Natal dispersal of Eagle Owls: a European scale project

Photo: Vincenzo Penteriani

Photo: Vincenzo Penteriani
Natal dispersal (i.e., the movement of wandering individuals from their birthplaces to their first breeding locations) can be considered one of the most intriguing ecological processes determining the spatial spreading of individuals. Dispersal is a field that embraces a multitude of disciplines, from population ecology and genetics to conservation biology. In addition, the understanding of the dispersal process is important for empirical, theoretical, and applied ecology. Finally, the study of dispersal has very important conservation implications, mainly because dispersers are the future breeders of animal populations, but the areas that are used during dispersal have been poorly studied.

Since 2010 Luomus, the Finnish Museum of Natural History has been involved in a 4-year study on eagle owl Bubo bubo natal dispersal which encompasses three European study areas: south-western Finland, southern Spain (Sierra Norte of Seville) and western Switzerland (Bern Alps). The project is granted by the Autonomous Government of Andalusia (Excellence Projects, Spain) and the research team is composed by Vincenzo Penteriani (principal investigator, Estación Biológica de Doñana, C.S.I.C., Spain), María del Mar Delgado (Metapopulation Research Group, University of Helsinki, Finland), Jari Valkama and Pertti Saurola (FMNH, University of Helsinki, Finland) and Raphäel Arlettaz (Institute of Ecology and Evolution, Bern University, Switzerland).

The main aim of the study is to disentangle the different drivers and factors affecting the process of natal dispersal by studying the movements of eagle owl juveniles under the different ecological constraints that act on the individual displacements across boreal forests, Mediterranean landscapes and alpine habitats.

In Finland, we have radio tagged altogether 39 juveniles with satellite units (Microwave, USA) which are expected to last 1.5 – 3 years. Over this period, every ten days and during the whole night, we receive the hourly locations of each radio marked owl. Here, we show the paths followed by some dispersing individuals, which will be refreshed every month.

Unexpectedly, the results of this project are going well beyond our expectancies. Actually, we are not only recording some amazing patterns of movements which are extremely valuable from a scientific perspective, but the repeated checking of the eagle owl nests from the egg-laying to the starting of dispersal showed us that several eagle owl nests are still persecuted by humans. Because we tag eagle owls with 70 grams satellite units, we cannot put transmitters on fledglings before they are at least 2 months old. Thus, to locate them after they leave the nest, we initially use very small VHF leg tags: the use of these radio tags, as well as the continuous following of the fledglings before they leave the natal area, allowed us discovering that many of them have been killed by humans. To prevent future killing by humans, we have been in contact with local police departments and some nests have now been placed under video surveillance.

During our researches on the Finnish population, we have received the continuous and indispensable help of several ornithologists and ringers; in particular, we would like to warmly thank (in alphabetical order) Mikko Honkiniemi, Kai Leppimäki, Heikki Lokki, Seppo Pekkala, Kirsi Reponen, Eino Salo and Jere Toivola.

The newest maps showing the movements of the individuals will open by clicking the name of the individual. By clicking the word Map below each image Google Earth will open with monitoring data (for viewing,Google Earth is required).

Eemeli is a male who was born in Kiikoinen, western Finland, in 2012. Eemeli left his natal territory in the beginning of October and started to fly towards southeast. On 10 October the satellite located him near the city of Sastamala, and on 31 October he was near the city of Forssa, after having traveled approximately 80 km from his natal territory. Unfortunately, soon after that Eemeli was found in poor condition and despite intensive care he did not survive. Map

 Elina is a female who grew up in Forssa, southwestern Finland, in 2012. She started her independent life during the last week of September and flew towards west. She passed the city of Loimaa and was in Turku on 10 October. In the end of October she was in southwestern Finland between Taivassalo and Kustavi. Then, for an unknown reason, the transmitter stopped sending location data. It is possible that Elina collided with a car or power lines which also resulted in transmitter failure. Map

Elviira was born in Pöytyä, southwestern Finland in 2011. She left her natal territory in late September. She first flew towards Turku, but finally ended up in Pori, where she has stayed since late October 2011. The last locations from that area were obtained in summer 2014. Unfortunately, the transmitter stopped to work then. Map

Olga was born in Jokioinen, near the city of Forssa in 2011. She started natal dispersal in late October towards southeast. From November to February Olga was wandering near the city of Sipoo, but during spring she flew a little north, and has been in a region between the cities of Järvenpää and Mäntsälä since spring 2012. Olga has already nested twice, in 2013 and 2015. To protect the breeding site, exact locations after spring 2012 are not shown on the map. Map

Menninkäinen was born in Urjala, some 45 km SSW from the city of Tampere in 2011. He left his natal territory very late, only during the last half of November. Like Olga, also Menninkäinen traveled southeast and spend her February and March in Helsinki and Espoo regions. Then, in late March, he started to move northwards and settled down in Orivesi, 40 km NE from the city of Tampere. He has been in that area since 2012. Although he is already 4 years old, he has not bred yet. Map

Taatu is a male who was born in Rusko, southwest Finland in 2011. Taatu left his natal territory after mid-October and started his journey towards south. He spent the whole winter in an archipelago area near Hitis by the open sea. During the last evening of April, Taatu started his “spring migration” towards north and finally arrived in Turku region where he has stayed from 2012 onwards. Like Menninkäinen, also Taatu has not bred yet. He has had an interesting behavior to move to Turku refuse dump for the winter period from his inland territory. Map

This paper was written by Jari Valkama and Vincenzo Penteriani, photo: Vincenzo Penteriani and Maria Delgado. Web management: Markus Piha

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