Black-fronted Terns Research Articles

New Zealand endemic open‐habitat specialist, the Black‐fronted Tern (Chlidonias albostriatus), experienced population expansion during Pleistocene glaciation and recent decline

Understanding how climatic and environmental changes, as well as human activities, induce changes in the distribution and population size of avian species refines our ability to predict future impacts on threatened species. Using multilocus genetic data, we show that the population of a threatened New Zealand endemic open‐habitat specialist, the Black‐fronted Tern Chlidonias albostriatus – in contrast to forest specialists – expanded during the last glacial period. The population has decreased subsequently despite the availability of extensive open habitat after human arrival to New Zealand. We conclude that population changes for open habitat specialists such as Black‐fronted Terns in pre‐human New Zealand were habitat‐dependent, similar to Northern Hemisphere cold‐adapted species, whereas post‐human settlement populations were constrained by predators independent of habitat availability, similar to other island endemic species.

Using meta-population models to guide conservation action

Biodiversity conservation is limited by resources, data, and time for execution. To maximize efficacy, it is best if conservation plans are strategically evaluated for cost, feasibility, and likely impact prior to implementation. We present a framework to systematically examine the likely impact of proposed conservation plans for threatened taxa. As a case study of this framework we use the national Action Plan for Seabird Conservation in New Zealand and 27 threatened seabirds identified for conservation interventions. To evaluate impact, we applied a recently developed seabird meta-population viability analysis model (seabird mPVA) that employs the most current population and adjustable demographic data to assess threatened seabird viability at a global scale under various management scenarios. This publicly available, web-based tool is intended to meet the needs of threatened seabird managers at the initial phase of conservation planning. We used the seabird mPVA to model population trends and potential seabird viability gains from conservation actions that include: bycatch mitigation, invasive species removal, and seabird translocation prescribed in the action plan for individual species. Our model’s ranking of New Zealand seabirds by current quasi-extinction vulnerability roughly correlated with the seabirds’ IUCN Red List status and New Zealand Threat Classification System. We found modeled conservation impact of proposed actions and assigned priority to be generally positively correlated, but variable in magnitude. If all prescribed conservations actions were implemented, our model predicted significant mitigation of quasi-extinction risk for nine species (Antipodean Albatross, Auckland Island Shag, Black-fronted Tern, Fairy Tern, Rough-faced Shag, Northern Royal Albatross, Pitt Island Shag, Stewart Island Shag, Yellow-eyed Penguin). This approach, and our model, can be adapted to other taxonomic groups to provide a consistent framing for the prioritization of species for conservation investment and predictions about the benefits of specific conservation actions for those species.

Longevity can mask low Nb if only Ne of mixed-age samples is estimated in threatened and mobile species

Knowing about a threatened species’ effective population size (Ne) is vital to assess population trends and guide conservation efforts. Highly mobile and migratory species are some of the most threatened yet hardest to monitor groups. Recently, a conversion has been proposed to convert estimates of the effective number of breeders (Nb) to Ne using two life history traits. We evaluated current methods to estimate Nb and Ne to inform conservation management using the black-fronted tern/tarapirohe (Chlidonias albostriatus) as a case study. Black-fronted terns are endangered, highly mobile and traditional monitoring methods have proven difficult. Based on 17 microsatellites and extensive sampling throughout the breeding range, we estimated mean Nb ca. 700 based on sibship assignment and linkage disequilibrium (LD) methods. Mean estimates of LD Ne based on the conversion of Nb and two life history traits was 668, while LD Ne based on samples of chicks and adults was 3216. The low ratio of Nb/Ne when using the Ne estimate based on mixed-age samples is probably driven by a combination of Nb being more sensitive to the large recruitment failure of individuals, large variation compared to mean reproductive success between same-age and same-sex individuals, and the ongoing overall population decline. We highlight that in relatively long-lived and threatened species, a combination of Nband Ne estimates are more appropriate to assess the population status rather than solely relying on Neof mixed-age samples. For black-fronted terns, we recommend increased conservation management and genetic monitoring based on Nb and Ne.

Contrasting patterns of population structure at large and fine geographical scales in a migratory avian disturbance specialist of braided river ecosystems

AbstractAimTo 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.LocationNew Zealand.MethodsWe 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.ResultsNuclear 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 conclusionsSignificant 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.

Social attractants, a conservation tool for black‐fronted terns

ABSTRACTSocial 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. © 2019 The Wildlife Society.

Clearing islands as refugia for black-fronted tern (Chlidonias albostriatus) breeding colonies in braided rivers

Clearing islands as refugia for black-fronted tern (Chlidonias albostriatus) breeding colonies in braided rivers

Isolation and Characterization of 18 Polymorphic Microsatellite Loci for the Endangered New Zealand Black-Fronted Tern (Chlidonias albostriatus)

Abstract. 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.

Seasonal and individual variation in selection by feral cats for areas with widespread primary prey and localised alternative prey

Context Seasonal and individual variation in predator selection for primary and alternative prey can affect predator–prey dynamics, which can further influence invasive-predator impacts on rare prey. Aims We evaluated individual and seasonal variation in resource selection by feral cats (Felis silvestris catus) for areas with European rabbits (Oryctolagus cuniculus) around a breeding colony of endangered black-fronted terns (Chlidonias albostriatus) in the Upper Ohau River, within the Mackenzie Basin of New Zealand. Methods Within a feral cat population subject to localised control (within a 1-km area surrounding the tern colony), we mapped the movements of 17 individuals using GPS collars, and evaluated individual and seasonal variation in third-order resource selection (i.e. within home ranges) by using resource-selection functions with mixed effects. The year was divided into breeding and non-breeding seasons for terns. Key results Three of the eight feral cats monitored during the breeding season used the colony in proportion to availability and one selected it. These four individuals therefore pose a threat to the tern colony despite ongoing predator control. Selection by feral cats for areas with high relative rabbit abundance was not ubiquitous year-round, despite previous research showing that rabbits are their primary prey in the Mackenzie Basin. Conclusions Results suggest that rabbit control around the colony should reduce use by feral cats that select areas with high relative rabbit abundance (less than half the individuals monitored), but is unlikely to alleviate the impacts of those that select areas with low relative rabbit abundance. Hence, predator control is also required to target these individuals. Results thus support the current coupled-control of feral cats and rabbits within a 1-km buffer surrounding the tern colony. Future research should determine what scale of coupled-control yields the greatest benefits to localised prey, such as the tern colony, and whether rabbits aid hyperpredation of terns by feral cats via landscape supplementation. Implications The present study has highlighted the importance of considering seasonal and individual effects in resource selection by predators, and the role of primary prey, when designing management programs to protect rare prey.

Species-specific responses by ground-nesting Charadriiformes to invasive predators and river flows in the braided Tasman River of New Zealand

Identifying factors causing population declines is imperative for conserving Charadriiformes worldwide. Inference of threatening factors from single-species and single-life-stage studies is common, but may be inadequate as sympatric species can exhibit different responses to common threats. In the Tasman River of New Zealand, we evaluated the responses of four sympatric Charadriiformes (banded dotterel (Charadrius bicinctus), wrybill (Anarhynchus frontalis), black-fronted tern (Chlidonias albostriatus), and kakī (black stilt, Himantopus novaezelandiae)) at different life stages, to river flows, and to mammalian predators subject to sustained control. Hatching success of dotterels and wrybills was generally high. For dotterels, hatching was adversely affected by low minimum river flow and by a combination of high maximum flow and high predator abundance. Only between-year and colony affects were found for the hatching success of wrybills and terns, respectively. Wrybill chick survival was reduced by predation, and by high minimum and low maximum river flows. Tern chick survival was mostly low. Survival of adult kakī increased with predator control and with lower kakī abundance. An age-structured model confirmed the importance of predator control for kakī persistence. In addition to quantifying predation impacts, the results suggest that low minimum and high maximum flows can have opposite effects on dotterels and wrybills, and that dotterels may be subject to a trade-off between predation and flooding risk. Also, localised predation on terns may be due to specialisation by individual predators. Managers conserving sympatric Charadriiformes should not assume consistent responses to threatening processes and should use indicator species with caution.

Dating chicks: Calibration and discrimination in a nonlinear multivariate hierarchical growth model

The motivation for this work was to investigate the possibility of accurately determining the age of a tern chick using easily obtained body measurements. We describe the construction of a nonlinear multivariate hierarchical model for chick growth and show how it can be estimated using Markov chain Monte Carlo techniques. A simple extension of the analysis allows for estimation of the ages of unknown chicks. Posterior distributions of the unknown ages are derived, so that the accuracy of age determination can be examined. We further extend our model and analysis to include the possibility that chicks fall into distinct groups with different growth characteristics. The technique is illustrated using data on the weight and wing length of black-fronted terns from the Ohau River, New Zealand. It is found that dating to within one day is possible, but only in some areas of the data space. The concept of “braiding” of multivariate growth curves is introduced to explain the varying accuracy of age determination.

Breeding biology of Black-fronted Terns (Sterna albostriata) and the effects of predation

Black-fronted Terns (Sterna albostriata) are an endangered species endemic to New Zealand whose breeding biology and survival are poorly understood, yet the species is in urgent need of management. I studied aspects of Black-fronted Tern breeding ecology and survival on the Ohau River, South Island, New Zealand, from 1998 to 2001. Over three breeding seasons, 50.2% of 1022 nests successfully hatched one or more eggs. Predation (24.6%) and desertion (21.4%) were the main causes of nest failure. At least 28% of all hatched chicks (n = 897) survived to fledge. Productivity for each of three breeding seasons was estimated at 0.23, 0.34 and 0.27 fledglings per nest. Hatching and fledging rates at individual colonies ranged widely, largely because of the impacts of predation by introduced mammals. Evidence from video cameras placed at nests suggested predators were a cause of nocturnal and permanent desertion of both eggs and chicks, and that single predators could destroy entire colonies. Based on re-sightings of 72 colour-banded adult Terns, adult annual survival rate was estimated at 0.88-0.92 but the associated confidence intervals were wide (0.57-0.99). Most re-sightings (77%) of banded adults that were nesting were either in the colony in which they were banded or elsewhere on the Ohau River. This is the first comprehensive study on the breeding biology of Black-fronted Terns and indicates that predator control is essential to the future survival of the species.

Does fledging equal success? Post-fledging mortality in the Black-fronted Tern

Fledging success is widely used as an index of reproductive success in avian studies, but survival of young after fledging is rarely estimated. In this study, I used radio telemetry to measure rates and causes of mortality of 63 Black-fronted Terns (Sterna albostriata) in the immediate post-fledging period on the Ohau River, South Island, New Zealand, in 1998–2000. Juvenile survival for four weeks after fledging was 0.795. Mean daily survival increased from 0.972 in the first week after fledging to 0.995 in the second week and 1.00 for the third and fourth weeks. Introduced predators such as feral cats (Felis catus) and Norway rats (Rattus norvegicus) were responsible for a minimum of nine out of 12 deaths, and all except one death occurred at the natal colony prior to dispersal. Larger, heavier juveniles that fledged at a younger age tended to have higher survival after fledging, but survival could not be accurately predicted based on measurements of growth. These results indicate that the post-fledging period can be an important period for mortality in young birds, and that survival until dispersal from the natal colony is the best measure of Black-fronted Tern reproductive success currently available.

Causes of mortality of Black-fronted Terns Sterna albostriata on the Ohau River, South Island, New Zealand

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.

Causes of mortality at nests of ground-nesting birds in the Upper Waitaki Basin, South Island, New Zealand: a 5-year video study

We used video cameras over 5 years to quantify causes of mortality at 172 nests of three species of ground-nesting birds that nest on braided riverbeds of the Upper Waitaki Basin, South Island, New Zealand. The species were banded dotterels Charadrius bicinctus ( n=114), black stilts Himantopus novaezelandiae ( n=23), and black-fronted terns Sterna albostriata ( n=35). Of 77 recorded lethal events (excluding four desertions caused by us), 66 involved deaths of only eggs, and 11 involved deaths of adults and/or chicks, and/or eggs. The main predators were cats Felis catus, hedgehogs Erinaceus europaeus, and ferrets Mustela furo, which were responsible for 43, 20, and 18% of lethal events, respectively. Cats were the only predator species to take adult birds. We recorded only two avian predations: a harrier Circus approximans took a chick and a hatching egg from one nest, and an Australian magpie Gymnorhina tibicen ate chicks at one nest. Other causes of mortality were incubating adult birds, floods, and sheep Ovis aries. Each accounted for <4% of lethal events. Ninety percent of visits (151 of 168) by predators or potential predators happened between sunset and sunrise. We found no evidence that video cameras or infra-red lighting influenced predation rates during 2 years of testing for such effects.