been associated with a significant expansion of the specie’s distribution area, which is still limited to the southern half of Navarre. The only relevant colonisation would be the 5 pairs established in the Pamplona district. Most pairs (86.3%) nested in colonies, with an average size of 9.2 nests. Most of the nests were located in trees (49.0%), followed by buildings (28.8%), cut trees (10.0%), pylons (6.9%) and other types of structures (antennas, chimneys, artificial nests, cranes..., 5.3%). A comparison of the current situation with previous censuses shows that there has been an annual population growth rate of 6.6%, with an important change in nesting habits, both in the percentage of pairs that nest in colonies and in the substrate selected to build the nest. The possible causes that could explain these changes and the conservation implications for the species are discussed.

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