Pond size: Some evidence suggests shorebirds are more abundant on larger ponds (Sánchez-Zapata et al. , 2005; Jackson et al. , 2019). Larger ponds have greater habitat heterogeneity and can therefore support a greater diversity of shorebirds. Preserving a range of pond sizes, but prioritising larger artificial ponds, will suit a larger number of shorebird species (Paracuellos, 2006). Availability of prey: The abundance and accessibility of mud-dwelling invertebrates in the area (Bolduc & Afton, 2004) will influence where shorebirds choose to roost and nest. Bird morphology, such as beak length, influences their feeding preferences. Vegetation : In general, vegetation is a significant deterrent to most shorebird species using a site for roosting, especially if it is tall or dense (Rogers, 2003; Jackson et al. , 2019). Shorebirds rarely settle in areas with >50% total vegetation cover and most prefer vegetation to be less than half of their height (Jackson & Straw, 2021). Shorebirds will not use the edges (for example bunds or walls) around a pond if they have vegetation on them (Jackson & Straw, 2021). A preference for unvegetated roost sites is understood to be related to avoidance of aerial predation by maintaining good site lines around the roost site. It has been observed that vegetation can spread and grow very quickly in some dry patches of an artificial pond (Chi- Yeung Choi, pers. comm.) Salinity: Salinity is an important factor for managing salt ponds. This affects the invertebrates and aquatic plants, which in turn influences shorebirds (Ma et al. , 2010). High levels of salinity can be harmful to waterbirds (Hannam et al. , 2003), but can also cause a superabundance of prey, such as brine shrimp, which shorebirds are greatly attracted to (Micha Jackson, pers. obs.). One study found that small birds use saltpans with higher salinity levels, while large birds use those with lower salinity levels (Velasquez, 1992). Shorebirds were found to forage in mid- salinity in San Francisco Bay, USA, with levels ranging from 81 – 150 ppt (Warnock et al. , 2002; Takekawa et al. , 2006), while shorebirds foraged in a wider range of salinities (25 – 220 ppt) in the Berg River Estuary in South Africa (Velasquez, 1992). Disturbance: Shorebirds are highly sensitive to disturbance while roosting, which may cause them to take flight or abandon otherwise suitable roost sites. Disturbance can be caused by human recreational activities, for example dog-walking, off-road driving, birdwatching or photography too close to birds, or operating aerial devices like kites and drones. Disturbance can also be caused by human production activities like aquaculture harvest, vehicles and machinery, and helicopters. Predation: The presence of predators will have a strong effect on the numbers of birds using ponds for roosting. Predator management may be considered, such as killing or exclusion using fences (Malcolm Ausden, pers. comm.). One study found that predator disturbance was higher in salt ponds compared to tidal flats, which was suggested as a reason why shorebirds preferred natural tidal flats for roosting (Rosa et al. , 2006).
4. Implementation
Water depth: Aquaculture and salt ponds can be managed for shorebird conservation by managing the water levels. Reducing the water levels (Velasquez, 1992; Rocha et al. , 2017;
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