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Ellen Paul

Colin Pennycuick 1933 - 2019

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Colin Pennycuick, who has died aged 86, was the pre-eminent researcher in animal flight over the last century. He focused on the flight of bats and birds (and their possible ancestors), and asked the question: how do they work? To answer this deceptively simple question he brought to bear a mix of sharp logic and original and practical invention.

Though he sought to ground his work in the rigorous application of physics and mathematics, he was not satisfied with abstract results and conclusions by themselves, but always sought to democratise his findings, first to the biological sciences community and then to the huge population of lay people fascinated with birds and their flight escapades.

Pennycuick was an expert glider pilot, and gained some notoriety by piloting his craft in and around flocks of vultures, storks and eagles in Africa, and condors in Peru.

The son of Brig James Pennycuick and his wife, Marjorie, Pennycuick was born in Windsor, Berkshire. His family followed his father’s army postings, which in 1938 took them to Singapore, which they left in 1941 shortly before the Japanese invasion. Pennycuick was later sent as a boarder to Wellington college, Berkshire, studied zoology as an undergraduate at Merton College, Oxford, and worked on his PhD at Peterhouse, Cambridge. There he studied muscle mitochondria, whose task of converting oxygen and nutrients into energy he viewed as the basic engine of flight.

During two years’ national service with the RAF, he flew Provosts and Vampires, early jet-powered aircraft. He subsequently worked as a postdoctoral fellow at the Animal Behaviour Laboratory in Madingley, Cambridge, and in 1964 began a long association with the zoology department at Bristol University as a lecturer.

Colin Pennycuick at work in Iceland in 1995. His career took him as far afield as Nairobi, Peru and the South Georgia Islands. Photograph: Sverrir Thorstensen

He used the first computer at the university to design a tiltable wind tunnel, which he built from scratch and hung in a stairwell. He developed and adapted aeronautical ideas from helicopter theory to bird flight and tested their application based on meticulous observations of the free-flying pigeons which he kept in a loft on the roof of the building.

In 1968 he traveled to Nairobi, which he made his base for three years, installing his tilting wind tunnel between two acacia trees to study bat flight in the same manner as he had previously done with pigeons. He then spent another two years in the Serengeti national park as deputy director of the research station there. He learned how to fly his powered glider alongside pelicans, storks and vultures, documenting for the first time their extraordinary and essential abilities to travel economically over large distances by exploiting thermals.

From here on, his career was not so much a list of academic positions and research topics as a restless migration (frequently aerial, frequently self-piloted) of his own. He flew back to Bristol in 1973 via Addis Ababa, Cairo and Crete, in and around the Shetlands, France and Sweden, and down to Bird Island in South Georgia, Antarctica. There he first used his “ornithodolite”, an instrument he designed for measuring birds’ flight paths and speed, to track in detail the soaring flight of albatrosses. He found that the standard explanation – that they could power their flight by following a specific trajectory through a wind shear profile – was only partly responsible for their ability to fly continuously, without flapping for very long times, and that instead they used the wind in several different ways.

In 1983, he left for Miami University, which became a handy launch point for expeditions to the Everglades, Tennessee, Pennsylvania and Idaho, and further afield in Puerto Rico, the Bahamas and Peru. In 1992 he left Miami, via Greenland, Iceland and Sweden. He began a continuing association with the animal ecology group at Lund University in Sweden, tracking migratory birds by radar, and in 1994 the bird flight wind tunnel was inaugurated there by the king of Sweden.

In the late 1990s he collaborated with the Wildlife and Wetlands Trust at Slimbridge, in Gloucestershire, in tracking whooper swans, which as the largest flapping bird can provide a stringent test of aerodynamic theory at relatively large extremes of scale. He appeared in the 2003 BBC radio series Swan Migration Live, which tracked six Bewick’s swans and a whooper swan from Arctic Russia to the UK, with updates on their progress on the Today programme each morning.

In 2008 Pennycuick took part in an even bigger and more ambitious Radio 4 project, World on the Move: Great Animal Migrations, which tracked brent and white-fronted geese from the UK to Canada. With the aid of very accurate meteorological data, combined with measurements of wing beat frequency and wing shape, he modelled a gauge that could estimate the fuel consumed while these geese were migrating: this would give audiences, and the scientific community, some idea of the effort involved.

Pennycuick’s primary goal was to provide and test a physically reasonable theory of vertebrate flight, which could then be used to predict and understand how and why birds and bats do what they do. Many of his inventions, in techniques, procedures and instrumentation, were absolutely novel because he thought his own thoughts and proceeded by himself, according to the rigorous rules of logic and scientific inquiry.

A rich and exuberant publication history burst from his activities, starting with the first practical flight theory papers in 1968 and going on to include the books Animal Flight (1972), Bird Flight Performance (1989) and Modelling the Flying Bird (2008). In later years he increasingly focused his efforts on his flight software package, which grew from a small custom Basic program to a rather versatile application with graphical interface. As well as biologists, engineers wanting to know how birds manage to achieve the things they do with apparent economy of effort and energy expenditure used the program, and both groups learned from it, which gave Pennycuick particular pleasure.

He was appointed research professor in zoology at the University of Bristol in 1993, and senior research fellow in 1997. He was elected fellow of the Royal Society in 1990, and was made honorary companion of the Royal Aeronautical Society in 1994. In 1996 he was awarded an honorary doctorate by Lund University.

In 1992 he married Sandy Winterson. She and his son, Adam, survive him.

Colin Pennycuick at work in Iceland in 1995. His career took him as far afield as Nairobi, Peru and the South Georgia Islands. Photograph: Sverrir Thorstensen

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From Fred C. Schaffner:

It’s taken me a long time to internalize this, and I can only offer my sincerest apologies to Heaven for delaying so long. Colin J. Pennycuick was the only true genius I have ever known and I cannot imagine meeting anyone of his calibre ever again. He was kind and patient with mortals like me, jovial, eccentric, and humble, sometimes hilarious, and always in good cheer. Often, we were the only ones in the room who understood one another’s jokes. I’ve tried to be as good a teacher and mentor as he, but matching his genius would be impossible. I had the honor of being his first PhD student after he came to the US from England. He taught me to fly, to master SI units in everything, and most importantly to see farther by patiently stepping back and starting with first principles.
We flew together from Miami to my research site at Culebra, Puerto Rico piloting the Cessna 182 pictured in the article, which he later flew from Miami to England vía Greenland.
I remember ground-breaking scientific articles he wrote on the backs of envelopes, and his home-built computers. And I remember a time when my mind was swirling with a tangled spaghetti of ideas as I tried to write my dissertation. He left the office with a magic marker in hand and returned from the restroom with a length of toilet paper on which he’d written, “When your thoughts come out, it helps to get them down on paper”. He told me to stick it on the wall and keep looking at it until the spaghetti got untangled. It worked!
I remember him calling me one afternoon, years after I graduated, to tell me that for his 65th birthday he’d taken up hang-gliding and had gone to Spain to glide with the Griffons. I can’t imagine who or what or where I would be without him. He was a truly unique and stellar human being.

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From The Ibis:

https://onlinelibrary.wiley.com/doi/full/10.1111/ibi.12822?fbclid=IwAR0nsfy9G0r78EzfGAJqJUpxes3utTyygvYwuruCG7qwuAzU3iitB8I1tpc

With the death of Colin Pennycuick on 9 December 2019 at the age of 86 years, the ornithological community has lost a doyen of avian biology whose passion for flying informed his pioneering research into avian flight for over five decades. His innovative studies, which famously include developing the use of wind tunnels for studying flight performance, led to him to describing key principles underlying the mechanics of flight. A leading authority on the mechanics and physiology of flight in birds and bats, he was also an expert on their navigation and migration. He was particularly driven by a wish to test, and thus understand, why birds and bats fly in the way that they do. His own enthusiasm for piloting light aircraft – pursued from his student days – provided him with fresh insights into the constraints encountered by the birds during their daily movements and longer distance migrations.

Colin James Pennycuick was born in Windsor, Berkshire, on 11 June 1933. His father, Brigadier James A.C. Pennycuick, served with distinction in the Royal Engineers during WWI, and his grandfather was Treasurer of Ceylon (now Sri Lanka). Educated at Wellington College, Berkshire, and at Merton College, Oxford, Colin enlisted in the Oxford University Air Squadron for the Royal Air Force Voluntary Reserve, and this triggered his life‐long love of flying. A keen birdwatcher since childhood, whilst still an undergraduate he joined a goose‐ringing expedition to Spitsbergen. The results were published in the Seventh Annual Report of the Wildfowl Trust (now the Wildfowl & Wetlands Trust; WWT). He moved on to Peterhouse, Cambridge, for a PhD study on muscle physiology, and as a research fellow at Cambridge, he studied the navigation of the Common Pigeon Columba livia, before moving to become a lecturer in the Zoology Department at Bristol University. His association with Bristol continued over many years, though interspersed with periods spent working elsewhere. He also became a regular visitor to the Wildfowl Trust at Slimbridge, and flew gliders with the WWT’s founder, Sir Peter Scott.

During his initial stint in Bristol, from 1964 to 1968, Colin used the university’s first computer to design and build a wind tunnel, which he famously hung in a stairwell in the Zoology Building and then trained and pigeons to fly within it. His observations led to him adapting the existing aerodynamic theory for helicopters to birds, using the results of his wind tunnel experiments to derive a quantitatively accurate mechanical model of bird flight, which was published in a landmark paper in the Journal of Experimental Biology. During this period, he also used the wind tunnel to estimate basic properties for birds in steady gliding flight, with information gained about wing lift and drag from the body and wings leading to his classic ‘momentum jet’ model of flapping flight mechanics, and to addressing the key point of how the mechanical power required to fly varies with airspeed. A second seminal paper on this theory appeared in Ibis in 1969, describing its significance for the flight of birds of different sizes and with varying migration ranges. Colin concluded at the time that there is an upper limit to the body mass at which birds are capable of flight and migration, with larger birds more limited by the amount of body fat which they can carry as fuel, which reduces their range, but they can economize by soaring. He suggested that the upper limit lay approximately with the Kori Bustard Ardeotis kori.

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With the death of Colin Pennycuick on 9 December 2019 at the age of 86 years, the ornithological community has lost a doyen of avian biology whose passion for flying informed his pioneering research into avian flight for over five decades. His innovative studies, which famously include developing the use of wind tunnels for studying flight performance, led to him to describing key principles underlying the mechanics of flight. A leading authority on the mechanics and physiology of flight in birds and bats, he was also an expert on their navigation and migration. He was particularly driven by a wish to test, and thus understand, why birds and bats fly in the way that they do. His own enthusiasm for piloting light aircraft – pursued from his student days – provided him with fresh insights into the constraints encountered by the birds during their daily movements and longer distance migrations.

Colin James Pennycuick was born in Windsor, Berkshire, on 11 June 1933. His father, Brigadier James A.C. Pennycuick, served with distinction in the Royal Engineers during WWI, and his grandfather was Treasurer of Ceylon (now Sri Lanka). Educated at Wellington College, Berkshire, and at Merton College, Oxford, Colin enlisted in the Oxford University Air Squadron for the Royal Air Force Voluntary Reserve, and this triggered his life‐long love of flying. A keen birdwatcher since childhood, whilst still an undergraduate he joined a goose‐ringing expedition to Spitsbergen. The results were published in the Seventh Annual Report of the Wildfowl Trust (now the Wildfowl & Wetlands Trust; WWT). He moved on to Peterhouse, Cambridge, for a PhD study on muscle physiology, and as a research fellow at Cambridge, he studied the navigation of the Common Pigeon Columba livia, before moving to become a lecturer in the Zoology Department at Bristol University. His association with Bristol continued over many years, though interspersed with periods spent working elsewhere. He also became a regular visitor to the Wildfowl Trust at Slimbridge, and flew gliders with the WWT’s founder, Sir Peter Scott.

During his initial stint in Bristol, from 1964 to 1968, Colin used the university’s first computer to design and build a wind tunnel, which he famously hung in a stairwell in the Zoology Building and then trained and pigeons to fly within it. His observations led to him adapting the existing aerodynamic theory for helicopters to birds, using the results of his wind tunnel experiments to derive a quantitatively accurate mechanical model of bird flight, which was published in a landmark paper in the Journal of Experimental Biology. During this period, he also used the wind tunnel to estimate basic properties for birds in steady gliding flight, with information gained about wing lift and drag from the body and wings leading to his classic ‘momentum jet’ model of flapping flight mechanics, and to addressing the key point of how the mechanical power required to fly varies with airspeed. A second seminal paper on this theory appeared in Ibis in 1969, describing its significance for the flight of birds of different sizes and with varying migration ranges. Colin concluded at the time that there is an upper limit to the body mass at which birds are capable of flight and migration, with larger birds more limited by the amount of body fat which they can carry as fuel, which reduces their range, but they can economize by soaring. He suggested that the upper limit lay approximately with the Kori Bustard Ardeotis kori.

In 1968 Colin moved to East Africa, where he was seconded to Nairobi University for 3 years and first acquired his own aircraft (a Piper Cruiser). There he used his wind tunnel to study gliding flight in the Egyptian Fruit Bat Rousettus aegyptiacus. This was followed by 2 years in the Serengeti National Park as Deputy Director of the research station, at which time he flew a powered glider with pelicans Pelecanus spp., storks Ciconia spp. and vultures Gyps spp. and discovered that soaring birds are able to travel across vast areas with little effort, using currents of rising air to gain height, then gliding to the base of the next thermal. In preparation for his return to Bristol in 1973, he adapted his Piper Cruiser for long‐distance flight and made a ‘stepping‐stone’ migration back to the UK, calling in at Addis Ababa, Cairo and Crete en route. This time he remained in Bristol until 1983, using the Piper to track migrating cranes in southern Sweden and also developing the ‘ornithodolite’, a portable instrument which recorded in real‐time on to a computer the azimuth, elevation and range of birds in flight. This he used in South Georgia to measure glide patterns for albatrosses Diomedea spp. and Phoebetria spp. to determine how the wind and waves of the Antarctic Ocean powered their flight, thus shedding light on gust‐soaring phenomena in the species. He also renewed his collaborative work with the WWT, including undertaking an aerial survey of Barnacle Geese Branta leucopsis across Scotland and Ireland in the Piper, and being instrumental in bringing the first computer to the organization.

In 1983 Colin moved to the US as the Maytag Chair of Ornithology at Miami University where he continued his studies of flight performance, using the ornithodolite to study frigate birds Fregata spp. flight, and the wind tunnel to refine his flight mechanics model. Here he developed his ‘Flight’ software, which he made readily available to other researchers, and his book Bird Flight Performance, a Practical Calculation Manual was published in 1989. He collaborated on several projects with the Patuxent Research Centre, including developing bird‐borne transmitters that could send data via the Argos satellite system, and recording basic flight characteristics data for several falconry‐trained raptors and wild sage grouse to test the effects of radio‐tagging on avian flight. When he returned to Europe in 1992 he again made an inter‐continental flight in his own aircraft, this time a Cessner 182, flying via Greenland and Iceland to Bristol. Once back in Britain, following much commuting between the US and the UK by both parties since the early 1980s, he married his wife Sandy, also in 1992. Several new projects commenced, with Colin making regular visits to Lund University where a new wind tunnel was inaugurated by King Carl XVI of Sweden and also, with WWT, tracking Whooper Swan Cygnus cygnus migration between Britain and Iceland. This was of particular interest to Colin because the species was deemed to be at the upper limits for making the long‐distance overseas flight. His VW campervan became a familiar sight in Lund and at Whooper Swan catch sites in Iceland.

Always generous with his time, Colin mentored a number of undergraduate and PhD students who went on to be highly successful in their fields, including such luminaries as Julian Hector, Anders Hedenström, Malcolm Ogilvie, Keith Scholey and Geoff Spedding, their tributes to Colin having contributed substantially to this article. Colin’s life‐long love of flying and his innovative spirit never diminished; on co‐supervising a PhD on Whooper Swan breeding biology during the early 1990s, he suggested that inaccessible parts of Iceland could perhaps be reached by the new method of paramotoring, a concept viewed less enthusiastically by others involved. He also took trouble to ensure that the results of his somewhat technical research were made accessible and understandable to a wider audience, including joining the WWT/BBC/Nenetskiy State Nature Reserve expedition to ring Bewick’s Swans Cygnus columbianus bewickii in the Russian arctic in 2003, an expedition which included tracking Bewick’s Swans fitted with satellite tags for BBC Radio 4’s ‘Migration’ programme. Although recovering from treatment for cancer at the time, Colin was a calm and steadfast presence throughout, clearly delighted to be back in the field.

Colin was elected Fellow of the Royal Society in 1990 for his innovative work on the flight of birds and bats, and was made Honorary Companion of the Royal Aeronautical Society in 1994. In 1996 he was also awarded an honorary doctorate by Lund University. His publications, including the textbook Modelling the Flying Bird (2008) and his ‘Flight’ software models on the mechanics of flapping and gliding flight and long‐distance migration, set out the principles of aeronautical engineering and how they may be adapted for exploring bird flight. These will remain valuable tools for future generations, and form a basis for the continuing research into avian flight and the dissemination of this information by those who he inspired.

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