Pauli Saag

Plumage bacterial load increases during nest-building in a passerine bird

AbstractPlumage 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.ZusammenfassungAnstieg in der Bakterienbelastung des Gefieders während des Nestbaus bei einer Singvogelart Gefiederbakterien spielen für Vögel möglicherweise eine bedeutende Rolle der Ausprägung ihrer Lebensgeschichte. Allerdings haben bisher wenige Studien die natürlichen Muster in der Variation von Gefiederbakterien untersucht. Wir haben bereits gezeigt, dass die Bakterienbelastung des Gefieders weiblicher Kohlmeisen (Parus major) in der Zeit vor der Eiablage höher liegt, als während der Jungenaufzucht. Hier haben wir nun untersucht, ob der Bakterien-Peak vor der Legephase bei weiblichen Kohlmeisen während des Nestbaus entsteht, bei dem die Weibchen in erhöhten Kontakt mit dem Boden und mit dem Nestmaterial kommen, oder ob er sich schon zu einer früher Zeit entwickelt. Die Weibchen wurden in drei Phasen des Nestbaus gefangen (Nest angefangen, Nest halb fertig und Nest fertiggestellt). Die Dichte an Gefiederbakterien und die Artenvielfalt Federn abbauender Bakteriengemeinschaften wurden mittels Durchflusszytometrie bzw. einer Analyse der ribosomalen intergenetischen Spacer (RISA) untersucht. Die Dichte anhaftender Bakterien auf den Federn stieg zwischen Nestanfang und -Fertigstellung signifikant an. Auf den Artenreichtum der Federn abbauenden Bakterien hatte die jeweilige Nestbauphase keinen nachweisbaren Einfluss. Unsere Ergebnisse deuten darauf hin, dass sich die Dichte anhaftender Bakterien im Gefieder freilebender Vögel während des Nestbaus schnell ändern kann, was für einzelne Vögel möglicherweise einen Teil der Nestbaukosten verursacht.

Behavioral and physiological responses of nestling pied flycatchers to acoustic stress.

The extended secretion of stress hormones in fully developed animals is known to have profound consequences. However, little is known about the effects of stress on the behavior and physiology of free-living young animals, and how such responses relate to each other. We repeatedly (during 5 consecutive days, 1 h/day) exposed the nestlings of a passerine bird, the pied flycatcher (Ficedula hypoleuca), to recordings of nestling distress calls and examined their behavioral and physiological responses to the stressor on the first and the last day of the experiment (on days 9 and 13 post-hatch, respectively). In comparison with control siblings, stressed nestlings reduced the amount of time that they devoted to vocalization and locomotion and increased levels of circulating corticosterone. In 9-day-old nestlings, the level of stress-induced hormone was negatively related to locomotor activity, but not to the rate of vocalizations. The repeated presentation of the stressor increased the heterophile-to-lymphocyte ratio in nestlings but did not affect nestling growth rate. In 13-day-old nestlings, the level of stress-induced corticosterone was not related to behavioral activity. These results suggest that the high level of corticosterone released by immature nestlings in response to a stressor may promote anti-predator behavior (e.g., passive avoidance behavior). Moreover, repeatedly induced stress may have a cumulative and potentially negative effect on individual physiology.

Development of stress response in nestling pied flycatchers

Birds respond to unpredictable events by secreting corticosterone, which induces various responses to cope with stressful situations. However, the evidence is still elusive whether altricial nestlings perceive and respond to external stressors. We investigated the development of adrenocortical stress response to handling-related stressor in nestlings of a small passerine bird, the pied flycatcher (Ficedula hypoleuca). Nestlings were held in isolation from their parents during the experiment to ensure that they indeed respond to handling, not to parental alarm calls. We found that both 9- and 13-day-old nestlings were able to elicit hormonal stress response. Although baseline as well as stress-induced corticosterone levels rose slightly with age, the magnitude of difference between the control and stress-induced levels remained similar in both age groups. However, comparison with adults showed that the stress response of nestlings prior to fledging was still incomplete and significantly lower than in adults. Overall, our results indicate that altricial nestlings do respond to acute stressors, but on the contrary to previous predictions the development of corticosterone stress response during growth period is not gradual and varies remarkably between different passerine species.

Plumage bacterial load is related to species, sex, biometrics and fledging success in co-occurring cavity-breeding passerines

Abstract. Plumage bacteria might influence the trade-off between parental and self-preening efforts in birds, therefore affecting breeding success. However, too little is known about natural variation patterns in plumage bacterial communities for these hypotheses to be thoroughly assessed. We studied the density and phylotypic richness of plumage bacterial assemblages in wild breeding populations of Pied Flycatchers Ficedula hypoleuca and Great Tits Parus major in the same area and breeding season, using flow cytometry and ribosomal intergenic spacer analysis (RISA). The density of plumage bacteria was higher in Tits than in Flycatchers, providing evidence that bacterial microflora differs even between co-occurring hosts that share habitat, nest site and foraging preferences. It is concurrent with the finding that migratory birds might have lower bacterial loads than sedentary birds. In both species bacterial loads were higher in females than in males, which along with two earlier studies, indicates the generality of this sex pattern. A negative correlation between parental body mass and the richness of feather-degrading bacterial phylotypes was found in Pied Flycatchers. In Great Tits, higher bacterial densities in the plumage of parent birds were associated with the production of fewer fledglings. However, the causality of these associations remains to be tested experimentally.

DRD4 gene polymorphism in great tits: gender-specific association with behavioural variation in the wild

Recent studies indicate that polymorphisms of the DRD4 gene may be related to behavioural variation in mammals and birds. The purpose of this study was to ascertain a connection between DRD4 genotypes and behavioural patterns in a wild passerine bird during breeding time. We evaluated changes in birds’ parental provisioning behaviour in the presence of a novel object. As a behavioural trait, we measured the duration of feeding interruption from the first time that each bird noticed the novel object until they entered the nest box. We found a gender-specific association between DRD4 gene polymorphism and parental behaviour. Males with a CC genotype delayed feeding for a longer period than those with CT and TT genotypes. No significant effect of genotype on provisioning behaviour was observed among females. We conclude that (i) DRD4 gene polymorphism in wild birds can be associated with behaviour related to fearfulness, and (ii) this effect is supposedly gender-specific during the breeding time, potentially explained by sex differences in parental care or hormonal levels.

Manipulation of parental effort affects plumage bacterial load in a wild passerine

It has been suggested that plumage microorganisms play an important role in shaping the life histories of wild birds. Some bacteria may act as pathogens or cause damage to feathers, and thereby reduce individual fitness. Intense parental care in birds can result in a reduction of self-maintenance and preening behavior in parents and therefore might affect the dynamics of microbiota living on their feathers. However, experimental evidence of this relationship is virtually absent. We manipulated the parental effort of wild breeding pied flycatcher (Ficedula hypoleuca) females by modifying their brood size or temporarily removing male partners. We expected that experimentally decreasing or increasing parental effort would affect feather sanitation in females and therefore also bacterial density on their plumage. In accordance with this hypothesis, manipulation affected the density of free-living bacteria: females with reduced broods had the lowest number of free-living bacteria on their feathers, while females left without male partners had the highest. However, manipulation did not have a significant effect on the densities of attached bacteria. Our results provide experimental evidence that a trade-off between self-maintenance and parental effort affects plumage bacterial densities in birds.