The blood stress protein response can be used to evaluate physiological or environmental stress in individuals and populations. It is important that sample conservation and transport are correct to avoid confounding effects on protein analyses. We show that Great Tit (Parus major) blood samples can be centrifuged and frozen any time within eight hours of collection, as during this period there are no significant changes in stress protein HSP70 and HSP60 levels. These findings simplify future research on the stress protein response in wild birds because samples can be safely kept in a cool box for a relatively long time.

This study was funded by project BOS2000-1125 of the Spanish Ministry of Science and Technology (to S. M. and J. M.). The El Ventorrillo field station collaborated in this study. G. T. was partly supported by a FPI grant from the Comunidad de Madrid and an accommodation grant from the Ayuntamiento de Madrid to reside at the Residencia de Estudiantes.