Werkgroep Lepelaar, a research team from the University of Groningen and the NIOZ Royal Netherlands Institute for Sea Research, has been tagging adult and juvenile Eurasian spoonbills (Platalea leucorodia leucorodia) with UvA-BiTS GPS tracking devices since 2012 to follow the birds’ movements while breeding, feeding and migrating. The team also places color-rings and takes measurements from spoonbills on the Dutch Wadden Sea Islands every year. Re-sightings by hundreds of volunteers all along the flyway show their migration routes and wintering sites.

Map of the spoonbill migration system. The sizes of the dots represent the number of individuals in the analysis that wintered at each site. (From Lok et al. 2015)

The team is hoping that GPS data from the tagged birds will shed light on why spoonbills experience higher adult mortality during the spring migration. Spoonbills that breed in the Netherlands during the summer migrate different distances (approximately 1000, 2000 and 4500 km) to winter in France, Iberia and Mauritania, respectively. Research done between 2005 and 2012 showed that mortality during spring migration was much higher (18%) for the birds that reached Mauritania, compared with those wintering in France (5%) or Iberia (6%) (Lok et al. 2015). The increased mortality observed during the long migration back from Africa may be due to suboptimal foraging areas and unfavorable weather conditions as the birds return to northern Europe along the western edge of the Sahara Desert. These conclusions are fascinating since previous observations of ringed spoonbills indicated that the birds are highly site faithful when choosing wintering areas, especially older individuals (Lok et al. 2011).

The story of the migration of a spoonbill that was tagged in April 2016 by Werkgroep Lepelaar is particularly interesting. The metal ring on spoonbill #6284 indicated that she hatched in summer 1994 on Schiermonnikoog Island in the Netherlands, in one of only 22 clutches on the island for that year, which now makes her 24 years old. During the 2017 breeding season on Schiermonnikoog, she chose a tagged male as a partner and went on to have a young chick that has also been GPS tagged.

Tagged spoonbills in the Guerande salt marshes of western France in January 2018 (Photo by Joel Fievre)

In September 2017, while her young continued to hang out on the eastern coast of Schiemonnikoog, 6284 started her trip south during the first quiet evening after an autumnal and stormy week. After one and a half days of flying (with an evening stopover in the Slikken van Flakkee along the southern Dutch border), she arrived in Baie D’Arcachon in France. This area is frequently used by spoonbills as a stopover, but is not considered a popular wintering area. From there she continued on to overwintering grounds in southern Spain.

The GPS tracking data indicates that 6284 spent the winter of 2017-2018 in southern Spain. In February 2018, she was spotted several times as she travelled over 500 km north from Huelva in southern Spain to the Mondego Delta in Portugal. She probably made the trek to forage on American crayfish, a favorite prey of spoonbills. But why didn’t this seasoned veteran just stay there all winter? For now, that remains a mystery.

Left: GPS tracks of spoonbills 6283 and 6284 on the Iberian Peninsula in January and February 2018. Top right: Spoonbill resting area in the Mondego Delta in central Portugal. Bottom right: American crayfish, a favorite prey of spoonbills.

References

Lok T, Overdijk O, and Piersma T. 2015. The cost of migration: spoonbills suffer higher mortality during trans-Saharan spring migrations only. Biol. Lett: 11. 20140944. http://dx.doi.org/10.1098/rsbl.2014.0944

Lok T, Overdijk O, Tinbergen JM, and Piersma T. 2011. The paradox of spoonbill migration: most birds travel to where survival rates are lowest. Animal Behaviour 82: 837-844