Island shape, size, and isolation affect nest-site selection by Little Terns

Abstract

Populations of many seabirds and other species that nest along coasts are declining due to habitat degradation and loss. An improved understanding of the species‐specific factors that determine nest density across a landscape is therefore critical for conservation efforts. We examined factors that affected the density (number per hectare) and abundance (number at a sampling site) of nests of Little Terns (Sternula albifrons) on the Sinai Peninsula, Egypt. Terns preferred to nest on islands rather than the mainland, with islands constituting 64% of the area surveyed, but containing 99% of the 439 tern nests we found. Nest densities were highest on islands that were small, located at moderate distances from the mainland, and irregularly shaped or elongated. Most nests (69%) were on islands with areas < 3 ha, although these islands represented < 5% of total island area, and islands with the highest nest densities were 80–300 m from the mainland. Terrestrial predators were more likely to occur on larger islands, visiting three of the largest four islands. Most tern nests were within 1 m of shorelines, causing island perimeter to be a strong influence on nest density. Island shape was the only factor that significantly affected nest abundance, with more nests on islands with relatively long perimeters for their size. Our results suggest that protection or creation of relatively small, slender islands at moderate distances from shore may be an effective means of increasing the number of breeding sites for Little Terns. Although not generally considered a potential determinant of nest site preferences for seabirds, island shape is likely to be important for species that prefer sites adjacent to water, including species that nest on beaches and seaside cliffs.

Island characteristics within wetlands influence waterbird nest success and abundance

“…Thus, small islands averaged similar nest numbers compared to large islands. Previous studies have reported that some waterbirds nest in greater numbers on small‐ to intermediate‐sized islands compared to large islands, perhaps to avoid predators large islands may harbor (Erwin et al , Eason et al ). We suspect that preference for nesting near water exhibited by avocets, stilts, and terns contributed to similar numbers of nests between large and small islands.…”

“…Nest abundance was predicted to be almost 3 times greater on an island with a shape index of 3.0 (i.e., island roughly 34 times longer than wide) relative to a round island (shape index of 0.9). Previous studies have reported that many waterbirds, including terns and shorebirds, often nest within a few meters of the water's edge (Cuervo , Stenhouse et al , Maxson et al , Eason et al ). In a companion study, we report that the probability of nesting peaked on island patches that were 2 m and 7 m from the water among terns and avocets, respectively (Hartman et al ).…”

“…For breeding waterbirds, islands can be extremely important nesting habitat because they may isolate nesting birds from terrestrial predators and limit human disturbances. Previous studies have reported waterbird nest abundance, nest density, and nest success can be greater on island habitats relative to mainland habitats (Lokemoen and Woodward 1992, Clark and Shutler 1999, H€ otker 2000, Anteau et al 2014, Eason et al 2012. As a result, wetland management for breeding waterbirds often includes the construction or maintenance of island nesting habitat (Parnell et al 1988, Quinn and Sirdevan 1998, Erwin et al 2003).…”

“…Yet, how to construct or manage islands for nesting waterbirds can be difficult to determine. A number of landscape characteristics may affect island use by nesting waterbirds including size, shape, topography, location, and land cover (Giroux , Erwin et al , Dahl et al , Shaffer et al , Eason et al ), and preferred island characteristics can vary dramatically among waterbird species. Thus, identifying island characteristics that promote greater use and nest success on islands could benefit waterbird habitat management efforts.…”

Bárcena Volcano, 1952: a 60-year report on the repopulation of San Benedicto Island, Mexico, with a review of the ecological impacts of disastrous events

“…34. The topography of the area destroyed will impact the kind and rate of recovery (Cox and Cox 1977;Eason et al 2012). 35.…”