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Creating a refuge from amphibian chytrid fungus for the critically endangered mountain chicken Alexander Jones, Luke, Dr Mike Hudson, and Calvin Fenton.. Durrell Wildlife Conservation Trust, 4 Jul 2018. Experiment. doi: 10.18258/11551
The animals will be released into an enclosure within their natural range on Montserrat. The enclosure will be 25 x 25 m in total, divided into two halves, ensuring frogs will be held at densities that are amenable to management of individual welfare. In total, 28 mountain chickens of between 18 and 24 months of age from the European bio-secure population will be introduced to the enclosure, half of the group in each side.
Within each side of the enclosure, there will be four artificial ponds, each to measure one meter in diameter and a maximum of 30 cm in depth in line with advice from captive managers. These will be dug into the substrate and lined with black pond liner. Each pond will sit in the centre of a ‘quarter’ of the enclosure. Two of the quadrants will be manipulated and two left as ‘background’ environment. Within the manipulated microhabitats, three manipulations will be trailed. Firstly, the ponds will be heated using a combination of dark refugia and modified solar pool heaters, the design of which will be determined during our manipulation trials taking place in Q2-Q4 2018. Secondly, small areas of canopy will be cleared, to increase the solar radiation exposure of the substrate. Thirdly, several large rocks will be placed around each manipulated pond, underneath the cleared canopy such that they are heated by the sun. Mountain chickens are often observed on rocks, especially when calling and defending territory (Hudson’s observations). The microhabitat manipulations have been chosen for likely efficacy and minimal non-target impact but will be subject to environmental impact assessment throughout.
The experiment will be conducted in a 'choice' framework where each animal can use manipulated or unmanipulated areas throughout. Each pond will be surrounded by an automatic microchip reader antenna. As each animal will be implanted with a microchip as a routine procedure during their captive rearing, these automatic readers will record each entry and exit of a frog to the artificial ponds continuously throughout the study. This will provide data on number, and length, of visits to the manipulated and non-manipulated microhabitats. Additionally, automatic interval camera traps will be used to record descriptive data of behaviour in an around the manipulated microhabitats. The main data collection phase of the project will run for 12 months from Q3 2019 to enable data to be collected for one full warm, wet season, followed by one full cool, dry season.
Fortnightly throughout the project, the mountain chickens will be skin swabbed to facilitate the collection of chytrid infection detection / non-detection and load. These swabs will be tested for chytrid DNA using a molecular diagnostic test - the gold standard chytrid-specific real-time Polymerase Chain Reaction. On every swabbing occasion, morphometric data will also be collected to allow body condition to be tracked and welfare maintained throughout.
There are several challenges to the successful implementation of this project. We have planned for each of these, and believe they will not prevent the successful implementation of the projection. Firstly, ensuring our ponds are heated to the required temperature. We are currently running trials to optimise the heating process to ensure this is the case.
The second challenge is ensuring animals become infected with chytrid. It is vital that there is sufficient chytrid at the reintroduction site to use this trial as a model for its application in the wider environment, from which chytrid fungus cannot be eradicated. Whilst there is no way to guarantee this, we will track background levels of chytrid at the release site, and neighbouring sites to explain local level variation in outbreaks of infection. We have monitored background levels of chytrid for a number of years on Montserrat, and have seen no marked decline in prevalence of load. We do not believe, therefore, that there will be any problems with lack of infection during the experiment.
A third challenge is to ensure the welfare of the animals throughout. To this end, we will measure body condition on a fortnightly basis and, through regular contact with local and international keepers and veterinarians, use pre-determined intervention points to decide on the best course of action for modifying husbandry for individuals animals. This might include providing more food in the territory of this individual, providing in-situ treatments or in extreme cases, temporarily removing the animal from the enclosure for intense management.
Finally, it is possible that the interventions will not be successful and some animals will contract infection which is not mediated, and develops into the disease, chytridiomycosis. In this scenario, we will utilise individual anti-fungal treatments (we have shown these to be successful in treating the infection in the field in the past) within the enclosure and this individual will be removed from the experiment (described as dead in the data to ensure the experiment remains robust).
The impact of chytridiomycosis can be mitigated in a population of reintroduced, captive-bred mountain chickens using scalable microhabitat manipulation strategies which are transferable to other species and systems. This hypothesis will be tested within the framework of two objectives.
Objective 1. To determine the extent to which mountain chickens use manipulated microhabitats within a ‘landscape’ context with a choice of manipulated and unmanipulated areas.
Objective 2. To determine the impact of manipulated microhabitat use on survival and Bd-infection and clearance rates of individual mountain chickens and the likelihood of long-term persistence.
To achieve this two objectives, the following data will be collected:
- Fortnightly body condition from each individual.
- Fortnightly chytrid infection status (negative or positive) and load (amount of chytrid).
- Amount of time spent in manipulated ponds for each individual.
Firstly, we will determine whether mountain chickens use manipulated areas when presented with both options in the wild (we have shown some individuals preferentially use heated ponds in captivity). This data will be collected using the automatic PIT tag readers and camera traps surrounding the manipulated pools. This is important in determining how successful this intervention will be when scaled-up and used at the whole-habitat level.
Secondly, the above data will be analysed within a multi-state mark-recapture framework to determine the impact of use of manipulated areas on chytrid infection status and survival within the enclosure. This will enable us to determine how effective use of manipulated areas is in mediating chytrid infection and preventing chytridiomycosis in free-living mountain chickens.
This project has not yet shared any protocols.