The question was first posed by an observer who heard that feeding cheese was the cause and subsequently others who believed garden pesticides and fertilisers might be to blame.
Prof Piper had made a comprehensive study of wagtails and said the phenomenon of leg deformities, missing toes and even feet was well known.
He quoteed two references, one of which goes back over 70 years. The first is by the Rev Robert Godfrey, 1933, in his book Blythswood Review, who says: "Of universal distribution through the city occurs the wagtail. In Cape Town, as in East London, the city wagtails are liable to some mysterious disease of the feet, and one such pair haunts the lawn of the house in which this is being written. Each of the pair still retains an effective leg and by its aid is able to hop along over the ground in search for food; one of the pair has lost all use of its second leg whose toes are in a permanently-contracted condition, the other still retains a very faint use of its second leg, tapping the ground with its curled-up toes."
The second is W Erskine, 1981, writing in the Witwatersrand Bird Club News. "For a number of years a Willie-wagtail and his mate were annual visitors to our garden. It was recognised by the fact that the right leg ended in a stump. Since then we have had regular visits from other wagtails, a number of them with deformed or missing feet which has also been observed on several occasions in other areas of Johannesburg. Insecticides could be the culprit."
Prof Piper said there are a number of issues that should be taken into account:
1. Fine threads from discarded carpets, cloths and clothes pose a particular problem for birds that "mess about in water" they get caught around toes and feet, constrict blood supply, cause toes and feet to swell and then drop off. I have seen this a number of times in my long-tailed wagtail study and after removing the threads the birds have gone on to survive for many years. Many Cape wagtails are individually recognisable from the nature of their injuries and losses.
2. All the nasty detergents and chemicals that we put in our streams and rivers cause problems for birds that spend most of their lives foraging therein. A comparison of two study sites, one in a pure mountain stream and the other in an urban area, show that only in the latter are there any foot or leg abnormalities in long-tailed wagtails.
3. There are many records of wading birds that have foot abnormalities from many different species in different genera from around the world. It is likely that the very nature of the habitat continually wet and cold exacts a toll on such species, even in the absence of humanity.
4. I'd guess that it has nothing to do with feeding semi-tame wagtails on a McDonald diet! Lots of urban, human-dependant species exist in happy abundance in similar circumstances.
5. There has been some debate recently on the presence of leg encrustation on wagtails and a number of other species. One of the causes for this is a small mite that enters the skin just below the leg scales and causes the "ugly" symptoms reported.
6. I don't think that pesticides via the food chain are the cause of these phenomena. If that were so, then many other garden birds would show the same symptoms.Palmiet Nature Reserve Copyright © 2010 All Rights Reserved