Survival rate, range use and dispersal of Little Owls

The Swiss population of little owls remained stagnant whilst the nearby French and German populations increased substantially. The causes of these trends are unclear. The research investigates potential ecological explanations. Specifically, we address open questions on habitat requirements, survival and dispersal moves of little owls, which are major determinants of a potential expansion of the population.

Aims

For many years bird conservationists have worked hard to preserve the last populations of the little owl. Their efforts have been rewarded, as the populations close to the border are steadily increasing, at least outside Switzerland. Why the Swiss populations have not increased so far, is not clear.

The project focuses on the dispersal and settlement behaviour of juvenile little owls. The period from fledging to settlement is a critical phase during which mortality is high. We analyse the strategies of dispersal (e.g. timing, distance, stop-over behaviour) in relation to the juveniles’ physical condition. Detailed survival data allow documenting the most critical ‘bottlenecks’ in the life history of the little.

Approach

The study is conducted in a large population of little owls in Württemberg (Germany), where habitat conditions are comparable to Switzerland. Some 100 young and adult birds are annually equipped with miniature radio-transmitters. The tracking of these birds shows that juvenile dispersal causes turbulent exchange of individuals between subpopulations. Telemetry also allows the survival rates to be determined with high temporal resolution.

Significance

The little owl is one of 50 priority species of the Swiss Species Recovery Programme. The investigation of survival and settlement behaviour of juvenile little owls will provide important information to facilitate the recolonisation of potential habitats in Switzerland. The populations in southern Germany and in the French Jura are the most important sources for a natural recolonisation of the Swiss lowlands.

Project management

Beat Naef-Daenzer und Martin Grüebler

Partners

Max Planck Institut for Ornithology, Vogelwarte Radolfzell
Forschungsgemeinschaft zur Erhaltung einheimischer Eulen e.V.

Financial support

Swiss National Science Foundation

Publications