RESUMEN
European starlings, Sturnus vulgaris, intermingle fresh herbs, especially species rich in volatile compounds, with their otherwise dry nest material. In this field study we investigated whether these herbs reduce ectoparasites and thereby protect nestlings (the nest protection hypothesis). We also considered whether volatile compounds in herbs improve the condition of nestlings (the drug hypothesis). As measures of condition we used body mass, haematocrit levels and immunological parameters. We replaced 148 natural starling nests with artificial ones: half contained herbs and half (controls) contained grass. The ectoparasite loads (mites, lice, fleas) in herb and control nests were indistinguishable. However, nestlings in herb nests weighed more and had higher haematocrit levels at fledging than nestlings in control nests. Fledging success was similar in herb and control nests, but more yearlings from herb nests were identified in the colony the year after hatching. The response of the immune system when challenged with phytohaemagglutinin did not differ in nestlings from herb and control nests. Nestlings from herb nests had more basophils and fewer lymphocytes in their blood than those from control nests, while the eosinophil and heterophil counts did not differ. We conclude that herbs do not reduce the number of ectoparasites, but they improve the condition of nestlings, perhaps by stimulating elements of the immune system that help them to cope better with the harmful activities of ectoparasites. Copyright 2000 The Association for the Study of Animal Behaviour.
RESUMEN
Twenty-eight stonechats of the European race (Saxicola torquata rubicula) from Austria and thirty-one stonechats of the Central African race (S.t. axillaris) from equatorial Kenya were handraised and subsequently investigated with regard to the temporal pattern of their postjuvenile molt. About one half of the birds of each race were held under their own native photoperiod and the other half under the photoperiodic conditions of the other race. The results demonstrated clear differences in the postjuvenile molt between the two races when birds were kept in the photoperiod under which they normally live. The African birds began to molt earlier and molted longer than their European conspecifics. The time course of postjuvenile molt was affected by photoperiod in both races as molt began and ended earlier under the equatorial photoperiod than under the European photoperiodic simulation. The question why the African birds showed strong photoperiodic reactions under these experimental conditions although in their natural environment they experience only minute photoperiodic variations, is critically evaluated: Three possible explanations are discussed: (1) the photoperiodic reaction may represent a relict from a time when ancestors of the tropical populations still lived in more temperate zones; (2) it may be due to the occasional immigration of conspecifics from populations living further north or south; (3) it may result from effects on a (possibly circadian) submechanism of the system controlling annual cycles which is normally affected by other environmental cues but can also be influenced by photoperiodic variations.