Conservation
Ecology of Natterjack Toads (Bufo calamita)
My research is supported by the Irish
Research Council for Science Engineering and Technology, and started in October
2004. Prior to this I spent the 2004 field season working in collaboration with
the National Parks and Wildlife Service whilst based at in the Department of
Zoology, Ecology and Plant Sciences at UCC. The project began by evaluating
the ecological factors that influence Natterjack toad (Bufo calamita)
breeding success. The monitoring of toad populations from 2004 to 2007 will
enable me to identify simple environmental and biological indicators that can
be used to determine and monitor the conservation status of the species.
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The Natterjack toad is a protected
species and this is the only toad living in Ireland. It is one of the
three amphibians found in the country with the common frog (Rana temporaria)
and smooth newt (Triturus vulgaris). Toads are restricted to twelve
native sites in County Kerry and one site in County Wexford where Natterjack
toads have been introduced in the early 1990s. Such a restricted distribution
leaves the species vulnerable to population reduction and extinction.
If toad populations remain healthy and manage to breed successfully, it
indicates that local environmental conditions are favourable for the species
and for other animals and plants living in these habitats.
In 2004, Natterjack toad populations
were regularly monitored during their breeding season (April-July) at
all sites in County Kerry where toads are known to breed: the Maharees,
Lough Gill, Stradbally golf course, Fermoyle, Tularee, Roscullen Island,
Loughs Yganavan and Nambrackdarrig, Dooks, Glenbeigh and Caherdaniel.
These sites represent mainly sand dunes, marshes and heathlands. The Inch
Peninsula is the only site that was not monitored in 2004.
During the breeding season,
most of the adult female toads lay a single egg string in shallow ponds.
Recording the total number of egg strings deposited in each pond between
April and July therefore provides an estimate of the total number of adult
females, and thus egg strings can be used as an index of adult breeding
population size at each site.
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Once tadpoles have metamorphosed
into toadlets in June and July, an estimate of the number of toadlets is used
to assess breeding success at each pond. Breeding success is then compared with
local environmental parameters (also measured at each pond visit), such as water
temperature, pH and conductivity, in order to investigate optimal conditions
for the toad breeding success.
In 2004, breeding activity (number
of egg strings deposited in each pond) and breeding success (larval survival
rates estimated from the numbers of eggs and toadlets) varied greatly among
ponds. Tadpole mortality was particularly high in 2004 and a key factor was
the early desiccation of many breeding ponds, in particular at the Maharees,
Dooks and Glenbeigh. At some sites, larval survival was higher in ponds with
low conductivity (e.g. 400 µS.cm-1) and with relatively high pH (e.g.
9). Preliminary modeling work and population growth analyses suggest that 8
out of the 11 studied populations are in decline.
Monitoring the toad breeding success
over three successive years (2004-2006) will provide sufficient data to determine
trends in population growth and provide a baseline against which to compare
future surveys. This will also enable researchers to take into consideration
annual variability when investigating the effect of environmental factors on
the toad breeding activity.