Royal Netherlands Institute for Sea Research
Royal Netherlands
Institute for Sea Research

How do birds with different feeding specialisations utilize the food landscape?

MSc student project

Wintering shorebirds in the Wadden Sea search during low tides for food on intertidal mudflats. Within species, individuals can specialize on different feeding techniques or different preys. In oystercatchers individual feeding specialisation is well developed. Some individuals almost exclusively eat mussels and cockles and are considered ‘Shellfish specialists’. Due to their habit to attack strong-shelled shellfish, they develop a blunt bill tip. Other individuals eat soft-bodied prey, such as clams and ragworms, and are considered ‘Worm specialists’. Worm specialists develop a pointy bill tip. In the Wadden Sea, we use GPS trackers (www.uva-bits.nl) on oystercatchers to study differences in behaviour among individuals with different feeding specialisations. From previous studies, we know that the feeding specialisation affects foraging time and foraging time allocation of individuals. Worm specialists tend to feed more and prioritize to forage in daylight, whereas shellfish specialists follow more strictly the tidal pattern.

In this project, space use between birds with different specialisations is compared and matched with food landscape maps. Oystercatcher GPS data is available from Balgzand, Vlieland, Ameland and Schiermonnikoog. Data on prey is available from an intensive monitoring scheme in the Wadden Sea, SIBES (Synoptic Intertidal Benthic Survey), carried out every year since 2008 by the NIOZ (Netherlands Institute for Sea Research). From these data, food landscapes can be constructed for foraging oystercatchers. The main goal of this project is to quantify resource landscapes, and study whether differences in spatial distributions of prey species drive variation in space use of individual oystercatchers depending on their feeding specialisation.

Space use of oystercatchers with GPS trackers around Vlieland, separated for shellfish specialists (left) and worm specialists (right) (bill shape drawings from Swennen et al., 1983). Map source: Bing maps.