Abstract
The impact of nest ectoparasites on chicks was studied for the first time in a free-living North African cavity nesting bird, an Algerian population of blue tits, Parus caeruleus ultramarinus. The proportion of nests (prevalences) with acarids (mite Dermanyssus, tick Ixodes) and insects (blow fly Protocalliphora, flea Ceratophyllus) varied between 80-100%. Compared to most European studies of cavity nesters, parasite intensities were high for blow flies and low for mites or fleas. Experiments to diminish the high parasite pressures in this population had little or no effect on different morphological measures of chicks that could reflect post-fledging survival, such as mass gain and body size (tarsus length, mass at fledging). Nestling mortality was only weakly affected by the experiments. Our results suggest that hosts can resist high parasite pressures. We conclude that understanding the mechanisms involved in host-parasite interactions requires both experimental and long-term multi-factor analyses.