Numbers of nesting frigatebirds, Fregata minor and F. ariel, on Aldabra Atoll nature reserve,Seychelles

Aldabra Atoll, a strict Nature Reserve and major breeding station of lesser and greater frigatebirds, may be developed for tourism. Determining whether this affects the frigate breeding populations is complicated by their extended annual laying seasons and the biennial breeding periodicity of individuals rearing fledgelings. This study, using a census method incorporating adjustments for seasonal changes in nest numbers, changes in nest ownership and replacement laying, indicates that there are at least 4000 pairs of greater frigatebirds and 6000 pairs of lesser frigatebirds annually involved in breeding activities. There is some evidence that more male than female greater frigatebirds attempt to pair each season. Comparison with an earlier census suggests that severe human disturbance induces curtailment of laying seasons, major changes in nest distribution and prevents many birds from breeding.     

Factors associated with survival of reintroduced riparian brush rabbits in California

The riparian brush rabbit (Sylvilagus bachmani riparius) is an endangered species found in dense, brushy habitat in the California’s Central Valley. We implemented a reintroduction program to bolster populations at a Federal Wildlife Refuge and to assess factors influencing mortality and subsequent survival of released individuals. Between July 2002 and July 2005, we reintroduced 325 captive-bred individuals to unoccupied habitat within their historic range using a soft-release strategy and monitored their subsequent survival with radiotelemetry. Longer time in soft-release pens resulted in increased monthly survival. Rabbits were most susceptible to post-release mortality during the first 4 weeks following reintroduction and both body mass and length of time in the soft-release enclosure influenced this relationship. When we controlled for release mortality during this acclimation period, subsequent monthly survival probabilities were most strongly influenced by release year (year 1 vs. years 2 and 3) and by a catastrophic flooding event; length of time in the soft-release enclosure remained an important variable in longer-term survival. Cause of mortality was unknown for the majority of deaths (61.9%), but predation (including presumptive predation) was the greatest known cause of death in translocated rabbits (26.4%). Reintroduction programs should employ an adaptive management approach with ongoing monitoring of target animals and concurrent analysis to allow managers to adjust methods as conditions dictate.     

Demography and conservation of the Tristan albatross Diomedea [exulans] dabbenena

The Tristan albatross Diomedea [exulans] dabbenena is the third rarest albatross species, with a breeding population of around 1500 pairs almost totally restricted to Gough Island in the Tristan da Cunha group, central South Atlantic. During January 2000, the entire breeding population of Gough was surveyed for the first time since 1956, and 2400 incubating pairs were counted. An analysis of the areas that are likely to have been surveyed most accurately in the past suggests that the population has decreased by around 28% over 46 years. The number of large chicks counted over three successive seasons (1999-2001) was highly variable (range 318-1129). The average count over this period (705 chicks) is less than counts made in 1979 (792) and 1982 (798). A total of 656 chicks were counted in September 2001, giving an island breeding success of just 27.3%. However, breeding success varied considerably in different areas of the island, ranging from 17.6 to 68.0%. During the 2001 season most breeding failures were of large chicks, and over 4 years where data were available, 75% of breeding failures occurred during the chick period. Predation by introduced house mice Mus musculus is the most likely cause of chick mortality. In a small study population, birds began breeding at an average age of 9.7 years and annual adult survival from 1985 to 2001 was 92.6% (SE=1.6%). Both breeding success and adult survival estimates are low in comparison with other Diomedea species and population modelling predicts a population decreasing at an annual rate of 2.9-5.3%. Further research is needed urgently to assess whether breeding success is typical, and to confirm that mouse predation is the cause of chick mortality. The low productivity of this species will compound the negative impacts of longline fishing mortality, which are likely to be reducing adult and juvenile survival.     

Reintroduction and establishment of the western barred bandicoot Perameles bougainville (Marsupialia: Peramelidae) at Shark Bay, Western Australia

The western barred bandicoot was reintroduced to the Australian mainland in 1995 after an absence of at least 60 years. The new population was derived from 14 animals, reintroduced to Heirisson Prong from Dorre Island in Shark Bay, Western Australia. Introduced predators (the European red fox and the feral cat) were controlled at the reintroduction site, but European rabbits were not. A large fenced area of natural vegetation within the reintroduction site was used as a secure refuge from mammalian predators. Bandicoots were released from this predator refuge to the 12 km² conservation site. Dispersal from the point of free release was minimal. The reintroduced population has persisted for 4 years and increased, with at least 175 bandicoots recruited to the population in this time. The recapture rate of marked bandicoots was low, suggesting that adult mortality was high. Reproductive output at Heirisson Prong appeared greater than that of the two surviving wild populations on Bernier and Dorre Islands. Litter size was similar, but there was an extended annual breeding season at the reintroduction site. Body condition of reintroduced and wild bandicoots were similar, although there was some indication that reintroduced males may have been in poorer condition than their island counterparts. The litter size of bandicoots increased with a decrease in rabbit abundance, however, bandicoots were able to reproduce, maintain condition, and sustain recruitment to allow the population to increase despite the presence of rabbits. Two fox incursions occurred during the 4-year period of establishment, and feral cats were present on occasion in low numbers. Feral cats may be responsible for a lower rate of population increase than that observed on predator-free Dorre Island. Ongoing predator control is essential for any mainland reintroduction of bandicoots.     

Re-introduction of the golden eagle into the Republic of Ireland

The golden eagle (Aquila chrysaetos) became extinct in the Republic of Ireland in about 1912. Historical evidence suggests that, in the early nineteenth century, the population exceeded 50 pairs. It is thought that the extinction was a consequence of persecution and habitat change. Because there seems little chance of natural recolonisation a re-introduction programme has been developed. It is intended to release up to 15 birds per year for 5 years, starting in 2001. Single chicks will be obtained from Scottish nests with twins. The ways in which this project adheres to the six main IUCN re-introduction criteria are addressed. Two simulation models are described. The first, GEPM, demonstrates that the removal of chicks from Scottish nests should not have a detrimental effect on the Scottish population. The second model predicts the probable home range occupancy if only 12 birds are released each year. It is expected that between 3 and 13 ranges will be occupied by 2007. The imprecision in this estimate is a consequence of uncertainty about juvenile survival rates. The rationale behind our reintroduction scheme is outlined to stimulate debate about the development of good practice.     

The immediate effects of ditching a saltmarsh on nesting herring gulls Larus argentatus

We examined the effects of water management for mosquito control on the behaviour and breeding success of a resident colony of herring gulls. The colony resided on three close islands, one of which was ditched in March before the start of the second breeding season. The number of breeding pairs on the ditched island remained the same before and after ditching although the breeding number increased by 46% and 90% on the other two islands. Breeding chronology was similar on all three areas. However, birds nesting on spoil laid eggs a mean of 8 days later than non-spoil nesting birds. Behavioural observations on aggression and display rates indicated that birds on spoil behaved similarly to those in open grassy areas but differed from those nesting in the bushes. Nest site selection, breeding densities, and breeding success were similar on all three islands. Thus the differences noted were attributed to the appearance of the marsh. We postulated that pairs having nested on the experimental island in the previous year continued to do so after the island was ditched. However, pairs searching for new territory did not move onto the island that was ditched, but instead colonised the nearby islands. Similarly, those pairs breeding on spoil nested later because of the need to defend their nest sites which were situated in areas used for displaying by unmated birds.     

Captive breeding genetics and reintroduction success

Since threatened species are generally incapable of surviving in their current, altered natural environments, many conservation programs require to preserve them through ex situ conservation techniques prior to their reintroduction into the wild. Captive breeding provides species with a benign and stable environment but has the side effect to induce significant evolutionary changes in ways that compromise fitness in natural environments. I developed a model integrating both demographic and genetic processes to simulate a captive-wild population system. The model was used to examine the effect of the relaxation of selection in captivity on the viability of the reintroduced population, in interaction with the reintroduction method and various species characteristics. Results indicate that the duration of the reintroduction project (i.e., time from the foundation of the captive population to the last release event) is the most important determinant of reintroduction success. Success is generally maximized for intermediate project duration allowing to release a sufficient number of individuals, while maintaining the number of generations of relaxed selection to an acceptable level. In cases where a long residence time in captivity cannot be avoided, the use of distinct, genetically independent captive breeding units allows more efficient purging of the genetic load in the reintroduced population, and substantially improves its viability. Overall, the study allows to identify situations in which the genetic cost associated with selection relaxation may overwhelm the demographic benefits of programs.     

The influence of food availability on breeding success of African penguins Spheniscus demersus at Robben Island, South Africa

From 1989 to 2004, the breeding success of African penguins Spheniscus demersus at Robben Island, South Africa was significantly related to estimates of the abundance of both their main prey species, anchovy Engraulis encrasicolus and sardine Sardinops sagax, and to the combined biomass of these species. When the combined spawner biomass of fish prey was less than 2 million ton, pairs fledged an average of 0.46 chicks annually. When it was above 2 million ton, annual breeding success had a mean value of 0.73 chicks per pair. Given previously estimated values of survival and age at first breeding, these levels of breeding success are inadequate to sustain the African penguin population. With the higher level of breeding success, an equilibrium situation might be attained if adult survival could be increased by 6-7% per annum. Attempts to reduce mortality of penguins have included the collection, cleaning and return to the wild of oiled birds, culling of Cape fur seals Arctocephalus pusillus pusillus seen preying on penguins around breeding localities and control of the spread of disease. Management of the purse-seine fishery should ensure adequate escapement of fish to maintain the combined biomass of anchovy and sardine above 2 million ton. The maintenance of suitable breeding habitat and removal of feral predators from breeding localities will also be important in improving breeding success.     

Brood ranging behaviour and breeding success of the threatened little bustard in an intensified cereal farmland area

Cereal pseudo-steppes hold the largest proportion of declining bird species in Europe. Understanding how this process of decline is driven is essential for designing adequate management practices. The little bustard (Tetrax tetrax) is one of such threatened steppe-land bird species, which has suffered recent dramatic range constrictions and population declines. Although low breeding success has been claimed to be the main threat for the viability of future little bustard populations, the surprising lack of studies dealing with ecological requirements of broods hinders the implementation of efficient conservation practices. We studied the ranging behaviour and the reproductive success of a little bustard population by means of female radio-tracking conducted during 2006–2008 breeding seasons in the Ebro basin (NE Spain). We recorded an average breeding success of 0.27 chicks/hen, which is not enough to sustain a viable population according to the demographic models for the species. Early-laid clutches showed more probabilities to hatch and to fledge. This was associated to two different ranging patterns (i.e. sedentary versus wandering respectively) which depended on the ability of the hen and its chicks to settle in suitable areas harbouring enough arthropods and shelter for chicks. Such resources decrease drastically as the breeding season progresses. Overall, data suggest that agricultural practices associated to agricultural intensification, particularly early harvest, reduce breeding success both directly by nest destruction and indirectly through a decrease on resource availability for broods. Based on our findings on the characteristics and structure of the home range of little bustard broods, we propose the creation of a network of permanent vegetation plots interconnected by high-quality field margins as a management practice to raise the breeding success of little bustards and other ground-nesting birds on cereal farmland.     

The distribution,population size,movements and conservation of the African black oystercatcher Haematopus moquini

The African black oystercatcher Haematopus moquini is endemic to southern Africa and occurs as a breeding species between Seal Island, South West Africa/Namibia and Mazeppa Bay, Transkei. Vagrants outside this area are rare further north than the Hoanib Estuary, South West Africa/Namibia and further east than Transkei. The present adult population is estimated to be 4781 birds of which 53% are found in the southwestern Cape Province, South Africa. Offshore islands support 29% of the world population and are identified as important localities for African black oystercatchers with a high breeding production. These birds face threats from human disturbance, expecially from off-road vehicles on the mainland, from introduced mammalian predators at islands and from competition with man for food and bait organisms. Ten islands and seven mainland sites are isolated as supporting more than 1% of the world population, and, together with their intertidal zones, are recommended for Nature Reserve status.     

Female biased mortality caused by anthropogenic nest loss contributes to population decline and adult sex ratio of a meadow bird

Meadow breeding birds such as the whinchat Saxicola rubetra have been declining due to increased farming intensity. In modern grassland management, the first mowing and the bird’s breeding cycle coincide, causing high nest destruction rates and low productivity of grassland bird populations. However, it is virtually unknown whether the mowing process directly affects adult survival by accidentally killing incubating females. We studied adult survival of an Alpine whinchat population during two breeding seasons using either colour-ringing or radio-tracking of 71 adults. Assessing territories, mowing phenology and nest destruction from 1988 to 2007 allowed changes in the factors associated with female mowing mortality to be estimated. Adult survival over 5-day-periods was Φ = 0.986, but during the period of mowing female survival was strongly reduced (Φ = 0.946). As a result, 80.6% of the males, but only 68.4% of the females survived the breeding season. Mowing undoubtedly killed two of 20 radio-tagged females when they were laying or incubating. In the 20-year period, an increasing proportion of nests were destroyed before the chicks hatched and this change was associated with an increased distortion of the adult sex ratio. Modelling the population growth rate showed that including the additional effect of mowing on female mortality resulted in a 1.7 times faster local population decline. These results are consistent with the hypothesis that the extinction of whinchat populations in the lowlands of central Europe was caused not only by habitat degradation and low productivity, but also by increased man-made female mortality.     

Captive-reared burrowing owls show higher site-affinity, survival, and reproductive performance when reintroduced using a soft-release

A remaining challenge for animal reintroductions is how best to aid individuals transitioning from captivity into the wild. We tested two techniques – ‘soft’ vs. ‘hard’ release – in a 7-year study on endangered Western burrowing owls (Athene cunicularia hypugaea) in British Columbia, Canada. Traditionally, captive-reared yearling adults were released into the wild, as pairs, directly from artificial burrows (hard-release). Only 46% of 201 owls released in this way (2001–2004) stayed at release sites. To test for improved success, soft-releases were performed in the same manner as concurrent hard-releases (2005–2007), except above-ground enclosures confined each soft-release pair to the vicinity of their burrow for 2 weeks before complete release. Of 140 soft-released owls, 86% stayed at release sites; whereas, 66% of 100 hard-released owls stayed. Breeding-season survival was 70% for soft-released owls vs. 50% for hard-released owls. On average, soft-released owls produced 50% more fledglings than concurrently hard-released owls. Post-fledging survival was 69% and first-year return rate was 7.0% for fledglings from soft-released parents, compared to 50% and 4.0% for fledglings from hard-release parents. Ultimately, 0.17 offspring were recruited into the local wild breeding population per soft-released pair, compared to 0.05 local recruits per hard-released pair. We recommend that enclosure-based soft-releases be used for reintroduction of burrowing owls in British Columbia and elsewhere in North America. We encourage other tests for improved release success with soft-releases, particularly for species with a high tendency for dispersal or those likely to experience significant predation pressure.     

The impact of predation by introduced stoats on Hutton's shearwaters, New Zealand

The Hutton's shearwater Puffinus huttoni is an endangered species of burrowing petrel, that is threatened at its two remaining breeding colonies by the activity of introduced stoats Mustela erminea. Predation of eggs, chicks and adult shearwaters was studied over 10 consecutive breeding seasons (1989/1990-1998/1999) and resident stoats were radio-tracked in two seasons. Stoats were estimated to be killing on average 0.25% of breeding adults and 12% of chicks in each season. Population modeling of Hutton's shearwaters indicated that the estimated impact of this predation was a reduction in the potential yearly population growth rate of 0.86±0.22%. The overall average growth rate derived from the population model of 0.44%, suggests that the population is not in immediate risk of decline and controlling stoats within the colony need not be a priority for management.     

Population assessments of gentoo penguins (Pygoscelis papua) breeding at an important Antarctic tourist site, Goudier Island, Port Lockroy, Palmer Archipelago, Antarctica

Goudier Island is located in the Palmer Archipelago, to the west of the Antarctic Peninsula; it is one of the most frequently visited tourist sites in Antarctica. A number of gentoo penguin (Pygoscelis papua) breeding colonies are located on the island and these have been the focus of one of the longest running experiments to examine the impacts of tourist numbers upon penguin breeding performance anywhere in the Antarctic. In this paper we describe the population trends and breeding productivity (chicks per nest) of the 10 colonies on Goudier Island, all of which have now been monitored for 12 consecutive years beginning in the 1996/1997 breeding season. Our results demonstrate that all colonies show considerable inter-annual variability for both the number of breeding pairs and breeding productivity. Of the six visited colonies, two showed an important and significant statistical decline in the number of breeding pairs. One of these declining colonies is used to determine the breeding chronology dates for all other colonies, an important part of the monitoring procedure used to assess breeding success. Our results suggest that in the future, it would be useful to control for this additional disturbance. Our results further suggest that understanding all of the many subtle influences that impact upon gentoo penguin breeding numbers is complex and that some factors may never be completely identified.     

Tortoises and tourists in the Western Indian ocean: The curieuse experiment

A colony of giant tortoises Geochelone gigantea from Aldabra Atoll was established in 1978 on the island of Curieuse in the granitic Seychelles, where tortoises have long been extinct. Ninety-five were landed in April 1978 and 78 in April 1980. The animals have shown considerable increases in wieght, and the first hatchling was found n February 1980. The main purpose of the colony is to provide a tourist attraction within easy reach of Mahé and deflect tourist pressure from Aldabra: at the same time the colony has considerable scientific potential. The environment and history of Curieuse are reviewed in the light of criteria initially established for the choice of an island for the project, and the future of the experiment is discussed.     

Optimal release strategies for captive-bred animals in reintroduction programs: Experimental infections using the guppy as a model organism

Reintroduction of captive-bred individuals for supplementation or re-establishment of wild populations has become increasingly important to prevent the extinction of many endangered species. Despite the importance of reintroductions for conservation biology, few studies have empirically evaluated the potential impacts of reintroductions of naïve organisms on disease outbreaks in native wild populations. Here, we use a model organism, the guppy (Poecilia reticulata) and its ubiquitous parasite (Gyrodactylus turnbulli) to evaluate: (i) the most effective release procedure (i.e. en masse vs. gradual release) that minimises host mortality and parasite load, (ii) the effect of pre-exposure to the parasite on host susceptibility, and (iii) the potential advantage of removing the most susceptible individuals before release. We could not detect a statistically significant difference in host survival rates between release protocols and pre-exposure regime. However, the parasite population went extinct significantly more often when pre-exposed fish were released. Furthermore, the parasite load of individual guppies by the end of the reintroduction was significantly lower in treatments where fish had been pre-exposed to parasites than in treatments with naïve guppies. Additionally, pre-exposure of hosts provided important information about their level of resistance when reintroduced. These findings suggest that pre-exposure to native parasites could be beneficial for the survival rate of captive-bred animals when reintroduced in the wild. We discuss the practicalities of these potential release strategies.     

An endangered population of Wattled Cranes (Grus carunculatus)

The Kafue Flats, a river floodplain in southern Zambia, supports the largest known population of Wattled Cranes. In a normal year fewer than 1,000 are present at high flood; but as the water subsides the population increases, and in the latter half of the dry season it numbers some 3,000 birds. Following widespread flooding in 1972, at least 300 pairs nested as the water fell. However, in 1973 there was little flooding and few pairs bred. Many full-grown birds moult their remiges between January and April, and are then flightless. The diet is largely of rhizomes dug from soft mud. Suitable feeding grounds in the dry season are created by a falling water-level. The population is threatened by a hydro-electric scheme that is scheduled to be completed in 1978. The scheme will reduce fluctuations in the water level on the floodplain and, in so doing, reduce the area of suitable habitat.     

Impact of West Nile virus and other mortality factors on American white pelicans at breeding colonies in the northern plains of North America

American white pelicans (Pelecanus erythrorhynchos) are colonial-nesting birds and their breeding sites are concentrated in a few small areas, making this species especially vulnerable to factors that can influence productivity, such as disease, disturbance, predation, weather events and loss of nesting habitat. Nearly half of the American white pelican population breeds at four colonies in the northern plains: Chase Lake National Wildlife Refuge (NWR) in North Dakota, Bitter Lake (Waubay NWR) in South Dakota, Medicine Lake NWR in Montana, and Marsh Lake in Minnesota. Thus, sustained productivity at these colonies is crucial to the health of the entire species. During the latter half of the 2002 and 2003 breeding seasons, unusually high mortality of pelican chicks was observed at these colonies. West Nile virus (WNv) was identified as one source of these losses. In 2004–2007 we monitored three major colonies in the northern plains to assess mortality of chicks during the late breeding season. We documented severe weather events, disturbance, and WNv as factors contributing to chick mortality. Before WNv arrived in the region in 2002, chick mortality after mid-July was 4%, and then jumped to as high as 44% in the years since WNv arrived. WNv kills older chicks that are no longer vulnerable to other common mortality factors (e.g., severe weather, gull predation) and typically would have survived to fledge; thus WNv appears to be an additive mortality factor. Persistence of lower productivity at American white pelican colonies in the northern plains might reduce the adult breeding population of this species in the region.     

Are Canadian foxes swift enough?

In 1983, the swift fox Vulpes velox was reintroduced to the Canadian prairie, after an absence of 45 years. We counter recent criticism of our efforts by Stromberg & Boyce (1986). Our initial breeding stock originated from Colorado and South Dakota. From those animals we have developed a successful captive breeding programme in Canada. The goal of our captive breeding programme is to maximise genetic heterogeneity. Once animals are released, natural selection over subsequent generations will produce locally adapted genotypes. Contrary to Stromberg and Boyce, we feel that our reintroduction programme is based on principles of sound genetic management. We do not believe that our efforts will diminish the genetic composition of what appears to be rare populations of swift fox in the northern United States.     

Giant tortoise and vegetation interactions on Aldabra atoll—Part 2: Coastal

Grazing by a large population of giant tortoises on Aldabra atoll in the western Indian Ocean may be linked to apparent changes taking place in the coastal grass and scrub lands. This paper presents a circumstantial case for the involvement of the tortoise population in a change from coastal, maritime, scrub-tussock vegetation to one of short, turf grassland.