Is the Natterjack toad about to croak?
10 Apr 2012 12:37 PM
One of Europe’s loudest amphibians faces uncertain breeding in Britain’s dry weather.
With its distinctive markings and a mating call that can be heard up to 2km away, the natterjack toad is one of Britain’s most striking amphibians. It is also one of the rarest, with less than 50 breeding populations in mainland Britain. Britain’s prolonged dry weather threatens to make it rarer still and Natural England is stepping in to take early action to help the natterjack make it through the drought.
In Britain, the natterjack favours coastal habitats and breeds in dune slacks – wet hollows between sand dunes. It’s this preference that’s putting the species in danger – for the last two years these shallow pools have been disappearing before the tadpoles have metamorphosed into toads. If the dry spells continue year on year, this could eventually spell disaster for this species in England.
Fortunately for the natterjack, Natural England is leaping into action to protect the toads’ remaining breeding habitat. With a large portion of the population on National Nature Reserves, Natural England have been doing their best to prevent the breeding ponds from drying out and to make sure that this noisy amphibian has at least some breeding success this year. A range of water saving techniques are being used at NNRs, including Saltfleetby Theddlethorpe in Lincolnshire, North Walney in Cumbria and Holkham in Norfolk and reserve teams are hoping that careful management of the toads’ pond habitats will be enough to see the natterjack safely through this breeding season.
Dr Pete Brotherton, Natural England’s Head of Biodiversity said, “The natterjack is one of our most charismatic amphibians, but its reliance on shallow ponds that can dry out easily in prolonged dry weather, leaves it vulnerable to drought. Natural England have been working hard on its National Nature Reserves to protect the toads’ breeding habitat to provide a lifeline to help this special species through this difficult year. We are confident that the toad can bounce back if conditions prove wetter next year”.
What’s going on at NNRs to help the natterjack
Saltfleetby Theddlethorpe Dunes NNR, Lincolnshire
The population is relatively small c40-50 adults and breeding success does rely upon favourable water level conditions in the dune slack pools, particularly in May and June which are the critical months. To side step the problem, staff at Saltfleetby Theddlethorpe have created captive pools for the tadpoles to mature. There are four captive pools which are designated areas where water levels are controlled and strings of natterjack spawn are transferred from the slack pools this gives the natterjack toadlets a chance. Once hatched they are free to escape into the surrounding dune habitat. The captive pools are butyl lined and every year in March they are drained, cleaned out of algal growth and topped up with water. Some turfs and sandy slopes are put in place which allows the developing toadlets to leave. To prepare for abnormally dry weather patterns, which would cause water levels in the pools to drop to dangerously low levels, Reserve staff have a filled water bowser on standby to top them up as required.
North Walney NNR, Cumbria
In the northwest, the picture is altogether better in terms of water levels – there are plenty of standing pools. The warm weather has brought other issues though. Natterjacks like clear water to breed in. Working with the Amphibian and Reptile Conservation Trust, volunteers and Reserve staff cleared some of the pools of vegetation to create toad-friendly conditions. The hot spring weather brought heavy algal blooms in the newly clear water. This year, barley straw has been deployed in 5 pools to keep them clear of algae and a further two pools have been cleared out by Cumbria Wildlife Trust volunteers. The natterjacks are calling two weeks earlier than expected at North Walney.
Holkham NNR, Norfolk
There’s been very little activity from Holkham’s natterjacks yet, which is normal for this time of year. There is water in quite a lot of the dune slacks, though the water-table is low and if the dry weather continues, they’re unlikely to hold water through the breeding season. The topography of the Reserve makes it difficult to get large water bowsers out to the slacks and with the water table so low any top-up water may well just drain way in any case. All is not lost, as there is a large freshwater lagoon next to the breeding pools, which the natterjacks will use if the slacks are dry. As the lagoon is used by breeding waders, it does make monitoring the population difficult as the Reserve staff don’t want to disturb the nesting birds.
Winterton Dunes NNR, Norfolk
There are ten artificial pools lined with clay at Winterton Dunes. It’s a waiting game with the rain now to see whether they will need topping up. In very dry conditions, it’s not possible to keep all the pools filled. Last year, Reserve staff managed to keep two of the pools filled and that led to several thousand toadlets making their way out onto the dunes. If the rains do come, it presents another problem – rain means cooler pools, which means the tadpoles take longer to metamorphose and that means a higher likelihood of predation.
Notes to editors
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The natterjack life-cycle
Natterjacks are our fastest metamorphosing amphibians – in warm conditions they can be out of the water as toadlets in around four weeks. The common toad could take ten weeks. This speedy metamorphosing is a key to their reproductive strategy. The advantage of breeding in ephemeral pools is that because they dry up each year, they don’t harbour predators such as dragonfly or diving beetle larvae, which stay in a larval stage for around two years. They also avoid competition with common toads and frogs, which favour permanent pools. The disadvantage is that if it is too warm, the pools dry out before the tadpoles can change and if it is too cold, they remain as tadpoles longer, which increases the chances of being eaten by other predators, such as birds or other amphibians. The natterjack is a resilient species and large populations can withstand a number of failed breeding seasons. The population in Britain is fragmented and threatened by habitat loss, so Reserve staff are taking steps to reduce its vulnerability to dry weather.
About National Natures Reserves
Many of the finest sites in England for wildlife and geology are National Nature Reserves. Almost all are accessible and provide great opportunities for people to experience nature. There are currently 224 NNRs in England (and one Marine Nature Reserve, Lundy) with a total area of over 94,400 hectares, which is approximately 0.6% of the country’s land surface. The largest is The Wash NNR covering almost 8,800 hectares, whilst Horn Park Quarry in Dorset is the smallest at 0.32 hectares