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Big toads travel long distances for several kilometers in order to reproduce, how many such stubborn migrants are there?

Time:2022-10-04 06:59:59 source:ucutxmastrees.com author:Botanical Garden Read:251次
Big toads travel long distances for several kilometers in order to reproduce, how many such stubborn migrants are there?

Large toads are widely distributed in Europe and West Asia. They are one of the few amphibians that can migrate long distances. Unlike reptiles, amphibians must keep their skin moist to survive. Therefore, most amphibians do not have the ability to migrate long distances. They have a small range of activities and must rely on water to survive. Among amphibians, giant toads are an exception, they can migrate more than 5 kilometers one way, a journey that most amphibians cannot make.

Perfect for terrestrial habitats

The preferred habitats of the giant toad include grasslands, bushes, woodlands and flowerbeds, where they can spend the day in damp corners under stones or logs. Compared to other amphibians, giant toads are well adapted to life on land: their hind limbs are semi-webbed, their forelimbs are unwebbed, and their powerful legs are ideal for burrowing and preying on spiders, earthworms, and slugs. They are voracious predators and can devour any animal they can swallow whole. But they don't feed in the water, and the aquatic phase of their life cycle is very short and has only one purpose, reproduction. While adult giant toads spend most of their time on land, the permeable skin they use to breathe needs to be moist, and their eggs and tadpoles need to develop in freshwater environments. This paradoxical way of living is only possible when the cool nights are active and they migrate to wetlands to breed—two key factors in the behavior of frogs and toads around the world.

Segmented migration

The big toad is driven by blind instinct to crawl towards the spawning pond during the mild and humid nights of early spring. Most of them crawl to the same pond within days, moving in large groups like nocturnal armies. The pond quickly fills with toads in heat, and they compete with each other for a mate. After a certain evening in February-April, depending on latitude and weather, swarms of toads migrate to their breeding grounds at a ludicrously broad pace, a journey that began months earlier. the final stage. They spread around feeding grounds in summer and begin their migration to spawning grounds in August or September. This is a sequential migratory movement, with a length of hundreds of meters or even one to two kilometers. The first cold snap of fall heralds the end of the giant toad migration, prompting them to hibernate in abandoned rodent burrows or leaf litter piles. The toad's migratory journey is restarted by gradually warmer temperatures and a certain amount of rainfall. Scientists speculate that later in hibernation, the toad's circadian clock becomes sensitive to changes in surrounding soil temperature. The toads will rejuvenate as the ground temperature rises, but it will not start again until the air temperature reaches 5 to 6 degrees Celsius in the evening for several consecutive days, and it is a rainy night. During mild winters, the migration starts very early; instead, the migration may be pushed back by prolonged cold weather.

Solid Migrants

Driven by the urge to breed, the giant toads are exceptionally determined to reach a breeding pond or stream, traverse obstacles such as roads and railways, and climb over walls. A study in Germany showed that the average migration distance of the giant beetle is 50 meters per night, almost always in a straight line. Although we already know they have very good night vision and potentially breed ponds through their sense of smell, their navigation systems remain a mystery to us. Tag-recapture studies of giant toads, including a long-term study at Landrindo Lake in Chengdu, have shown that many giant toads return to the same spawning grounds that they used, but not all of them. Some large toads switched to other ponds, perhaps because they encountered new breeding grounds during their migration, or because the original breeding grounds were in poorer condition. But no matter what the situation, big toads can occupy new breeding grounds, thus ensuring the continuation of the population.

Courtesy Feast

For several days after the toads arrive at the pond, the night sky is filled with the male toad's abdominal courtship "quack". There are scenes of excited male toads fighting frantically to get a mate, clinging to the female toad in a hug. By the end of the breeding season in late April, the toads were no longer in the pond, leaving only sticky, gelatinous toad eggs attached to aquatic plants. After spawning, the toads return to the feeding grounds to replenish the depleted energy. Instead of following the migratory route back as they do to the breeding grounds, they choose a more direct route, but seem to be less determined. In the Austrian Alps, scientists used radio tracking technology to study the migration process of toads after reproduction, and found that some toads would climb 65-degree sloping cliffs to find the best summer feeding area, and a few individuals would climb to a height of 400 meters , which is the maximum known vertical migration height for amphibians. Meanwhile, in breeding ponds, tadpoles develop hind legs after 2 to 3 months. These little toads will climb onto land and spread into the surrounding vegetation. Male toads mature after two years, while females take longer, after which they begin their migratory journey just like their parents.

Death Road

Some of the giant toads never complete their migration because they are killed prematurely on busy roads. Under the dazzling headlights, the sluggish animals were dizzy and unable to escape the speeding cars in time, squashing hundreds of giant toads. To make matters worse, the toads often traverse several roads to reach the breeding pond in the early spring evenings, a time of heavy traffic. Since large toads can be found all over Europe, there are many dead toads in various European countries. About 20 tonnes of giant toads die on UK roads alone each year. In some places, excessive mortality may even cause the extinction of small local breeding populations. Human activities have severely affected the migration of this amphibian. , causing their survival to be threatened. In order to reduce the number of deaths of these toads during migration, some volunteers in many European countries will organize patrols to help these toads cross the road during the peak migration period, and erect temporary warning signs to remind passing drivers to slow down stroll. These measures are not required when large toads return from breeding grounds to feeding grounds, as their return journeys are usually carried out in small flocks late at night, when the roads are much quieter and there are generally no large numbers of toads being run over by cars death situation.

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