Colony site selection by eight species of gulls and terns breeding in the ≪Valli di Comacchio≫ (Italy)

Efficacy of created and restored nesting sites for the conservation of colonial Laridae in the South of France

By rapidly modifying key habitat components, habitat restoration is at risk of producing attractive cues for animals without providing habitats of sufficient quality. As such, individual fitness components, such as reproduction, could be reduced and restored habitats could become ecological traps. This risk notably appears by using artificial constructions in restoration projects, yet few studies have evaluated their efficacy in a robust way. We investigated this by analyzing 154 islets that were created or restored to improve the conservation status of 7 colonial Laridae species in the South of France. From 2007 to 2016, we compared occupancy dynamics and breeding parameters of these species between the restored sites and 846 unmanaged nesting sites. We also explored species' preference for different nesting site characteristics and their respective effect on breeding parameters. Restored nesting sites were 2-9 times as attractive as unmanaged sites for all species except the Black-headed Gull (Chroicocephalus ridibundus). Colonization probability was up to 100 times higher in sites already used by other species the previous year and increased with distance to the shore until >0.2 when distance was over 250 m. Abandonment probability was 29-70% lower when breeding was successful the previous year in all species except the Sandwich Tern (Thalasseus sandvicensis). Productivity and breeding success probability were 2 times higher on managed sites. Distance from the shore was an important attractive characteristic of artificial nesting sites in all species. Other nesting site characteristics had species-specific effects on colonization, abandonment, and breeding success. Our results indicate that managed nesting sites are successful conservation tools for colonial Laridae in the Mediterranean and do not act as ecological traps. Our study showed that testing the ecological trap hypothesis is a robust way to evaluate the success of restoration projects of breeding habitats.

Sex-biased parental-care allocation in three tern species (Laridae, Aves)

We studied parental-care allocation by males and females in three tern species. Female Common Terns (Sterna hirundo) and Little Terns (S. albifrons) performed more incubation and brooding than males, whereas in the Sandwich Tern (S. sandvicensis) the sexes shared these duties equally. In all three species, agonistic behaviors were performed equally by females and males. Prey types brought by males and females of each species were similar, but males tended to bring larger prey and had higher delivery rates than females. Information on parental-care allocation by female and male seabirds of various species, 5 gulls, 6 terns, and 1 skimmer, indicates that females perform most of the incubation and brooding in both gulls and terns, whereas males perform most territory attendance and agonistic behavior (gulls) and more prey provisioning (terns). These patterns are qualitatively consistent with the explanation that the differences between gulls and terns in sex-biased parental care are related to the fact that gulls exhibit sexual size dimorphism but terns do not. Contrary to theoretical predictions that in monogamous birds, females contribute more reproductive effort than males, in all the seabird species studied so far the total parental expenditure by males seems to equal or outweigh that by females.