Born in East Barnet, London and after leaving school joined a firm of shipping agents. He did National Service with the Royal Armoured CVorps in the early 1950s and his career really took off when he was employed by British Petroleum, becoming their senior ecologist, especially mapping the ecology of the proposed Trans-Alaska Pipeline from Valdez to Prudhoe Bay in 1969.

His early enthusiasm for natural history was stimulated as a boy by the local countryside and he joined the London Natural History Society and later became active in a field group of the British Naturalists Association. His particular interest at this time was birds and after he joined the Hertfordshire Natural History Society in the late 1950s he published The History of the Birds of Hertfordshire when only 29 years old. Later birds would lead him to undertake an expedition with the Royal Navy to document them in Labrador, and to the Shetlands to mitigate potential problems with the Sullon Voe oil terminal. Later he published general wildlife books including Alaska and Its Wildlife (1973) and as co-author with Eric Hosking Antarctic Wild Life (1982) and with Hugh Danks The Arctic and its Wildlife (1986).

Sage's enthusiasm for beetles had already developed when he was in his 20s becoming the Hertfordshire beetle recorder (and also for Birds and Dragonflies) and James (2018) registers a debt to him for supplying a special contribution. In the year following this publication James also wrote Sage's obituary in Col., 28(3), 2019, 114-15, from which much of the above is taken.

Sage's real enthusiasm for beetles developed after his move to Norfolk in 1978. Martin Collier, writing a follow-up to James obituary in the same journal, recorded 'Bryan was, by some margin, the most regular and longest-standing provider of Norfolk beetle records, making huge contributions to the county list. Over a period of more than thirty years (1986-2018), he sent me a total of 171 neatly typed lists of records for approximately 1,275 species. These lists included many first county records and nationally rare species, some of which have never been found here subsequently...Bryan was also recording here long before he moved here in 1978. For example, back in 1956 when Bryan was just 26, he stayed on Scolt Head Island for three days and kept records of the spiders and beetles he found [published in Ent.,1957]. Although Bryan recorded throughout the county he favoured three sites in particular Swanton Novers Woods NNR, Holkham NNR, and the Stanford Training Area [detailed lists in Transactions of the Norfolk and Norwich Naturalists Society.]

James records that Sage's collections, 'became quite extensive, boosted by acquisitions of material from Dr Ian White, mainly a dipterist, working at the Natural History Museum in London. His beetle collection and notes have gone to the Norwich Castle Museum.'

He was at one time President of the Herts, Nat. Hist. Soc. and founder of the Herts Bird Club. There are photographs in James (1918) and on the  Hertfordshire Natural History Society's website. James (191) mentions that he had compiled a bibliography of Sage's publications available as a pdf. here is another obituary in the Eastern Daily Press 12 December 2018. (MD 1/22)