Forum The spatial and temporal repeatability of PHA-responses

The capacity to mount a cell-mediated immune response in birds is often quantified as the swelling following an injection of phytohaemagglutinin (PHA) into the wing-web. Most studies have found the repeatability of consecutive measure-ments of the same swelling to be high (e.g., Alonso-Alvarez and Tella, 2001; Fargallo et al., 2002; Saino et al., 1997; Smits et al., 1999; Tella et al., 2000). However, as pointed out by Siva-Jothy and Ryder (2001), repeatability calculated this way only estimates the precision with which an experimenter measures the size of a particular swelling; it does not encompass other components of measurement error. Furthermore, such estimates of repeatability do not capture temporal variation in individuals ’ PHA-responses. To our knowledge, no study has reported the latter types of repeatability estimates. Thus, the aim of the present study was to investigate the re-peatability of the response to PHA both at a given time and between different occasions separated in time. MATERIALS AND METHODS We investigated the immune responsiveness of European starling (Sturnus vulgaris) nestlings and fledglings in th