One list of the world's worst invasive species includes foxes, rabbits, mice and pigeons.

After spotting a red squirrel crossing a road at a traffic light, Woolfson begins to ponder the odd and often tortuous logic by which so-called native species are regarded as inherently superior to 'invaders'. Little in the world of conservation is simple, and this is particularly true of the vexed subject of invasion biology. Rats, meanwhile, have been proved to refuse to take food if by doing so they cause pain to other rats, a sign suggestive that they, like us, experience empathy. Some slugs, she reports gleefully, mate by way of what is known even in scientific papers as a 'love dart', a small blade of chitin or cartilage that may have provided the Greeks with the inspiration for Eros's arrow. There's nothing mystical about her enthusiasm for spiders, worms, shrews and foxes, but rather a kind of bustling curiosity about their strange and purposeful lives. Though her hidden city extends back through time, it's the living inhabitants that capture the larger part of Woolfson's attention and enthusiasm. 'More than part of the city unseen, it seemed like the city's secret a strange irony considering that it's where most of the city came from.' Abandoned in 1970, it filled with water to form a vast lake. Behind a chain-link fence, she discovers the largest quarry in Europe, out of which much of the granite for Aberdeen's houses derived. Woolfson borrows a key to investigate an otherwise inaccessible strip of wilderness between two rows of houses, where a Victorian botanist once led his students on summer expeditions. The Aberdeen she unearths is a beguiling city. Is this androgenic climate change, Woolfson wonders, and her growing anxiety infuses the book with a kind of hyper-attentive urgency, a desire to record exactly 'the lives and time and place' among which she finds herself. It's too wet the winter's untimely and summer barely lasts a week.

Over the course of a year, her sense that something has gone awry intensifies. The weather is off-kilter, and the bird 'seemed to symbolise the fragility that suddenly I felt was there, at the heart of everything'. Finding a wounded pigeon flailing in the lane, she takes it home to nurse. Her diary begins on a day of uncommon snowfall, the harbinger of a period in which the entire city shivers to a standstill. In Field Notes, Woolfson turns her beady eye to the muddled and fascinating ecology of her hometown of Aberdeen. An ideal candidate, then, for a larger take on urban wildness, and why it's so important for our wellbeing, not to mention our continued survival. She possessed a naturalist's loving attention to detail, combined with a likable fondness for demolishing superstitions. Back in 2008, Esther Woolfson published Corvus, a delightful ode to the maligned crow family, many of which she'd adopted over the years. An example would be the magpie, that egg-stealing bandit of urban mythology.

Corvus by Esther Woolfson