Juan Arizaga

Crimean-Congo Hemorrhagic Fever Virus in Ticks from Migratory Birds, Morocco

Crimean-Congo hemorrhagic fever virus was detected in ticks removed from migratory birds in Morocco. This finding demonstrates the circulation of this virus in northwestern Africa and supports the hypothesis that the virus can be introduced into Europe by infected ticks transported from Africa by migratory birds.

Trophic ecology of a resident Yellow-legged Gull (Larus michahellis) population in the Bay of Biscay

Stable isotopes analyses (SIAs) are an efficient tool to obtain a general insight into the diet of generalist consumers, such as the Yellow-legged Gull (Larus michahellis). Here we analysed δ(13)C, δ(15)N and δ(34)S values in feathers of chicks and adults, and used Bayesian triple-isotope mixing models to reconstruct the diet of a Yellow-legged Gull population breeding in the southeastern Bay of Biscay. Questions to test were (1) whether adults and chicks rely on different feeding resources during breeding period; (2) whether there is a seasonal foraging effect involving a higher proportion of refuse food in winter compared to summer, and (3) the magnitude of the annual variation in diet. Prey consumption differed between colonies, among years, and also varied slightly between seasons, and this was mainly due to a differential use of prey of marine origin. However, diet did not differ between age classes. These results suggest a relatively monotonous diet with only slight variations from year to year, seasonally and at a local geographic scale.

Fuel management and stopover duration of Blackcaps Sylvia atricapilla stopping over in northern Spain during autumn migration period

Capsule Fuel load is correlated with fuel deposition rate; stopover duration is affected by arrival fuel load. Aims To determine the stopover duration, fuel management and flight ranges at departure of Blackcaps stopping over in northern Spain. Methods Systematic mist-netting and ringing allowed the use of mark–recapture Cormack–Jolly–Seber models for the estimation of stopover duration. Trapped birds were measured and weighed in order to estimate mass gain. FLIGHT software was used to estimate flight ranges. Results Stopover duration ranged from 3.6 to 13.6 days, and was negatively correlated with arrival body mass (assessed by body mass at the first capture event). On average, arrival body mass was 18.4 g, whilst body mass at departure was 19.8 g. No significant differences in arrival body mass and departure body mass were observed between age or sex classes. Mass deposition rate did not differ between age or sex classes (mean = 0.20 g/day). Birds recaptured one day after the first capture event lost mass, whilst recaptures from the second day onwards had a mean gain of mass; mass was observed to increase linearly with the stopover duration. Mass deposition rate was positively correlated with departure body mass. Finally, with a mean departure body mass of 19.8 g, a Blackcap stopping over in northern Spain should be able to fly up to 1100 km. Conclusions Stopover duration assessed by Cormack–Jolly–Seber models was longer than that observed in birds recaptured more than once (‘minimum stopover duration’). Stopover was longer for birds arriving with less fuel. The positive relationship between departure body mass and mass deposition rate suggests a time-minimizing strategy. The lack of difference in fuel deposition rate between age and sex classes suggests a relatively abundant food supply at the study site, but other explanations might also account for the lack of age and sex differences, for example if competition for food was not determined by social hierarchies but by scramble competition. Departing fuel load would allow these birds to arrive at their wintering areas in southern Spain under still-air conditions, without needing to refuel.

First-Year Movements of Yellow-Legged Gull (Larus Michahellis Lusitanius) from the Southeastern Bay of Biscay

Abstract. Information on when and where the Yellow-legged Gull (Larus michahellis Iusitanius) population breeding in northern Iberia moves throughout the year is lacking. Here, distances and directions of gull movements during their first year of life were elucidated. Data on 2,776 sightings of 728 out of 2,421 gulls banded as chicks in the southeastern Bay of Biscay were analyzed. Overall, most (69.2%) gulls were found less than 50 km from their natal colonies and practically all gulls (95.9%) were found along the coast of northern Iberia, confirming the low mobility of this Yellow-legged Gull population. Distances at which gulls were found did not vary with time, suggesting that stable feeding resources exist across the area used by the population.

Effect of fuel load, date, rain and wind on departure decisions of a migratory passerine

Meteorological conditions, fuel load and date in the season can affect the departure decisions among migratory birds. However, it is poorly understood to what extent the departure decisions are more influenced by some parameters in relation to others, and how they interact with each other. We explored here how fuel load, date, rain and wind (measured on the ground and at high altitude, codified as a tailwind component) influenced the departure decisions of migratory Blackcaps (Sylvia atricapilla) from a stopover site. We used mark–recapture data of 947 Blackcaps collected during the autumn migration period 2005 at a stopover site in northern Iberia, estimating the emigration likelihood with Cormack-Jolly-Seber models, in which we tested for the effect of these four study variables. Best models fitting data showed an additive and positive effect of tailwind and fuel load on the emigration likelihood.ZusammenfassungDie meteorologischen Verhältnisse, der Energievorrat sowie das konkrete Datum können bei Zugvögeln die Entscheidung darüber beeinflussen, wann sie ihren Zug beginnen, bzw. fortsetzen. Dabei ist jedoch nur wenig dazu bekannt, in welchem Ausmaß welcher dieser Parameter relativ zu den anderen die Abflugentscheidung beeinflusst und inwieweit sie untereinander interagieren. In dieser Studie haben wir für ziehende Mönchsgrasmücken (Sylvia atricapilla) untersucht, wie ihr Energievorrat, das jeweilige Datum, Regen und Wind (gemessen am Boden und in größerer Höhe, angegeben als Rückenwindkomponente) die Entscheidung für den Weiterflug von einem Zwischenstop beeinflussten. Hierfür verwendeten wir die Daten von 947 markierten Mönchsgrasmücken, die während des Herbstzuges 2005 in einem Zwischenstop-Gebiet im Norden der iberischen Halbinsel wiedergefangen wurden. Die Weiterzug-Wahrscheinlichkeit wurde anhand von Cormack-Jolly-Seber-Modellen abgeschätzt, mit denen wir die möglichen Auswirkungen der vier untersuchten Variablen testeten. Das den Daten am besten angepasste Modell zeigte einen additiven, positiven Effekt von Rückenwind und Energievorrat auf die Weiterzugswahrscheinlichkeit.

Fuel Load and Potential Flight Ranges of Passerine Birds Migrating through the Western Edge of the Pyrenees

Abstract. The estimation of fuel load and the potential flight ranges of migrant birds are crucial to understanding the ecological and evolutionary significance of bird migration strategies. The movement of migrant birds between Iberia and the rest of Western Europe is thought to be shaped by the Pyrenees and nearby seas. Because of this areas unique geography, the routes of migrants that move to (autumn migration) or from (spring migration) Iberia tend to pass through the western and eastern edges of the Pyrenees. Fuel-load analyses and the assessment of potential flight ranges from these edges can provide insights about the extent of Iberias use as a consistent stopover and fuelling area. Using data obtained over a period of six years (2004–2009), we calculated fuel load and potential flight ranges for ten common passerines (pre-Saharan, i.e. that overwinter mainly within the circum-Mediterranean region: Robin Erithacus rubecula, Bluethroat Luscinia svecica, Chiffchaff Phylloscopus collybita, Blackcap Sylvia atricapilla; sub-Saharan, i.e. that overwinter in tropical Africa: Sedge Warbler Acrocephalus schoenobaenus, Reed Warbler Acrocephalus scirpaceus, Melodious Warbler Hippolais polyglotta, Willow Warbler Phylloscopus trochilus, Garden Warbler Sylvia borin, Common Whitethroat Sylvia communis that stopover at Txingudi marshlands, at the western edge of the Pyrenees. The fuel load for the 25% heaviest fraction of caught birds ranged from 10.6% over lean body mass to 25.5% (mean: 18.3%) in spring and from 6.7% to 39.7% (mean: 25.2%) in autumn. Thus, potential flight ranges tended to be longer during autumn than during spring, particularly for the sub-Saharan species. All pre-Saharan species except one (Bluethroat) had sufficient fuel to arrive in southern Iberia or northern Africa, and three sub-Saharan species (Sedge Warbler, Garden Warbler, Common Whitethroat) had sufficient fuel to reach the north of the Sahara Desert but not its southern border. The potential flight ranges in spring were rather similar among species (ca. 1000 km from Txingudi).

Sex Differentiation of Yellow-legged Gull (Larus michahellis lusitanius): the Use of Biometrics, Bill Morphometrics and Wing Tip Coloration

Abstract We used feathers and skeletal measurements, white and black areas at the wing tip and bill morphometrics of Yellow-legged Gulls (Larus michahellis lusitanius) in order to test for possible sex-differences. Overall, 157 individuals from the eastern Bay of Biscay (N Spain) were measured, and the sex determined in 155 individuals, by means of DNA-analyses. All feathers and skeletal-associated measurements, except the distance between each primary (P1 to P5) feather and the wing tip in a folded wing varied between the sexes, with males being larger than females. Sexual selection is discussed to be the major cause explaining these differences. A discriminant function is provided to separate sexes. By contrast, both wing tip patterns of coloration and bill morphology did not vary between sex classes.

Spatial Behaviour and Habitat use of First-Year Bluethroats Luscinia svecica Stopping over at Coastal Marshes during the Autumn Migration Period

Abstract. Coastal marshes play a relevant role as stopover and fuelling sites for birds during migration period. The importance of tide in such ecosystems is well studied for aquatic species such as waders, but its impact on the stopover behavior of land birds that also depend on these sites is still unknown. Bluethroats Luscinia svecica are small-sized passerines that feed on the ground and low vegetation and, therefore, experience continuous changes of habitat availability due to the tide regimens. The aim of this study was to analyse the habitat use and to test the impact of tide on home range size of Bluethroats stopping over at coastal marshes. For that, we used data on radio-tagged birds at a tidal marsh in Northern Iberia. Bluethroats were radiotracked from the 20th of August to the 20th of September. Individuals were surveyed from 3 to 17 days, and birds with lower body mass at the day of capture stayed for longer period. Mean home range size was 2.0 ha (SE = 0.2), and the main habitats occupied were reedbeds (ca. 30% of a home range area) together with tidal flats with both free- and low-halophytic vegetation (30%). Reedbeds were situated at a higher altitude over the sea level than open waters, mudflats and low halophytic vegetation. Home ranges tended to be larger in birds found to occupy zones close to the sea level, thus with a longer tide-mediated flooding period, suggesting a negative effect of tide on home range size, and/or that Bluethroats staying at lower altitude did not find as much food as at higher altitude, so they were forced to move over larger surfaces.

Connectivity in Reed Warblers Acrocephalus scirpaceus Between Breeding Grounds in Europe and Autumn Stopover Sites in Iberia

We determined the degree of connectivity in the Eurasian Reed Warbler Acrocephalus scirpaceus between breeding regions in central and northern Europe and stopover sites in Iberia, during the autumn migration. We used both recovery data and wing length analyses to achieve this. Biometric data were obtained during 2009 at 11 sampling localities in Iberia, which we amalgamated into four major migratory areas within the region (Central, Western, Eastern and Southwestern Iberia, hereafter CI, WI, EI, SW). From the EURING database, we selected birds captured at their breeding sites in Europe and recaptured in Iberia during the autumn migration. Reed Warblers passing through WI had shorter wings than those in CI, EI and SW, suggesting that birds in WI migrated shorter distances, a fact also supported by recovery data. Although Reed Warblers showed some population overlap when passing through Iberia, we found that birds passing through EI and CI came from areas further to the east (continental Europe) than those passing through WI (mainly British Isles), thus supporting parallel migration. Reed Warblers tended to converge in southwestern Iberia, suggesting an effect of nearby geographical barriers.

Biometrics of Citril Finch Serinus citrinella in the west Pyrenees and the influence of feather abrasion on biometric data

Biometric data are an essential component of studies into the breeding biology of bird populations. Citril Finches Serinus citrinella in the Pyrenees mainly feed on pine seeds, and coniferous habitats in the west Pyrenees are of significant conservation importance. The aim of this study was to increase our understanding of morphological variation in Citril Finches breeding in the west Pyrenees, north Iberia, within a region of grasslands and woodlands of Scots pine Pinus sylvestris. Individuals (1,118) were mist netted, ringed and measured. Wing and tail length were influenced by feather abrasion, particularly in juvenile birds. Overall, male Citril Finches were larger than females for all structural and flight‐feather measurements (wing, tail, tarsus and culmen length, bill depth and width and lower mandible length), and adults were larger than young birds (except for tail length, culmen length and bill depth). There was significant year‐to‐year variation for all measurements apart from tail length, but the reasons for this are unknown. Principal Components Analyses (PCA) were used to analyse wing and bill morphology. Adult birds had narrower, more pointed wings than young birds, and the wing shape in males was more pointed than in females. There were only sex‐specific differences in bill morphology, with males having more robust bills. We obtained a discriminant function to classify the sex of birds before their post‐juvenile moult.