Naturally a matter of life and death

ACCORDING to the Woodland Trust, autumn lasted two weeks longer than usual this year and there were lots of berries. This augurs well for wild creatures facing the trials and tribulations of winter.

So will more of them make it through to spring? The swallows and martins departed en masse as usual. So did the warblers, apart from a few chiffchaffs. Our Irish blackcaps left, only to be replaced by German ones which come here for the winter.

Wheatears from Iceland Greenland and Canada have just passed through on their way to Africa. Migrants seldom had it so good; conditions were mild and there was plenty of food.

Most of our songbirds are ‘partial migrants’; some go, some stay. It’s a gamble either way. Travelling is dangerous; a bird can get lost, collapse exhausted into the sea, die of thirst in the arid wastes of the Sahara or fall victim to a predator.

Remaining here, on the other hand, also has its risks. A winter resident avoids the dangers of migration but getting enough food, when the ground is hard or frozen, is a challenge.

Berries and seeds become progressively more difficult to find and, as the days shorten, there’s less time to forage. Fattening up during a bountiful autumn isn’t an option; a bird must remain light and agile to avoid sparrowhawks and cats. Moving to towns and cities helps; bird tables are a lifeline. In severe winters resident bird population collapse.

Crows and tits store food in secret larders. A jay will bury thousands of acorns in the ground, each one at a separate location. When times are hard, it locates and digs them up, even from under the snow, an extraordinary feat of memory. The mild autumn, this time around, will have benefited hoarders.

Land mammals, apart from bats, can’t fly, so migration isn’t an option. Some hibernate, most remain active. For our largest hibernator, the hedgehog, autumn is a nail-biting time. Food demand soars as layers of brown fat, heating fuel for the long winter months, are being laid down. When temperatures fall below 16°C the big sleep begins in a sheltered nest of leaves and grass. Body temperature drops from 34°C to as little as 4°C. The heartbeat slows from 190 to 20 beats per minute. If the sleeper weighs less than 450 grams when retiring, it will probably die of hypothermia. Youngsters born late in the season are especially vulnerable.

In a normal year, hibernation begins in October but, this year, hedgehogs could stay up until late November. This time around, hibernation would seem to be the perfect survival strategy. Though they spend much of the winter sleeping, badgers don’t hibernate. They check on the weather each night to see if it’s mild enough to forage for worms. If not, it’s back to bed; more energy would be squandered venturing out than could be obtained by hunting.

Squirrels, contrary to popular belief, don’t hibernate. Instead, they hide seeds and nuts in caches to see them through the bad times. Mice avail of our unofficial rodent welfare system; they move in with us.

But there are no free lunches for wild creatures. A mild autumn and winter means more mouths to feed in early spring. By then, however, nuts seeds and the larvae of creepy crawlies will be thin on the ground. ‘April is the cruellest month’ said TS Eliot. For an animal population to remain stable, the death rate must equal the birth rate. Hedgehogs can breed when a year old, producing four or five youngsters per brood. Females may have a second brood in late summer. Mortality, therefore, has to be high; otherwise the countryside would be overrun with hedgehogs. If hypothermia during hibernation doesn’t kill them, starvation during the lean months of early spring will. For the mouse sheltering in your home this winter, the figures are even more startling.

A female can produce up to 10 litters of five to seven babies annually. The same number must die. ‘In the midst of life we are in death’.