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Randler C.,University of Education, Heidelberg | Forschler M.I.,Institute of Avian Research Vogelwarte Helgoland
Animal Behaviour | Year: 2011

Passerine mobbing calls are, in part, addressed to conspecific and heterospecific prey individuals, and may encourage them to join a flock mobbing a predator. We examined whether conspecific and heterospecific individuals differ in their response to natural and manipulated contact and mobbing calls. We assumed that conspecifics would be more sensitive to slight variation in call elements and manipulations, whereas heterospecifics most likely cannot distinguish subtle differences. We used chaffinch, Fringilla coelebs, contact and mobbing calls, which differ only slightly in structure (start and maximum frequency and frequency bandwidth). Despite these subtle differences in call parameters, mobbing calls of chaffinches could be transformed into artificial contact calls by using fewer elements/min, and vice versa. Contact calls could be transformed into mobbing calls by reducing the pauses between the single elements. The results show that intense calling attracted more conspecific and heterospecific prey individuals than less intense playbacks of the calls made of the same elements. Responses to natural calls compared to manipulated calls were similar in minimum distance to the speaker in conspecifics and heterospecifics, in the number of conspecific and heterospecific individuals alerted and in the number of heterospecific species attracted. The frequency of calls per time unit was the most significant factor affecting whether other birds interpreted the vocalization as a mobbing or a contact call. In conspecifics, the effect sizes of the response were smaller, suggesting that conspecifics perceive the manipulation as conflicting information. © 2011 The Association for the Study of Animal Behaviour.

Schmaljohann H.,Institute of Avian Research Vogelwarte Helgoland | Fox J.W.,Migrate Technology Ltd. | Bairlein F.,Institute of Avian Research Vogelwarte Helgoland
Animal Behaviour | Year: 2012

Migrants' responses to varying meteorological and magnetic conditions and their consequent costs in terms of energy and time are crucial for the understanding of the spatial principles guiding migration. Until now, studies of birds' phenotypic responses to environmental conditions and estimated costs of migration in terms of energy and time have focused on single sites and have rarely followed individuals along entire migration routes. We used individual-based light level geolocators to track birds' daily phenotypic responses to the environmental conditions experienced along a 30 000. km migration between Alaska and Africa. In autumn, departures of northern wheatears, Oenanthe oenanthe, were highly dependent on low temperatures and light winds but there was no such apparent dependence in spring. Migration was 1.4-times faster in spring than in autumn. There was an unexpected shift in the ratio of migration:stopover time towards less stopover time in spring, reducing spring's total energy costs for migration with respect to distance covered by nearly 50% in comparison to autumn. Despite strong changes in declination during migration, offering near-experimental conditions, birds did not navigate exclusively along any major compass course. In contrast to expectations, these high-Arctic migrants did not follow great circle routes; their hypothetical energetic benefit (ca. 20% for flying) might be insufficient and conditions for orientation too unfavourable to favour its evolution. © 2012 The Association for the Study of Animal Behaviour.

Bauch C.,Institute of Avian Research Vogelwarte Helgoland
Proceedings. Biological sciences / The Royal Society | Year: 2013

Telomere length is associated with cellular senescence, lifestyle and ageing. Short telomeres indicate poor health in humans and reduced life expectancy in several bird species, but little is known about telomeres in relation to phenotypic quality in wild animals. We investigated telomere lengths in erythrocytes of known-age common terns (Sterna hirundo), a migratory seabird, in relation to arrival date and reproductive performance. Cross-sectional data revealed that, independent of age, individuals with short telomeres performed better: they arrived and reproduced earlier in the season and had more chicks in the nest. The latter effect was stronger the older the brood and stronger in males, which do most of the chick provisioning. Longitudinal data confirmed this pattern: compared with birds that lost their brood, birds that raised chicks beyond the 10th nestling day experienced higher telomere attrition from one year to the next. However, more detailed analysis revealed that the least and most successful individuals lost the fewest base pairs compared with birds with intermediate success. Our results suggest that reproductive success is achieved at the expense of telomeres, but that individual heterogeneity in susceptibility to such detrimental effects is important, as indicated by low telomere loss in the most successful birds.

Szostek K.L.,Institute of Avian Research Vogelwarte Helgoland | Schaub M.,Swiss Ornithological Institute | Becker P.H.,Institute of Avian Research Vogelwarte Helgoland
Journal of Animal Ecology | Year: 2014

Immigration is a major demographic factor shaping population dynamics. However, due to methodological difficulties, the extent of immigration and factors affecting immigration are insufficiently studied. This is also true for seabird colonies. We estimated annual immigration based on a long-term study of a colony of common terns Sterna hirundo marked with transponders, using a Bayesian integrated population model that links colony size and productivity with individual life histories. Strong annual fluctuations in the number of immigrants were found. To identify whether colony-specific covariates influenced immigration, we related the number of immigrants to various proxy variables for breeding site quality, specifically colony size, productivity, number of local subadults and local recruits. Numbers of local recruits and local subadults showed strong positive correlations with number of immigrants. We found that variation in immigration rate had strongly contributed to variation in colony growth rate, more so than variation in local recruitment or adult survival. Collectively, results suggest that immigration strongly affects colony growth rate, that the driving force behind immigration is natal dispersal and that immigrants were attracted by local recruits. © 2014 British Ecological Society.

Bauch C.,Institute of Avian Research Vogelwarte Helgoland | Becker P.H.,Institute of Avian Research Vogelwarte Helgoland | Verhulst S.,University of Groningen
Molecular Ecology | Year: 2014

Telomeres, DNA-protein structures at chromosome ends, shorten with age, and telomere length has been linked to age-related diseases and survival. In vitro studies revealed that the shortest telomeres trigger cell senescence, but whether the shortest telomeres are also the best biomarker of ageing is not known. We measured telomeres in erythrocytes of wild common terns Sterna hirundo using terminal restriction fragment analysis. This yields a distribution of telomere lengths for each sample, and we investigated how different telomere subpopulations (percentiles) varied in their relation to age and fitness proxies. Longer telomeres within a genome lost more base pairs with age and were better predictors of survival than shorter telomeres. Likewise, fitness proxies such as arrival date at the breeding grounds and reproductive success were best predicted by telomere length at the higher percentiles. Our finding that longer telomeres within a genome predict fitness components better than the shorter telomeres indicates that they are a more informative ageing biomarker. This finding contrasts with the fact that cell senescence is triggered by the shortest telomeres. We suggest that this paradox arises, because longer telomeres lose more base pairs per unit time and thus better reflect the various forms of stress that accelerate telomere shortening, and that telomeres primarily function as biomarker because their shortening reflects cumulative effects of various stressors rather than reflecting telomere-induced cell senescence. © 2013 John Wiley & Sons Ltd.

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