Download (A) Background, Problem Statement and Strategies for Mountain

(A) Background, Problem Statement and Strategies for
Mountain Chickens in Montserrat
1. Background
The mountain chicken Leptodactylus fallax, a frog, is currently assessed as Critically
Endangered by IUCN due to a severe population decline inferred from chytridiomycosis
infection (‘chytrid’) and habitat loss through volcanic damage (Fa et al 2008). The species is
now known only from two Eastern Caribbean Islands, Montserrat and Dominica. The causative
agent of chytrid, the fungus Batrachochytrium dendrobatidis (Bd), was first recorded from
Dominica in 2002 and is thought, within a single year, to have lead to an 80-90% decline in that
island’s mountain chicken population, which has remained at these greatly reduced levels since.
Symptoms of chytrid were first reported from Montserrat on 14th February 2009, when
Montserrat Department of Environment (DOE) forestry officers found dead and dying mountain
chickens in the island’s Centre Hills reserve. In response, the Durrell Wildlife Conservation Trust
(Durrell) and DOE organized an immediate evacuation of 50 uninfected mountain chickens to
biosecure (quarantined) captive breeding facilities in Europe. Since then, an apparent collapse
of the wild population similar to that found in Dominica in 2002, has been reported. By May
2009, an international collaboration, the Mountain Chicken Recovery Programme (MCRP), was
established between Durrell, The Zoological Society of London (ZSL), Chester Zoo (CZ),
Parken Zoo (PZ) and the Government of Montserrat (GOM). The aim of this programme is to
recover wild populations of the mountain chicken, focussing initially on Montserrat.
This document details activities proposed for 2011 under the Darwin Initiative project Enabling
Montserrat to save the Critically Endangered mountain chicken (project HYR1) lead by Durrell
and DOE in partnership with ZSL’s Institute of Zoology (IOZ). It focuses on efforts to augment
the mountain chicken population in Montserrat by reintroducing captive-bred frogs to their native
range and to develop optimal strategies and protocols for future reintroductions.
2. Problem statement
Chytrid causes severe long-term declines in mountain chicken populations, to the point where
they may have little or no viability. Chytrid is highly infectious to mountain chickens and persists
in the environment; it is also spread by other amphibian species infected by it but less severely
impacted. Managing mountain chickens in a chytrid-infected environment is further hampered
by other ongoing threats: non-native predators, habitat loss and hunting.
The experience of trying to manage chytrid infection of the mountain chicken population on
Dominica indicates the disease has a severe and long-lasting effect on this species. It seems
likely, though not yet confirmed, that the mountain chickens population on Dominica is at
densities now so low that they compromise breeding in those frogs. This now also appears to be
the case in Montserrat. Chytrid is also infecting the other two amphibian species on Montserrat
(the tree frog, Eleutherodactylus johnstonei, and the cane toad, Rhinella marina), albeit with less
severe impacts on these populations. These species provide a reservoir for Bd – which can also
survive in soil and water – and a vector for spreading it across the island and infecting mountain
chickens. In 2010, it was confirmed that chytrid was present at the southern-most tip of
Montserrat, in the island’s volcanic Exclusion Zone, uninhabited by people since 1997. It thus
appears that the whole of Montserrat must now be considered infected with this disease.
The fundamental problem facing efforts to re-establish a viable population of mountain chickens
in Montserrat is the island-wide occurrence of chytrid and the severe impacts, normally fatal, of
the disease on this species. Infected frogs can be treated to remove the infection (typically, in
captivity). The reservoir of the fungus in the environment (including other amphibian species),
however, means that the benefits of this treatment are only temporary: Frogs released back into
their native range are re-exposed to the disease and can be re-infected.
Secondary to the problem of chytrid infection once mountain chickens are reintroduced to
Montserrat are the other threats also facing this species. A number of invasive alien species
occur at high densities on Montserrat and are known to predate mountain chickens and/or
damage their habitat. These are believed to be primarily rats (Rattus norvegicus and R. rattus)
and feral pigs (Sus scrofa). Domestic and feral cats and dogs are other likely predators and
other feral livestock.
Loss of habitat in Montserrat due to the volcanic eruptions from 1995 to the present has been
severe. Most of the mountain chicken habitat known from pre-1995 does, however, remain,
primarily in Montserrat’s Centre Hills reserve. This is, nonetheless, a relatively small area of
suitable mountain chicken habitat, and it is subject to periodic falls of acidic volcanic ash.
Hunting mountain chickens for food is believed to have led to marked population declines on
Montserrat before chytrid reached the island. At present, there seems to be little if any hunting
whilst mountain chickens are at such low densities. It does, however, remain a potential threat if
the population begins to recover.
3. Programme objectives
The MCRP aims to recover populations of the mountain chicken to viable levels across its
native range. We have restricted this document to covering the project activities for
reintroducing mountain chickens to Montserrat in 2011 in support of this aim.
3.1. Project objectives for 2011 – reintroduction of mountain chickens to Montserrat.
In 2011, Durrell, DOE and IOZ aim to investigate the factors that determine the success of a
reintroduction. Montserrat’s Centre Hills mountain chicken population by the reintroduction of
chytrid-free frogs bred in captivity in 2009-2010. There will be two reintroductions that will take
the form of pilot studies to examine the effects of various factors on the success of
reintroductions. These pilot studies will allow us to develop optimal strategies and protocols for
future reintroductions to augment mountain chicken populations in their native range.
The specific objectives of the 2011 reintroductions are to:
1. Determine survival of released frogs and causes of mortality over the next three years,
but with a three-month intensive monitoring period immediately after release.
2. Determine the effect of age-at-release, season (wet or dry), and parentage on dispersal,
survival of released frogs and causes of mortality
3. Determine if reintroduction leads to increased levels of chytrid in mountain chickens and
other amphibian species on Montserrat which are part of the mountain chickens’
environment
4. Determine state of surviving frogs on Montserrat over the next three years, especially
their infection and health status and, if possible the population distribution and trend in
numbers
The hypotheses that are to be tested to meet these objectives are:
1. A proportion of reintroduced frogs survive
2. (a) A higher proportion of older age-at-release and larger frogs will survive
(b) A higher proportion of frogs released in the wet season will survive
3. Introducing frogs at a density of 8 frogs per hectare does not trigger mass mortality in the
introduced population.
3. Reintroduction does not lead to increased levels of chytrid in other amphibian species or
mountain chickens surviving at sites other than the reintroduction site.
4. Surviving (non-reintroduced) frogs remain chytrid-free (or infected but surviving)
5. The reintroduced population will breed within in the year
4. Ethical statement
We believe that the long term survival of this species in its native range depends on finding
ways to recover the wild population. We propose that a critical approach to this is to determine
the factors affecting the survival of (a) the few mountain chickens still remaining in Montserrat
and (b) captive bred mountain chickens reintroduced back into Montserrat. To do this we need
to monitor surviving frogs and test reintroduction protocols. The welfare of mountain chickens
will be paramount during these activities. Strict biosecurity protocols will mitigate the risk of
transferring infections between frogs and between field sites. Frogs’ health status will be
monitored intensively and humane euthanasia used for frogs whose health status is severely
compromised by chytrid infection.
We recognize that at least some chytrid-free mountain chickens reintroduced into Montserrat
are likely to become infected with chytrid and that this infection may prove fatal. We recognize
that at least some of the secondary threats to mountain chicken populations may also confront
reintroduced frogs, primarily non-native predators. We also recognize, however, that some
mountain chickens are still surviving in Montserrat since the arrival of, and (we believe) in the
presence of, chytrid. They are also surviving in the face of any secondary threats.
With no known method for removing the environmental reservoir of Bd on Montserrat, we
believe the best course of action is to determine what affects the degree to which
reintroductions are successful. We aim to identify which factors that are under our control to
maximize the survival of reintroduced mountain chickens and their ability to reproduce. These
factors include the season in which frogs are reintroduced; the age of frogs at reintroduction; the
location of reintroductions on Montserrat and the density at which frogs are introduced.
Without determining these basic parameters we believe we will never be able to move beyond a
situation of a small population of frogs held in captivity indefinitely or until funds expire. Our aim
is to re-establish viable mountain chicken populations in the wild in their native range. To do this
we need determine why surviving frogs are surviving – albeit at apparently very low densities –
and how we can ultimately augment their numbers. We believe we can only attempt to
determine this if our captive-bred frogs confront the conditions now present in their native range.
Released frogs will be very closely monitored to learn as much about their responses and fates
as possible. A large sample of 34 will be individually tracked using radio transmitters and all
frogs will be individually identifiable from PIT tags (‘microchips’). Their health status will be
monitored throughout and detailed protocols are presented for the humane euthanasia of any
frogs that do contact chytrid.
At all stages of this work, robust biosecurity protocols are being implemented to prevent project
workers from inadvertently transferring Bd between frogs (of the same species or between
species) or between sites.
It may be that the continued survival of mountain chickens on Montserrat is a result of them
having been reduced to very low densities. Reintroduced frogs will not be released at any sites
currently known, or believed, to support small numbers of surviving mountain chickens on
Montserrat, so that we don’t increase the density of these survivors during our 2011 releases.
The reintroduced frogs will be introduced at densities comparable to those known from the
release site prior to chytrid reaching Montserrat. They will not all be released at a single point
leading to inflated densities and hypothesized greater risk of chytrid infection.
Candidate release sites have been assessed prior to the release to determine the presence of
suitable habitat, the likely level of non-native predators and the risk of human foot traffic
spreading chytrid between sites. The release site selected is known to have supported a healthy
mountain chicken population prior to chytrid infecting Montserrat and is only rarely visited by
people. Field monitoring programs have been designed with the welfare of individual animals in
mind using information gained over many years on the reaction of frogs to handling and
disturbance in captivity and in the wild. Given the location of the selected release site relatively
far from human population, we believe that the secondary threat of predation by introduced
predators will be minor. We have, however, developed protocols for rapidly implementing rat
control at the release site if our monitoring of the reintroduced frogs reveals significant numbers
of injuries from rats.
Implantation of radio transmitters will be completed under anaesthesia and with a supervised
recovery period of 10 days in captivity and under quarantine. Transport of frogs from Europe to
Montserrat will follow the welfare in transport guidelines presented in this document and frogs
will be held under supervision in secure captive conditions on arrival in Montserrat for a further
four days prior to being released. Supplying food to the frogs during this period of captivity in
Montserrat necessitates importing live insect food, with the danger that it could escape and
contribute further to the diversity of invasive species already found on the island. Mitigative
measures have been put in place to prevent this.
Concurrent with the release, chytrid levels in the environment (i.e. in other, more numerous,
amphibian species) will be monitored at the release site and at two control sites: one known to
be still supporting surviving mountain chickens and one not known to be. We believe it is
unlikely that chytrid levels at sites known to be still supporting surviving mountain chickens will
be elevated as a result of our reintroduction of mountain chickens at a separate site. We have
however, in 2009, demonstrated our ability to be able to rapidly evacuate frogs from an infected
area to biosecure accommodation if deemed appropriate.
We have been very successful in breeding the species in captivity. We believe that captive bred
frogs have the maximum chance of surviving in the wild if they have not been maintained in
captivity for an extended period of many years (>2yrs). Therefore we propose that an early
release will improve their chances of surviving in the wild.
5. Strategy for reintroducing mountain chickens to Montserrat in 2011
5.1. Biosecurity and animal welfare
Robust biosecurity protocols will be observed before during and after the captive-bred mountain
chickens arrive in Montserrat. They will also be observed during all phases of the field work
described below to mitigate the risk of transferring infections between frogs and between field
sites. Frogs’ health status will be monitored intensively and humane euthanasia used for frogs
whose health status is severely compromised by chytrid infection.
Detailed protocols to ensure strict biosecurity throughout this work are presented in the
biosecurity maunals. These were developed successfully for field work during the 2009
evacuation of mountain chickens from Montserrat to biosecure ex situ accommodation will be
applied in all phases of the work. Our veterinary staff are providing a detailed diagnostic
protocol for assessing health and infection status of mountain chickens in the wild that will be
used by field staff to determine when humane euthanasia is indicated. All field staff will receive
hands-on training in biosecurity and euthanasia protocols.
5.2. Reintroduction
Chytrid-free mountain chickens bred in biosecure captivity are reintroduced to Montserrat in
January 2011 (Montserrat’s dry season) and August 2011 (wet season). In January 2011, frogs
are released at a single site known to have supported mountain chickens in the past, but not at
present. The frogs in each release are in two cohorts: younger frogs bred in 2010 and older
frogs breed in 2009. A sample of 34 released frogs are radio tracked to monitor their health
status and determine their fates during the first three months after release.
Uninfected frogs bred under strict quarantine will be released at a single site (for logistical
reasons, primarily to make radio tracking feasible) in Montserrat. Prior to reintroduction a survey
assessed candidate release sites (ghauts, as watercourses are known locally) was completed,
to select a release site on (a) presence of suitable mountain chicken habitat; (b) ease of access
to and within the site for radiotracking; and (c) low human usage (and, by implication, lower nonnative predator levels). Sweetwater Ghaut in the north east of Montserrat has been selected
based on these criteria:

It had a healthy mountain chicken population prior to chytrid arriving on Montserrat and
we have a baseline population density estimate from mark-recapture data collected in
2005.

It is relatively far from centres of human population on Montserrat and is believed to
have relatively low human foot traffic visiting it. For these reasons, non-native predator
levels are also believed to be relatively low.

It is not a site from which mountain chicken calls have reportedly been heard in 2010.
This is to minimize the risk of compromising the existing surviving mountain chickens on
Montserrat for example by through increasing frog density and triggering a chytrid
outbreak.
All released frogs PIT tagged for individual recognition and a sample of 34 will be implanted with
radio transmitters (and supervised for 10 days afterwards) in Europe prior to being transported
to Montserrat. The radio transmitters will allow us to intensively monitor the status and fates of
this sample over three months. Frogs will be transported from ex situ facilities under biosecure
conditions and held for 4 days in Montserrat prior to reintroduction, to monitor general health
post-transit, post-radio transmitter implantation.
Frogs will be released along a ghaut to achieve mountain chicken densities equivalent to what
was estimated for this site pre-chytrid (namely about 10 frogs for every 100m length of
Sweetwater)
One release will be carried out during the dry season, followed by a second one in the wet
season to examine effect of season on survival. The protocols presented in this document have
been developed, in the first instance, for the first January/February) release. They will be
reviewed and adapted if necessary prior to the second (July/August) release.
Each release cohort will contain frogs born in 2009 and 2010 to examine effect of age-atrelease on survival. Each release cohort will also contain frogs from multiple crosses (i.e.
different parents) which may allow us to examine any effect of parentage on survival (though
sample sizes may be too small to detect any such latter effect). As far as possible, given
existing stock, sexes will be equally represented within the cohort of 34 radio tagged frogs.
5.3. Monitoring reintroduced frogs
A sample of 34 radio tagged frogs will be located as frequently as possible (at least once every
ten days per individual, with approximate locations taken daily) to monitor dispersal, health
status and survival. Data on non-radio tagged frogs will also be collected opportunistically.
Radio transmission and reception characteristics of the release site and surrounding sites will
be assessed using a non-implanted transmitter
Radio-tagged frogs will be relocated (but not captured) as frequently as possible to examine (a)
dispersal, (b) habitat and microhabitat use. Habitat variables will be extracted from a GIS posttracking; a few simple microhabitat measures will be recorded in situ. We will also record the
proximity of other mountain chickens and cane toads.
Radio-tagged frogs will be captured at least once every ten days to (a) (to assess chytrid load)
through swabbing, (b) record any visible signs of illness, (c) record any signs of injury (i.e.
primarily from predators).
Radio transmitters from which no signal has been obtained for a week or more will be searched
for intensively to determine if loss of signal is due to (a) dispersal, (b) frog mortality, (c) frog
location (e.g. in a burrow that attenuates radio transmission), (d) transmitter failure.
This intensive monitoring is projected to last for three months (depending on frg and radio
transmitter survival). During this period, a less intensive monitoring protocol will be developed to
continue mountain chicken monitoring at the release site beyond radio tracking. This protocol
will use automated call recording (‘frog loggers’) and intensive searches two days every week to
find and record and sample the health status surviving mountain chickens… Individual PIT tags
will allow us to follow the fates of individual frogs beyond the radio tracking period.
Non-radio tagged frogs will be opportunistically mapped (GPS) and captured to sample
chytrid/health/injuries. Habitat and microhabitat variables will also be recorded for these
locations as above.
From July onwards bi-weekly surveys at this site will also allow us to look for the presence of
juveniles and/or signs of reproductive activity in adults indicating breeding by the frogs we
introduced.
5.4. Monitoring surviving mountain chickens
A sample of sites at which mountain chicken are believed to still survive on Montserrat will be
monitored concurrently with the release monitoring. Where possible, surviving frogs will be
captured to determine their health and infection status. Individual marking of these mountain
chickens will be used to attempt a mark-recapture estimate of the abundance of these frogs.
A sample of four sites (ghauts) from which mountain chickens are reported to have been heard
calling from in 2010 will be sampled concurrently with the reintroduction and radiotracking work
outlined above. Four ghauts will be selected and each will be monitored once a fortnight.
These sites will be monitored using the transect monitoring protocol established in Montserrat in
1997, but traversing longer lengths of the ghaut (i.e. including but not limited to the 1997
transects). We will capture any mountain chickens located during these transects to sample
chytrid load and assess health and breeding status. In addition, captures will be individually
marked with PIT tags in an attempt to estimate population abundance from mark-recapture
data.
Location, microhabitat, and any injuries of captured frogs will be also be recorded as for radiotagged reintroduced frogs (above). We will also take DNA samples from buccal swabs (as,
speculatively, it may be possible to identify genetic differences – potentially heritable resistance
– in surviving frogs compared with DNA from frogs captured pre-chytrid).
As with the radio tagged frogs, this intensive monitoring is projected to continue through the
year.
5.5. Monitoring chytrid levels
Chytrid load in mountain chickens and their environment (in this case, in tree frogs and cane
toads and cane toads) may vary between sites or within sites over time. These variations may
be an effect that explains survival of frogs at the release site or the sites where mountain
chickens are believed to still survive. We also need to monitor whether the release appears to
lead to an increase in chytrid load at the surviving frog sites, though we believe this to be
unlikely as they are in different watersheds.
Tree frogs and cane toads will be sampled and swabbed to determine chytrid load at (a) the
mountain chicken release site plus (b) a control site from which mountain chickens are not
known to survive, and (c) a control site at which small numbers of mountain chickens are
believed to be surviving. We will attempt to obtain minimum samples of swabs from 60 tree
frogs (and up to 300 tree frogs and cane toads if possible). This sampling will be done
immediately prior to the first release of mountain chickens and then monthly thereafter for the
remainder of the year.
At the reintroduction site we will individually mark cane toads so we can monitor any
progression of chytrid in a second amphibian species in the immediate vicinity of the introduced
mountain chicken's.
We will attempt to relate the chytrid loads in mountain chickens, and mountain chicken survival,
to chytrid loads in the tree frogs and cane toads that make up part of their environment.