Total white blood cell counts but not HL ratio changes in the transition from post-juvenile molt to autumn migration in the first-year Eurasian blackcap (Sylvia atricapilla)

Theoretically, seasonal changes in immune functioning in animals are shaped by the trade-off between a probability of encountering pathogens and availability of resources. We used leukocyte profile (absolute and relative leukocyte counts) as a simple measure of immune system condition to study how it changes during the transition from postjuvenile molt to autumn migration in a free-living migratory songbird, the Eurasian blackcap (Sylvia atricapilla). We observed the higher white blood cells (WBC) and lymphocyte counts in molting birds compared to migrating individuals, but we did not find differences in heterophils and ratio of heterophils to lymphocytes (HL ratio). We suppose that the high number of WBC in molting blackcaps could reflect the heightened ability of their immune system to resists infections. The lower WBC counts in migrants compared to molting birds were mostly due to reduced lymphocyte numbers, thus representing in a downregulation of specific immunity. An absence of heterophil differences between molt and migration might indicate that various components of immunity can change relatively independently (or at different pace). Fat scores had no effect on WBC counts and HL ratio. Therefore, we found no strong evidence for a resource-immune functionality trade-off during transition from postjuvenile molt to autumn migration in immature Eurasian blackcap. This study is an important step in understanding how immune system in general and leukocyte profile in particular changes in transition between life-history stages in migratory songbirds.

Rapid sex determination of a wild passerine species using loop-mediated isothermal amplification (LAMP)

Many bird species are sexually monomorphic and cannot be sexed based on phenotypic traits. Rapid sex determination is often a necessary component of avian studies focusing on behavior, ecology, evolution, and conservation. While PCR-based methods are the most common technique for molecularly sexing birds in the laboratory, a simpler, faster, and cheaper method has emerged, which can be used in the laboratory, but importantly also in the field. Herein, we used loop-mediated isothermal amplification (LAMP) for rapid sex determination of blood samples from juvenile European blackcaps, Sylvia atricapilla, sampled in the wild. We designed LAMP primers unique to S. atricapilla based on the sex chromosome-specific gene, chromo-helicase-DNA-binding protein (CHD), optimized the primers for laboratory and field application, and then used them to test a subset of wild-caught juvenile blackcaps of unknown gender at the time of capture. Sex determination results were fast and accurate. The advantages of this technique are that it allows researchers to identify the sex of individual birds within hours of sampling and eliminates the need for direct access to a laboratory if implemented at a remote field site. This work adds to the increasing list of available LAMP primers for different bird species and is a new addition within the Passeriformes order.

Evaluating the efficacy of restoration plantings through DNA barcoding of frugivorous bird diets

Frugivores are critical components of restoration programs because they are seed dispersers. Thus, knowledge about bird-plant trophic relationships is essential in the evaluation of the efficacy of restoration processes. Traditionally, the diet of frugivores is characterized by microscopically identifying plant residues in droppings, which is time-consuming, requires botanical knowledge, and cannot be used for fragments lacking detectable morphological characteristics (e.g., fragmented seeds and skins). We examined whether DNA barcoding can be used as a universal tool to rapidly characterize the diet of a frugivorous bird, Eurasian blackcap (Sylvia atricapilla). We used the DNA barcoding results to assess restoration efforts and monitor the diversity of potentially dispersed plants in a protected area in northern Italy. We collected 642 Eurasian Blackcap droppings at the restored site during the autumn migration over 3 years. Intact seeds and fragmented plant material were analyzed at 2 plastidial barcode loci (rbcL and trnH-psbA), and the resulting plant identifications were validated by comparison with a reference molecular data set of local flora. At least 17 plant species, including 7 of the 11 newly transplanted taxa, were found. Our results demonstrate the potential for DNA barcoding to be used to monitor the effectiveness of restoration plantings and to obtain information about fruit consumption and dispersal of invasive or unexpected plant species. Such an approach provides valuable information that could be used to study local plant biodiversity and to survey its evolution over time.

Evolution of seasonal transmission patterns in avian blood-borne parasites

In temperate regions, many vector-borne parasites maximise their transmission prospects by adjusting reproduction to seasonal cycles of host susceptibility and vector availability. Nevertheless, in these regions there are areas where environmental conditions are favourable throughout the year, so that parasites could benefit from a year-round transmission strategy. We analysed how different transmission strategies (strict summer transmission, extended summer transmission - including spring and autumn, and year round transmission) have evolved among the different genetic lineages of Haemoproteus parabelopolskyi, an avian blood-borne parasite shared by three sibling species of passerine hosts. Our results indicate that the ancestral state of this clade of parasites had a strict summer transmission with the blackcap (Sylvia atricapilla) as the host. Other transmission strategies and switches to the other host species (Sylvia abyssinica and Sylvia borin) evolved recently, several times, independently. This suggests that, although year-round transmission is ecologically successful at present, seasonal transmission may have become more stable over evolutionary time. Switches from strict summer to an extended or year-round transmission strategy could have ecological consequences, if they promote the spread of parasites into more distant regions, transported by the migrating bird hosts. Therefore, a deeper knowledge of how different parasite transmission strategies are structured among birds in temperate areas is essential for understanding how disease emergence risks may develop in the future.

Population differentiation of migratory directions in birds: comparison between ringing results and orientation behaviour of hand-raised migrants

Blackcaps (Sylvia atricapilla) from five areas in Central Europe were hand-raised. Their autumn migratory orientation was tested in funnel-shaped cages. Their directional choices were compared to recoveries of conspecifics ringed during the breeding season in the same areas, which are situated on a transect across a migratory divide between southeastward and southwestward migrating populations. Results from ringing and orientation tests were in good agreement with respect to mean direction and dispersion of flight directions. An exception is the area around Linz (NW Austria), right on the migratory divide, where ringing yielded a strong scatter, but hand-raised birds chose westerly directions. The recent establishment of a novel migration route toward the British Isles was reflected in both data sets: in southern Germany the percentage of northwestward migrants is 6.8% according to orientation tests and 11.8% according to ringing recoveries. Testing the orientation of young passerines in captivity can yield valuable information about population differentiation of migratory behaviour. It is more efficient than ringing in this respect, because it circumvents the low recovery rates and is free of biases affecting ringing data. In the blackcap, geographic differentiation of migratory directions occurs on a finer scale than previously recognized and can change significantly within 2-3 decades.