Priit Kilgas

ABSTRACT Plumage bacteria may play an important role in shaping the life histories of birds. However, few studies have examined natural patterns of variation in plumage bacteria. We have previously shown that plumage bacterial load is higher during the pre-laying period than during the brood rearing period in female Great Tits (Parus major). Here, we examined whether the pre-laying bacterial peak in female Great Tits develops during nest-building, where the females come into increased contact with the ground and nest materials, or dates back to an earlier period. Females were captured during three stages of nest-building (nest initiated, nest half ready, and nest completed). The density of plumage bacteria and the species richness of feather-degrading bacterial assemblages were studied using flow cytometry and ribosomal intergenic spacer analysis (RISA), respectively. The density of attached bacteria on feathers increased significantly between nest initiation and nest completion. No effect of nest-building stage on feather-degrading bacterial species richness was found. Our results indicate that the density of attached bacteria in the plumage of free-living birds can change rapidly during nest-building, providing one potential cost of nest-building for individual birds.

ABSTRACT Plumage bacteria may play an important role in shaping the life histories of birds. However, to design suitable experiments to examine causal relationships between plumage bacteria and the fitness of host birds, natural variation in plumage bacterial communities needs to be better understood. We examined within-individual consistency of plumage bacterial contamination in Great Tits (Parus major), comparing different body regions (ventral vs. dorsal) and comparing contamination between years. Numbers of free-living and attached bacteria and the species richness of feather-degrading bacterial assemblages were studied using flow cytometry and ribosomal intergenic spacer analysis (RISA). Numbers of both types of bacteria were higher on dorsal than on ventral feathers. Numbers of free-living, but not attached, bacteria on the two body regions were highly positively correlated. There was also a strong within-individual correlation between numbers of attached bacteria during the same breeding stages in different years. These results suggest that, despite variation in absolute levels of feather bacterial loads between years and different body regions, sampling individual birds can provide reliable estimates of relative levels of bacterial contamination, as long as sampling time and body region are carefully standardized.RESUMENLas bacterias del plumaje pueden jugar un papel importante en el moldeamiento de las historias de vida de las aves. Sin embargo, para diseñar un experimento adecuado que examine la relación efecto causa entre las bacterias del plumaje y el éxito de las aves hospederas, se necesita entender mejor la variación natural de la comunidad de bacterias en el plumaje. Examinamos la consistencia en la contaminación de bacterias dentro de los individuos de Parus major, comprando diferentes regiones del cuerpo (ventral vs dorsal) y comparando contaminación entre años. Números de bacterias viviendo libremente y adheridas y la riqueza de especies del ensamble de bacterias degradadoras de plumas fueron estudiadas usando citometria de flujo y análisis ribosomal intergenetico espaciado (RISA). Números de ambos tipos de bacterias fueron más elevados en el dorso que en las plumas ventrales. Números de bacterias viviendo libremente, pero no las adheridas, en las regiones del cuerpo estuvieron altamente y positivamente correlacionados. También hubo una fuerte correlación dentro del individuo entre los números de bacterias adheridos durante el mismo estado reproductivo en años diferentes. Estos resultados sugieren que a pesar de la variación absoluta en los niveles de las cargas de bacterias del plumaje entre años y diferentes regiones corporales, individuos muestreados pueden proporcionar estimativos consistentes en los niveles relativos de contaminación bacteriana, siempre y cuando los tiempos de muestreo y la región corporal sean cuidadosamente estandarizados.

Differences in competitive abilities of siblings in birds can be caused by a combination of hatching asynchrony and intra-clutch variation in egg quality. However, very little is known how within-brood hierarchies affect the allocation of resources between different functions of the body. We examined the effects of within-brood hierarchy on growth of morphological parameters, blood plasma antioxidant protection and immune function of free-living great tit Parus major nestlings. To assure that competitive hierarchies occur, we experimentally delayed the start of incubation of the last two eggs in the clutch. At pre-fledging stage (day 13 post-hatch), late-hatched nestlings were smaller in body mass and wing length when compared to early-hatched nestlings, but no differences between siblings were found in tarsus length, plasma antioxidant potential, uric acid concentration, residual antioxidant potential (from regression with uric acid), hematocrit and response to phytohaemagglutinin injection. In early-hatched nestlings, the antioxidant potential and residual antioxidant potential measured in the middle of nestling period (day 6 post-hatch) were negatively related to body mass growth at early nestling stage, indicating that fast initial growth could reduce antioxidant properties of blood plasma.