At the age of twelve I developed a profound interest in the ecology of European Nightjars (Caprimulgus europaeus), and I promised myself to study these mysterious birds as I grew older. Another twelve years later I was very fortunate to write my master thesis on the foraging behaviour of nightjars at KULeuven. In 2014, I was granted a PhD-candidate position at Hasselt University which allowed me to continue my work on the life of these crepuscular birds.
My current research is focussed on studying the ecology of nightjars during their four-month-breeding season in Belgium. However, it is impossible to ignore that nightjars spend the majority of the year on migration and in Africa. Therefore, unravelling their migratory behaviour is an important side-story to my study.
In February 2016, the Nightjar Research Group was launched to facilitate collaborative work, streamline data collection and share ideas on the ecology of nightjars. Following this meeting, I collaborated with Brian Cresswell, Ian Henderson, Greg Conway and Frederic Jiguet to unravel the migratory pathways of western European nightjars.
The European Nightjar is a light-weight (70g) long-distance, trans-equatorial migrant, protected under the Conservation of Migratory Species of Wild Animals. It breeds on dry sandy soils in Eurasia, mainly in open semi-natural habitats, such as heathlands. Recovery rates of ringed Nightjars in their non-breeding areas are extremely low, with two found in Africa, out of a total of 131 recoveries globally, up until 2009.
Little is known about the Nightjars’ migratory behaviour. It was generally assumed that Nightjars’ wintering range was split into two major regions: the first extending along the eastern coast of Africa from Kenya to South Africa and the second in the western Sub-Saharan region from Senegal to Cameroon. In 2013, a geolocator study from Cresswell and Edwards lead to the discovery of new wintering sites in the Democratic Republic of Congo (DRC) and the identification of a possible loop migration pattern.
Still, detailed information about general migration routes, migration timing, stopover zones and wintering range of Western European Nightjars was lacking. We used a combination of geolocators and GPS-loggers to reconstruct the entire migratory cycle of eleven Nightjars from five sites in three Western European countries. We were also very fortunate to recapture one third-calendar-year bird which was equipped with a geolocator as a juvenile. This bird was the only juvenile we tagged, and it collected information on two full migration routes.
Our tracking results confirm a well-defined loop migration pattern. This pattern indicates that Nightjars follow different trajectories during autumn and spring migration, making an elaborate detour throughout Western Africa in spring. All Nightjars overwintered south of the Central African Tropical Rainforest in two sub-tropical ecoregions (Southern Congolian forest-savanna mosaic, Central Zambezian Miombo woodlands), outside their formerly-presumed wintering range. GPS-data also confirms that our Nightjars are stationary during the entire winter and stay in a distinct, small habitat patch. The juvenile nightjar showed remarkable capabilities to search for stopover zones and wintering areas, similar to those of adult Western European nightjars, during its first naïve migration and to locate specific areas again the next year.
We observed a strong convergence near common stopover zones in Northern, Central and Western Africa where our birds stayed for two to three weeks. These zones are situated in areas with a high-normalized difference vegetation index (NDVI; www.vito-eodata.be). It seems plausible that Nightjars track seasonal rains in these regions in order to profit from the emergence of aerial insects. Regained fuel loads are required to ensure successful crossing of ecological barriers, such as the Mediterranean Sea and the Sahara. Based on our observations we also hypothesise that the CATR is also an ecological barrier for Nightjars.
Our findings suggest that juvenile nightjars’ innate migration program allows them to reach species-specific stopover-zones and wintering grounds during their first migration and experience allows them to fine-tune this program in order to re-use them the next year. However, Nightjars use the same stopover sites as several other European migrants such as Common Swift Apus apus, Great Reed Warbler Acrocephalus arundinaceus, and European Rollers Coracias garullus. This indicates the importance of these specific zones and highlights the vulnerability of Western European bird populations to habitat destruction en route, and/or to a mismatch between arrival times and food availability caused by climate change. Therefore, it would be great to study Nightjars’ 1) wintering-ecology, 2) migratory connectivity and 3) ecological requirements en route.
More information: Ruben Evens (This email address is being protected from spambots. You need JavaScript enabled to view it.), www.rubenevens.com
Centre for Environmental Sciences, Research Group Zoology: Biodiversity & Toxicology.
Hasselt University - Campus Diepenbeek, Agoralaan Building D - B-3590 Diepenbeek
• Evens, R., Conway, G. J., Henderson, I. G., Cresswell, B., Jiguet, F., Moussy, C., Sénécal, D., Witters, N., Beenaerts, N. and Artois, T. (2017), Migratory pathways, stopover zones and wintering destinations of Western European Nightjars Caprimulgus europaeus. Ibis. doi:10.1111/ibi.12469
• Evens, R., Beenaerts, N., Witters, N. and Artois, T. (2017), Repeated migration of a juvenile European Nightjars Caprimulgus europaeus. J Ornithol, doi:10.1007/s10336-017-1459-2, https://link.springer.com/article/10.1007/s10336-017-1459-2?wt_mc=Internal.Event.1.SEM.ArticleAuthorOnlineFirst