Prey Distribution, Physical Habitat Features, and Guild Traits Interact to Produce Contrasting Shorebird Assemblages among Foraging Patches

Abstract

Worldwide declines in shorebird populations, driven largely by habitat loss and degradation, motivate environmental managers to preserve and restore the critical coastal habitats on which these birds depend. Effective habitat management requires an understanding of the factors that determine habitat use and value to shorebirds, extending from individuals to the entire community. While investigating the factors that influenced shorebird foraging distributions among neighboring intertidal sand flats, we built upon species-level understandings of individual-based, small-scale foraging decisions to develop more comprehensive guild- and community-level insights. We found that densities and community composition of foraging shorebirds varied substantially among elevations within some tidal flats and among five flats despite their proximity (all located within a 400-m stretch of natural, unmodified inlet shoreline). Non-dimensional multivariate analyses revealed that the changing composition of the shorebird community among flats and tidal elevations correlated significantly (ρs = 0.56) with the spatial structure of the benthic invertebrate prey community. Sediment grain-sizes affected shorebird community spatial patterns indirectly by influencing benthic macroinvertebrate community compositions. Furthermore, combining sediment and macroinvertebrate information produced a 27% increase in correlation (ρs = 0.71) with shorebird assemblage patterns over the correlation of the bird community with the macroinvertebrate community alone. Beyond its indirect effects acting through prey distributions, granulometry of the flats influenced shorebird foraging directly by modifying prey availability. Our study highlights the importance of habitat heterogeneity, showing that no single patch type was ideal for the entire shorebird community. Generally, shorebird density and diversity were greatest at lower elevations on flats when they became exposed; these areas are at risk from human intervention by inlet sand mining, construction of groins and jetties that divert sediments from flats, and installation of seawalls on inlet shorelines that induce erosion of flats.

How do macrobenthic resources concentrate foraging waders in large megatidal sandflats?

“…The unequal use of the flat by the four considered wader species confirms the conclusions of VanDusen et al (2012), which stipulate that the habitat heterogeneity explains the non-random spatial distribution of foraging shorebirds. In the bay of Saint-Brieuc, only part of the flats benefit of a high protection level (National Nature Reserve).…”

Mixed effects of an introduced ecosystem engineer on the foraging behavior and habitat selection of predators

“…The abundance, biomass, and availability of prey are crucial predictors of shorebird communities on intertidal mudflats (Dugan et al 2003, Spruzen et al 2008, VanDusen et al 2012, with shorebirds known to forage in areas with greater prey availability (Fraser et al 2010). Across microhabitats and entire mudflats, prey availability is constrained directly by abiotic factors, such as sediment composition and tidal cycle (Burger et al 1977, VanDusen et al 2012. The presence of vegetation on mudflats also influences shorebird distributions due to its effects on macroinvertebrate abundance and shorebird foraging efficiency.…”

Landscape structured by physical settings and benthic polychaete and avifauna habitat uses in a mangrove-vegetated estuary

“…Landscape structure and biotic interactions are inherently connected [14,15]. The landscape of the Wazihwei Nature Reserve, as illustrated in the present study, is similar to brocade in relation to the interplay of layers represented by the physical to polychaete and avian landscapes.…”

“…Most suggestions regarding mangrove-associated landscape management have focused on avifauna and the anthropogenic effects of different types of land use on bird communities [11-13]. There are few studies reporting the landscape- and/or physical habitat-based connections between avifauna and their food sources [15]. Macrobenthos polychaetes and bivalves and fishes, for instance, are the main preys of shorebirds and egrets [15-17], while insects are a major food source of foliage gleaners [18].…”

“…There are few studies reporting the landscape- and/or physical habitat-based connections between avifauna and their food sources [15]. Macrobenthos polychaetes and bivalves and fishes, for instance, are the main preys of shorebirds and egrets [15-17], while insects are a major food source of foliage gleaners [18]. Polychaete and bivalve distributions are largely controlled by local physical driving forces, including hydrology, geomorphology and sedimentology [19-23], while insect distributions are tightly associated with vegetation composition [24].…”