A NATURALIST of the old school, before the era of specialisation, which tended to militate against the use of the term, Richard Fitter set out, above all, to render his adventures into nature intelligible to a lay audience. This he did with a series of field guides, starting with birds, but branching out into a series of floras, which made life easier for the amateur by dispensing with scientific classification and arranging their subjects by size and habitat, and, in the case of flowers, by colour.

Though this procedure might raise eyebrows in the ranks of professionals, it worked for the average untutored nature lover, and its popularity soon began to translate into sales. The Collins Pocket Guide to British Birds, illustrated by R. A. Richardson, which appeared in 1952, was one of the first of the modern field guides, of the type which have now become an indispensable tool, and it sold more than 100,000 copies. To a generation of young birdwatchers it was known simply as “Fitter and Richardson” — and one did not leave home for a ramble in the countryside without it.

Richard Sidney Richmond Fitter (he always wrote as R. S. R. Fitter) was born in 1913 in South London, an environment in which his sharp eyes and natural curiosity gave him a love and knowledge of the birds of the area. He was educated at Eastbourne College, from where he went to London School of Economics, where he obtained an economics degree.

Deciding on a career as a social scientist, in 1936 he joined the research staff of the Institute of Political and Economic Planning. There he worked for the next four years, refining the skills in obtaining clarity from masses of heterogeneous information that were to stand him in good stead as a compiler of works of natural history. In 1940 he moved to Mass-Observation, which was engaged in an analysis of “ordinary” life in Britain. In 1942 he joined the Operational Research Section of Coastal Command, where he spent the remainder of the war.

After the war he became secretary of the wildlife conservation special committee of the Hobhouse Committee on National Parks. In 1946 he joined The Countryman as an assitant editor, remaining there for 13 years until 1959. In 1958 he had become the charmingly styled “open air correspondent” of The Observer, a post he held until 1966.

He had opened his account as an author with London’s Natural History, which appeared in December 1945. Beginning with the geology and prehistory of the area, it continued with the growth of London in historic times, tracing the growth (and decline) of wildlife as it interacted with humanity over the centuries. Bedbugs, he noted, first coming to prominence in 1583 at Mortlake, had caused “alarm among ladies of high degree”.

Fitter’s work as the bird recorder of the London Natural History Society next led to London’s Birds (1949), which first exemplified the habitat-based principle as a means of getting into its subject. Highly readable, it was much admired as a serious ornithological study. British Birds in Colour (1951), which Fitter edited, was followed by “Fitter and Richardson”, which established him as one of the foremost ornithological authorities of his day.

Then, in 1956, he teamed up with David McClintock to produce a flora for Collins, The Pocket Guide to Wild Flowers. This was greatly admired by reviewers for its arrangement of all the species illustrated according to colour, a method which, while unscientific, provided a way into the subject for the layman which made it of much greater popular educational value than scientific classification might have done.

The environment was now becoming a central concern for Fitter. In 1959 he was appointed director of the intelligence unit of the Council of Nature, and his voice became increasingly heard, urging the public to be more aware of the need to protect the natural heritage, at a time before “conservation” had become a hot issue.

He continued prolific as an author, both on his own account and in harness with others. The Ark in our Midst (1959) discussed the mammals, birds, reptiles and amphibians of the British Isles, with reference to which of the successive waves of invaders might have introduced those species which are not native. His Guide to Birdwatching (Collins, 1963) examined the hows, whats and wheres of setting about discovering new species. There was a Penguin Dictionary of Natural History (1967) with his wife Maisie Fitter; The Penitent Butchers: The Fauna Preservation Society 1903-1978 (1979), with Sir Peter Scott; and a number of books in collaboration with one of his sons, A. Fitter, (Professor Alistair Fitter, of York University; his other son, Julian, is also a naturalist).

Fitter travelled widely. He was a vice-chairman of Falklands Conservation, 1986-94, and of the Galapagos Conservation Trust from 1995. Among his honours were the Peter Scott Medal of the British Naturalists Association and appointment as an officer of the Order of the Golden Ark of the Netherlands.

His wife, Maisie, whom he married in 1938, died in 1996. He is survived by a daughter and two sons.

Richard Fitter, naturalist and author, was born on March 1, 1913. He died on September 3, 2005, aged 92.