Breeding habitat selection in an obligate beach bird: a test of the food resource hypothesis

The food resource hypothesis of breeding habitat selection in beach-nesting birds suggests that birds breed at sites with more prey to meet the increased energetic requirements associated with breeding. We compare prey resources using pitfall traps and core samples at breeding sites and absence sites of the eastern population of hooded plover, Thinornis rubricollis rubricollis, which, in this part of its range, is a threatened obligate beach bird. Breeding sites had higher abundances, equivalent species richness, and different assemblages of invertebrate prey compared with absence sites. Assemblages at breeding sites were characterised by more isopods, and fewer beetles of the family Phycosecidae. Breeding habitat selection by plovers appears to be associated with selection for sites with more food, and any process that degrades food resources at a site (e.g. kelp harvesting or marine pollution events) may reduce the likelihood of occupancy of that site by breeding birds.

The early shorebird will catch fewer invertebrates on trampled sandy beaches

Many species of birds breeding on ocean beaches and in coastal dunes are of global conservation concern. Most of these species rely on invertebrates (e.g. insects, small crustaceans) as an irreplaceable food source, foraging primarily around the strandline on the upper beach near the dunes. Sandy beaches are also prime sites for human recreation, which impacts these food resources via negative trampling effects. We quantified acute trampling impacts on assemblages of upper shore invertebrates in a controlled experiment over a range of foot traffic intensities (up to 56 steps per square metre) on a temperate beach in Victoria, Australia. Trampling significantly altered assemblage structure (species composition and density) and was correlated with significant declines in invertebrate abundance and species richness. Trampling effects were strongest for rare species. In heavily trafficked plots the abundance of sand hoppers (Amphipoda), a principal prey item of threatened Hooded Plovers breeding on this beach, was halved. In contrast to the consistently strong effects of trampling, natural habitat attributes (e.g. sediment grain size, compactness) were much less influential predictors. If acute suppression of invertebrates caused by trampling, as demonstrated here, is more widespread on beaches it may constitute a significant threat to endangered vertebrates reliant on these invertebrates. This calls for a re-thinking of conservation actions by considering active management of food resources, possibly through enhancement of wrack or direct augmentation of prey items to breeding territories.

Regional drivers of clutch loss reveal important trade-offs for beach-nesting birds

Coastal birds are critical ecosystem constituents on sandy shores, yet are threatened by depressed reproductive success resulting from direct and indirect anthropogenic and natural pressures. Few studies examine clutch fate across the wide range of environments experienced by birds; instead, most focus at the small site scale. We examine survival of model shorebird clutches as an index of true clutch survival at a regional scale (∼200 km), encompassing a variety of geomorphologies, predator communities, and human use regimes in southeast Queensland, Australia. Of the 132 model nests deployed and monitored with cameras, 45 (34%) survived the experimental exposure period. Thirty-five (27%) were lost to flooding, 32 (24%) were depredated, nine (7%) buried by sand, seven (5%) destroyed by people, three (2%) failed by unknown causes, and one (1%) was destroyed by a dog. Clutch fate differed substantially among regions, particularly with respect to losses from flooding and predation. ‘Topographic’ exposure was the main driver of mortality of nests placed close to the drift line near the base of dunes, which were lost to waves (particularly during storms) and to a lesser extent depredation. Predators determined the fate of clutches not lost to waves, with the depredation probability largely influenced by region. Depredation probability declined as nests were backed by higher dunes and were placed closer to vegetation. This study emphasizes the scale at which clutch fate and survival varies within a regional context, the prominence of corvids as egg predators, the significant role of flooding as a source of nest loss, and the multiple trade-offs faced by beach-nesting birds and those that manage them.

An obligate beach bird selects sub-, inter- and supra-tidal habitat elements

Few habitat models are available for widespread, obligate, high-energy sandy shore vertebrates, such as the Eastern Hooded Plover Thinornis cucullatus cucullatus. We examined habitat attributes which determined the difference between sites where plovers breed and randomly-selected absence sites (determined from long-term systematic monitoring). A variety of habitat variables were derived from aerial photography and bathymetric and terrestrial Light Detection And Ranging (LiDAR) data. Logistic regression against eight candidate variables, in a model selection framework, revealed considerable support for four variables with respect to explaining the presence of breeding territories. In particular, the amount of unvegetated dune and foredune which was unvegetated, and the amount of intertidal and sub-tidal reef were positively associated with the presence of breeding territories. Thus, plovers apparently select certain habitat in which to breed, involving sub-tidal, intertidal and supra-tidal habitat elements. The model also helps explain the virtual absence of breeding plovers from long sections of superficially suitable habitat, such as the fourth longest continuous beach in the world.