Abstract
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.
Highlights
Several iconic, threatened species of the world’s coastlines nest on ocean-exposed sandy shores and are thought to use nest-site selection to increase clutch success, hatchling survival, and fitness (Refsnider & Janzen, 2010; Spencer, 2002)
Viability of resident coastal bird populations is limited by failed nesting attempts and high chick mortality resulting from predation, flooding, and human disturbance (Erwin et al, 2006; Martín et al, 2015; Tjørve & Underhill, 2008)
Mitigation of all threats places a heavy burden on beach-nesting bird managers, who are already constrained for time and resources, and such efforts may be fruitless if nests are lost to flooding
Summary
Several iconic, threatened species of the world’s coastlines nest on ocean-exposed sandy shores (e.g., turtles, birds) and are thought to use nest-site selection to increase clutch success, hatchling survival, and fitness (Refsnider & Janzen, 2010; Spencer, 2002). Researchers have examined potential factors influencing clutch survival of coastal birds They have identified a suite of egg and chick predators across several taxonomic groups (Brooks et al, 2014; Ivan & Murphy, 2005), evaluated links between direct and indirect human interference and reproductive failure (Ruhlen et al, 2003; Weston & Elgar, 2007), and quantified the impact of high tides and storms on reproductive success (Brooks et al, 2013; Pol et al, 2010). By definitively assigning clutch fate to a set of artificial nests distributed across varying beach habitats and examining an exhaustive list of predictor variables hypothesized to influence clutch failure, we determined the relative importance of predation, flooding, and human disturbance on the probability of clutch loss
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