On 31st January 2011, Frank Blackburn and I were photographing Waxwings Bombycilla garrulus at Yateley in Hampshire. The birds were feeding on Cotoneaster berries in their traditional winter habitat – a supermarket car park. After the session, we exchanged photographs and Frank sent me the one that accompanies this note. Neither he nor I had seen anything like this before.
Thanks to Mick Marquiss, who has far more experience of Waxwings than we southerners do, I have learnt that their excretory habits are well known in Aberdeen. To quote Mick, the photograph shows ‘classic waxwing goo’. He continued: ‘When berry intake is rapid and the berries are high in sugar, the gut contents flush through quickly so roosting trees in parks and roadsides are easily identifiable by a characteristic ring of sticky goo that surrounds the base.’
It is known that fruit-eating birds typically have low digestive efficiencies. Work on Cedar Waxwings B. cedrorum (Levey & Duke 1992) has shown that their digestive system is modified to extract the maximum amount of nutrients from their berry diet. The phenomenon of ‘Waxwing goo’, as demonstrated so clearly in the photograph, suggests that this process is far from 100% efficient.
Thanks to Frank Blackburn for his excellent photographs and to Mick Marquiss for his help in shedding light on this unusual topic.
Levey, J. D., & Duke, G. E. 1992. How Do Frugivores Process Fruit? Gastrointestinal transit and glucose absorption in Cedar Waxwings (Bombycilla cedrorum). Auk 109: 722-727.
John Eyre, 3 Dunmow Hill, Fleet, Hampshire GU51 3AN