RADIO-PTILOCHRONOLOGY - TRACING RADIOACTIVELY LABELED FOOD IN FEATHERS

Ingested radioactive sulphur, S-35, in amino acids. is readily incorpo rated in growing feathers. In a growing rectrix, or tail feather, the radioactivity will be deposited in the part of the feather that develo ps during the day(s) after ingestion. In an autoradiographic picture i t will appear as a dark band across the feather. In a combined laborat ory and field study of Willow Parus montanus and Marsh Tits P. palustr is, I used this (1) to assess the accuracy of ptilochronology and in a n effort to improve that method and (2) to test the technique's useful ness for studies of food retrieval in food-hoarding bird species. The study confirmed that one growth bar (consisting of one light and one d ark portion) represent one day's growth of the feather. It also demons trated that radioactive labelling can be used to pinpoint the exact da te at which a particular growth bar was formed. It can also be used to identify simultaneously grown bars in successively plucked rectrices thus extending the period during which ptilochronology can be used, e. g. to study birds' nutritional status over the whole winter. During se lective provisioning of radioactive seeds to either partner of a Willo w Tit pair, the bird first ate a couple of seeds and then stored the r est. However, some radioactivity showed up in the rectrix of the partn er (who was only fed unlabelled seeds on this occasion) indicating tha t it had been able to pilfer the partner's caches.