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Figure 2. UK distribution of the Harvest mouse
(https://data.nbn.org.uk/imt/#4-
33.320,45.600,26.710,62.503!091ELC)
The Role Played By Chester Zoo in the Captive Breeding and Reintroduction of the Harvest
Mouse (Micromys Minutus)
Ecology & Distribution
Weighing only six grams, the harvest mouse (Micromys minutus) is the smallest mouse in
Europe (Plate 1). Brown in colour, the harvest mouse can
grow between 50 to 70 millimetres in length with an
additional 50 to 60 millimetres just for its prehensile tail
which acts as a fifth limb to provide stability when
negotiating the heads of cereal crops (Leach 1990). Their
diet consists primarily of grain, cereal and berries though
it is supplemented with insects and young grasses (Gibson
et al 2010). Harvest mice are predominantly nocturnal
though they become more active in daylight hours in the
winter months when food is scarce. Populations are under
increasing threat of decline due to predation by domestic cats, greater exposer to birds of prey
and sudden frost (Leach1990). Typically the harvest mouse has a low average life expectancy
of six months.
The harvest mouse has a historical distribution across most of Europe and some parts of Asia.
Within the UK the distribution is restricted to southern England with small populations in
Chester and Yorkshire and a few fragmented
populations recorded in Wales and some regions
of Scotland (Figure 2) (Harris 1979).
Historically, the harvest mouse was abundant
within crop fields and lowland woodland with
population peaks during the height of summer
when food supply was plentiful (McDonald &
Tattersall 2001). However, due to habitat loss
and fragmentation as a result of the
intensification of agriculture, the species is now
largely recorded in wetlands, long grasses and
hedgerows bordering crop fields (Wildlife Trust
& Severn Trent Water 2010)(Wildwood Trust
2006). According to the Wildwood Trust (2006)
UK population estimates are 1,425,000 with
10,000 individuals in Wales and 1,415,000
within England.
Species Status
The Harvest mouse is currently categorised as “least concern” by the IUCN (Aplin et al
2008). Taxa categorised in this way are not considered to be under any immediate threat of
Plate 1. Micromys minutus
(http://www.arkive.org/harvest-mouse/micromys-minutus/)

2. Nicola snow: 13111472 28/11/2014
extinction. This means that the threat of extinction for the Harvest mouse is low, which is due
to the species abundance across the globe.
Across Europe and most parts of Asia the Harvest mouse is common in rice fields and other
wetlands, as well as any agricultural fields that aren’t maintained regularly. Currently there
are no major recorded threats to its global distribution. However within the UK, decline in
population size has been recorded in localised regions where loss or degradation of wetland
has been observed (Macdonald & Tattersall 2003: Flowerdew 2004).
A population can be established and even thrive provided a habitat contains some quantity of
long grass and wetland (Gibson 2010). As the Harvest mouse is very adaptable across a range
of habitats, variation in range has been recorded throughout the globe, whilst populations
within regions of Asia common amongst bamboo and rice paddies; populations within
Western Europe are most common in alpine grassland, tall grass fields and the edge of humid
forests (Råberg et al 2013). Throughout England, Harvest mice are most abundant within
hedgerows or in landscapes where hedgerows feature as crop borders and boundaries.
Conservation
Decline of the Harvest mouse within the UK has been attributed to the increase in modern
farming techniques and the advancement of agricultural technology (Toms et al 1999;
Sargent 1997). In addition to this, changes in seasonal temperature and fluctuating crop yield
due to the effects of increasingly turbulent weather, are impacting on the species breeding
patterns which usually coincide with the abundance of cereal crops in summer (Tom et al
1999). The Harvest mouse typically nest within cereal fields, creating a nest from wheat and
corn stems on the mid-area of the cereal shaft. However, due to the widespread use of
agricultural machinery which limit time for escape during harvesting, the species has now
adapted to dwell within the bordering hedgerows of large cereal fields to avoid nest
destruction (Macdonald & Tattersall 2001). This adaptation has also led to further decline of
the species due to aggressive hedgerow management. Population numbers of the Harvest
mouse were found to decrease in density down to as low as 0.002 -0.76 animals per hectare in
2004 and 2006 across a number of sites in the Upper Thames tributaries region (Mammal
trust UK 2007).
Conservation efforts include captive breeding and reintroduction in addition to crop margin
management which involves the implantation of long grass margins along the parameter of
crop fields. This provides shelter for the Harvest mouse during harvesting of the crops
(Fischer & Schroder 2014).
Role of Chester zoo
Chester zoo has established a captive breeding and reintroduction programme since the 1980s
in collaboration with the Cheshire Wildlife Trust; the zoo has bred the Harvest mice in
controlled and monitored conditions to ensure the greatest birth rate. Litters are reared in

3. Nicola snow: 13111472 28/11/2014
captivity until they are between 3 and 12 months old where they are reintroduced into sites in
the Cheshire countryside that have been specially selected to provide optimal habitat for the
Harvest mice (Wildwood trust 2006). In 2003, 270 mice were released on land owned by
Chester zoo at a sex ratio of 50:50,with a further twenty radio-tagged mice later being
released (UK BARS 1999). These mice were then monitored periodically until 2006 to
determine any population increase and overall success of the release.
Captive bred mice at Chester zoo are housed in a series of tanks containing small groups of
two to four mice per tank. Each tank is filled with a layer of sawdust and a selection of
nesting materials such as straw, leaf litter and other vegetation available to them in the wild.
The mice fed on a mix of cereal, fruit and millet which is available to them throughout the
day. The tanks are designed to mimic wild habitat whilst providing optimal conditions for
breeding. The mice will not mate unless some degree of competition has taken place to
establish a dominant female and male. Due to this, initially each tank contains four
individuals which are monitored until a dominant pair has been established and conceived
their first litter. Once the dominant pair is established the submissive pair is removed
allowing for the remaining pair to nest without further competition for up to seven litters.
Beyond seven litters the risk of death during birth increases significantly (Wildwood trust
2006).
Following the release of captive bred mice, radio tagged mice are monitored and any
population increase is recorded as well as the general health and fitness of the population.
Overall captive bred mice released by Chester zoo successfully integrated into wild
communities with a limited number of individuals lost to predation or sickness. However
minimal information is available as to the success of Chester zoo’s captive breeding
programme; but continued monitoring of the released individuals over a four year period
indicated that they were still present throughout the release sites but had dispersed
significantly into surrounding habitats (UK BARS 1999).
Based on the methods used by Chester zoo for captive breeding and the presence of
reintroduced individuals within the release sites four years after the first reintroduction; the
programme can be evaluated as a success. The environmental enriched methods and breeding
management effectively produced a captive population not only capable of integrating with
the wild community, but thriving over generations within the release site. This is extremely
crucial to the re-establishment of a stable Harvest Mouse population as it demonstrates that
decline in wild populations can be offset by the release of captive bred individuals.

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The Role Played By Chester Zoo in the Captive Breeding and Reintroduction of the
Mountain Chicken Frog (Leptodactylus Fallax)
Ecology and distribution
Leptodactylus fallax also known as the Mountain Chicken Frog due to its apparent chicken
like flavour when eaten, is the world’s largest frog species and can grow up to twenty one
centimetres in length. Individuals appear Brownish-orange in colour with either dark stripes
or spots across its body. They have distinctive cloudy
eyes commonly red in colour (Plate 3) (Kaiser 1994).
The species diet consists of crickets and other insects as
well as small vertebrates and crustaceans. They have also
been known to eat other frogs and small mammals
(Martin et al 2007). As with most other frogs the
Mountain chicken also reproduces by spawning tadpoles,
however their offspring are not reared in water and
instead develop terrestrially in underground burrows
(Gibson & Buley 2001).
The Mountain Chicken Frog has a limited global distribution and currently only natively
occurs in regions of Dominica and Montserrat (Fa et al 2010). Historically the Mountain
Chicken Frog was present throughout many of the western islands of Caribbean including
Guadeloupe, Martinique, St Kitts and Nevis. However, due to rapid decline in population
numbers the Mountain Chicken Frog now only occurs on two small island in the East
Caribbean; Montserrat and Dominica (Plate 4) (Kaiser 1995). Though exact figures are not
known it is estimated that numbers could be as low as 8,000 animals in the wild with only
eight breeding pairs and 44 individuals currently recorded; with the species as a whole under
great threat of extinction (Tapley et al 2014). The species range is greatly limited by its
requirements for reproduction and its habitat preference. The species occurs in dense
vegetation within or in proximity to flooded regions such as forests and gullies regularly
exposed to floodwaters. As the species is nocturnal, individuals spend most of their time
burrowed underground in leaf litter and soil (Daltry 1999). Soil type preference is a key
factor in the restriction of the species range as soil requirements need to allow for borrowing
and nesting (Gibson & Buley 2001). The Mountain Chicken Frog is in captivity in many zoos
throughout the globe. These zoos are taking part in captive breeding programmes in an
attempt to improve population numbers and prevent its extinction (Tapley et al 2001). This
species can be found in captivity in zoos throughout Europe, America and Africa, with some
zoos actively involved in its protection, research and conservation within its native
environment of Dominica. The zoological Society of London, Parken Zoo (Sweden) and the
North of England Zoological Society (Chester Zoo) are all partners with the “saving the
Mountain chicken” campaign which is based in Dominica (Mountain chicken project 2007).
Plate 2. Leptodactylus fallax
http://www.arkive.org/mountain-chicken/leptodactylus-fallax/

5. Nicola snow: 13111472 28/11/2014
Plate 3. Distribution map of The Mountain Chicken Frog across the Caribbean (http://maps.iucnredlist.org/map.html?id=57125)
IUCN status
According to the IUCN red list, the Mountain Chicken Frog’s global threat status is currently
set at critically endangered (Fa et al 2010). The IUCN determines “critically endangered” as
“… considered to be facing an extremely high risk of extinction in the wild” (IUCN 2012).
This means that due to the species limited distribution and increasing rate of decline,
extinction in the wild is impending unless measures are taken to protect, conserve and
recover the species population numbers.
Conservation
Historically the Mountain Chicken, as the name implies, was a food source to the inhabitants
of Dominica and Montserrat with between 8,000 and 36,000 individuals hunted annually
(Schwartz & Henderson 1991; Malhotra et al 2007). Though hunting of the species reduced
population numbers, in 2002 the population crashed. Originally, the cause of such a dramatic
decline in species abundance was unclear and attributed to threats such as the brown rat
(Atkinson & Atkinson 2000), increased hunting due to tourism, habitat loss due to agriculture
and natural disasters such as cyclones and volcanic activity (Fisher et al 2009). However,
though these threats are current and persistent it was determined by the London Zoological
Society that such a significant decline in population numbers was due to an outbreak of a
fungal disease known as Chytridiomycosis which affects the frog’s keratin deposits within its
skin, inhibiting its ability to hydrate, breathe, osmoregulate and thermoregulate this
ultimately results in a 100% mortality rate of any infected individuals (Garcia et al 2009).
Current conservation efforts include global captive breeding programmes and outreach
programmes designed to research alternative methods of aiding the species recovery as well
as educating local government organisations to better manage and protect this threatened
species. Most notably the London Zoological Society has established a captive breeding

6. Nicola snow: 13111472 28/11/2014
facility and conservation reserve within Dominica in partnership with the Commonwealth of
Dominica and the government of Montserrat (Martin et al 2007).
Role of Chester Zoo
A number of zoos throughout the world are involved in captive breeding programmes in an
attempt to help establish a so-called “safety net” population. In July 2014, the London
Zoological Society and Durrell Trust successfully returned a number of individuals to the
wild. Fifty-one captive bred Mountain Chicken Frogs were transported to the National
Botanical Gardens in Montserrat where they were housed overnight and then later soft
released with the aid of tents back into the wild. The London zoological Society and Durrell
Trust have now implemented a twenty year action plan to monitor and treat all reintroduced
individuals to ensure maximum survival as well as further the research and understanding
into the spread of the Chytridiomycosis fungus (Durrell Trust 2008).
The Durrell Trust, London zoological Society and Chester zoo established a cooperative
captive breeding programme for the Mountain Chicken Frog and outlined species
management guidelines. These guidelines identify key species requirements for captive
management to enable optimal breeding conditions as well as regulating exposure to the
Chytridiomycosis fungus. Chester zoo, in accordance with the guidelines, photo ID all
individuals keeping a catalogue of all unique markings in addition to micro-chipping via the
lymph sacs beneath the frog skin. Environmental conditions of the frogs housing is monitored
strictly ensuring that temperature is regulated between 24 to 28°C during the day and 19 to
13°C during the night. The temperature is also alternated to mimic natural temperature
fluctuations in the wild such as seasonal temperature change. Environmental enrichment is
considered right down to the frog’s substrate preference, ensuring that adults and juveniles
have a good mixture of soil, bark chippings and leaf litter to maintain adequate humidity
within the enclosure. Breeding is encouraged between the frogs during the month of May
through to July by introduction of a female into a male’s enclosure to promote pairing and
subsequently burrowing. Once the burrow is established, the pair will mate for up to 10 hours
during which a foam nest is created and up to 50 small eggs are deposited. After 7 to 10 days
the eggs hatch and the female frog will remain with the clutch for 6 to 8 weeks. Once the
larva are 150 mm in length they will absorb their tail and leave the burrow. Chester zoo then
continue to feed the clutch 4 to 5 times per week until they have reached adequate size for
removal into independent enclosures. From this stage the zoo then perform health checks to
establish if individuals are free from the Chytridiomycosis fungus. Once a sufficient number
of individuals (usually 50 to 80) have been produced in captivity, they are transferred to the
release facility in Montserrat (Durrell Trust 2001). Individuals released from the Montserrat
facility are a mix of captive bred frogs from a number of different zoos participating in the
captive breeding programme and regulated by the same species management guidelines. Not
only does this increase the number of individuals released into the wild, it too increases
genetic diversity amongst the re-established population; ensuring reduced inbreeding and
consequently strengthening resilience to potentially devastating stochastic events.

7. Nicola snow: 13111472 28/11/2014
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