Derek was a pupil at Surbiton County Grammar School (Surrey, UK) in the late 1950s, whence he progressed to University College London (UCL) graduating from there to become one of the most versatile and ‘complete’ zoologists of his generation. He joined The Mammal Society, attending his first Annual Conference in 1963. Derek contributed significantly to The Mammal Society's Occasional Publications and to the early editions of the Handbook of British Mammals, finally overseeing the massive task of completing its fourth edition (Harris & Yalden 2008). He was awarded the Society's Silver Medal in 1989. He also served as Editor of Mammal Review for 22 years (1980–2002) and as a very active, enthused President of The Mammal Society for 16 years (Fig. 1), a post that he held at the time of his death. Derek's research activity is reminiscent of that of some of the most famous naturalists of Britain's past. This was recognized most deservedly in 2010 when the Linnean Society of London awarded him its Gold Medal in Zoology. Throughout his career, Derek also popularized his broad scientific interests as a member of 17 zoological and natural history societies, by frequently presenting lectures, and through regular contributions on the radio.
The UCL zoology syllabus in the 1950s and 1960s was strongly focussed on morphology, taxonomy and palaeontology. These disciplines provided a core to Derek's subsequent academic life but he was also deeply interested in field studies. As a student, he joined an expedition to study the ecology of Cap Gris Nez, comparing the nearest part of France with Britain, and he returned there in 1964 to concentrate on small mammals. He also attended a specialist field course at Flatford Mill, Suffolk, UK, taught by leading mammalogists. His burgeoning interest in mammals was further boosted by meeting W. G. (‘Bunny’) Teagle, Mammal Recorder for the London Natural History Society, who was conducting the first systematic surveys of mammals in the London area. Derek and a school friend, Pat Morris, whose career closely followed Derek's for 50 years, mapped badger Meles meles setts in Surrey, an interest that ultimately led to Britain's first National Badger Survey (Clements et al. 1988), while Derek and Pat Morris went on to publish The Lives of Bats (Yalden & Morris 1975). Derek graduated from UCL in 1962, gaining lifelong friends and one of the few First Class degrees then awarded in Zoology. Transferring to Royal Holloway College (University of London), where he had taken an intercollegiate course in mammals as a specialist part of his BSc, Derek completed his PhD on the functional morphology of the mammalian carpus in 1966, working under the supervision of Percy Butler. He had a natural aptitude for research and the classical skills required to produce seminal papers on mammalian wrist bones and locomotion. His facility for hard graft, meticulous work, detailed observation, data collation and illustration became the hallmarks of his later research and publications in archaeozoology, taxonomy, biogeography, macroecology, ecology and conservation. Derek also pursued interests in palaeontology, using his morphological insight to debate the locomotory capability of Archaeopteryx, publishing another six papers on this uniquely important fossil bird, and another on the origin of early vertebrates, supporting monophyly of the lampreys (Order Petromyzontiformes) and hagfish (Myxinidae).
In 1965, Derek was appointed as an Assistant Lecturer in the Department of Zoology at the University of Manchester, UK, which he served until his retirement as Reader in 2005. Manchester University allowed Derek to pursue his wide range of interests and, in particular, focus on the ecology of mammals and birds. He produced early papers on urban ecology, but it was in the nearby Peak District where he began long-term studies on moorland restoration, upland ecology and climate change involving sandpipers (Scolopacidae), golden plovers Pluvialis apricaria, mountain hares Lepus timidus and feral wallabies Macropus rufogriseus. Fieldwork remained a regular, high priority most weekends for more than 40 years, and led to a series of influential papers in leading journals.
Derek's life in Manchester revolved around work. For many years, he cycled home for supper, and returned to the University to work late into the night, even after he married Pat Brayley in 1972. Later, they moved to a smallholding at Chapel-en-le-Frith with easier access to his study sites. His work on upland waders was well supported by Pat, and even their dog Chad got involved by frequently finding dead shrews. As ever, Derek kept detailed records (Yalden 1993) and began to discover important ecological differences between the common shrew Sorex araneus and the pigmy shrew Sorex minutus in terms of their ability to colonize moorland, with a direct bearing on the vexed question of why pigmy shrews occur in Ireland and common shrews do not. Thus began Derek's interest in Irish faunal origins and more widely the history of the fauna of the British Isles based on archaeological excavations and the analysis of place names, and he published original papers and reviews on Quaternary and Holocene mammals and birds. In time, this led to two excellent, critically acclaimed books (Yalden 1999; Yalden & Albarella 2009) which together epitomize Derek's approach to research and publication. Derek's interest in postglacial colonization and his role as President of The Mammal Society made him a regular and very welcome visitor to Ireland where he enthused and encouraged a new generation of researchers interested in the biogeography and phylogeography of mammals.
Derek focussed on the British and Irish fauna and he rarely travelled abroad. Occasionally, he took short ‘holidays’ to good wildlife places, e.g. the Gambia where his Peak District sandpipers spent the winter. A significant exception was in 1968, when he joined Pat Morris as a zoological advisor to the Great Abbai Expedition, an attempt to travel by boat down the Blue Nile in Ethiopia which even with the assistance of the British Army was a dangerous activity that had not previously been accomplished. The scientific objective of this highly successful expedition was to collect specimens for the Natural History Museum in London (Figs 2, 3). Derek took part in another five expeditions to the wilder parts of Ethiopia (without the Army), which significantly advanced knowledge of the mammals and amphibians of Ethiopia. Several species new to science were discovered, including three (a frog Leptopelis yaldeni, and two rodents Desmomys yaldeni and Otomys yaldeni) formally named in recognition of Derek's contribution to studies of the Ethiopian fauna. Derek and his colleagues later published over 20 papers on the Ethiopian fauna, including the first behavioural observations of the elusive giant mole rat Tachyoryctes macrocephalus (Yalden 1975) and a six-part catalogue and taxonomic review of Ethiopian and Eritrean mammals (Yalden & Largen 1992). The final part of this series formed a revised checklist, covering zoogeography and conservation, and is stunning in both its breadth and depth (Yalden et al. 1996). Derek also developed strong links with the University of Addis Ababa, supervising Afework Bekele's doctoral work and examining the latter's PhD students on a recent visit to the country. Over his career, he supervised 20 graduate students successfully and served as external examiner for 34 theses at 21 different universities.
At Manchester, Derek rapidly acquired a deservedly high reputation as a teacher. His ‘introductory’ course in Vertebrate Evolution was regarded as a rite of passage, and was not only delivered with all of Derek's enthusiasm and clarity, but also supported by a series of super-charged demonstrations of material, much of which Derek had collected, prepared, illustrated and annotated himself, often in his distinctive handwriting. His ability to create a stink in the department was unrivalled as he boiled up some long-dead animal for its skeleton. Derek presided in lab coat, sleeves up, white shirt, red tie, grey flannels and sandals like an endlessly patient, living encyclopaedia. Likewise, on field courses, he instructed and led students into field ecology, engendering interest among the most unmotivated. His apparently effortless ability to recall names of any plant, invertebrate or vertebrate, as well as those of the students he taught, made Derek not just a font of valuable information but a friend to those who had drifted into university. Derek gave many students a goal and a means to achieve it.
Derek's charm and good humour put strangers at their ease and entertained friends and colleagues. He was witty and self-deprecating, a compulsive tease who could take a joke and, sometimes, he was a little cheeky. There are numerous stories about Derek, especially about his nocturnal excursions. The discovery of a colony of particularly noisy frogs in the deep water of Black Pond, Esher Common, Surrey, UK, persuaded Derek of the necessity to catch one in the interests of science, and he did so despite cold water and his inability to swim. This reflected his healthy disregard for personal safety and it led to the publication of his first paper (Yalden & Morris 1961) while he was still a student. Once Pat Morris passed his driving test and got a car, he and Derek were able to expand early surveys to include studies of hibernating bats in some of Surrey's old stone mines and further afield. Checking traps on the way home from Royal Holloway led to the first of Derek's brushes with the law, when he was apprehended by a policeman baffled by the sight of someone wearing bicycle clips, thick gloves and short sleeved shirt leaving a copse long after dark. Derek later literally bumped into the legs of one of Manchester's policemen in the dead of night in a locked city park while following hedgehogs Erinaceus europaeus. On another occasion he spared the blushes of several female students, greeting them with a polite ‘Evening …’ out of a darkened bush where he had been waiting for badgers. Derek was keen on the idea of restoring extinct species to Britain, leading to some of his colleagues ribbing him about more practical issues and his failure to embody ecological principles within his more imaginative proposals dredged from the depths of the Quaternary.
Academia was Derek's natural environment but it has become increasingly harsh for those refusing to conform to fashion or some ill-considered norm. One former Head of Department dismissed Derek's diverse interests as ‘mere natural history’, illustrating his own limitations rather than Derek's. Derek was dismayed, but stoical, responding through over 235 formal publications, many reflecting new areas of research which have subsequently become fashionable, such as urban ecology, macroecology, global change and habitat restoration. He was involved in early meta-analyses on abundance, body size and species richness relationships (Greenwood et al. 1996), and was invited to join a group of researchers to consider the 100 ecological questions of highest policy relevance in the UK (Sutherland et al. 2006). Other publications in less prestigious but highly appropriate journals led to major syntheses. Derek held to his principles in everything he did and remained active, publishing up to the present, with further work in hand. He made a major contribution to the first Atlas of British Mammals (Arnold 1993) and was working on a new version, as well as on new research on postglacial colonization by mammals.
Derek was proud of his former students, and encouraged them in everything they did. He was always available to give sound advice to more junior mammalogists, whether amateur or professional, novice or experienced. Derek was not only a highly regarded researcher, teacher and scholar, he will remain much admired and loved as a person by all those who were fortunate enough to have him as a friend or enjoy his support. He died quietly in his sleep during a rare and brief holiday in the Forest of Dean, UK, where he was looking forward to seeing his first British wild boar Sus scrofa. His paper on the ecology and final demise of the wallaby population in the Peak District was published the week after his death (Yalden 2013).