Dunlin Habitat Use and Diet

Ecostudies Institute, in collaboration with Washington Department of Fish and Wildlife and support from many organizations, initiated a study in two large estuaries in north Puget Sound to determine what habitats shorebirds use and in which habitats they feed. We studied Dunlin, an overwintering species, because they are relatively common in the area, but also have likely suffered long-term population declines. We used radio telemetry to determine what estuarine and agricultural habitats they preferred and we used stable isotope measurements of whole blood to estimate the relative use of estuarine vs. upland agricultural zones in their diet. Finally we tested the transferability of distribution models for Dunlin created in the nearby Fraser River delta to the Skagit River delta.

Dunlin Habitat Use and Diet

Shorebirds are a conspicuous feature in coastal estuaries of Washington, and over 30,000 Dunlin winter in North Puget Sound. These long-distance travelers rely on intertidal habitats and adjacent agricultural lands as refueling sites during migration and for overwintering. With over 85% of estuarine habitats in north Puget Sound converted to agriculture, understanding how individual shorebirds navigate this highly altered landscape is critical for crafting long-term conservation strategies.

Key Findings

  • Using mist-nets and net guns, we radio-tagged 168 Dunlin over 3 winters and tracked them from the ground and with fixed-wing aircraft.
  •  We found Dunlin preferred tide flat and low marsh habitats over all other habitats, including agricultural cover types.
  • Despite their preference for estuarine habitats, isotopes indicated that Dunlin obtained about 62% of dietary protein input from agricultural lands and 38% input from the estuary. Dunlin increased their use of agricultural habitats later in the winter.
  • Dunlin habitat models between the Skagit and Fraser River deltas showed similar relationships with some predictor variables; for example Dunlin showed strong preferences for organically-rich sediment, proximity to tide line, and intertidal channels.
  • However, two important predictors – distance to vegetation cover (high-shore) and mudflat elevation, were not important in the Skagit River delta, but were in the Fraser River delta.
  • Our results underline the urgent need to combine estuarine and upland agricultural management strategies for shorebird conservation.
Dunlin Habitat Use and Diet

Photo by Gregg Thompson

Publications and Reports

  • Hobson, K. A., G. L. Slater, D. B. Lank, R. M. Milner, and R. Gardiner. 2013. Agricultural lands subsidize winter diet of Pacific Dunlin (Calidrus alpine pacifica) at two major estuaries. Condor 115:515-524. {PDF}
  • Zharikov, Y. and Slater, G. L. 2012. Limitations to spatio-temporal transferability of distribution models for Dunlin (Calidrus alpina) in the Pacific Northwest. Final Report to Pacific Coast Joint Venture. {PDF}
  • Slater, G. L., R. Milner, and R. Borkhateria. 2011. Space use and habitat selection by wintering Dunlin in the Skagit River Delta, Final Report to Seattle City Light. {PDF}

 Project Supporters

Dunlin Habitat Use and Diet