Long-term population changes among breeding shorebirds in the Outer Hebrides, Scotland, in relation to introduced hedgehogs (Erinaceus europaeus)

In 1974, hedgehogs (Erinaceus europaeus) were introduced to the island of South Uist, which forms part of an area holding one of the largest concentrations of breeding shorebirds in Western Europe. By the 1990s these mammals had spread widely and become major predators of shorebird eggs. Breeding shorebirds were surveyed in 1983, when hedgehogs were confined to a small part of South Uist. They were surveyed again in 2000 by when hedgehogs had occupied all of the southern part (South Uist and Benbecula) of the 250 km² of lowland shorebird nesting habitat for at least 10 years but had not yet colonised large parts of North Uist and adjacent small islands. Between surveys the overall numbers of shorebirds in the hedgehog-free northern zone increased by 9% but in the southern zone, where hedgehogs were present, numbers decreased by 39%. Population changes differed among species, but for all species the population in the hedgehog-free northern zone outperformed that in the southern zone. The most marked differences occurred in northern lapwing (Vanellus vanellus) and common redshank (Tringa totanus), which both showed large declines in the southern zone and moderate to large increases in the northern zone. The north-south differences in population change could not be explained in terms of habitat change and were probably largely driven by hedgehog predation.     

Reedbeds as refuges for water voles (Arvicola terrestris) from predation by introduced mink (Mustela vison)

The water vole has recently undergone a catastrophic decline in the UK. This has resulted from loss and fragmentation of suitable habitat leaving water vole populations highly vulnerable to the impact of predation by introduced American mink. However, at some reedbed sites water voles and mink have apparently coexisted for many years. To determine if reedbeds offer a refuge from predation, 70 voles were radio-tagged at three sites in England and overwinter mortality monitored. Water vole perception of predation risk was also assessed. Mortality was high (64%), predation by mustelids, including mink, being the chief cause. Experiments suggested that voles failed to perceive areas of highest predation risk. However, predation rate declined strongly with the distance water voles lived from a main water channel. Thus, reedbeds provide a refuge from predation, even by mink, and calculations suggest that they may support source populations enhancing the viability of water vole metapopulations. Consequently reedbeds are now being used as one focus for the conservation of water voles in England and Wales.     

Translocations of eight species of burrow-nesting seabirds (genera Pterodroma, Pelecanoides, Pachyptila and Puffinus: Family Procellariidae)

Development of seabird translocation techniques is required to meet species recovery objectives, to improve conservation status, and to restore ecological processes. During 1997-2008 we undertook translocation trials on eight petrel species of four genera within the New Zealand region: common diving petrel (Pelecanoides urinatrix), fairy prion (Pachyptila turtur), grey-faced petrel (Pterodroma macroptera gouldi), Pycroft’s petrel (Pterodroma pycrofti), Chatham petrel (Pterodroma axillaris), Chatham Island taiko (Magenta petrel; Pterodroma magentae), fluttering shearwater (Puffinus gavia), and Hutton’s shearwater (Puffinus huttoni). A total of 1791 chicks within 5 weeks of fledging were moved up to 240 km, placed in artificial burrows and hand-fed until they fledged. Of these, 1546 fledged, and so far at least 68 have returned as adults to the translocation sites. Most birds were crop-fed a puree based on tinned sardines and fresh water. This diet worked well for all species regardless of their typical natural diet (planktonic crustaceans, squid, or fish) with all species fledging above or close to mean natural fledging weights.     

Population viability of the narrow endemic Helianthemum juliae (CISTACEAE) in relation to climate variability

Narrow endemic plants are highly vulnerable to extinction as a result of human disturbance and climate change. We investigated the factors affecting the population viability of Helianthemum juliae, a perennial plant endemic to the Teide National Park on Tenerife, Canary Islands. One population was demographically monitored from 1992 to 2001 and analysed using matrix projection models to determine finite rates of increase and critical stages in the life cycle. Lambda values varied between 0.697 and 1.740, and were highly positively correlated with annual precipitation, but not with temperature. Survival of adults had the highest elasticity, and summed elasticities of the growth and fecundity transitions correlated positively with lambda and precipitation. Most of the mortality in the population seemed drought-related, and no other threats were identified. Deterministic simulations showed population increase, but introducing environmental stochasticity by modelling variation in precipitation from existing data of the past 85 years revealed high extinction probabilities (0.74-0.83 in the next 100 years). This plant is likely to be at risk under scenarios of global warming. Our simulations suggest that augmenting the population would only delay extinction. A more viable option for long-term conservation seems to be the introduction of populations at more humid locations within the Teide caldera.     

Using a five-factored structured decision analysis to evaluate the extinction risk of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus)

In 2005, the National Oceanic and Atmospheric Administration’s (NOAA) National Marine Fisheries Service initiated a status review of Atlantic sturgeon to determine if the species warranted a threatened or endangered listing under the Endangered Species Act (ESA). The Atlantic sturgeon status review team intended to rely on previously used methods to assess extinction risk, but found that most quantitative extinction risk analyses were performed on data-rich populations and often did not systematically consider the five factors specified in Section 4(a)(1) of the ESA as required for listing a species. Taking cues from structured decision analysis theory, the team created a framework, based around the five factors, which can be used to evaluate the status of data-poor species. Potential scoring biases were minimized in this analysis by providing experts with standardized reference points for scoring, dividing the analysis into smaller units, and using both individual and group opinion. Using this five-factored structured decision analysis, the status review team recommended that three of the five distinct population segments warranted listing as threatened. The status review team offers their approach to increase transparency about their scientific recommendation and to aid other teams who are tasked with systematically evaluating the status of data-poor species.     

Conservation action in the Galàpagos: feral pig (Sus scrofa) eradication from Santiago Island

Introduced mammals are major drivers of extinction and ecosystem change. As omnivores, feral pigs (Sus scrofa) are responsible for wholesale adverse effects on islands. Here, we report on the eradication of feral pigs from Santiago Island in the Galápagos Archipelago, Ecuador, which is the largest insular pig removal to date. Using a combination of ground hunting and poisoning, over 18,000 pigs were removed during this 30-year eradication campaign. A sustained effort, an effective poisoning campaign concurrent with the hunting program, access to animals by cutting more trails, and an intensive monitoring program all proved critical to the successful eradication. While low and fluctuating control efforts may help protect select native species, current eradication methods, limited conservation funds, and the potential negative non-target impacts of sustained control efforts all favor an intense eradication effort, rather than a sustained control program. The successful removal of pigs from Santiago Island sets a new precedent, nearly doubling the current size of a successful eradication, and is leading to more ambitious projects. However, now we must turn toward increasing eradication efficiency. Given limited conservation funds, we can no longer afford to spend decades removing introduced mammals from islands.     

Physiological evidence for reproductive suppression in the introduced population of brown tree snakes (Boiga irregularis) on Guam

Introduced species are an increasingly pervasive problem. While studies on the ecology and behavior of these pests are numerous, there is relatively little known of their physiology, specifically their reproductive and stress physiology. One of the best documented introduced pest species is the brown tree snake, Boiga irregularis, which was introduced onto the Pacific island of Guam sometime around World War II. The snake is responsible for severely reducing Guam's native vertebrates. We captured free-living individuals throughout the year and measured plasma levels of stress and sex hormones in an effort to determine when they were breeding. These data were compared to reproductive cycles from a captive population originally collected from Guam. Free-living individuals had chronically elevated plasma levels of the stress hormone corticosterone and basal levels of sex steroids and a remarkably low proportion were reproductively active. These data coincide with evidence that the wild population may be in decline. Captive snakes, had low plasma levels of corticosterone with males displaying a peak in plasma testosterone levels during breeding. Furthermore, we compared body condition between the free-living and captive snakes from Guam and free-living individuals captured from their native range in Australia. Male and female free-living snakes from Guam exhibited significantly reduced body condition compared to free-living individuals from Australia. We suggest that during the study period, free-living brown tree snakes on Guam were living under stressful conditions, possibly due to overcrowding and overexploitation of food resources, resulting in decreased body condition and suppressed reproduction.     

Experimental use of salt to control the invasive marine alga Caulerpa taxifolia in New South Wales, Australia

Caulerpa taxifolia was first discovered in New South Wales, Australia, in April 2000 and is now present in nine waterways. Infestations, which range from sparse distributions of scattered runners to dense beds 40 cm thick, covered approximately 8.1 km² by mid 2004. Various methods for controlling the alga were trialed. The application of coarse sea salt at a concentration of 50 kg/m² was found to be the most effective method as it rapidly killed the alga, had relatively minor effects on native biota (seagrass and infauna) and was relatively inexpensive. In small-scale trials, frond density of C. taxifolia had decreased by 70-95% one week after salting and no fronds were present after 1 or 6 months. Seagrass and infauna were also affected by salt, but abundances had generally recovered after 6 months. The effectiveness of salting at larger scales depended on the method of application and salting appeared to be most successful in the cooler months when C. taxifolia dies back naturally. Results of large-scale salting trials were mixed. In one waterway, a single application of salt resulted in the apparent removal of almost 5200 m² of C. taxifolia; in another, repeated salting of a 3000 m² infestation led to a considerable reduction in the density of the alga, but no overall change in the boundaries of the infestation. Eradication of C. taxifolia from New South Wales is unlikely, but local control measures, extensive monitoring and experimentation are continuing in an attempt to limit the impact of this invasive alga.     

Mass mortality of native anuran tadpoles in tropical Australia due to the invasive cane toad (Bufo marinus)

Specific pathways of the ecological impact of invasive species remain poorly known. Although the spread of toxic cane toads (Bufo marinus) through tropical Australia is widely believed to have caused extensive mortality of native reptiles and mammals, effects of toad ingestion on native anurans have been virtually ignored. Our studies on the Adelaide River floodplain show that the most numerous vertebrate victims of toad invasion are native tadpoles that die when they attempt to consume toad eggs. We documented 11 episodes of mass mortality, totalling >1300 tadpoles of 10 species, in five waterbodies within a single wet-season shortly after the toads invaded. A causal link between toad breeding and tadpole mortality is supported by observations that: (1) in at least 9 of the 11 waterbodies involved, toads bred immediately prior to mortality events; (2) water quality was indistinguishable from that of control ponds, and tadpoles placed in that water remained healthy; (3) dead tadpoles showed no sign of disease; and (4) laboratory trials showed rapid, 100% mortality in native tadpoles exposed to freshly-laid toad eggs. Despite these high mortality rates, toad invasion does not appear to threaten the viability of anuran populations because frogs often breed in ponds not used by toads, and because density-dependent growth and survival within tadpole communities mean that additional mortality may not reduce the total effective recruitment of metamorph frogs from a waterbody.     

Survival, dispersal and early migration movements of captive-bred juvenile eastern loggerhead shrikes (Lanius ludovicianus migrans)

Avian captive breeding programs pose a particular challenge with migratory birds due to natal dispersal and high mortality during migration. In Canada a captive breeding program for the eastern loggerhead shrike (Lanius ludovicianus migrans) has released over 400 juveniles since 2001, but the fate of almost all these birds is unknown. In 2007 and 2008, we used radio-telemetry of captive-reared juveniles to determine pre-migration survival and dispersal movements away from the release site. Overall, 76% (29 of 38) of shrikes survived from release to the initiation of migration and the daily survival rate was 0.987. Most deaths (78%) occurred in females, suggesting a possible sex-biased pre-migration mortality. Shrikes typically dispersed independently, there was little overlap between dispersal sites, and the average pre-migration dispersal distance from the release site was 4.2 km (SD 2.4). Release date was negatively correlated with time spent at the release site prior to dispersal, but did not have a significant effect on survival, time spent at dispersal sites or distance of dispersal. Migration initiation date ranged over 6 weeks and early-hatched juveniles were the first to begin migration. Using aerial telemetry, we located five of 29 birds that had begun migration at distances up to 180 km from the release site; no birds were found dead after initiating migration despite the extensive search area. High juvenile survival to migration for captive-reared juveniles suggests that the captive breeding and release program has high potential to augment wild populations of the eastern loggerhead shrike.     

Herbicides, weeds and endangered species: management of bitou bush (Chrysanthemoides monilifera ssp. rotundata) with glyphosate and impacts on the endangered shrub, Pimelea spicata

Environmental weed invasion threatens the biodiversity of native species. Unfortunately, managing these weeds may also affect biodiversity adversely. A recent example occurred when glyphosate, a herbicide used to control the highly invasive weed, bitou bush (Chrysanthemoides monilifera ssp. rotundata), accidentally drifted over a small population of an endangered shrub, Pimelea spicata. Following concerns that the affected population would not recover and, thereby, cause the local extinction of P. spicata, we conducted a series of glasshouse and field experiments to explore the impacts of glyphosate on this endangered species. Seedlings and young plants of P. spicata, in which the tap root was undeveloped, were killed by a single application of glyphosate. Older plants with a well developed tap root also died back initially, but about 50% of individuals re-sprouted. This re-growth was associated with a significant decrease in tap root diameter, implying that further disturbance, including repeated treatment with glyphosate, would kill plants by impairing their potential for recovery. Unlike some sclerophyllous native shrubs, the tolerance of P. spicata to glyphosate was limited, even when its growth was slowed artificially by limiting water availability. Winter applications of glyphosate to manage infestations of bitou bush will impact adversely on populations of P. spicata and may also affect the other rare and endangered species whose survival is threatened by this species, even though some natives are unaffected by the herbicide. Protecting native biodiversity from bitou bush will involve sustainable weed management that minimises impacts on non-target native species.     

Population ecology of the Chinese grouse, Bonasa sewerzowi, in a fragmented landscape

We report the first population ecology study of the endangered Chinese grouse (Bonasa sewerzowi). The study population was stable during 1995-2000. Annual rates of survival were 0.64 for adults and only 0.17 for chicks to 13 weeks of age. Reproductive parameters were 6.1 eggs/clutch, 63% nest success, and overall 3.6 chicks hatched/female/year. The spring sex ratio was 64% males, with 44% of the males unmated in spring. Local people found an estimated 10-29% of the nests and took the eggs for food. Only about 9% of the reserve containing the study area is mature mixed forest, the preferred habitat. Inadequate brood habitat may have influenced chick survival and the skewed adult sex ratio may be a result of habitat fragmentation. We recommend protecting the remaining mixed forest, creating more brood habitat, and stopping the taking of eggs.     

Geographic information system (GIS) predictions of past, present habitat distribution and areas for re-introduction of the endangered subtropical rainforest shrub Triunia robusta (Proteaceae) from south-east Queensland Australia

The endangered Australian subtropical rainforest understorey shrub Triunia robusta, is restricted to the south-east Queensland region of Australia. The potential pre-clearing and current distribution of the species was modelled by relating species presence at recorded locations to correlated abiotic and biotic factors, which in combination, were then used as a surrogate for predicting distribution of the species habitat over its known range. From a defined study area of 330,000 ha, output of geographic areas likely to contain T. robusta habitat at three levels of probability were generated for pre-clearing vegetation, and vegetation classified as remnant in 1999. Potential pre-clearing distribution was compared with potential current distribution to ascertain the likely impact of clearing of native vegetation on the extent, pattern, and contiguity of T. robusta habitat. For pre-clearing vegetation, a total area of 45,480 ha was identified as potential T. robusta habitat. For vegetation classified as 1999 remnant, 13,440 ha were identified, representing an overall reduction of 70% in potential habitat for T. robusta. The model was partially validated, with T. robusta found at six new locations. Allowing for errors from spatial mismatching, five of the sites were located within habitat patches predicted by the model. A number of local areas containing high densities of predicted habitat patches were identified to guide searches for unrecorded populations. Strategically located areas linking known populations containing suitable or potentially suitable habitat that may be available for introduction of new populations were identified. The results indicate that the species former centre of range was in lowland areas adjacent to the north arm of the Maroochy River. Clearing and fragmentation of T. robusta habitat is the most likely cause of the apparent decline in distribution and abundance of the species.     

Impact of the colonisation of Zaprionus (Diptera, Drosophilidae) in different ecosystems of the Neotropical Region: 2 years after the invasion

The drosophilid Zaprionus indianus was not collected in Brazil, despite on-going drosophilid collecting, until 1999. Since 1999 this species has become common in Brazil. We present data on collections of Z. indianus in central Brazil, since its first occurrence in this region, with the goal of discussing its route of introduction in South America and aspects of its adaptation to the environment. Collections made during a 2-year period show different seasonal distribution patterns of this insect. In contrast with the low population sizes registered in 1999, during the summer of 2000 a large proliferation of this insect was detected. We show that Z. indianus is more common in the savanna sites and that its population peaks during the wet season. These preferences are discussed, and the hypothesis that the introduction in South America should have occurred in the southeast region of this continent is defended.     

Impact of introduced birds on the recovery of the Tahiti Flycatcher (Pomarea nigra), a critically endangered forest bird of Tahiti

In 1998, only 25 Tahiti Flycatchers (Pomarea nigra), a forest bird endemic to Tahiti (French Polynesia) remained. A recovery programme, aimed at nest protection through both rodent control and tree banding, was initiated. At this time it was supposed that the species was mainly the victim of island infestation by ship rats (Rattus rattus). In the 3 years of this study 54 nests were found and 17 fledged young produced, of which 12 survived the early stage of fledging. Despite an excellent 1999 breeding season and efficient nest protection against rodents, only five of 19 nests produced fledged young in 2000. This was related to higher (P=0.002 and 0.015 respectively) Indian Mynah (Acridotheres tristis) encounters and aggressive interactions in 2000 and 1998 than in 1999. Indian Mynah encounters and interactions were also higher during reproductive activities (and particularly at incubation and nestling stages) in comparison with the non breeding period (P <0.001). In contrast, Red-vented Bulbul (Pycnonotus cafer) encounters and interactions were more uniform throughout. Significantly more Indian Mynah and Red-vented Bulbul were observed in flycatcher territories which experienced nest failure or early fledgling death in comparison with those which experienced reproductive success (P=0.003 and 0.002 respectively). This strongly suggests that these two introduced species represent an important threat to the Tahiti Flycatcher’s survival. Currently, young birds (less than 4 years old) represent 42% of the population, an increase from 12% at the start of the recovery programme.     

Effects of an alien fish, Gambusia affinis, on an endemic California fairy shrimp, Linderiella occidentalis: implications for conservation of diversity in fishless waters

The introduction of exotic fishes to naturally fishless waters is often associated with declines in species native to those waters. Mosquitofish, Gambusia affinis, have been introduced to waters worldwide for mosquito control. Taxa negatively affected by mosquitofish potentially include fairy shrimp (Crustacea: Anostraca) that often show high rates of endemism, and which are characteristic of naturally fishless wetlands on every continent. We tested the effects of mosquitofish on a fairy shrimp, Linderiella occidentalis, in experimental ponds that included a community of native aquatic invertebrates. We supplemented field experiments with lab trials to test whether mosquitofish preferred L. occidentalis to other prey. Survival of the fairy shrimp was significantly reduced in ponds with mosquitofish. Only 16.9% of fairy shrimp survived in ponds with mosquitofish, while 64.0% survived in control ponds. Fish presence also reduced abundance and biomass of other invertebrates. Results from feeding trials demonstrated that mosquitofish frequently prefer L. occidentalis to alternative prey. Our results suggest that introduction of mosquitofish into naturally fishless wetlands may lead to loss of diversity of their highly specialized aquatic fauna.     

Habitat selection by the pale-headed brush-finch (Atlapetes pallidiceps) in southern Ecuador: implications for conservation

The pale-headed brush-finch (Atlapetes pallidiceps) is threatened with extinction due to habitat loss, but very little is known about its ecological requirements. We used multiple logistic regression to study habitat selection of this species at landscape, territory, and nest site scales in order to make recommendations about effective management. Habitat selection by the sympatric stripe-headed brush-finch (Buarremon torquatus) was examined with the same methods in order to analyse interspecific resource partitioning and potential competition. The pale-headed brush-finch selected semi-open habitat types with intermediate scrub heights, and avoided forests. Nest sites depended on the presence of vines or bamboo. By contrast, the stripe-headed brush-finch chose dense habitat with low ground cover under tall vegetation and avoided semi-open habitat. The two species had overlapping territories but differed significantly in microhabitat use and the use of vegetation strata. We found no convincing evidence that the stripe-headed brush-finch displaces the pale-headed brush-finch from optimal habitat. The preservation of semi-open scrubland maintained by low-intensity grazing is suggested for future conservation of the pale-headed brush-finch.     

Monitoring the recovery of smalltooth sawfish, Pristis pectinata, using standardized relative indices of abundance

The US population of smalltooth sawfish, Pristis pectinata, is currently listed as endangered under the Endangered Species Act. An important component of monitoring the recovery of this species is establishing long-term baseline trends in abundance. In the absence of scientific survey data, assessing and monitoring the status of some marine species has required the utilization of fishery-dependent data. Using voluntary dockside interviews of sport fishers collected in Everglades National Park, a standardized index of abundance was created for smalltooth sawfish using the delta method. The index was developed as the product of separate generalized linear models of the proportion of positive trips and the positive catch rates on successful trips. Development of the final model included testing factors that were expected to influence the catch of smalltooth sawfish. The final model assumed a binomial distribution for the proportion of positive trips and a lognormal distribution for positive catch rates. Year was significant as a main effect in the binomial model whereas year and skill level of the fishing party were significant in the lognormal model. The relative abundance index shows a small increase in abundance at an average rate of about 5% per year since 1989. These results indicate that the population of smalltooth sawfish in Everglades National Park has at least stabilized and may be increasing. However, additional data and analyses from multiple sources are required before definitive conclusions on the recovery of smalltooth sawfish can be established.     

Translocation of Choctawhatchee beach mice (Peromyscus polionotus allophrys): hard lessons learned

Translocation of species for conservation purposes is a key element of many recovery programs. While the benefits of translocations seem obvious, potential negative effects have been described. For endangered beach mice (Peromyscus polionotus ssp.), repopulation of native, unoccupied habitat using translocated individuals has been extremely successful. Once populations are established, concerns over founder effects and isolation have led to proposals for continued secondary translocations. Unfortunately, little information is available to help formulate protocols for these actions. To test the effectiveness of translocation, the fates of 18 translocated Choctawhatchee beach mice (Peromyscus polionotus allophrys) were followed as they attempted to integrate into an established population. We found that translocated groups, repeated for two seasons, tended to use larger homeranges and significantly more burrows than did resident mice. The monthly (31 day) survival rate of resident mice was 3.4 times greater than for translocated individuals. We hypothesize that differential predation pressure was directly linked to the failure of mice to integrate successfully into the existing population. Given our results, we must advise caution and that additional knowledge be obtained before translocations are used to supplement existing populations.