Do haemosporidians affect fuel deposition rate and fuel load in migratory blackcaps Sylvia atricapilla?
Published: Volume 56(1), June 2009. Pages 41-47.
Aims: Fuel deposition rate is one of the main parameters determining bird migration strategies. Accordingly, factors compromising fuel deposition rate, such as parasite infections, might have relevant effects not only on migration, but also on other life history events that depend on migration success, such as breeding. We analysed the effect of haemosporidians on fuel load and fuel deposition rate in a population of migratory blackcaps (Sylvia atricapilla) during stopover in northern Iberia.
Locality: Loza lagoon, northern Iberia (42º 50'N, 01º 43'W, 400 m a.s.l.).
Methods: From blood samples of recaptured blackcaps we determined haemospiridian content by amplification of 479 bp of the parasite's cytochrome b gene. Independent on body size, of the sampled birds, 35 % were infected by Haemoproteus-Plasmodium.
Results: Mass deposition rate, fat score and body mass showed similar values in non-infected as in infected blackcaps. No differences in age or body size proportions were detected between infected and non-infected birds.
Conclusions: These results may be explained by infected birds with high virulence (compromising fuel accumulation) being unable to migrate south from their breeding areas in central and northern Europe. In contrast, more resistant birds may be able to tolerate the parasitaemia and gain fuel normally. Another possibility is that only birds with a low intensity of parasite infection were captured (presumably birds able to overcome the parasitaemia successfully), since these birds may be able to accumulate fuel at a similar rate to non-infected birds. Furthermore, highly infected birds may have a lower likelihood of capture than non-infected birds, because birds lose mobility with a high intensity of infection and under these circumstances they are less likely to be captured.