Adjustments of the annual cycle in long-distance migrants according to elevational and latitudinal phenology

In this study, we aim at describing how long-distance migrants, like the House Martin, adjust their annual cycles and migration timing in accordance with environmental phenology at their breeding sites. We are specifically interested in revealing the spatiotemporal organization of the annual cycles of House Martins breeding at different elevations (e.g., 500, 1000, and 1500 m a.s.l.) in Switzerland and compare that with breeding sites at different latitudes where the phenology of spring green-up matches the phenology of the selected elevational sites in Switzerland.

In addition to traditional bird ringing, we use light-level and multi-sensor geolocators to track adult birds from different breeding populations. Our core study sites are located in Lausen and Eptingen (both canton Basel Land), Switzerland and in Saxony-Anhalt, Germany and in Latvia. Additionally, we use lab-based techniques to investigate the prevalence and diversity of blood parasites (i.e., avian malaria) in house martins to better understand host-parasite-interactions and their significance for migratory birds.

Migratory birds adjust their annual cycles to the phenology of the environment at their main residency sites throughout the year. This includes, for example, matching arrival at the breeding sites to the timing of local spring onset or departing from the breeding sites as autumn sets in. This generally holds true across latitudinal gradients as more northerly populations migrate later compared to their southern counterparts. However, it remains unknown whether this pattern exists across an elevation gradient, where local phenology mirrors the one found at different latitudes.

First results indicate that house martins from the same breeding site can use different migration routes and occupy very distant non-breeding sites in the sub-Saharan Africa. Spring arrival phenology, however, is tightly linked with the onset of spring at each breeding site. House Martins in our study show very variable prevalence for avian malaria parasites with exceptionally high values in the Basel district colonies and decreasing prevalence towards north-eastern Europe. Preliminary results further indicate high blood parasite diversity including Trypanosoma and Hepatozoon species.

• Kurt Mohler & Ueli Schaffner, Naturschutzverein Lausen
• Ingolf Todte & Stefan Fisher, Staatliche Vogelschutzwarte Steckby
• Ivo Dinsbergs, University of Latvia, Institute of Biology