Academic literature on the topic 'South Island saddleback'

This paper reviews and updates the distribution and status of two geographically distinct subspecies of New Zealand Saddleback Philesturnus carunculatus, a New Zealand forest passerine that is highly susceptible to predation by introduced mammals such as stoats and rats. The recovery of the North Island and South Island saddleback populations has been rapid since translocations to offshore islands free of exotic predators began in 1964, when both subspecies were on the brink of extinction. South Island saddlebacks have gone from a remnant population of 36 birds on one island to over 1,200 birds spread among 15 island populations, with the present capacity to increase to a maximum of 2,500 birds. We recommend that South Island saddleback be listed under the IUCN category of Near Threatened, although vigilance on islands for invading predators and their subsequent rapid eradication is still required. North Island saddlebacks have gone from a remnant population of 500 birds on one island to over 6,000 on 12 islands with the capacity to increase to over 19,000 individuals. We recommend that this subspecies be downgraded to the IUCN category of Least Concern. The factors that limited the early recovery of saddlebacks are now of less significance with recent advances in predator eradication techniques allowing translocations to large islands that were formerly unsuitable. The only two predators that still cohabit some islands with saddleback are Pacific rats or kiore Rattus exulans and Weka Gallirallus australis, a flightless native rail. Although North Island saddlebacks coexist with kiore, South Island saddlebacks do less well in their presence, possibly because the relict population had no previous history with this species of rat. The impact of Weka as predators of saddlebacks is less clear, but population growth rates appear to be slowed in their presence. It is recommended that while current recovery strategies involving island habitat restoration and translocations be maintained, management effort should also be directed towards returning saddlebacks to selected, “mainland island” sites, where introduced pests are either excluded by predator-proof fences or controlled at very low levels by intensive pest management.

The choice of a place to live and reproduce is crucial for species� survival in providing them with adequate resources and shelter from predators or climatic conditions. Determining habitat suitability in endangered species is important for the success of translocation as a conservation tool. In addition, understanding mechanisms (source/sink system versus ecological traps) that drive habitat selection in translocated animals may be critical to population viability. In New Zealand, where ecosystems are highly vulnerable to extinction, habitat restoration on predator-free off-shore islands is an important recovery tool. Therefore, there is a need to understand the relationship between the establishment of the translocated populations and the characteristics of their new environment. Previous research indicated that re-introduced populations of Stewart Island robin (Petroica australis rakiura - Toutouwai) and South Island saddleback (Philesternus carunculatus carunculatus - Tieke) on Ulva Island (Stewart Island), New Zealand, showed preferences for coastal habitats that were characterized by low-lying dense vegetation and open ground cover. In this study, we further investigated territorial establishment in these two populations since re-introduction and looked at how birds utilised the landscape. I hypothesised that sites colonised soon after re-introduction were of high quality and later on, birds moved into unsuitable habitats. I defined habitat quality at a micro-scale in terms of vegetation structure, nest characteristics and food availability. I modeled bird presence and nesting success in relation to habitat components to determine factors in the environment that influenced breeding site selection and contributed to successful nesting in these two species. I discussed results in comparison to similar bird-habitat models developed for the South Island saddleback population on Motuara Island (Marlborough Sounds) and examined explanatory variables in each model. Translocated birds in the three studied populations first established territories in coastal scrub, and in the following years moved into larger coastal forest stands. Although vegetation structure was the primary variable explaining site selection in these populations, vegetation composition should still be considered important as it dictated the suitability of nesting substrate and the availability of food items. There was no evidence that first-colonised areas were more suitable habitats, and I concluded that these cases could not be used as examples of ecological traps. Instead, results suggested that with increased density robins and saddlebacks on Ulva have more recently settled in sites less suitable to nesting and foraging, thus underlying a source/sink structure. However, the sparse distribution of food items on Motuara contributed to a lack of territorial behavior and environmental effect on breeding success; therefore a source/sink system could not be confirmed in this population. I recommended that future translocation sites give preference to mixed-size stands with broadleaved species that are characterised by dense canopy below 4 m height and with suitable cavities in live trees. Lastly, due to robins� and saddlebacks� attraction to conspecifics and their territorial behavior, resources evenly distributed across the landscape could also increase their survival and reproductive success.

Severe population bottlenecks and the small size of many remnant habitats may render many bird populations prone to extinction from disease outbreaks. Bottlenecks may increase inbreeding which in turn may result in a low diversity of resistance and an immune system that is impaired or defective. Thus, bottlenecked populations may be less immunocompetent and more vulnerable to microbiological and parasitic perturbations. Few studies have assessed the effect of bottlenecks on the immunocompetence of birds. In this study, I used twelve saddleback (Philesturnus carunculatus) and two New Zealand robin (Petroica a. australis) populations, to determine if the severe bottlenecks reduce the immunocompetence of birds. When I experimentally challenged the immune system of two robin populations I found that despite the two populations having similar parasite loads, robins from the severely bottlenecked Motuara Island population exhibited a significantly lower T-cell mediated immune response than the source population (Nukuwaiata Island) suggesting that birds passing through severe population bottlenecks have a compromised immunocompetence. In the saddleback, severe bottlenecks, as well as high population densities and small island size, lead to individuals exhibiting higher stress levels and feather mite loads and lower immune function, as was evident by lower lymphocyte counts. I did not find levels of fluctuating asymmetry of saddlebacks to be directly influenced by bottleneck size. However, I did find that individuals with higher levels of fluctuating asymmetry had higher loads of hippoboscid flies and lower loads of coccidia suggesting a possible trade-off between growth and immune function. In contrast to previous studies looking at behavioural secondary sexual traits, I found no effect of founder number on the size of wattles in saddleback. I did however demonstrate that wattle size reflected the level of immune function in females as well as males, suggesting that females play a far greater role in offspring fitness than has been appreciated in traditional theories of sexual selection. Overall, my results indicate that severe bottlenecks can lead to reductions in immunocompetence in the resulting populations, especially in those populations that pass through the most severe bottlenecks. Based on the evidence from my thesis, I recommend conservation managers should aim to use at least 90 individuals to found new populations in order to reduce the deleterious effects of bottlenecks on immune function. If the costs of population bottlenecks and inbreeding are to be avoided, conservationists must adequately address the role of genetic factors in susceptibility to disease, and work towards minimising the risk of severe population bottlenecks in the management of endangered birds

Species translocations result in demographic bottlenecks that may produce inbreeding depression and reduce genetic variation through random sampling and drift, an outcome that could decrease long-term fitness and adaptive potential of many New Zealand species. Despite considerable evidence for costs associated with inbreeding and reduced genetic variation, some species have recovered from a small number of individuals and are thriving, perhaps via high growth rates, differential survival of heterozygous individuals or inbreeding avoidance. I examined the genetic consequences of species translocations in saddlebacks (Philesturnus carunculatus) with additional data provided for robins (Petroica australis) where possible. I first assessed whether contemporary genetic variation represented historical levels or a decline following demographic bottlenecks. I then examined whether sequential demographic bottlenecks caused sequential genetic bottlenecks and reviewed whether populations founded with a small number of birds were likely to go extinct. This analysis was followed by an investigation of two mechanisms that may maintain or reduce fitness costs, differential survival of heterozygous individuals and mate choice to avoid genetically similar individuals. Evidence from museum specimens suggests that low levels of genetic variation in contemporary saddlebacks is no different to historical genetic variation in the only source population, Big South Cape Island. An ancient founding event to Big South Cape Island is probably the cause of severe genetic bottlenecking rather than the demographic bottleneck caused by rats in the 1960s. In robins, genetic variation decreased slightly between museum and contemporary samples suggesting that recent population declines and habitat fragmentation have caused reductions in current levels of genetic variation. Serial demographic bottlenecks caused by sequential translocations of saddlebacks did not appear to decrease genetic variation. Loss of genetic variation due to random sampling was probably minimized because the low level of genetic variation remaining in the species was probably represented in the number of birds translocated to new islands. Models assessing future loss of genetic variation via drift showed that high growth rates combined with high carrying capacity on large islands would probably maintain existing genetic variation. In contrast, low carrying capacity on small islands would probably result in considerable loss of genetic variation over time. Saddleback populations on small islands may require occasional immigrants to maintain long-term genetic variation. Saddleback and robin populations established with a small number of founders did not have an increased risk of failure, suggesting that inbreeding was not substantial enough to prevent populations from growing and recovering. However, modelling showed that translocated saddleback and robin populations grow exponentially even when egg failure rates (a measure of inbreeding depression) are extremely high. Although inbreeding depression may be considerable, populations may be judged healthy simply because they show strong growth rates. Discounting the problem of inbreeding depression may be premature especially under novel circumstances such as environmental change or disease. Finally, two mechanisms proposed to avoid or delay the costs of inbreeding depression and loss of genetic variation do not appear to be important in saddlebacks or robins. Heterozygosity was not related to survivorship in saddlebacks that successfully founded new populations, and neither saddlebacks nor robins chose genetically dissimilar mates to avoid inbreeding. In conclusion, most saddleback populations should not require genetic management, although populations on small islands will probably need occasional immigrants. In robins, large, unfragmented populations should be protected where possible.