Álvaro Ramírez

Are Iberian Chiffchaffs Phylloscopus (collybita) brehmii long-distance migrants? An analysis of flight-related morphology

CapsuleIberian Chiffchaffs Phylloscopus (collybita) brehmii are genetically, morphologically and bioacoustically different from European Chiffchaffs (P. [c.] collybita). Aim To examine the difference in migratory pattern between brehmii and collybita. Methods We inferred variation in distance of migration between brehmii and collybita by analysing differences in flight-related morphology (wing-length, wing shape and tail-length) between individuals breeding or wintering in the Iberian Peninsula. Results Controlling for body size and allometry of feather dimensions, birds captured in spring had more pointed wings (more concave wing shapes and pointed wing tips) and a shorter tail than birds caught in winter, although no spring-to-winter difference was found for wing-length. Conclusion Iberian breeders appear better suited to long-distance migration (their traits are likely to give a higher speed and a lower energy consumption during long non-stop flights) than wintering individuals, which strongly supports the hypothesis that brehmii move south of the Sahara in autumn and are substituted by central European collybita populations in winter. This different migration pattern of brehmii and collybita has important implications for the maintenance of differentiation in their contact zone, because selection against hybrids with maladaptive, intermediate migratory behaviours might contribute to reproductive isolation.

The importance of northern Spanish farmland for wintering migratory passerines: a quantitative assessment

Migratory birds are critically dependent on adequate wintering habitats for their long-term survival. Cantabrian farmland, a mixed agricultural landscape extending across the coastal lowlands of northern Spain, constitutes an important wintering area for many short-distance migrants coming from central-western and northern Europe. Unfortunately, the Common Agricultural Policy of the European Union and national afforestation schemes have resulted in a massive replacement of farmland by pine Pinus spp. and eucalypt Eucalyptus sp. plantations. This work assesses the importance of Cantabrian farmland as wintering grounds for short-distance European migrants and for wintering species that originate in nearby woodlands. We examined the seasonal changes in passerine bird populations in the Cantabrian region and used winter ringing recoveries obtained in the area to evaluate the contribution made by European migrants to winter populations. Bird communities were surveyed along 299 500-m long transects distributed between 67 farmland patches, 67 lowland forests and 14 upland forests. Winter assemblages were more diverse and species more abundant in farmland than in lowland or upland forests, whereas these differences were smaller in the spring. Bird numbers in farmland tripled in winter, numbers increasing by about 6.9 million birds compared to breeding populations. Most of this increase was accounted for by species that also bred in the region and that considerably increased their abundance (65.6% of all wintering birds, with the Chaffinch Fringilla coelebs responsible for 31.4% of the total increase) and by five exclusively wintering species (34.4%, with the Meadow Pipit Anthus pratensis accounting for 25.2% of the total increase). The main bulk of this increase is caused by the influx of European migrants. The importance of halting the current spread of eucalypt plantations (which increased over 400% over the past 30 years) and of applying more effective agri-environment schemes to achieve appropriate farmland conservation is discussed.

Conservation Opportunities in Spanish Juniper Juniperus thurifera Woodlands: The Case of Migratory Thrushes Turdus spp.

Summary. Conservation opportunities in Spanish juniper Juniperus thurifera woodlands: the case of migratory thrushes Turdus spp. Spanish juniper Juniperus thurifera woodlands are the core habitat of several sites included in the Nature 2000 Network and the wintering ground of many European thrushes Turdus spp. These birds have a major ecological role as seed dispersers and are increasingly taken into account in the design of strategies aimed to conserve or restore plant communities. Socio-economic changes in rural Spain have reduced traditional sheep grazing in juniper woodlands, which are now increasingly used for wood production. This has brought the opportunity to improve their carrying capacity for migratory thrushes. Here we explore the spatio-temporal patterning of fleshy cone production and the way birds track this resource. We also investigate whether fleshy cone availability constrains bird numbers. The results show sharp losses of cones during the ripening period, inter-site and inter-winter changes in cone production and the tracking of ripe cones by birds. Mean availability of ripe cones in poorly productive patches was insufficient to maintain thrushes in mid January and highly productive patches offered resources to maintain birds for around 12 days. This suggests an insufficiency of food in the woodlands to permit thrushes to complete the winter and to begin their return northward migration in March. These results are used to suggest some guidelines for improving the carrying capacity of these woodlands for migratory thrushes.

Use of restoration plantings to enchance bird seed dispersal at the roadside: failures and prospects

AbstractPlantings are commonly used in roadside reclamation for ornamental purposes and for increasing slope stability and road safety. However, the role of these plantings in restoring ecological processes, such as seed dispersal, has received little attention. We carried out a study to assess the potential role of plantings on roadside embankments to attract frugivorous birds and to enhance seed dispersal mediated by birds from the surrounding landscape. We examined: (1) bird species richness and abundance; (2) patterns of avian spatial distribution within embankments and (3) seed dispersal mediated by birds. Bird richness and abundance did not differ between embankments with and without plantings. However, birds were not distributed randomly within embankments, with levels of species richness and abundance for facultative frugivorous between 4.8–8 times higher in areas closer to plantings. An analysis of bird droppings showed that birds only dispersed seeds of the planted species since no seeds of wood...

How residents behave: home range flexibility and dominance over migrants in a Mediterranean passerine

Residency has repeatedly evolved in many migratory animals, some of which have preserved the anatomical adaptations to perform long-range movements. This is the case for partially migratory populations of Mediterranean passerines in which migrants and residents both have a migrant morphology. The question of how selection maintains residency in this situation remains unclear. Using radiotelemetry, we followed the resident fraction of a partially migratory population of blackcaps, Sylvia atricapilla, from eastern Spain and studied changes in home range size and habitat composition throughout three breeding and two wintering seasons. We then compared these birds with two groups of migratory blackcaps present in the area: in winter with migrants that breed in northern populations and in spring with migrants that breed locally. In addition, we observed aggressive interactions between individually marked birds to explore dominance relationships during winter. The home ranges of resident blackcaps were six times larger in winter than during the breeding season, but within each season, they were comparable in size to those of migrants. The habitats used by residents markedly differed between seasons as well as from those of migrants in winter, but not during the breeding season. In winter, resident birds were dominant over migrants, although migrants were generally larger. Overall, residents showed high between-season flexibility in home range size and habitat use. Winter home ranges of residents included breeding sites and more diverse types of habitats than those of northern migrants. This suggests that in winter, the importance of dominance for obtaining priority access to food may be high but not crucial, given that residents may reduce competition by feeding separately from migrants. Future studies should focus on whether residents show specific personalities and on the role of yearly oscillations in environmental conditions in maintaining residency in this type of partially migratory population.