Roger Akester, veterinary anatomist at Cambridge from 1959 until 1991, will be remembered by all those with an interest in how birds work for his seminal contributions, made during the 1960s and obtained by x-ray and radio-opaque tracers, on the control of blood flow through the renal portal blood vessels and the passage of urine from the cloaca into the rectum and caeca by reverse peristalsis. The latter finding, which at the time was unexpected and contrary to the accepted view, provides the opportunity for modificaton of the salt and water content of the urine and for the uric acid to be metabolised by gut bacteria into useful products like volatile fatty acids; in other words, the recycling of waste products to get a second bite of the cherry.
The result of the mixing of urine, with its white uric acid, and faeces in the hind gut of birds is that both are voided together, as those who have been the target of a passing bird will testify. When I have to clean my car after an aerial assault by gulls that abound here, I cannot help thinking of both Erik Skadhauge, who went on the work on the salt and water aspects of modifying urine in the hind gut, and Roger Akester who discovered what was happening.
In the few hours since seeing the announcement in The Times, I have been able to find this radiograph (reproduced by W.J. Cliff in his book, Blood Vessels, Cambridge University Press, 1976), originally from Roger Akester's paper, on blood flow in the renal portal vessels and its control by the renal portal valves:
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