Because of difficulties to sample the diet of adult seabirds, only few studies have simultaneously examined the diets of adults and chicks. For some species, such as most terns, it is0often assumed that chicks and adults feed on the same forage species, although central-place foraging theory predicts that single-prey loaders should bring more energy rich prey to their chicks than they feed on themselves. Here we report on a new and easy sampling technique we used to assess the diet composition of adult Sandwich Terns Sterna sandvicensis by collecting faecal samples each week throughout the breeding season. The study shows that the adult diet varies through the breeding period. In the first weeks after egg-laying, adults primarily fed on sandeel, clupeids and Nereid worms (the latter being absent in the chick diet) although most energy was obtained from sandeel. Clupeids became increasingly important, sometimes already early during the egg-period, but in terms of energetic composition herring only became important when the first chicks hatched or shortly thereafter. Surprisingly, the composition of the chicks' diet closely followed that of the adults, suggesting that adults did not select different prey species for their chicks. However, the length of the prey items (especially of clupeids) found in the adult diet was much smaller than that fed to the chicks. Adults thus seemed to adapt prey size (and not prey species) to the energy demands of their growing chicks, but fed on a constant small fish size themselves. These results are in line with the optimal sharing theory depicting that parents should ingest all small prey, and fly off to the colony only with large prey, with the threshold being determined by their relative needs.
|Number of pages||1|
|Publication status||Published - 2015|
- Sea and coastal birds
EWI Biomedical sciences