Richard Collins: Why nature’s routines and schedules are being disrupted at an alarming rate

Song thrush: A bird’s body clock tracks the light, eventually triggering the release of sex
hormones, and the return of singing.

My local song-thrush has lost the run of himself; he started singing during the second week of January. Normally, it’s the mistle-thrush who proclaims the approach of spring and he does so well in advance of his smaller cousin. The large ‘storm-cock’ may hold forth even in the teeth of a late winter’s gale. He usually begins nesting a month earlier than his more melodious relative, making the latter’s early singing all the more odd.

Why is this avian insanity happening? Is climate change responsible? Not directly, it might seem, on the face of it. A songbird’s reproductive organs shrink after the breeding season, rendering it virtually sexless. Daylight length begins to increase from December 21. A bird’s body clock tracks the light, eventually triggering the release of sex hormones. Singing is the overture to mating and nesting; ‘happy days are here again’. Global warming can’t alter the sun’s schedule, but it ‘acts in mysterious ways, its wonders to perform’.

The world isn’t a fixed unchanging entity, as Enlightenment philosophers thought. It’s a work in progress as Hegel claimed. That was not a new idea; ‘you can’t step into the same river twice’ declared Heraclitus, who died in 475BC. It wouldn’t be the same river the second time around, nor would it be the same person doing the stepping . Plants and animals, like Heraclitus’ river, are in a perpetual state of flux. They must adapt to change or die. Global warming may seem to be a slow process but, for wild creature such as thrushes, it’s racing ahead. ‘Gather ye rosebuds while ye may, old Time is still a-flying’.

Richard Collins: 'The world isn’t a fixed unchanging entity, as Enlightenment philosophers thought. It’s a work in progress as Hegel claimed.'

Nature’s routines and schedules, honed over eons by natural selection, are being disrupted at an alarming rate. Swallows, reluctant to cross the Sahara, opt increasingly to remain in southern Europe. Siberian Bewick swans no longer ‘ winter’ in Ireland; they ‘short-stop’ in mainland Europe. Fish from southern climes are visiting our waters. Eels can no longer navigate the changing currents to reach their Sargasso Sea breeding grounds.

But climate change isn’t responsible for all wildlife ills; other human impacts are also implicated. Salmon, for example, have become smaller. Ocean warming, altering fish migration patterns, may be a factor, but overfishing and pollution also take their tolls. Evolution, in the popular mind, seems to proceed at a snail’s pace, too slowly to be perceived in everyday life, but it can move very quickly indeed.

A team, led by Sarah Sanderson of McGill University, has been documenting changes in wildlife populations occurring over the last half-century. Her database now contains details of almost 7,000 adaptations resulting from climate change and human environmental impacts.

The most damaging effects, her team found, occur in populations subject to multiple threats. In a paper published last month, she and colleagues say that ‘harvesting by humans‘ causes ‘higher rates of change than other types of disturbance’. Also, a species introduced to a new location tends to undergo more rapid change than non- introduced ones.

Cope’s Rule states that animal body-size tends to increase steadily. Sanderson’s results, however, showed ‘no average increases through time’.

• Sarah Sanderson et al. The Pace of modern Life, revisited. Molecular Ecology 2021.