Eurasian Reed Warbler Acrocephalus Scirpaceus Research Articles

Connectivity in Reed WarblersAcrocephalus scirpaceusBetween 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.

Using stable hydrogen isotopes (δ2H) and ring recoveries to trace natal origins in a Eurasian passerine with a migratory divide

Despite recent advances in technology, it remains difficult to connect breeding and non‐breeding areas of populations of migratory organisms due to the challenges of year‐round tracking. Here, we used the Eurasian reed warbler Acrocephalus scirpaceus, a passerine with a pronounced migratory divide to demonstrate the promise of integrating several sources of information within the Bayesian modelling framework for the study of migratory connectivity. To this end, we combined data from stable hydrogen isotope ratios (δ2H) of feathers, ring recoveries, and the geographic delineation of sub‐populations on either side of the migratory divide. Feather δ2H measurements from local juvenile birds sampled across the breeding range tightly correlated with amount‐weighted mean annual precipitation δ2H values predicted for the natal sites. Predicted natal origins of birds intercepted en route in the Mediterranean region largely differed among the five stopover sites. Thanks to the different migratory pathways used by different breeding populations and the existence of a migratory divide, we were able to effectively narrow the assigned regions of origin. Our results show that spatial resolution of likelihood‐based assignments of geographic origins based on δ2H measurements may improve significantly when prior probabilities derived from population‐specific migratory directions are included. Integrating information from stable isotopes, ring recoveries, geolocators and other sources within the Bayesian modelling framework will provide an extremely useful toolbox for the study of animal movements in the future.

Wing morphology and plumage characteristics of the eastern form of Eurasian Reed Warbler Acrocephalus scirpaceus fuscus in Cyprus

The breeding distribution of Eurasian Reed Warblers Acrocephalus scirpaceus in the Western Palearctic is highly fragmented and their taxonomy is complex. Eastern Mediterranean populations lie between the ranges of the nominate scirpaceus and the eastern race fuscus. The aim of this study was to use biometrics and plumage criteria to elucidate the racial affinities of Reed Warblers breeding at a site in Cyprus. The population appears to belong to fuscus, but has notably short and rounded wings. Either true emargination or a narrowing of the outer web of the fourth primary was observed in adults. The results are discussed in relation to the wing lengths of passage Reed Warblers in Cyprus.

Estimating fat and protein fuel from fat and muscle scores in passerines

Fat is the prime energy source for birds during prolonged exercise, but protein is also catabolized. Estimates of the amount of catabolizable fat and protein (termed fat and protein fuel) are therefore important for studying energetics of birds. As fat and protein fuel can only be measured by sacrificing individuals or by use of technically complex methods, scoring systems were invented to estimate fat and protein fuel of birds in the field. The visible subcutaneous fat deposits and the thickness of the flight muscles are each scored on an ordinal scale but these scales do not correspond linearly to fat and protein fuel within species, which is needed for analyses such as flight range estimates. We developed an anova‐type model to estimate fat and protein fuel from fat scores (FS) and muscle scores (MS) along with total mass and a size measurement. Using data from 11 337 individuals of eight passerine species (Common Nightingale Luscinia megarhynchos, Eurasian Reed Warbler Acrocephalus scirpaceus, Melodious Warbler Hippolais polyglotta, Willow Warbler Phylloscopus trochilus, Orphean Warbler Sylvia hortensis, Garden Warbler Sylvia borin, Common Whitethroat Sylvia communis, Subalpine Warbler Sylvia cantillans) mist‐netted in Mauritania, West Africa, we tested for independence of FS and MS and for variation in the relationship between scores and associated mass in response to physiological state. FS, MS and third primary length (size) explained variation in body mass of all eight species analysed (R2: 0.56–0.77). The parameter estimates of the model showed that fat and protein fuel increased monotonically with increasing fat and muscle scores. In two species we found small differences in the estimates between physiological states (seasons). We evaluated our model by comparing the predicted body mass of birds with both FS and MS equal to 0 with the mean body mass of individuals mist‐netted with both scores equal to zero. The values were very close. The amount of fat extracted from dead Garden and Willow Warblers was within the range of predicted fat fuel derived from the model. We conclude that our model is a useful non‐invasive method to estimate simultaneously mean fat and protein fuel of small passerines and we provide recommendations on its use.