02-14-2008, 07:10 PM
Different strategies enable them to survive winter's rigors.
JEFFERSON CITY-Looking across the desolate surface of a winter marsh or stream, it is easy to forget that a thousand wild voices will announce the arrival of spring there in a few weeks. The vernal emergence of frogs and toads that mystified ancient people continues to thrill modern-day nature lovers. Science is discovering the secrets of their winter survival, but has yet to unravel them all.
Frogs and toads are different from many other animals that disappear during the winter. Woodchucks, chipmunks and bats truly hibernate during the winter, going into a profound sleep. These mammals produce their own body heat during hibernation. In contrast, frogs are at the mercy of surrounding temperatures. In warm conditions, they are very active, but in cold weather they have no choice but to be dormant. Their small bodies are too cold to move around or eat. In some cases, it is even too cold to breathe. When they emerge, they are fully committed to a season of activity, usually starting with breeding.
Herpetologist Jeff Briggler, the Missouri Department of Conservation's reptile and amphibian expert, says none of Missouri's more than 20 frog and toad species remain active throughout the winter.
'Frogs are programmed to get below the surface when winter approaches,' says Briggler. 'They get cues from surrounding air and soil temperature. In a lot of cases, the adults know their territories.
They have their favorite crayfish holes, their favorite muddy bottom or even their favorite cave. They start arriving at their overwintering spots a few weeks before winter arrives. The young of the year typically forage on the surface as long as they can, trying to get their growth rates up.'
Exactly where a frog spends the winter depends mostly on its species.<br />
Green frogs seek out spaces beneath rocks in small springs or seeps, where upwelling water prevents freezing. Pickerel frogs prefer to spend the winter in wet caves where available. Several thousand may migrate to suitable caverns and spend the winter together. Spring peepers, green frogs, bullfrogs and American toads also sometimes use caves to escape winter.
Northern crawfish frogs crawl down below the water table in prairie crayfish burrows to wait for spring. Eastern and plains spadefoot toads use tiny shovels on their hind feet to burrow deep into sandy soil.<br />
Illinois chorus frogs go headfirst, using their well-developed front legs to burrow beneath the sandy soil. Green tree frogs hide beneath leaves at the bases of cypress or tupelo trees when the weather in southeast Missouri gets frosty.
Bullfrogs bury themselves in mud at the bottoms of ponds, lakes or wetlands. Briggler says pond owners often ask why all their bullfrogs have disappeared.
'The first thing I ask them is if they have renovated their ponds.<br />
People notice that their pond is filling up with mud, so they dig out the pond and remove the mud layer that is needed for bullfrogs to survive through the winter.'
Where some frogs go and what they do in the winter remains a mystery.
'You would think in this day and age we would know where everything goes,' said Briggler, " but we don't. Cricket frogs and narrow-mouthed toads are so small that we haven't been able to put radio transmitters on them and track them to their winter homes. We believe they hide in little holes and crevices around wetlands, but we don't know for sure.'
Frogs have amazing adaptations for winter survival. Perhaps the most striking is producing 'cryoprotectants,' natural antifreeze agents that allow them to survive sub-freezing temperatures.
Some of these substances, such as glycerol and glucose, lower the freezing point of water inside living tissues. Wood frogs, western chorus frogs and some tree frogs have a different type of freeze protection. Their bodies use urea, a metabolic byproduct, to modify the shape of water crystals so they do not form jagged shapes that poke through cell walls and other delicate structures.
Temperature is the main trigger for frogs' and toads' reappearance from dormancy to breed. Heavy rain also stimulates many species to start breeding.
When conditions are right, the emergence of a frog or a toad species in a particular locality can be a spectacular event.
'Wood frogs are explosive breeders,' says Briggler. 'Thousands of thousands may breed at one time, after a heavy rain in late February or early March. When they are done, they disappear into woods again.'
Once the temperature is right and rains arrive, the earliest emergers can be heard calling. Illinois chorus frogs begin singing in the Bootheel as early as late January. Western chorus frogs, wood frogs and spring peepers join the choir in February in southern counties. Their relatives farther north and west may not tune up until March or early April. Crawfish frogs, leopard frogs, gray tree frogs and toads begin singing next, followed by late bloomers, including narrow-mouthed toads, green frogs and bullfrogs.
The Conservation Department tracks the number and annual appearance of some frog species. Volunteers provide the eyes and ears for this effort, spending a few minutes at each of several sites throughout the breeding season and recording their observations. To learn more about frogs and toads, visit www.mdc.mo.gov/nathis/whatanimal.htm.
JEFFERSON CITY-Looking across the desolate surface of a winter marsh or stream, it is easy to forget that a thousand wild voices will announce the arrival of spring there in a few weeks. The vernal emergence of frogs and toads that mystified ancient people continues to thrill modern-day nature lovers. Science is discovering the secrets of their winter survival, but has yet to unravel them all.
Frogs and toads are different from many other animals that disappear during the winter. Woodchucks, chipmunks and bats truly hibernate during the winter, going into a profound sleep. These mammals produce their own body heat during hibernation. In contrast, frogs are at the mercy of surrounding temperatures. In warm conditions, they are very active, but in cold weather they have no choice but to be dormant. Their small bodies are too cold to move around or eat. In some cases, it is even too cold to breathe. When they emerge, they are fully committed to a season of activity, usually starting with breeding.
Herpetologist Jeff Briggler, the Missouri Department of Conservation's reptile and amphibian expert, says none of Missouri's more than 20 frog and toad species remain active throughout the winter.
'Frogs are programmed to get below the surface when winter approaches,' says Briggler. 'They get cues from surrounding air and soil temperature. In a lot of cases, the adults know their territories.
They have their favorite crayfish holes, their favorite muddy bottom or even their favorite cave. They start arriving at their overwintering spots a few weeks before winter arrives. The young of the year typically forage on the surface as long as they can, trying to get their growth rates up.'
Exactly where a frog spends the winter depends mostly on its species.<br />
Green frogs seek out spaces beneath rocks in small springs or seeps, where upwelling water prevents freezing. Pickerel frogs prefer to spend the winter in wet caves where available. Several thousand may migrate to suitable caverns and spend the winter together. Spring peepers, green frogs, bullfrogs and American toads also sometimes use caves to escape winter.
Northern crawfish frogs crawl down below the water table in prairie crayfish burrows to wait for spring. Eastern and plains spadefoot toads use tiny shovels on their hind feet to burrow deep into sandy soil.<br />
Illinois chorus frogs go headfirst, using their well-developed front legs to burrow beneath the sandy soil. Green tree frogs hide beneath leaves at the bases of cypress or tupelo trees when the weather in southeast Missouri gets frosty.
Bullfrogs bury themselves in mud at the bottoms of ponds, lakes or wetlands. Briggler says pond owners often ask why all their bullfrogs have disappeared.
'The first thing I ask them is if they have renovated their ponds.<br />
People notice that their pond is filling up with mud, so they dig out the pond and remove the mud layer that is needed for bullfrogs to survive through the winter.'
Where some frogs go and what they do in the winter remains a mystery.
'You would think in this day and age we would know where everything goes,' said Briggler, " but we don't. Cricket frogs and narrow-mouthed toads are so small that we haven't been able to put radio transmitters on them and track them to their winter homes. We believe they hide in little holes and crevices around wetlands, but we don't know for sure.'
Frogs have amazing adaptations for winter survival. Perhaps the most striking is producing 'cryoprotectants,' natural antifreeze agents that allow them to survive sub-freezing temperatures.
Some of these substances, such as glycerol and glucose, lower the freezing point of water inside living tissues. Wood frogs, western chorus frogs and some tree frogs have a different type of freeze protection. Their bodies use urea, a metabolic byproduct, to modify the shape of water crystals so they do not form jagged shapes that poke through cell walls and other delicate structures.
Temperature is the main trigger for frogs' and toads' reappearance from dormancy to breed. Heavy rain also stimulates many species to start breeding.
When conditions are right, the emergence of a frog or a toad species in a particular locality can be a spectacular event.
'Wood frogs are explosive breeders,' says Briggler. 'Thousands of thousands may breed at one time, after a heavy rain in late February or early March. When they are done, they disappear into woods again.'
Once the temperature is right and rains arrive, the earliest emergers can be heard calling. Illinois chorus frogs begin singing in the Bootheel as early as late January. Western chorus frogs, wood frogs and spring peepers join the choir in February in southern counties. Their relatives farther north and west may not tune up until March or early April. Crawfish frogs, leopard frogs, gray tree frogs and toads begin singing next, followed by late bloomers, including narrow-mouthed toads, green frogs and bullfrogs.
The Conservation Department tracks the number and annual appearance of some frog species. Volunteers provide the eyes and ears for this effort, spending a few minutes at each of several sites throughout the breeding season and recording their observations. To learn more about frogs and toads, visit www.mdc.mo.gov/nathis/whatanimal.htm.