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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 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. Results: 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. Conclusion: 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.

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 Total Allowable Catch (TAC) should not be discarded at sea. This European discard ban is expected to impact some gulls, as several gull populations have been observed to be heavily reliant on this resource. In this work, GPS tracking data from adult Yellowlegged Gulls Larus michahellis and Vessel Monitoring System (VMS) data (i.e. detailed data of the spatial distribution of fishing vessels) are used to determine the utilization of the marine habitat and the level of interaction of gulls with fishing activity offshore and discards in the south-eastern part of the Bay of Biscay. We found that these gulls had a low use of the marine habitat (ca. 15%) compared with terrestrial habitats, in contrast to the ca. 40% of the diet of this population which comprises marine prey. Furthermore, we detected that most of the gull tracking positions at sea did not interact with the fishing vessels (an overlap of 21.5% between gulls and VMS data). Conversely, other gull populations of the Iberian Peninsula were found to depend much more strongly on fishing activity. Therefore, the Yellow-legged Gull population of the SE Bay of Biscay did not obtain most of its fish prey from interactions with offshore fishing activity but most possibly by taking fish remains in harbours and by feeding themselves. Consequently, we expect a minimal effect of the European policies oriented to ban fishing discards offshore on this population, which would be more affected by policies directed towards the reduction of food availability in landfills or fish landing management in harbours.

El anillamiento científico de aves es una técnica de estudio con más de un siglo de historia que, probablemente, ha contribuido como ninguna otra metodología al conocimiento de la biología de este grupo faunístico. A pesar del desarrollo de nuevas tecnologías, el marcaje individual de aves mediante anillamiento sigue siendo una técnica plenamente vigente y necesaria. Aunque la evidencia científica sobre los beneficios de la aplicación del anillamiento en la Ornitología moderna es abrumadora, hoy vivimos un proceso de creciente desinformación que cuestiona el anillamiento de aves y su utilidad. Este dosier se ha elaborado con el fin de ofrecer una visión actualizada de la utilidad del anillamiento científico de aves en España. Ha sido elaborado por un nutrido grupo de expertos asociados a universidades y centros de investigación que abarcan buena parte de las áreas del conocimiento implicadas en el estudio y conservación de las aves. El dosier se divide en cuatro grandes apartados. (1) En primer lugar se hace una introducción sobre el anillamiento como metodología y se resumen las grandes cifras del anillamiento en España donde, hasta la fecha, se han anillado algo más de 10.000.000 de aves y se han registrado 700.000 recuperaciones (en la actualidad se anillan unas 380.000 aves y se obtienen unas 30.000 recuperaciones anualmente). (2) En un segundo bloque se resume la aplicación del anillamiento en diferentes aproximaciones al estudio científico de las aves, que van apoyadas por numerosas referencias bibliográficas sobre trabajos llevados a cabo en España. Gracias al anillamiento se han podido abordar múltiples estudios sobre movimientos y migraciones, reproducción, demografía, enfermedades, morfología, muda e identificación y taxonomía. (3) Un tercer bloque se centra en la utilidad del anillamiento más allá de la investigación básica. Es el caso de la conservación, la gestión de especies cinegéticas y el estudio de los impactos del cambio global sobre las aves, por un lado, y la educación ambiental, formación y ciencia ciudadana, por otro. (4) Finalmente, se abordan algunas ideas sobre los retos actuales y perspectivas de futuro del anillamiento en España.

Supplementary methods, results and JAGS code

Additional file 1: Appendix S1. A simple population model to check whether our population was stable, decreasing or increasing (i.e., showed a lambda, λ, equal, below or above 1).

Additional file 1: Table S1. Number of sampling days, per month and year, at Badina Escudera. Table S2. Mean values of the mean and minimum temperature and accumulated precipitation (Tmean, Tmin, Prec, as in Table 2) at Badina de Escudera, during the three time units considered in this study.

Aves - Orden Passeriformes - Familia Turdidae en la Enciclopedia Virtual de Vertebrados Españoles, http://www.vertebradosibericos.org/. Versiones anteriores: 23-02-2011, A comprehensive review of the natural history of the Bluethroat Luscinia svecica in Spain.

The spatio-temporal host-parasite relationships have a high interest to understand the coevolutionary processes between parasites and their hosts. Our main aim here was to analyse whether the prevalence and intensity of infection by haemoparasites in migrating blackcaps (Sylvia atricapilla), at a stopover site in N Iberia, varied throughout and between migration periods. Moreover, we studied whether the parasitaemia had any effect on fuel load. Blood smears were studied from 132 individuals. Only Haemoproteus spp. and Plasmodium spp. were detected. Trypanosoma spp., microfilaria or Leucocytozoon spp. were absent. The prevalence was 35% and it did not differ throughout and between periods or between age classes, but between the sexes. Prevalence was higher among males (45.5% versus 22.7%), suggesting that males were more prone to be infected, which could be due to sex-associated immunologic variations. The mean intensity of infection was low (2.8 parasites/2000 erythrocytes). We did not find any effect of parasitaemia on fuel load.