Why Did the Frog Cross the Road?

Warum Überquert der Frosch die Straße?

A white bucket in hand, Christine Zorn walks along the knee-high tarpaulin fencing a road in Buch, in north Berlin. The air is thick with the sound of noisy seagulls from a pond on the other side of the road.

Every few metres, Zorn stops and looks behind the fence into a pail whose open mouth is level with the ground. In each pail is a stick, which she uses to carefully stir the dead leaves inside.

She finds nothing, until lucky number 13. Inside this pail is a thumb-sized Rana esculenta, otherwise known as the Teichfrosch (edible frog). It is a sub-adult and she gladly transfers it to the white bucket and notes it down.

Another two pails further along the fence reveal similar catches.


With her bounty of three frogs, Zorn crosses the road to release it into the pond.

Zorn, 37, is a volunteer with the Amphibian Conservation Programme, run by the German Society for Nature Conservation (NABU). A major aim of the programme is to reduce roadkill, which has been devastating amphibian numbers.

According to NABU-Berlin’s homepage, central Europe is crisscrossed by so many roads that “a density of 60 cars per hour kills 90 per cent of migratory toads”. That’s a lot of squashed frogs.

While that imagery might be cartoon-like, the consequences are far from funny.

Scientists believe that frogs and other amphibians are important indicators of the health of ecosystems, because they are very vulnerable to stresses in the environment that could eventually affect humans.

In Europe, they are most at threat when they migrate in their thousands in Spring, back to the ponds and rivers where they were born.

Germany’s amphibian numbers have dropped so much that since 1980, all its 21 amphibian species are legally protected.


However, with more and more roads coming between them and their spawning waters, conservation programmes such as NABU’s and volunteers such as Zorn, are crucial.

The so-called toad fences like the one Zorn checks, are erected all over Germany, about 3,000 in all; NABU manages about a quarter of them.

These are temporary fences set up between February and May each year to intercept frogs, toads, newts and salamanders as they make their way to spawning waters.

Fences are about 50cm high and of varying lengths. On the catchment side, pails are buried at ground level at intervals so that when migrating amphibians try to surmount the fence, they will eventually fall into the pails.

These pails have to be checked every day and the creatures tallied before being transported across the road so they can continue their journey.

It is painstaking work, “but I love it,” says Zorn. “It is important for the environment.”

Indeed, looking into each pail feels rather like a treasure hunt, and I feel pleasure each time a “treasure” is rescued. When Zorn releases the frogs into the pond, I bid them a silent good luck as they dive into the mud or swim into the reeds.


After four years of working with toad fences, Zorn is appreciate of what she has learned.

“I know about the different species, when in the year they start migrating and when they return, where their preferred places are .. It’s very interesting to see how this changes from year to year.”

In 2010, for instance, because of the severe Winter, there are fewer amphibians.

Zorn vividly recalls a different scenario at another toad fence.

“Only for that single day last year, every pail was full! There were 24 pails in total, and in the end, I counted 600 amphibians. It was only a small pond at that place, but during the season, 4,000 amphibians went there to spawn.”

Even the small-scale Buch toad fence yielded impressive numbers.

Measuring a mere 25 m wide and 400 m long in addition to being hemmed in by a road and a busy railway line, it saw about 2,000 amphibians recorded in 2009. An estimated 10,000 returned after the spawning season.

Sadly, though, this is not indicative of population health.


Survival rates are notoriously difficult to record. Some scientists estimate that while 95% of eggs laid by frogs may hatch, only one to five percent of the tadpoles become froglets. Out of these, only a handful survive long enough to reproduce.

Taken together with other man-made threats such as larger-scale habitat destruction, infectious diseases and climate change, more permanent solutions are needed to safeguard these migrating amphibians.

NABU-Berlin’s Head of Species Conservation Jens Scharon drives me a few kilometres away to the Buch Forest and parks by an sandy paved path leading into the woodland. There is an innocuous-looking grill over the path, but it is part of a permanent structure – an amphibian tunnel.

The structure runs almost 90 m along the busy road, and slopes down to the middle where there is a tunnel running beneath the road. No need for buckets, no need for volunteers, and Scharon says that it saves not only amphibians from roadkill, but hedgehogs, mice and other creatures too.

The structure is impressive but getting funding for it is always a struggle, says Scharon. “They tell us the money we ask for could be used to build a kindergarten.”


And so, the services of volunteers such as Zorn continue to be greatly appreciated.

In fact, her experience and knowledge are being passed on in several ways. She introduced this conservation activity to, and trained a colleague at a former workplace, who has since become another of the four volunteers at this north Berlin toad fence.

A biologist by training, she also sometimes oversees students doing their amphibian-related practical work with NABU.

In addition, she totes her 10-year-old along whenever she checks the toad fence on weekends. “My daughter doesn’t like the big frogs,” Zorn says with a laugh. “She prefers the newts. But it’s important for her to learn.”

Others appreciate what Zorn does too. As she walks along the fence, she is greeted by walkers and passers-by.

One interested local questions her effusively about the collection this year and commends her for her work, stating that he has photographed the frogs in the pails and also donates money to the programme.

Awareness is, as always, crucial to conservation.


An ironic Earth Day Canada adaptation of a popular joke goes thus: “Why did the frog cross the road? To get to the other half of his home!”

The toad fences help tremendously but do not eliminate road kill. For NABU, limited resources means that toad fences are not erected for the return migration after spawning season.

So migration areas are sometimes identified by “Frogs Crossing” signs on road shoulders, and notices are placed in newspapers alerting the public of the migration season. Data is uploaded onto websites so that people can track what is happening.

Sometimes, roads are closed during the season. The permanent decommissioning of roads takes that one step further. But protecting key habitats is of course the ultimate ideal.

NABU’s Scharon has a permanent solution for the habitat where Zorn volunteers.

The road that currently dissects the habitat currently serves as a parking lot for a train station. If a proper parking area were built away from the migration route, the frogs and fellow amphibians would be able to move safely and freely to the pond.

But the idea has yet to gain support.


That would be a shame, for amphibian migrations are quite a sight to behold: hundreds and sometimes thousands of creatures of all sizes jumping, crawling, running and scrambling to get to a pond or back home.

For the time being, it is up to volunteers like Zorn, who, when she is done with her checking, can put her collection bucket down satisfactorily, knowing that she has done something to keep this natural phenomenon going. ω


All About Toad Fences:
The Buch toad fence is part of a German-wide network of toad fences under NABU’s watch. NABU hosts a databank of all toad fence information and a comprehensive website on amphibian and reptile conservation, including practical information on toad fence-building and species monitoring (in German).

 

Photo Gallery


Up to 2,000 frogs and other amphibians have been recorded in the narrow 400m strip by the S2 train line in Buch. - <em>by SL Wong</em>

Up to 2,000 frogs and other amphibians have been recorded in the narrow 400m strip by the S2 train line in Buch.


However, they mate here at the beautiful Moorlinse wetland. - <em>by SL Wong</em>

However, they mate here at the beautiful Moorlinse wetland.


But to get there, they have to cross a road, along which cars travel and are parked. - <em>by SL Wong</em>

But to get there, they have to cross a road along which cars travel and are parked.


Once they make it across the road, another barrier stands between amphibians and their mating grounds - a groundsill, which prevents the road from flooding. - <em>by SL Wong</em>

Once they make it across the road, another barrier stands between amphibians and their mating grounds – a groundsill, which prevents the road from flooding.


Hence, toad fences, which aim to prevent amphibians from becoming road kill during mating season. - <em>by SL Wong</em>

Hence, toad fences, which aim to prevent amphibians from becoming road kill during mating season.


Toad fence programmes need volunteers such as Christina Zorn to check the presence of amphibians that get trapped behind the fences and record them. - <em>by SL Wong</em>

Toad fence programmes need volunteers such as Christina Zorn to check the presence of amphibians that get trapped behind the fences and record them.


This sub-adult <em>Rana esculata</em> or <em>Teichfrosch</em> (edible frog) has a higher chance of growing to maturity thanks to the programme. - <em>by SL Wong</em>

This sub-adult Rana esculata or Teichfrosch (edible frog) has a higher chance of growing to maturity thanks to the programme.


This particularly good collection comprises the <em>Rana lessonae</em> (<em>Kleine Wasserfrosch</em>/pool frog), <em>Triturus vulgaris</em> (<em>Teichmolch</em>/common newt) and <em>Rana arvalis</em> (<em>Moor Frosch</em>/moor frog).- <em>by Scharon-NABU</em>

This particularly good collection comprises the Rana lessonae (Kleine Wasserfrosch/pool frog), Triturus vulgaris (Teichmolch/common newt) and Rana arvalis (Moor Frosch/moor frog).


After being recorded, the amphibians are released to their breeding ground. - <em>by SL Wong</em>

After being recorded, the amphibians are released to their breeding ground.


In heat: the male moor frog (left) turns blue during the mating season, while the male <em>Bufo bufo </em>(<em>Erdkröte</em>/common toad) enthusiastically mount females, grasping them under their armpits. - <em>Scharon-NABU</em>

In heat: the male Moorfrosch (moor frog) (left) turns blue during the mating season, while the male Bufo bufo (Erdkröte/common toad) enthusiastically mount females, grasping them under their armpits.


Maring season is quite a sight, with ponds filled with amphibians, such as these <em>Moorfrösche</em> (moor frogs). - <em>Scharon-NABU</em>

Maring season is quite a sight, with ponds filled with amphibians, such as these Moorfrösche (moor frogs).


<em>Clockwise from left</em>: The ultimate solution to roadkill is the animal bypass or tunnel, which runs underneath roads. A split level directs amphibians and other creatures to the tunnel. Likewise with grating that also enables humans to enjoy the protected area. - <em>by SL Wong</em>

Clockwise from left: The ultimate solution to roadkill is the animal bypass or tunnel, which runs underneath roads. A split level directs amphibians and other creatures to the tunnel. Likewise with grating that also enables humans to enjoy the protected area.


This article was first published in the Malaysian daily, ‘The Star’, on 15 June 2010 under the title ‘Safety Fence’. Words by SL Wong. Photos by SL Wong and courtesy of Jens Scharon-NABU.

Experienced: 30.04.2010 || Recounted: 24.03.2015 Click here for bigger map
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