The time to protect a species is while it is still common.
— Rosalie Edge
Surveying raptor migration at  Batumi Raptor Count , Georgia, August 2011.

Surveying raptor migration at Batumi Raptor Count, Georgia, August 2011.

As a movement ecologist, ornithologist and conservation biologist I try to understand what causes birds to move the way they do, focusing especially on long-distance migrations of diurnal raptors. To do this I combine bio-logging data with atmospheric models, remote sensing data and good old field observations. In so doing, I try to look at the world from a bird’s perspective and to foster greater appreciation for birds as cognitive and social beings. Find out more about my various research projects below and don’t hesitate to get in touch if you are looking to team up for an exciting project or if you’d like me to speak at one of your events!


Estación Biológica de Doñana (ES)
Figuerola Lab, Dept Wetland Ecology
Postdoc (April 2019 - present)
Juan de la Cierva Formación

University of Amsterdam (NL)
Theoretical & Computational Ecology
Guest Researcher (2016 - present)


Migrant Landbird Study Group
Co-founder & Secretary (2014 - present)

Batumi Raptor Count (GEO)
Research coordinator (2008 - present)

Dutch-Georgian Ornithological Foundation (NL)
Board member (2017 - present)

editor for …

Ibis - British Ornithologists Union
(2017 - present)

Ardea - Dutch Ornithological Union (2018 - present)

Natuur.oriolus - Natuurpunt.studie
(2017 - present)

ongoing projects

understanding how eleonora´s falcons tune their trans-African migrations to environmental conditions

Pale morph Eleonora’s Falcon carrying an UvA-BiTS GPS logger.  - Photo by Laura Gangoso.

Pale morph Eleonora’s Falcon carrying an UvA-BiTS GPS logger. - Photo by Laura Gangoso.

Outbound (blue) and return (red) migrations of Eleonora’s Falcons  breeding on Isla de Alegranza in the Canary Islands. Black dots show stop-over events.

Outbound (blue) and return (red) migrations of Eleonora’s Falcons breeding on Isla de Alegranza in the Canary Islands. Black dots show stop-over events.

Eleonora’s Falcons (Falco eleonorae) engage in one of the most remarkable migrations of all raptors. They are highly aerial hunters that breed colonially on islands and coastal cliffs throughout the Mediterranean Basin and in the East Atlantic. While this species preys on flying insects during most of the year they raise their offspring almost entirely on a diet of migratory passerines. After their exceptionally late breeding season all Eleonora’s Falcons escape he European winter by migrating to northern Madagascar. During their long-distance migrations adult falcons from multiple colonies converge at specific stop-over areas (e.g. Horn of Africa). But despite this convergence the trans-Saharan migration corridors of adult falcons seem to differ between colonies, and also between individuals from the same colonies.

For my postdoctoral research in the Figuerola group at the Dept. of Wetland Ecology at Estación Biológica de Doñana (EBD-CSIC, Sevilla, Spain) I aim to determine how seasonal resource availability and wind regimes shape the seasonal trans-African migration routines of this enigmatic raptor. I am especially interested to determine how individual and population-specific stop-over schedules are tuned to predictable spatiotemporal patterns in rainfall, vegetation growth and wildfires across Africa (all of which may result in ephemeral eruptions of flying insects). Furthermore, I aim to investigate how wind conditions influence individual variability and flexibility in route choice between stop-over areas .

This study is funded by a Juan de la Cierva Formacion Fellowship and integrated in the broader study on the ecology of Canarian Eleonora’s Falcons lead by Dr. Laura Gangoso.

how do juvenile honey buzzards learn safe migration routes between europe and africa?

Juvenile Honey Buzzards (Pernis apivorus) Ivar and Sven  at their natal nest in southwestern Finland. This was an unlikely brood, as Ivar died shortly after leaving the nest in Finland, and Sven perished in Algeria after a two-day flight across the Mediterranean during which he stopped to spend the night on a fishing vessel. - picture by Patrik Byholm

Juvenile Honey Buzzards (Pernis apivorus) Ivar and Sven at their natal nest in southwestern Finland. This was an unlikely brood, as Ivar died shortly after leaving the nest in Finland, and Sven perished in Algeria after a two-day flight across the Mediterranean during which he stopped to spend the night on a fishing vessel. - picture by Patrik Byholm

Over the past few decades tracking technology has allowed us to map migration strategies for a wide range of species. However, in order to maximise the amount of data collected with expensive tracking devices most studies have focused on adult migrants. As such, we know very little about the way in which migrant birds learn their often highly complex and flexible migration routines, and how this leads to the emergence of individual and population-specific migration patterns. This is also true for the species on which I conducted most of my migration research so far: the European Honey Buzzard (Pernis apivorus). However, since 2011 Patrik Byholm at the Bioeconomy Research Team of Novia University of Applied Sciences has equipped more than 30 juvenile and 10 adult European Honey Buzzards (Pernis apivorus) born or breeding in southwestern Finland with satellite transmitters and GPS-GSM loggers. The Finnish Honey Buzzard project thus provided an unique opportunity to investigate how innate and external factors shape individual migration routines in a long-lived thermal-soaring migrant.

Routes taken by juvenile Honey Buzzards on their first autumn migration from Finland to sub-Saharan Africa, coloured according to the longitudinal wind speeds they encountered along the way. For full details see Vansteelant et al. 2017 in Proceedings of the Royal Society B: Biological Sciences.

The learning process of Honey Buzzards is of particular interest because of the pronounced age-specific differences in migration behaviour. While adults engage in highly synchronised migrations along narrow overland migration corridors, juveniles depart on their first autumn migration approx. two weeks later and find their own way over a broad front, often engaging in long and risky flights over the Mediterranean Sea. How they eventually learn to use the traditional overland flyways is a mystery.

As a first step towards unravelling the migratory development in this species I analysed how wind and geography shape the first autumn migration and distribution of juvenile Honey Buzzards across sub-Saharan Africa. This revealed that the wind conditions that these birds encounter on their first migration determine the longitude at which they finally settle south of the Sahara, more so than individual (innate) differences in orientation (Vansteelant et al. 2017).

In a follow-project I am currently analysing how the route choice and migratory schedules of these birds develop with age and experience. Results are expected to be published by summer 2019.

comparing migration strategies of marsh harriers from the Low Countries and southern sweden

The adult male Marsh Harrier ‘Walter’ was equipped with an UvA-BiTS GPS logger at his breeding site in Flandres (Belgium). - Photo by Anny Anselin (INBO)

While the number of tracking studies on migrant raptors is rapidly increasing new opportunities are emerging to make comparative studies of migratory behaviour across multiple populations of certain species. In this project I am collaborating with researchers of the Knowledge Center Grauwe Kiekendief (Netherlands), the Research Institute for Nature and Forest (Flandres, Belgium) and Lund University (Sweden) to make such a comparative analysis of migration corridors and schedules across multiple breeding populations of Marsh Harrier (Circus aeruginosus).

West African non-breeding sites of adult Marsh Harriers that were GPS-tracked from breeding areas in Belgium (BE), the Netherlands (NL) and Sweden (SW). Birds from all three areas have a largely overlapping non-breeding range. However, our analyses (in prep) reveal surprising differences in migration corridors and schedules between Marsh Harriers breeding in the Low Countries (BE, NL) vs. those breeding in Sweden (SW).

The project started when I was hired as a freelance ecologist to investigate the migratory behaviour of Marsh Harriers breeding in the Low Countries (Flandres and the Netherlands). However, as soon as I started analysing the data I noticed the migration corridors and schedules of harriers from the Low Countries differed substantially from the corridors and schedules that have been described for Marsh Harriers satellite-tracked from southern Sweden over a decade ago (Standberg et al 2008, Klaassen et al 2010). This was surprising, given that nearly all the adult Marsh Harriers from both population are long-distance migrants using roughly the same flyway to reach an overlapping wintering range in sub-Saharan West Africa (see Fig.2, right).

Fortunately, Marsh Harriers in Sweden have also been tracked with GPS-based trackers in recent years, allowing for a detailed comparison with the GPS-tracked individuals from the Low Countries. We are currently in the process of writing up our results for publication in a reputable ornithological journal. Stay tuned to learn more about the intriguing migration strategies of Flemish and Dutch Marsh Harriers as our results will soon are expected to be published in summer 2019!

batumi raptor count: monitoring one of the world´s largest raptor migration spectacles with citizen scientists

Peak passage of European Honey Buzzards at the BRC count station in Sakhalvasho (Georgia) on 2 Sept 2017. - video by Elien Hoekstra

Hundreds of thousands of raptors converge through geographical bottlenecks like the Central American Istmus, the Strait of Gibraltar or the Bosphorus Strait as they rely on overland migration routes between Europe and Africa. For some species the passage at these sites represents a large fraction of certain populations, and systematic migration counts can be a useful tool for monitoring. My journey in raptor migration ecology started at Batumi Raptor Count (BRC) in 2008, where we developed a highly standardized protocol for monitoring the autumn passage of more than one million raptors between the eastern Black Sea coast and the Lesser Caucasus Range in Adjaria, in the Republic of Georgia.

Timing of juvenile and non-juvenile passage of Marsh Harrier (top), Black Kite (middle) and Honey Buzzard (bottom) inferred from volunteer-based migration counts. (A) The cumulative daily proportion of each age group is derived from a large subset of aged birds and reveals highly synchronized passage between both age groups for Black Kite, a longer and more variable migration period for Marsh Harrier, and a pronounced delay of juvenile vs. non-juvenile passage for Honey Buzzards. (B, C) We monitor timing by looking at changes in quantile passage dates across years separately for non-juveniles (B) and juveniles (C).

In 2011, after publishing our assessment of the global relevance of the Batumi passage for various species (Verhelst et al. 2011), we settled on a protocol to monitor raptor abundance, demography and timing for 8 target species. We went on to develop a largely automated data management scheme, including daily online updates of migration counts. Following the 10th anniversary of the BRC project in 2017, and with the help of the Dutch-Georgian Ornithological Foundation (DuGOF), we secured an NLBIF grant to fund the open access publication of the BRC dataset through the Global Biodiversity Information Facility (GBIF). In the accompanying Zookeys data paper we detail our automated data recording and processing protocol, and describe important pitfalls and best practices for end users (Wehrmann et al. 2019).

The NLBIF grant also funded a first analysis of changes in abundance, demography and timing for 8 target species in the BRC monitoring (in review). With this paper we will scientifically consolidate BRC´s approach to estimating age-specific trends from migration count data, and establish a solid benchmark for the volunteer-based monitoring of raptor migration in the Batumi bottleneck during the 21st century.

Previous affiliations

Hawk Mtn. Sanctuary (PA, USA)
Guest Researcher (Feb - Mar 2017)
Conservation Leadership Intern (Mar - Jun 2011)

University of Amsterdam (NL)
Postdoc (Aug - Dec 2015)
Ph.D. candidate (Jul 2011 - Aug 2015)

Vansteelant Eco Research (NL)
Freelance ecologist (June 2016 - June 2019)
Chamber of commerce: 66266858
VAT-nr.: NL683203320B01

Dutch Montagu´s Harrier Foundation (NL)
Research biologist (April 2017 - present)

Novia University of Applied Sciences (F)
Postdoc (Sep 2017 - Jan 2018)