Feeding, roosting and nesting sites for shorebirds
The availability of feeding, roosting and nesting sites in coastal habitats is essential for shorebirds. Many migratory shorebirds use coastal habitats as stepping stones in their migratory flyway. They use them as stopover or staging sites, where they stop for a period of days to weeks during migration to feed and refuel before a (often long-haul) flight (Warnock, 2010). Shorebirds mostly forage on tidal flats during low tide, following the tide as it moves across the flat. During periods of high tide they must leave their feeding grounds in intertidal areas. They move to areas where they are safe from high water and threats like predators, mostly to roost, but sometimes to continue feeding. They roost in so-called high-tide roosts (Rogers, 2003), either on exposed ground or in shallow water. The availability of both suitable high-tide roosting sites and feeding sites in a given area will affect bird abundance (Rogers et al. , 2006). Some shorebirds prefer to roost in the upper portion of the tidal flats where they feed, in areas above the water level, but will also roost (and forage) in man-made features in intertidal wetlands (Rosa et al. , 2006; Fidorra et al. , 2015; Scarton & Montanari, 2015), such as aquaculture ponds (such as fish or crab ponds) (Li et al. , 2013) or salt production ponds (Sripanomyom et al. , 2011). Some species actually show a preference for such artificial habitats (Green et al. , 2015). It has been suggested that artificial habitats provide a buffer, a secondary role, or a complementary habitat for shorebirds when natural sites are not available (Li et al. , 2013; Rocha et al. , 2017; Jackson et al. , 2019). There are some concerns about the reliance of shorebirds on artificial wetlands in coastal areas (Jackson et al. , 2020). For example, if aquaculture or salt ponds fall out of use, or if they are converted to other land uses, shorebirds may be at risk. Therefore, management of artificial habitats should be considered alongside natural habitat creation and restoration.
In addition to providing valuable stop over sites for migratory birds, many coastal areas also provide nesting habitat to birds. As roosting and nesting are vulnerable behaviours, shorebirds prefer sites that are safe from disturbance from humans or predators (Rogers et al. , 2006; Rosa et al. , 2006). However, with the continuing loss of coastal habitat, safe and accessible roosting and nesting sites are becoming fewer (Studds et al. , 2017). This means that birds may spend more time flying between foraging and roosting sites, which uses up their precious energy reserves needed for migrating or reproducing.
Maintaining undisturbed roosting sites is essential for shorebirds. Here, Whimbrels Numenius phaeopus are roosting during high tide in the upper tidal flats that have not been covered by seawater in Moreton Bey, Queensland, Australia. [Credit: Micha V. Jackson].
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