Avian prey exhibit repeatable abundances on intertidal mudflats

Consistency in the spatial distribution of prey enhances the foraging efficiency of predators by reducing search time. Predictable foraging locations are particularly useful for shorebirds in tidally structured habitats where foraging time is limited to periods of low tide. Locations with sessile prey, such as endobenthic bivalves, likely have consistent abundances between tides, however, locations with mobile prey, such as brown shrimp Crangon crangon and shore crab Carcinus maenas , may have inconsistent abundances due to the high mobility of crustacean species. To what extent mobile prey in intertidal habitats show repeatable distributions is unknown. A metric called ‘repeatability’ is often used to quantify behavioural consistency among individuals over time and across contexts. Here, we studied whether locations showed consistent abundances over time for both sessile and mobile epibenthic prey by calculating the repeatability of abundances at sampling locations in the Dutch Wadden Sea across weeks. Weekly sampling from July to October revealed that, consistent with our prediction, abundances of a sessile species (flat furrow-shell Abra tenuis ) were highly repeatable across locations and time (R_{flat furrow-shell} = 1.00). Contrary to our predictions, locations with mobile prey were also predictable as indicated by non-zero repeatability of abundance (R_shrimp = 0.33, R_crab = 0.19). The repeatability in abundances between locations allows foragers to target areas with prey and thus increase their efficiency, even when consuming highly mobile crustacean prey.