Sandpiper faeces DNA reveals broader diet than suspected

Semipalmated Sandpipers feed on a much wider number of organisms from a greater number of habitat sources than previously thought. Photo: Dan Pancamo (commons.wikimedia.org).
Semipalmated Sandpipers feed on a much wider number of organisms from a greater number of habitat sources than previously thought. Photo: Dan Pancamo (commons.wikimedia.org).
Researchers have shown that Semipalmated Sandpipers eat a far broader diet than anyone suspected on their annual stop-over in Canada’s Bay of Fundy, and they did it by analysing poo.

Analysis of stomach contents had led researchers to believe that Semipalmated Sandpipers in the Bay of Fundy rely on an amphipod species called Corophium volutator as their major food source. However, the new study of faeces by a team from the University of New Brunswick shows that the sandpipers’ diet knits together several adjacent food webs: freshwater insects that wash down onto the beach in streams and the eggs of ocean-going fish deposited on the shore by tides also get eaten alongside organisms that live in the beach’s intertidal zone.

This broader diet may increase their exposure to pesticides and other toxins, in addition to making the birds more resilient to changes in their habitat due to climate change and other factors.

“Current Semipalmated Sandpiper conservation efforts in the Bay of Fundy focus on beach and intertidal habitats, neglecting terrestrial, pelagic and freshwater systems that may not only supply nutrients, but harmful chemicals or pesticides as well,” according to lead author Travis Gerwing. “Future studies need to explore this possibility, attempting to determine if bioaccumulation of harmful toxins from multiple ecosystems in the Semipalmated Sandpipers are having any negative impacts upon this species.”

Gerwing and his colleagues obtained their data using a technique called 'molecular scatology', which is simply analysing the DNA contained in the sandpipers’ faeces. “The best part of molecular scatology is that it can be entirely non-invasive. I never touched a single Semipalmated Sandpiper,” says Gerwing. “I would get to relax on a beach with my wife and watch these birds forage through our binoculars. Once they naturally moved on, we would run down to where they were foraging and pick up their faeces. My poor wife had to watch as I spent the next few minutes crawling over rocks and mud, picking up bird poop with a pair of sterile tweezers.”

“Molecular detection of [ecological] interactions through next-generation sequencing is a technique increasingly used in [biological] studies to address various questions regarding predation, herbivory and parasitism. By using this approach, Gerwing et al showed that Semipalmated Sandpipers utilised diverse foods and foraging habitats during fall stop-over in the Bay of Fundy, Canada, which opposes the traditional view about the prevalence of amphipods ... in the diets of birds at this location,” according to Ivana Novcic of Kean University, an expert on the foraging ecology of shorebirds. “This study provides better insights into the diet of Semipalmated Sandpipers, which may have important implications regarding the study of group foraging, competition, niche partitioning, food webs and other ecological phenomena.”

Gerwing, T G, Kim, J-H, Hamilton, D J, Barbeau, M A, and Addison, J A. 2016. Diet reconstruction using next-generation sequencing increases the known ecosystem usage by a shorebird. The Auk 133: 168-177.