He was the head of the Skansen's natural history department between 1953 and 1974.
Between 1974 and 1983 he was a visiting professor at the University of California, Berkeley, and in 1974 and 1978 at the University of Guelph, Ontario.
From 1974 until his death he was an advisor to UN agencies UNESCO, FAO, UNEP, and about 35 African governments from his base in Nairobi. During most of that time he was also linked to the Swedish Environmental Secretariat.
- Animals and humans in the Swedish countryside, 1955, Stockholm
- Some animal species distribution - Animal Geography, 1957, Stockholm
- Forests and animals, 1961, Stockholm
- Europe's natural, 1971, Stockholm
- Conservation for Survival: An Ecological Strategy, New York, 1972
- Lemming - a artmonografi, 1975, Bonnier, Stockholm, ISBN 91-0-039966-3
- The endangered animals worldwide, 1982, Stockholm
- The Future Of The Cairngorms, 1982, North East Mountains Trust with Adam Watson & R Drennan-Watson
- Our fish, 1985, Stockholm
- Mammals, amphibians & reptiles, 1988, Stockholm
- Tropical mountains, 1953, Stockholm
- The birds of Mount Nimba, Liberia ISBN 0-565-00982-6 British Museum (Natural History) 1986 with Colston, Peter R