Obituary: Rudolf (Rudi) Herman Drent (1937–2008)

Rudi Drent was born on 24 April 1937 in Los Angeles (USA) to a Dutch father and a German mother. His father was a sea captain (from Groningen) who moved his family to Los Angeles because its location allowed him more time at home. After his father’s retirement, the family moved to Vancouver, where Rudi studied at the University of British Columbia from 1954 to 1961. Although he was more interested in biology, his original intention was to specialize in forestry because it offered better job prospects. However, his university teachers convinced him that there was a living to be made in biology too. Lars von Haartman, who visited Vancouver from 1958 to 1959, probably played a critical role in his decision to become an ornithologist. Rudi’s masters’ project was on Pigeon Guillemots Cepphus columba breeding on Mandarte Island, where he built himself a hut to live in. He was on Mandarte during the 1959 and 1960 breeding seasons, and his studies resulted in a publication in Ardea (Drent 1965). This scientific journal of the Dutch Ornithologists’ Union was by then a natural outlet for his work, since he moved to the University of Groningen (the Netherlands) in 1961 to commence his PhD studies on incubation in Herring Gulls Larus argentatus under the supervision of Gerard P. Baerends. More huts were built, now to observe birds from. He never stopped building huts, carrying a hammer and a bag of nails in his rucksack on expeditions to make the best use of some driftwood or whatever was available. He defended his PhD thesis Functional aspects of incubation in the herring gull in 1967. It was published in 1970 as part of a Behaviour supplement that he edited together with Gerard Baerends: The herring gull and its egg. Incubation remained an interest in years to come, culminating among other things in an influential review (Drent 1975) in the book series ‘Avian Biology’. In the course of his work on incubation, Rudi became interested in physiology, in particular the role of energy in birds’ lives. Together with Serge Daan he laid the foundation for a tradition of work on avian energetics in an ecological and life-history context that is still actively pursued today. His interest in energetics culminated in what is undoubtedly Rudi’s most important paper, known as ‘The Prudent Parent’ [co-authored by Serge Daan (Drent & Daan 1980)]. This wide-ranging paper is probably best known for the suggested upper limit of energy expenditure (4–5 times basal metabolic rate), but it further presents an integrative view on energetics in a life-history context that dominated many a research agenda for a long time. Its influence, with more than 50 citations annually, is still considerable. Much of Rudi’s research in Groningen concentrated on geese, perhaps because he shared their habitat preferences and migratory tendencies: Wadden Sea islands in winter and spring, and the Russian tundra or Spitsbergen in summer. Whenever possible he studied individually marked geese. This enabled him to link foraging and social behaviour to fattening, migration and fitness components on an individual level. Fattening was quantified in the field using abdominal profiles, famously referred to as the ‘Rubens index’. Furthermore, studies of foraging behaviour often included detailed measurements of food supply. These two elements, studying individuals and quantifying food supply, also characterize the work of many of his students. However, Rudi’s greatest successes were achieved not by publishing papers such as ‘the prudent parent’ but through the personal influence he had on the work and inspiration of fellow ornithologists. Foremost among these were the students that he took out to the field, where according to his inaugural lecture they were to find their own inspiration. The University field station ‘de Herdershut’, on the Dutch Wadden Sea island of Schiermonnikoog, where many guests were also taken over the years, was instrumental in this. Being too far away from the rest of the world to go home very often, students discovered the beauty of fieldwork by being immersed in it, in an environment where this was the norm. At de Herdershut and elsewhere Rudi led his students by example, being the earliest in the field, doing more than his share of domestic chores, but also by always being actively present at seminars, book discussions and never missing one of the monthly bird counts in ‘de Lauwersmeer’ or ‘de Dollard’ (his last one only weeks before he passed away). In total 65 students went on to do their PhD under Rudi’s (co-)supervision at the University, but also many at government research institutes spread over the country. He would visit his PhD students at their field sites, when possible in ‘de Ilse’, a ship he inherited from his father. Rudi’s style in supervision was unique, in that he was exceptionally skilled in helping others in their thinking. As one of his students put it, ‘he always made me feel so bright’. In this way, his achievement was that students experienced the progress they made as their personal success, which is a potent source of motivation. It is understandable from this perspective that he co-authored only a small percentage of the scientific papers his students produced, despite his substantial contributions. When he was not in the field, Rudi was at his best at small-scale conferences. Being a lover (and master) of words and well-designed graphs, he was in demand as a speaker. Perhaps even more important was the way he contributed to the atmosphere and discussion, often intervening in a constructive and humorous way. These meetings, and much else, will never be the same without him.

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