Laysan Research Articles

Feather corticosterone is lower in translocated and historical populations of the endangered Laysan duck (Anas laysanensis).

Identifying reliable bioindicators of population status is a central goal of conservation physiology. Physiological stress measures are often used as metrics of individual health and can assist in managing endangered species if linked to fitness traits. We analysed feather corticosterone, a cumulative physiological stress metric, of individuals from historical, translocated, and source populations of an endangered endemic Hawaiian bird, the Laysan duck (Anas laysanensis). We hypothesized that feather corticosterone would reflect the improved reproduction and survival rates observed in populations translocated to Midway and Kure Atolls from Laysan Island. We also predicted less physiological stress in historical Laysan birds collected before ecological conditions deteriorated and the population bottleneck. All hypotheses were supported: we found lower feather corticosterone in the translocated populations and historical samples than in those from recent Laysan samples. This suggests that current Laysan birds are experiencing greater physiological stress than historical Laysan and recently translocated birds. Our initial analysis suggests that feather corticosterone may be an indicator of population status and could be used as a non-invasive physiological monitoring tool for this species with further validation. Furthermore, these preliminary results, combined with published demographic data, suggest that current Laysan conditions may not be optimal for this species.

Examining distribution patterns of foraging and non-foraging sperm whales in Hawaiian waters using visual and passive acoustic data

Following the end of over a century of intensive commercial whaling in 1986, the monitoring and assessment of sperm whale populations is essential for guiding management and conservation decisions for their recovery. Species distribution models (SDMs) are a useful tool for examining and predicting cetacean distribution patterns and typically incorporate visual, ship-based observations. However, understanding sperm whale distribution and habitat use based solely on surface visual observations is challenging due to the significant amount of time sperm whales spend foraging at depth. For the endangered sperm whale population occurring in Hawaiian waters, we used visual and passive acoustic data collected during four annual NOAA marine mammal line-transect surveys and a suite of biologically relevant environmental variables to develop SDMs within a generalized additive modeling framework to study the distribution of sperm whale groups throughout the island chain. Additionally, the passive acoustic data allowed us to differentiate sperm whale groups as foraging or non-foraging based on their click types to account for differences in distribution and behavior within the archipelago. Foraging groups were predicted primarily in the northwestern region of the archipelago between Laysan Island and Pearl and Hermes Reef as well as north of Maui and Hawaiʻi in the main Hawaiian Islands. Non-foraging groups were predicted to be more uniformly distributed throughout the archipelago. Foraging whale models selected temperature at 584 m depth, surface chlorophyll, and location, while the only significant variables for non-foraging whale models included the standard deviation of sea surface height and location. Each variable provides insight into the oceanographic processes influencing prey abundance and, thus, sperm whale foraging behavior. This study furthers our understanding of the distribution patterns for the sperm whale population in Hawaiʻi and contributes methods for building SDMs with visual and passive acoustic data that may be applied to other cetacean species.

Avian botulism is a primary, year-round threat to adult survival in the endangered Hawaiian Duck on Kaua‘i, Hawai‘i, USA

AbstractAdult survival is the most important demographic parameter influencing population dynamics for many bird taxa. Thus, understanding how survival probabilities and causes of mortality vary throughout the annual cycle is critical for developing informed and effective management strategies. In this study, we used radio-telemetry data to evaluate the effects of biotic (e.g., sex, peak [September–April] vs. off-peak [May–August] nesting seasons) and abiotic factors (e.g., rainfall, year, bi-monthly interval) on adult survival, estimate annual survival probabilities, and identify primary sources of mortality for Hawaiian Ducks (Anas wyvilliana), an endangered, non-migratory dabbling duck, on the island of Kaua‘i, Hawai‘i, USA over 2013 and 2014. Additionally, we used contemporaneous Hawaiian Duck carcass recovery and surveillance data to examine temporal and climatic associations with avian botulism outbreaks. Our results suggested bi-monthly survival decreased with total rainfall during the preceding 2-month interval. Survival did not vary with sex, between peak and off-peak nesting seasons, or between the two years of this study. Annual survival probabilities (62–80%) were relatively low compared to the closely related Laysan Duck (Anas laysanensis) on Laysan Island. Primary causes of mortality included avian botulism and presumed predation by cats (Felis catus). The botulism surveillance dataset revealed support for the effect of rainfall on the number of sick and dead birds recovered (n = 216), with generally a greater number of recoveries during months with middle-range total rainfall during the concurrent and preceding months. Our study provides critical baseline demographic data for population monitoring and highlights the importance of managing botulism risk and non-native mammalian predators for the recovery of the endangered Hawaiian Duck.

Moving Birds in Hawai'i: Assisted Colonisation in a Colonised Land

In September 2011, a delicate cargo of 24 Nihoa Millerbirds was carefully loaded by conservationists onto a ship for a three-day voyage to Laysan Island in the remote Northwest Hawaiian Islands. The goal of this effort was to establish a second population of this endangered species, an “insurance population” in the face of the mounting pressures of climate change and potential new biotic arrivals. But the millerbird, or ulūlu in Hawaiian, is just one of the many avian species to become the subject of this kind of “assisted colonisation.” In Hawai'i, and around the world, recent years have seen a broad range of efforts to safeguard species by finding them homes in new places. Thinking through the ulūlu project, this article explores the challenges and possibilities of assisted colonisation in this colonised land. What does it mean to move birds in the context of the long, and ongoing, history of dispossession of the Kānaka Maoli, the Native Hawaiian people? How are distinct but entangled process of colonisation, of unworlding, at work in the lives of both people and birds? Ultimately, this article explores how these diverse colonisations might be understood and told responsibly in an era of escalating loss and extinction.

Undescribed Juvenile Plumages of the Laysan Rail Or Crake (Zapornia palmeri: Frohawk, 1892) and A Detailed Chronology of Its Extinction

ABSTRACT The extinct Laysan Rail or Crake (Zapornia palmeri) was a small, flightless rail endemic to Laysan Island in the northwestern chain of the Hawaiian Archipelago. I detail the collections made, including eggs, nests, juveniles, and numerous adults prior to its extinction. The juvenile plumage was seemingly well documented, but my study of a series of juvenile specimens collected in 1891 and 1896 provides hitherto undescribed molt changes, from downy chick to definitive plumage. Morphometric data show that sexual size dimorphism is present with males being slightly more robust in bill, legs, and feet. I provide a detailed review of the literature showing the chronology of events that led to the extinction of the species and how this easily could have been avoided.

Lessons from the Tōhoku tsunami: A model for island avifauna conservation prioritization.

Earthquake‐generated tsunamis threaten coastal areas and low‐lying islands with sudden flooding. Although human hazards and infrastructure damage have been well documented for tsunamis in recent decades, the effects on wildlife communities rarely have been quantified. We describe a tsunami that hit the world's largest remaining tropical seabird rookery and estimate the effects of sudden flooding on 23 bird species nesting on Pacific islands more than 3,800 km from the epicenter. We used global positioning systems, tide gauge data, and satellite imagery to quantify characteristics of the Tōhoku earthquake‐generated tsunami (11 March 2011) and its inundation extent across four Hawaiian Islands. We estimated short‐term effects of sudden flooding to bird communities using spatially explicit data from Midway Atoll and Laysan Island, Hawai'i. We describe variation in species vulnerability based on breeding phenology, nesting habitat, and life history traits. The tsunami inundated 21%–100% of each island's area at Midway Atoll and Laysan Island. Procellariformes (albatrosses and petrels) chick and egg losses exceeded 258,500 at Midway Atoll while albatross chick losses at Laysan Island exceeded 21,400. The tsunami struck at night and during the peak of nesting for 14 colonial seabird species. Strongly philopatric Procellariformes were vulnerable to the tsunami. Nonmigratory, endemic, endangered Laysan Teal (Anas laysanensis) were sensitive to ecosystem effects such as habitat changes and carcass‐initiated epizootics of avian botulism, and its populations declined approximately 40% on both atolls post‐tsunami. Catastrophic flooding of Pacific islands occurs periodically not only from tsunamis, but also from storm surge and rainfall; with sea‐level rise, the frequency of sudden flooding events will likely increase. As invasive predators occupy habitat on higher elevation Hawaiian Islands and globally important avian populations are concentrated on low‐lying islands, additional conservation strategies may be warranted to increase resilience of island biodiversity encountering tsunamis and rising sea levels.

Long-distance translocations to create a second millerbird population and reduce extinction risk

Translocation is a conservation tool used with increasing frequency to create additional populations of threatened species. In addition to following established general guidelines for translocations, detailed planning to account for unique circumstances and intensive post-release monitoring to document outcomes and guide management are essential components of these projects. Recent translocation of the critically endangered Nihoa millerbird (Acrocephalus familiaris kingi) provides an example of this planning and monitoring. The Nihoa millerbird is a passerine bird endemic to Nihoa Island in the remote Northwestern Hawaiian Islands. The closely related, ecologically similar Laysan millerbird (Acrocephalus familiaris familiaris) went extinct on Laysan Island in the early 20th century when the island was denuded by introduced rabbits. To reduce extinction risk, we translocated 50 adult Nihoa millerbirds more than 1000km by sea to Laysan, which has recovered substantially in the past century and has ample habitat and a rich prey-base for millerbirds. Following five years of intensive background research and planning, including development of husbandry techniques, fundraising, and regulatory compliance, translocations occurred in 2011 and 2012. Of 11 females in each cohort, 8 (2011 cohort) and 11 (2012 cohort) produced at least one brood of fledglings during their first year on Laysan. At the conclusion of monitoring in September 2014, 37 of the translocated birds were known to survive, and the population was estimated at 164 birds. The reintroduction of millerbirds to Laysan represents a milestone in the island's ongoing restoration.

Microsatellite variation and rare alleles in a bottlenecked Hawaiian Islands endemic: implications for reintroductions

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 28:117-122 (2015) - DOI: https://doi.org/10.3354/esr00681 NOTE Microsatellite variation and rare alleles in a bottlenecked Hawaiian Islands endemic: implications for reintroductions Michelle H. Reynolds1,*, John M. Pearce2, Philip Lavretsky3, Pedro P. Seixas4, Karen N. Courtot1 1US Geological Survey, Pacific Island Ecosystems Research Center, PO Box 44, Hawai‘i National Park, Hawai‘i 96718, USA 2US Geological Survey, Alaska Science Center, 4210 University Drive, Anchorage, Alaska 99508, USA 3Wright State University, 3640 Colonel Glenn Hwy, Dayton, Ohio 45435, USA 4Centro de Reprodução Anatideos, Rua Mário Pais da Costa, no. 53, 3515-174 Viseu, Portugal *Corresponding author: mreynolds@usgs.gov ABSTRACT: Conservation of genetic biodiversity in endangered wildlife populations is an important challenge to address since the loss of alleles and genetic drift may influence future adaptability. Reintroduction aims to re-establish species to restored or protected ecosystems; however, moving a subset of individuals may result in loss of gene variants during the management-induced bottleneck (i.e. translocation). The endangered Laysan teal Anas laysanensis was once widespread across the Hawaiian archipelago, but became isolated on Laysan Island (415 ha) from the mid-1800s until 2004 when a translocation to Midway Atoll (596 ha) was undertaken to reduce extinction risks. We compared genetic diversity and quantified variation at microsatellite loci sampled from 230 individuals from the wild populations at Laysan (1999 to 2009) and Midway (2007 to 2010; n = 133 Laysan, n = 96 Midway birds). We identified polymorphic markers by screening nuclear microsatellites (N = 83). Low nuclear variation was detected, consistent with the species’ insular isolation and historical bottleneck. Six of 83 microsatellites were polymorphic. We found limited but similar estimates of allelic richness (2.58 alleles per locus) and heterozygosity within populations. However, 2 rare alleles found in the Laysan source population were not present in Midway’s reintroduced population, and a unique allele was discovered in an individual on Midway. Differentiation between island populations was low (FST = 0.6%), but statistically significant. Our results indicate that genetic drift had little effect on offspring generations 3 to 6 yr post-release and demonstrate the utility of using known founder events to help quantify genetic capture during translocations and to inform management decisions. KEY WORDS: Anas laysanensis · Island endemic · Genetic diversity · Laysan duck · Reintroduction biology Full text in pdf format PreviousNextCite this article as: Reynolds MH, Pearce JM, Lavretsky P, Seixas PP, Courtot KN (2015) Microsatellite variation and rare alleles in a bottlenecked Hawaiian Islands endemic: implications for reintroductions. Endang Species Res 28:117-122. https://doi.org/10.3354/esr00681 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 28, No. 2. Online publication date: July 14, 2015 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2015 Inter-Research.

Long-Term Monitoring of Endangered Laysan Ducks: Index Validation and Population Estimates 1998–2012

Abstract Monitoring endangered wildlife is essential to assessing management or recovery objectives and learning about population status. We tested assumptions of a population index for endangered Laysan duck (or teal; Anas laysanensis) monitored using mark–resight methods on Laysan Island, Hawai'i. We marked 723 Laysan ducks between 1998 and 2009 and identified seasonal surveys through 2012 that met accuracy and precision criteria for estimating population abundance. Our results provide a 15-y time series of seasonal population estimates at Laysan Island. We found differences in detection among seasons and how observed counts related to population estimates. The highest counts and the strongest relationship between count and population estimates occurred in autumn (September–November). The best autumn surveys yielded population abundance estimates that ranged from 674 (95% CI = 619–730) in 2003 to 339 (95% CI = 265–413) in 2012. A population decline of 42% was observed between 2010 and 2012 after consecutive storms and Japan's Tōhoku earthquake-generated tsunami in 2011. Our results show positive correlations between the seasonal maximum counts and population estimates from the same date, and support the use of standardized bimonthly counts of unmarked birds as a valid index to monitor trends among years within a season at Laysan Island.

Bibliographic Catalogue of the Marine Benthic Algae in the Papahānaumokuākea Marine National Monument (Northwestern Hawaiian Islands)

The algal bibliographic catalogue of the Papahānaumokuākea Marine National Monument (PMNM) is based on previously published records for the 10 northwestern islands, atolls and shoals in the Hawaiian Archipelago, and includes, aligned from northwest to southeast, Kure Atoll (90 species), Midway Atoll (123 species), Pearl & Hermes Atoll (74 species), Lisianski Island including Neva Shoals (52 species), Laysan Island (131 species), Maro Reef (79 species), Gardner Pinnacles (75 species), French Frigate Shoals including La Pérouse Pinnacle (173 species), Necker Island (118 species) and Nihoa Island (33 species). The first section (I. Classification) provides a listing of classes, orders, and families of the 148 genera reported from the PMNM. The second section (II. Species-Reference Index) provides an alphabetized listing of the 335 algal species under the four Phyla, i.e., Cyanobacteria (18 species), Rhodophyta (198 species), Ochrophyta (45 species) and Chlorophyta (74 species) with the applicable reference citations for each island, atoll or shoal. Brief notes are provided, when appropriate, for selected species. The third section (III. Island-Reference Index) provides a chronological listing of all published algal references for each respective island, atoll or shoal. The Reference section contains the complete citation for each reference.

Major histocompatibility I gene diversity in the critically endangered Laysan duck (Anas laysanensis).

Quantifying the genetic composition of founder populations is important to the success of reintroduction programmes, especially for bottlenecked and/or specialized species, such as island endemics. By implementing admixture schemes based on genetic variability, captive breeding programmes can minimize the detrimental effects of bottlenecking, inbreeding depression, outbreeding depression, etc. Particular attention has been given to genes within the major histocompatibility complex (MHC) due to their direct correlation to an individual’s immunity. However, isolating and amplifying MHC haplotypes remains difficult owing to the high diversity and paralogous nature. We describe a method of MHC I haplotype isolation based on an iterative process of primer design for the endangered island endemic, the Laysan duck (Anas laysanensis). Ultimately, haplotype-specific primers allow for direct genotyping after gel electrophoresis based on the presence/absence of their respective amplicons. Using the developed techniques, a total of eight unique haplotypes were isolated and assayed across 21 Laysan duck individuals from Laysan Island (N = 10) and Midway Atoll (N = 11). The presence/absence of seven haplotypes were variable across individuals with three haplotypes present in 95% of individuals, three in 38% of individuals, and one in 90% of individuals. The protocols described herein provide a simple, cost-effective method for isolating haplotypes and monitoring existing MHC variation in Laysan ducks, and the general approach can be applied to other molecular markers and species with low genetic diversity.

Demographic variation, reintroduction, and persistence of an island duck (Anas laysanensis )

Population variation in life history can be important for predicting successful establishment and persistence of reintroduced populations of endangered species. The Laysan duck (Anas laysanensis) is an endangered bird native to the Hawaiian Archipelago that was extirpated from most islands after the introduction of mammalian predators. Laysan ducks were restricted to a single remote island, Laysan Island (4.1 km2), for nearly 150 years. Since the species is not known to disperse between distant Hawaiian Islands today, 42 wild birds from Laysan Island were translocated to another mammalian predator-free low-lying atoll (Midway Atoll; 6.0 km2) to reduce extinction risk. We explored how variation in demography influences establishment and longer-term retention of genetic diversity (rare alleles) for reintroductions of this species. We observed dramatic differences in population growth between the source (λ = 1.18) and reintroduced (λ = 3.28) population. The number of eggs hatched at Midway Atoll was greater than at Laysan Island, however, we found no difference in hatching success (proportion of clutch hatched) between populations. Adult females produced 3 times as many fledglings per breeding year on Midway Atoll compared to Laysan Island. We estimated population abundance of both populations until 2010 and applied a Gompertz model with a Bayesian approach to infer density dependence, process variation, observation error, and carrying capacity for the Laysan Island and Midway Atoll populations. The carrying capacity from the Gompertz model for Midway Atoll (K = 883 ± 210 SD) was estimated to be greater than that of Laysan Island (K = 598 ± 76 SD). Translocations with small numbers of founders and no immigration can create population bottlenecks, leading to loss of genetic variation over time, and potentially reducing the reintroduced population's viability or its potential to serve as a source for future translocations. Therefore, we also assessed the probability of retaining rare alleles in an isolated reintroduced Laysan duck population using life history parameters observed from the Laysan Island and Midway Atoll populations; we concluded that additional founders are needed under scenarios using demographic estimates from both Laysan Island and Midway Atoll to retain either 90% or 95% of source population genetic diversity. © 2013 The Wildlife Society.

Population Status of the Endangered Laysan Finch

Abstract The Laysan Finch (Telespiza cantans) is an endangered Hawaiian honeycreeper that occurs on only a few small islands in the northwestern Hawaiian Island Archipelago. Twenty-two years of recent population estimates (1991–2012) from Laysan Island were analyzed to ascertain the current status of this endangered species; the entire 44 years of census data available were then used to identify long-term population trends. Laysan Finch population estimates have exhibited extreme fluctuations that can be attributed at least in part to spring rainfall patterns. The average population size has remained at ∼10,000 individuals. The Poisson regression analysis conducted for the last 22 years indicates a slightly deceasing annual population trend. However, when all 44 years of data were included in a comprehensive trend analysis, a stable population trend was documented. These results highlight the importance of long-term data sets when monitoring small closed populations - a situation commonly encountered with...

Experimental reintroduction reveals novel life-history variation in Laysan Ducks (Anas laysanensis)

ABSTRACT. Subfossil remains indicate that the Laysan Duck (Anas laysanensis) formerly occurred throughout the Hawaiian archipelago, but for more than 150 years it has been confined to a single, small atoll in the northwestern chain, Laysan Island. In 2004–2005, 42 ducks were reintroduced from Laysan to Midway Atoll, where they exhibited variation in life history never observed on Laysan. On Laysan, females have never been observed to breed successfully at age 1 year and few attempt it, whereas on Midway, females routinely raised young at <1 year of age. Mean (± SD) clutch size on Midway (7.0 ± 1.1, n = 41) was larger than the maximum clutch size of six eggs observed on Laysan. On Midway, renesting following nest failure (0.55 probability, n = 27) and double brooding (0.50, n = 54) were routine, and two instances of triple brooding were observed, whereas on Laysan, renesting and double brooding are rare (0.05 probability for both during our study; n = 21 and 19, respectively) and triple brooding has never ...

Influence of space use on fitness and the reintroduction success of the Laysan teal

AbstractTranslocation is an important tool for wildlife conservation and biodiversity restoration, but an inefficient one because of the unpredictability of success. Predictors of success such as habitat quality of the release site and number of individuals released have been identified, but the dynamics of successful translocations remain poorly understood. In particular, little is known about the relationship of individual post‐release movements to population establishment. In 2004, Laysan teal Anas laysanensis were reintroduced by translocating 20 wild birds from Laysan Island to Midway Atoll. Twenty‐two additional wild founders were brought the next year. We monitored the survival, reproductive success and movements of the 42 translocated individuals and their offspring for 4 years. Additionally, we monitored population size from 2004 to 2010. Unlike most translocations, we did not observe elevated post‐release mortality despite flight‐feather trimming to prevent immediate dispersal off‐island: first year survival was &gt; 90% and survival rates until 2009 were 0.65 ± 0.08 for founding adults. Laysan teal flew between the two main islands of Midway Atoll, and offspring had significantly larger maximum movement distances than founders. We monitored 84 nests and observed a significant, negative relationship of home range size to productivity for founding females. Flightless founders did not show fidelity to their release sites, but had strong fidelity to annual home ranges after attaining flight. Although we observed a component Allee effect on mate‐finding, this did not translate into a demographic Allee effect, and generally, the high fitness of founders contributed substantially to successful population establishment. Laysan teal abundance increased linearly until 2009, but showed evidence of population regulation afterwards. The population estimate was 473 (95% confidence interval 439–508) in 2010. On the much larger main Hawaiian Islands, we expect greater post‐release movement, a stronger component Allee effect, lower survival and lower reproductive rates because of predation to preclude successful reintroductions of this species to sites without predator management.

Effectiveness of an antihelminthic treatment in improving the body condition and survival of Hawaiian monk seals

Food limitation and poor body condition are significant factors affecting the survival of juvenile Hawaiian monk seals Monachus schauinslandi in the Northwestern Hawaiian Islands. Previous research has indicated that juvenile monk seals infected with cestodes are in worse body condition than those that are uninfected. To test whether individual growth and survivorship are boosted by intermittently reducing parasites, we initiated a deworming study on juvenile seals at Laysan Island. Forty-three unique juvenile seals were captured, weighed, measured, feces-sam- pled, and either given an injectable antihelminthic (praziquantel) or used as untreated controls up to 4 times at 8 to 16 wk intervals across a 7 month period. The effect of treatment on survival, egg shedding, and gain in mass was evaluated. Survival of the subset of the 3 cohorts included in the study was 100% for the 2007 and 2008 cohorts and 85.2% for the 2009 cohorts. Egg prevalence did not differ significantly between control and treated seals. Percent daily mass gain was greatest in the March to May period. Older juveniles gained more mass than young-of-the-year (treated and control), which lost mass between the first 2 treatments. Percent mass gain was significantly greater for treated than control seals during March to May, but not during December to March or over the entire treatment period (December to May). The questionable efficacy of injectable praz- iquantel indicates that a different route of administration or dosage of praziquantel or a different antihelminthic may be more suitable for treatment of cestodes in this species.

Invasive mammal eradications: the value of an ecosystem view

The removal of introduced organisms is controversial (Myers et al., 2000; Simberloff, 2002), especially when they are relatively charismatic vertebrates. Even attempts at eradicating such species far from the public gaze can generate negative reports from the press (Ebbert & Byrd, 2002) and hostility from the public (Towns, Atkinson & Daugherty, 2006; Webb & Raffaelli, 2008). Conflicts over such eradications are reduced with increased public awareness and education (Bremner & Park, 2007), but this requires a thorough understanding of the effects of invasive species on native ecosystems (Towns, in press). Demonstrating the relationship between invasive species of mammals and the degradation of native ecosystems is not an easy task. Only rarely have there been detailed reports of simple single-species invasions, and the observed subsequent responses of native ecosystems. Likely pathways for interaction are difficult to test; planned invasions are irresponsible and can have unforeseen consequences (Ricciardi & Simberloff, 2009). If we are to learn about the effects of invasive species, often the best remaining option is to remove them and study how ecosystems respond (Veltman, 1996; Courchamp & Caut, 2005). This is not necessarily easy, even on small islands, which often have complexes of introduced mammals. The most instructive examples are thus those where only one species of invasive mammal is present. Brodier et al. (2011) provide such an example. They describe the responses of plant cover and three species of petrels to the removal of rabbits, Oryctolagus cuniculus, from an island in the Kerguelen archipelago. They found that rabbit eradication benefited a species of burrowing seabird in deep soils, most likely the result of a release from competition for space. Interestingly, two other species of burrowing seabirds in shallower soils showed no response to the removal of rabbits. Rabbits are notorious for their detrimental effects on island ecosystems, in particular for suppressing native plants (Courchamp, Chapius & Pascal, 2003). Perhaps the most famous example is on Laysan Island in the Hawaiian islands, where 26 species of native plants and three species of birds disappeared after rabbits were released (Atkinson, 1989). Similarly, rabbits combined with the earlier presence of goats had devastating effects on Round Island in Mauritius (Atkinson, 1988), ultimately leading to severe erosion, destruction of habitats used by burrowing seabirds and the extinction of an endemic species of snake. The rabbits have since been eradicated, but soil replacement could take centuries. Ecological effects such as these have been a powerful incentive for rabbit eradications. However, rabbits can have hidden effects, such as suppression of invasive plants. Eradication of rabbits may be followed by unpredicted outbreaks of weeds. On Motunau Island off New Zealand, rabbit eradication was followed by the spread of boxthorn, Lycium ferocissimum, a shrub that invaded native grasslands and impeded seabird access to nest areas (Beach, Wilson & Bannock, 1997). Fortunately, the unpredicted consequences of the rabbit removal studied by Brodier et al. (2011) were largely beneficial. Predicted declines of skua after the loss of their rabbit prey did not happen, whereas blue petrels, Halobaena caerulea, increased in abundance. However, like previous examples, introduced plants have progressively invaded native plant cover (Chapuis, Frenot & Labouvier, 2004), which may cause problems similar to those found after rabbit eradications elsewhere. Brodier et al. (2011) emphasized that their aim was to understand the ecosystem responses of eradications of invasive animals. The need to understand eradications in a whole of ecosystem context has been emphasized for some time (e.g. Zavaleta, Hobbs & Mooney, 2001; Courchamp et al., 2003). We often see complex and unpredicted responses to eradications, especially of herbivores. With more studies like those by Brodier and co-workers, such ‘surprise effects’ should reduce in frequency. This should help to add scientific credibility to proposed eradications as their scale, complexity and cost increase.

Translocation as a tool for conservation of the Hawaiian monk seal

The deteriorating demographic status of the endangered Hawaiian monk seal has motivated renewed and expanded proposals for conservation action, including translocation of seals to improve survival. Over the past three decades, numerous monk seal translocations have been conducted with a variety of objectives, including mitigating shark predation and conspecific male aggression, reducing human–seal interactions, and taking advantage of favorable foraging habitats to improve survival. Here, we analyze our cumulative experience with translocation of Hawaiian monk seals. We found a strong correlation between the time seals remained in the vicinity of the release site and their age. Recently weaned pups (with little or no at-sea foraging experience) exhibited high fidelity to release sites commensurate with that shown by untranslocated pups to their birth location. In contrast, juvenile and adult seals tended to stray from their release locations farther and sooner. Nevertheless, when 21 adult male seals were moved more than 1000 km from Laysan Island in the Northwestern Hawaiian Islands (NWHI), to the main Hawaiian Islands (MHI), they subsequently dispersed among the MHI; however, only one was observed to return to the NWHI. Translocated seals appeared to survive at rates comparable to seals native to the release site. Outcomes suggest that in most cases the intended objectives of translocations were achieved. Except for one notable case, translocations within the MHI to arrest human–seal interactions were mostly unsuccessful. These findings will be essential for informing successful large-scale translocation plans in the future.

Spatiotemporal variation in the population ecology of scaly slipper lobsters Scyllarides squammosus in the Northwestern Hawaiian Islands

Scaly slipper lobster (Scyllarides squammosus) population ecology was examined using tag/recapture information at Necker Island (23°30′N; 164°35′W), Gardner Pinnacles (25°00′N; 168°50′W), Maro Reef (25°30′N; 170°45′W), and Laysan Island (25°48′N; 171°45′W) in the Northwestern Hawaiian Islands (NWHI) USA from 2002 to 2008. Although many aspects of S. squammosus life history and population dynamics were similar to those of other scyllarids, somatic growth differed from its congers. Scyllarides squammosus growth abruptly declined at maturity and, because of this, growth at length was better described using the Schnute as opposed to the more commonly von Bertalanffy growth model. Growth varied among locations, and survival varied among years; thereby being the first documentation of variability in the life history of a scyllarid. This study has expanded knowledge of scyllarid biology and documented that spatiotemporal variability in biological characteristics must be considered to understand and describe the population ecology of this species and probably of other scyllarids.

Impacts of sex ratio reduction on male aggression in the Critically Endangered Hawaiian monk seal Monachus schauinslandi

High female mortality due to male aggression in Hawaiian monk seals led us to investi- gate the role of habitat use and social structure on sex ratios and aggression at Laysan Island, Hawaii. The sex ratio was strongly skewed towards males in the early 1980s and this, combined with the social structure, asynchronous reproduction, and terrestrial habitat use patterns, resulted in dramatic sex ratio imbalances in particular areas. Male:female ratios approached 1:1 in the northeast, whereas the overall ratio in the southwest was 5:1 ranging up to 25:1. Most of the aggressive incidents were observed in the southwest and females using this area were more likely to incur injuries. To reduce aggression, we selectively removed 37 males between 1984 and 1994, bringing the adult sex ratio to parity. Here, we evaluate the effect of this correction on aggression and female mortality. Before the removals, aggression accounted for an average annual mortality of adult females of 4.1% (range 0 to 12.9%), with up to 8 females being killed per year. The male removals, together with natural pro- cesses, decreased the absolute sex ratio from 2.1:1 in 1983 to 0.9:1 in 1994. Both the proportion and the absolute number of injuries and deaths declined after this date. Although some adult females still incurred severe mounting injuries, the proportion of females that were lost decreased to 0.3% yr -1 (range 0 to 2.6%), and only 3 females are believed to have been killed through 2005. Thus, sex ratio reduction through selective male removals proved to be a valuable tool in reducing mortality in this Critically Endangered species.