Monday, January 18, 2010
"THERE’S no bad publicity, except an obituary," declared Brendan Behan.
During the recent cold spell many birds, thanks to timely media exposure, avoided the obituary columns.
Appeals to the public to feed them paid off; there wasn’t a bag of bird-seed left in the shops. Furry mammals, however, had a much lower profile.
There were no disaster-relief programmes for them, so how have they fared?
Cold-blooded creatures can’t really hunt at night; the energy demands are so great that hypothermia soon sets in. About 200 million years ago, a reptile took a fateful step; it began to generate its own body heat.
Its forebears had relied on the sun for warmth but the descendants of this innovator would generate heat within their bodies by burning food and fat. Soon little mouse-like creatures, with newly evolved internal battery packs, were staying up as late as they liked and a whole range of possibilities opened up for them. There was a price to be paid, off course; central heating is expensive.
Much more food is required to keep a warm-blooded creature in the luxury to which it’s accustomed than is needed by a cool reptilian one. A large crocodile may go without food for a year, whereas a lion needs to eat every few days.
The freeze-up of the last few weeks made huge demands on wildlife.
Fat-strapped birds and mammals were in trouble. Birds, however, have a trick up their sleeves; when the going gets tough they can pack their bags and leave. Ireland was the destination of choice for millions of Scandinavian thrushes and bullfinches this winter.
Fat Nordic blackbirds could be seen rummaging in our gardens. Fleeing is not an option for land-bound mammals but they too know a trick or two.
One option is hibernation, a deep sleep in which most of a creature’s organs shut down, reducing energy demand to the minimum.
A hedgehog’s body temperature will drop from 31C to about 10C.
The heart slows to 20 beats per minute and anti-coagulants, released into the bloodstream, prevent clotting. Hibernation is particularly important for bats; they have huge areas of exposed skin, from which heat is lost in cold weather.
But shutting down body systems is not an option for creatures much bigger than a hedgehog. Big bodies need so much heat that getting a large animal back on its feet in the spring is just too daunting.
Some big animals would love to hibernate; female polar bears take to their dens in the autumn and sleep through the winter, giving birth while doing so.
This, however, is not true hibernation; body temperature drops a mere 10C producing a state known as "dormancy".
Hibernation has its drawbacks.
A sleeping animal is at the mercy of predators and snug secure hideouts are not that easy to find. In confined spaces, the build-up of carbon dioxide can lead to problems and, if the winter is particularly severe, hibernators may not have the fat reserves to see them through.
Most Irish mammal species prefer to stay up for the winter.
Squirrels, contrary to popular belief, don’t hibernate. Nor do badgers. Checking on the weather each evening, a badger will decide whether it’s worth venturing out or remaining in bed. It’s a demanding time; badgers lose about half of their body weight in winter.
Stoats and rats lose heat rapidly but severe weather brings a bonus. Weak starving birds are easy for stoats to catch and the carcasses of cold victims provide rich pickings for rats.
How hares and rabbits fare is difficult to gauge. Snow may block access to food but the fastest Irish mammal is not called the "mountain hare" for nothing; evolution has equipped it to cope with cold winters.
Rabbits, on the other hand, are of Mediterranean ancestry. Brought to northern latitudes by the Romans and Normans, they don’t really belong in cold climates.
When the going gets tough, burrows provide shelter but getting access to food may be a problem when it snows. But the greatest winter virtuoso performer of all must surely be the pigmy shrew.
This tiny creature will die if deprived of food for more than a few hours yet it manages, somehow, to survive.
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