Wrens are among the very lightest of our birds, weighing one third of an ounce or ten grams, about the weight of two sheets of paper, too small to survive cold for long. The frost is murderous for them. In hard winters, they can be found roosting together, usually not more than ten in one place, but 61 were once found crammed into a sheltered nook. No wren spends the winter anywhere that January temperatures drop below –7 degrees Celsius and many in Europe migrate to escape the cold, either southwards—Swedish wrens have been known to fly 1,500 miles to northern Italy for a Mediterranean winter—or in the Alps down off mountains where they have summered.

British wrens are not so mobile and there can be little doubt that the birdhouse and its louvre-entrance had been a life-saver for this bird. At regular intervals, frost devastates them. Between January and March 1963 England suffered its coldest winter since 1740. There were widespread reports of high numbers of dead and dying birds. Moorhens, lapwings, mistle thrushes and song thrushes all died in numbers. Thousands of robins and blackbirds were found dead in the fields and under hedges. But no bird suffered more than the wren, whose population fell by 79 percent in that one winter. It took until 1967 for their numbers to recover.

There is no need to be sentimental about this. Whatever the winter, three-quarters of all wren chicks will die in their first year of life and almost 70 percent of the survivors die the following year, and 70 percent of those survivors the year after that. Most wrens can expect to live no more than two years. The oldest recorded was seven years and four months old.

The pattern repeats. After that harsh winter, there was a steep increase up to the mid-1970s, when a series of cold winters slashed the numbers again, with parts of the country seeing a mortality rate of more than two-thirds, only for the wrens to recover once more. The population went through a sleigh ride, crashing again in the winter of 1996, peaking in 2006, crashing in 2011, reaching an even higher peak in 2017, dipping again, before rising in Britain and Ireland in 2023 to a record 11 million wren territories (each with a male bird and potentially several mates). The wren is now the commonest bird in the British Isles. They may summon our nurturing instincts but we need have no fear for them. They combine spectacular vulnerability with spectacular resilience, and it is a successful genetic strategy. They remain small because it is less costly to maintain a small body, even if smallness makes them vulnerable to the cold. Wren genes can risk mass destruction at regular intervals on the assumption that after the crash growth will return. Averaged out over decades, wren populations are almost stable.

The motor for this multi-generational life pattern is an urgent erotic energy. The answer to death is sex. If the wrens suffer in cold winters, their full-on approach to breeding will start to refill the niches the following spring, a fierce compulsion to propagate that has driven it to world success. Like many other wrens, ours began as an American species, and the sheer vehemence of its tiny life has driven it, drop by drop, territory by territory, across the whole of Eurasia.

Look at a wren and you are not seeing a sweet little fragmentary being but the demands of life itself, the product of tens of millions of generations bundled into a tiny round cocktailed package. Its evolutionary history is scarcely believable. It flies at a little more than twelve miles per hour, and is known in Shetland as “the wee brown button… too much like a mouse to lay eggs,” but wrens have spread from the Atlantic coast of Canada to the Pacific Northwest of the United States, across the Aleutians, island by island, each one with a different subspecies, to Japan, and on to Tibet and the Himalayas, thriving in Sikkim and Kashmir, to the shores of the Caspian and Turkestan, on into Europe, up to 7,700 feet in the snows of Psiloriti in Crete, to the High Atlas in Morocco, to France, Britain, and Iceland and only stopping short of the shores of Greenland. Wrens have landed and developed into separate subspecies on St Kilda and Fair Isle. Its essence is not vulnerability but vibrancy.

The spectacular life-drive of the wren has long been recognised deep within European culture, having played a part in a pair of rituals that survived until the twentieth century. The first took place either on 26 December, St Stephen’s Day, or Twelfth Night, 6 January. Men and boys would beat the hedgerows until they caught or killed a wren. The bird would be nailed to a pole or put in a cage dressed with ribbons that were tied into holly and ivy and other winter greens. The shrine would then be taken from house to house, where the “wren boys” would sing at the door and ask for food and drink. In return the householders would be given “lucky feathers from the bird.” At the end of the day the wren, by now almost naked, would, if not already dead, be solemnly killed and buried.

In the depths of winter, a tiny radiant creature was captured, sacrificed, reverenced and buried. This was the remains of a fertility rite, a ritual to banish the deathliness of winter and, like all sacrifices, to offer up the beautiful in the hope of appeasing the brutal and destructive forces of the world. Winter sacrifice of the wren was accompanied by a spring version, when the bird was again captured and displayed in little boxes decorated with leaves and spring flowers, though this time not killed but honoured before being released back into the wild. These May festivities were sexualised, a celebration of the power of the procreative drive in people as much as in birds. And the wren was well chosen because it does indeed turn out to be the most lustful of creatures.

Shakespeare knew it so that when King Lear looked for a symbol of the sexuality that ruled the world, it was the insects and the wren he chose:

The wren goes to ’t, and the small gilded fly does lecher in my
sight.
Let copulation thrive …
To ’t, luxury, pell-mell …

Sheer procreative energy and sexual demand on the wing is what the little cocked tail and the bright habits of the wren’s darting, dancing body, popping in and out of the shadows, now say to me. It is a ten-gram bundle of desire.

Eurasian wren (Troglodytes troglodytes) in Franconville, France, 2021.

Photo: Alexis Lours

With the last of the frosts, growing light levels make deep physiological changes in them, as in all birds. In the females, as the days lengthen and brighten, the egg-laying mechanism grows and thickens. In the males, the testicles start to grow by a factor of a hundred or more. A winter testicle that might occupy less than a cubic millimetre—a mustard seed—could be almost one hundred cubic millimetres—the size of a pea—by mid-April, having increased in size by four or five cubic millimetres a day until it occupies three percent of the wren’s body, pumping it full of aggressive male hormones.

Wrens now begin their preparations for breeding. They re-establish the boundaries of their territories by singing their hard, metallic territorial songs at any of up to seven neighbouring rivals. When not singing, the males start to build what are called cock nests, often made only of sticks roughly laid together, or in this wood of moss torn from the boles of fallen trees.

These nests are signals of their own excellence made to the females, who have much larger and overlapping territories and who in early spring roam the woods and rough grounds looking for suitable mates. Nests are expensive to make. Each one can take between half a day and five days to build. By the time it is finished, the cock nest weighs on average four times as much as the bird that created it.

This expense is part of the point. A high-quality cock is one that builds strings of nests (the most that have ever been found is twelve on one wren’s territory) and female wrens judge a male by how many candidate nests he has made. The more a wren has built, the more likely it is that a female will mate with him. He controls an acre or even two—a lot of land for a small bird. Other, bigger songbirds tend to hold less ground: a reed warbler only 500 square yards, a willow warbler about a third of an acre, a blackcap or a garden warbler a little more. It seems that a wren in particular depends for his well-being on making something of a show in the world, part of the widespread phenomenon in nature of the displayed handicap: if a male peacock can cope with such a tail, or a wren waste so much energy on unused nests, he is a mate worth having.

He sings and displays high in his territory, with his tail erect. Scientists have found a correlation between the length of that tail and high breeding success. Huge testicles, a long upright tail standing high above him, and an extensive, nest-filled territory with plenty of cover in which to hide: these are the foundations of wren triumph.

Once he has filled his spreading acres with potential homes, he finds a female prospecting and takes her on a tour, showing her nest after nest with a sweet cooing, quite unlike the machine-gun rattle he fires off at his male rivals. He sings outside or on top of each one and then inside to demonstrate its qualities. He is advertising to her the genetic likelihood that her offspring will also be top birds, capable of controlling and furnishing a territory as splendidly as he has. She is choosy. Female wrens have been seen flying from one territory to another, taking the tour and moving on to see if they could improve their chances. Her investment, after all, is in the even more energy-expensive process of creating, laying and incubating eggs.

Wren coupling is less like a marriage than a merger. Both birds are more interested in profitable outcomes than the lovability of their partner. The fact that he has persuaded her to fit out and lay in one of his nests does not stop him courting other females or showing them the other nests he has made, nor mating with them and fathering several further broods that summer, each with a different hen. Individual cock wrens can have up to nine wives in one year. She too, having raised her chicks in May or June, will not hesitate to find another cock in another territory (almost never the same wren again) to lay and raise a second, third or fourth brood before the summer comes to an end. Polygyny rules, the male wrens holding their accommodating territories, the females cruising between them, the genetic material proliferating through the woods.

In this way, even though a variety of predators take a fifth of all nests, if not more, removing both eggs and nestlings, the population pump restores the damage the winters have wrought.

It is as if the wrens are the matadors of the songbird world. Each time they add a stick or a piece of moss to their cock nests, the wren will sing snatches of song at steady intervals beside it. Here I am! This is me! Look at Nest Seven! It is one way in which birders can locate the otherwise well hidden and disguised structures the birds have made.

It is a paradox. Make every effort you can to conceal the precious nest and then shout about its location to all enemies and predators. The ornithologists Matthew Evans and Joe Burn have speculated that this is a flamboyant gesture by the male wrens. If they are doing something that carries with it a high possibility of harm, they are demonstrating to any passing hen a quality that might be called courage, or at least bravado. Who but a top wren would dare in the omnipresent face of the enemy to sing about his nests so clearly? In the shrubland of Hollow Flemings, the kind of territory a wren likes to inhabit, with plenty of bramble and bracken, I was surrounded by unseen nests. Its acre or two would have been the size of a city block for a wren, full of hidden alleyways and rewarding corners, its geography and resources intimately known by the bird who would have spent nearly all its life there, familiar with the routes through, the resting places, the convenient bypasses. Only the occasional sight of a wren hop-skipping in the shadows between the leaves and the insistent territorial song gave their pervasive presence away. ♦

Excerpted from BIRD SCHOOL: A Beginner in the Wood by Adam Nicolson. Published by Farrar, Straus and Giroux. Copyright © 2025 by Adam Nicolson. All rights reserved.