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Social attraction techniques for species restoration and conservation projects predominantly target colonial breeding species, which commonly use conspecific cues as indicators of habitat quality. The black-fronted tern (Chlidonias albostriatus) is a globally endangered species that primarily breeds in transient colonies in New Zealand’s braided rivers. Currently, predator control and habitat enhancement are the primary management strategies for improving black-fronted tern populations. Methods that increase the probability of black-fronted tern colonies being protected by management through an increase in site fidelity of breeding colonies, both within and among years, may greatly increase effectiveness of management. Social attractants, decoys, and audio playback were deployed at 10 sites within 9 Canterbury braided rivers over the 2016 breeding season (September–December). We found that terns interacted with the social attractants compared with the paired untreated plots absent of social attractants. Nearest locations of tern breeding were recorded for 8 of the 10 sites, with breeding recorded within 300 m of the social attractant experimental plots at 5 of these sites. These results suggest that social attraction has the potential for use in black-fronted tern conservation by drawing breeding terns into habitat that has added predator or habitat management.

Aim To understand the population structure and its potential drivers at different spatial scales in a migratory bird, the black‐fronted tern (Chlidonias albostriatus), a specialist of the spatially and temporally dynamic environments of braided rivers. Location New Zealand. Methods We used a three‐pronged approach based on 17 microsatellites, two mitochondrial loci (cytochrome b/control region) and phenotypic data (head‐bill length, bill depth, wing length, weight). We determined large‐scale genetic structure throughout the whole breeding range (approx. 150,000 km2), calculated genetic divergence of breeding colonies and tested for isolation‐by‐distance between colonies. We investigated the level of fine‐scale genetic structure based on spatial autocorrelation analyses and assessed the presence of a body size cline based on phenotypic data. Lastly, we compared phenotypic divergence (PST) and the level of divergence by genetic drift (FST) among breeding colonies to test for underlying mechanisms of population differentiation. Results Nuclear and mitochondrial DNA showed that across their range black‐fronted terns were effectively panmictic, with low genetic divergence between breeding colonies overall and no isolation‐by‐distance. However, at fine geographical scales black‐fronted terns accrued significant genetic structure for distances up to 75 km, primarily driven by males, indicating more frequent female dispersal. Furthermore, a phenotypic cline in accordance with Bergmann's rule was evident. PST exceeded FST in three traits, suggestive of local adaptation. Main conclusions Significant fine‐scale structure can be present in highly mobile, specialist species while not affecting spatial structures at larger scales. Hence, methodologies applied to both whole landscapes and local scales are important to appropriately estimate connectivity in dynamic metapopulations and investigate the processes behind connectivity. Conservation management will need to include protecting currently uninhabited patches to facilitate natural colonization of suitable habitat. For black‐fronted terns, managing whole catchments throughout the entire breeding range would be preferable to managing single patches.

Eighteen polymorphic microsatellite loci were isolated and characterized from the endangered Black-fronted Tern (Chlidonias albostriatus), a species endemic to New Zealand. The loci were initially tested on seven individuals spanning the entire breeding range and then for a larger dataset of 345 samples covering 30 colonies from throughout the species' range. The number of alleles per loci ranged from 4 to 24, and observed and expected heterozygosity ranged between 0.46 and 0.95 and 0.45 to 0.86, respectively. One locus showed significant heterozygote deficit and appears to be sex-linked. The similar annealing temperatures across loci and the wide fragment sizes allowed multiplex polymerase chain reaction and rapid multilocus genotyping. The microsatellite markers will be useful tools for further investigation into the genetic diversity, population structure and effective population size of this endangered species and for informing conservation management.

We examined the carcasses of 148 Black-fronted Terns Sterna albostriata found during the 1998-2000 breeding seasons on the Ohau River, South Island, New Zealand. Predation was the primary cause of mortality of adults, juveniles and chicks, resulting in 47% of all deaths. Video footage showed Feral Cats Felis catus were responsible for 6% of all predator-caused deaths, and physical evidence at carcass remains linked cats to another 19% of predations. Further evidence suggested Norway Rats Rattus norvegicus and Stoats Mustela erminea were responsible for 51% and 6% of predator-caused deaths, respectively. The prey remains left by the different predator species are described. Other causes of mortality included starvation (4%), power lines (1%), road traffic (1%) and various natural causes of mortality (5%). Causes of mortality could not be assigned to 41 % of Black-fronted Terns, but most of these were young chicks that died at the nest soon after hatching. We suggest that predators are potentially the main cause of population decline in black-fronted terns and that predator control targeting cats and Norway Rats during the breeding season should be trialled.