Denis Summers-Smith, who has died aged 99, belonged to the pioneering pre-second world war generation of birdwatchers whose contributions to our understanding of bird behaviour helped transform the science of ornithology.
In particular Summers-Smith wrote about, and made a lifelong study of, the house sparrow, a bird he chose partly because it was so abundant. Yet towards the end of the 20th century house sparrow numbers suddenly began to plummet, in urban and rural settings alike. Several theories were proposed to explain the decline, and in 2000 the Independent newspaper offered a prize of £5,000 for the first peer-reviewed scientific paper to find a solution, with Summers-Smith acting as referee.
Eight years later, the prize was finally awarded to scientists at De Montfort University, Leicester, who ascribed the decline to a fall in numbers of insects, on which sparrows feed their chicks during their first few days of life. The reason this affected sparrows more than other songbird species was connected with their sedentary nature – rarely travelling more than a mile from their birthplace in their brief lives.
In his first book, a Collins New Naturalist monograph entitled The House Sparrow (1963), Summers-Smith had confidently predicted that the species would enjoy a bright future. After all, no other bird had adapted quite so well to living alongside humanity, having spread – with our help – to six of the world’s seven continents. Despite experiencing an unprecedented fall in its numbers, in the final years of his life the species at last showed signs of recovery.
Born in Glasgow, Denis was the son of Thomas, a lawyer, who died when he was just three years old, and his wife, Eleanor (nee Robinson). She brought Denis and his older brother, Robert, up in a strict Presbyterian household. On childhood holidays in County Donegal in Ireland, his uncle – a country parson and naturalist – ignited Denis’s passion for birds.
Educated at Glasgow Academy, Summers-Smith earned a scholarship to Glasgow University, where in 1937 he began studying metallurgy. In 1939, at the outbreak of the second world war, his university course came to an abrupt halt when he enlisted as an intelligence officer in the army.
Commissioned in 1940, he rose to the rank of captain, serving with the ninth battalion of the Cameronians regiment on the east coast of England. Despite his duties, he managed to find occasional moments for birdwatching – notably when surveying likely spots for a German invasion on the Suffolk coast.
In June 1944 he was involved in the second wave of the D-day landings in Normandy, for which, 75 years later in 2019, he was appointed Chevalier de la Légion d’Honneur. While serving in France he was badly injured, spending 18 months in hospital; once discharged, he married his fiancee, Margaret (nee Mau) in 1947.
Following the end of hostilities, Summers-Smith began work at Imperial Chemical Industries (ICI) as a mechanical engineer. Like many people whose education had been interrupted by the war, he resumed his studies, gaining degrees in engineering and, in 1953, a PhD in physics. He specialised in tribology: the study of friction, wear and lubrication.
However, his passion for birdwatching remained, and in 1948 he had decided to make an intensive study of a single species of bird. With petrol rationing still in force he was unable to travel far, so the house sparrow’s abundance and proximity to people was ideal. Having risen early to study the birds before he started work, he was twice reported to the police by neighbours, who wondered why a suspicious character was peering through binoculars into their gardens.
After his son, Mike, was born in 1949, the family moved from Hampshire to County Durham; then, in 1961, to Guisborough in North Yorkshire, where he remained for the rest of his life. Two years later he published his first book, and during the next few decades he took advantage of the opportunities for global travel afforded by his job to study the entire sparrow family. His studies were published in several books: The Sparrows (1988), The Tree Sparrow (1995) and a memoir, In Search of Sparrows, published in 1992.
His writings revealed a fascination not just with the behaviour of the house sparrow, but with its social and cultural history too. Biblical references were cited, there was a fascinating account of the “sparrow clubs” of early 20th century Britain, which organised culls of a bird considered an agricultural pest, and, more recently, details of an incident in the Netherlands in which a rogue sparrow ruined a world record attempt at the “domino effect” by inadvertently collapsing thousands of dominoes. His book On Sparrows and Man: A Love-Hate Relationship was published in 2006.
He also penned numerous scientific papers, and served on the committees of organisations such as the British Ornithologists’ Union and the British Trust for Ornithology. His honours included the Stamford Raffles award, given for distinguished contributions to zoology, which he received from the Zoological Society of London in 1992.
In his public and private life he was, like the subject of his studies, a friendly, unassuming and humble man, always willing to share his knowledge with others.
After Margaret’s sudden death in 1972 he married another Margaret (nee Rebbeck), who died in 2004. He is survived by Mike.
• James Denis Summers-Smith, ornithologist and mechanical engineer, born 25 October 1920; died 5 May 2020
