Consequences of late breeding on moult and recovery rate of a long-distance migrant, the Wheatear (Oenanthe oenanthe)

Unsere Studie hat am Steinschmätzer die Folgen einer verlängerten Brutzeit durch zusätzliche Spätbruten für das Zeitmanagement von Weitstreckenziehern untersucht. Wir fragten, ob der Zeitverlauf der Mauser verändert wird, ob saisonale Aktivitäten verschachtelt werden und ob die Geschlechter unterschiedlich auf spätes Brüten reagieren. Zudem erwarteten wir eine verminderte Rückkehrrate von Spätbrütern. Die Ergebnisse zeigen, dass Steinschmätzer beider Geschlechter ohne Spätbruten kurz nach dem Ausfliegen der Jungen gleichzeitig mit der Mauser beginnen, während spät brütende Steinschmätzer den Mauserbeginn verzögern. Die Verzögerung ist bei den Weibchen (23 Tage) viel ausgeprägter als bei den Männchen (6 Tage). Infolgedessen überlappten spätbrütende Männchen häufig Brut und Mauser, während die Weibchen möglicherweise vor dem Zugbeginn in Zeitdruck gerieten. Trotz des späten Mauserbeginns wechselten Spätbrüter beider Geschlechter ihr Gefieder tendenziell um etwa eine Woche langsamer und konnten somit ihre Verspätung nicht kompensieren. Obwohl zwei Bruten für den Steinschmätzer sicher eine höhere Belastung darstellen, zeigten die Rückkehrraten keine Benachteiligung auf. Unabhängig von Alter, Geschlecht und Anzahl der Bruten lag die Rate im Populationsmittel bei 23,5 %. Vermutlich ziehen nur Steinschmätzer in ausgezeichneter körperlicher Verfassung Spätbruten auf und gleichen die zusätzliche Belastung aus.The present study investigates consequences of late breeding for the seasonal time management of long-distance migrants, as exemplified by the Wheatear. We examined whether the time course of moult was changed, whether seasonal activities were overlapped, and whether the sexes differed in the ways they modified seasonal behaviour when breeding late. Furthermore, we expected that late breeders would incur a cost of additional late breeding by reduced return rates. The results of the study showed that in Wheatears without late clutches both sexes initiated moult simultaneously soon after fledging of the clutch. Late breeders, in contrast, delayed moult onset. The delay was much more pronounced in females (23 days) than males (6 days). As a consequence, late breeding males but not females frequently overlapped breeding and moult, while females may have incurred time pressure to finish moult in time for migration. Despite the late onset of moult, its duration was extended by approximately one week, and therefore, late breeders did not compensate for their seasonal delay. Yet although double clutches are most likely to be demanding, late-breeding Wheatears showed no signs of decreased, but instead, tentatively elevated return rates. Return rates were independent of age, sex, and number of clutches and averaged 23.5 %. We propose that only Wheatears in excellent physical condition initiate additional late clutches and are able to compensate for any arising costs

Offspring pay sooner, parents pay later:Experimental manipulation of body mass reveals trade-offs between immune function, reproduction and survival

Introduction: Life-history theory predicts that organisms trade off survival against reproduction. However, the time scales on which various consequences become evident and the physiology mediating the cost of reproduction remain poorly understood. Yet, explaining not only which mechanisms mediate this trade-off, but also how fast or slow the mechanisms act, is crucial for an improved understanding of life-history evolution. We investigated three time scales on which an experimental increase in body mass could affect this trade-off: within broods, within season and between years. We handicapped adult skylarks (Alauda arvensis) by attaching extra weight during first broods to both adults of a pair. We measured body mass, immune function and return rates in these birds. We also measured nest success, feeding rates, diet composition, nestling size, nestling immune function and recruitment rates.Results: When nestlings of first broods fledged, parent body condition had not changed, but experimental birds experienced higher nest failure. Depending on the year, immune parameters of nestlings from experimental parents were either higher or lower than of control nestlings. Later, when parents were feeding their second brood, the balance between self-maintenance and nest success had shifted. Control and experimental adults differed in immune function, while mass and immune function of their nestlings did not differ. Although weights were removed after breeding, immune measurements during the second brood had the capacity to predict return rates to the next breeding season. Among birds that returned the next year, body condition and reproductive performance a year after the experiment did not differ between treatment groups.Conclusions: We conclude that the balance between current reproduction and survival shifts from affecting nestlings to affecting parents as the reproductive season progresses. Furthermore, immune function is apparently one physiological mechanism involved in this trade-off. By unravelling a physiological mechanism underlying the trade-offs between current and future reproduction and by demonstrating the different time scales on which it acts, our study represents an important step in understanding a central theory of life-history evolution.</p

Divergent patterns of telomere shortening in tropical compared to temperate stonechats

Abstract Telomeres have emerged as important biomarkers of health and senescence as they predict chances of survival in various species. Tropical birds live in more benign environments with lower extrinsic mortality and higher juvenile and adult survival than temperate birds. Therefore, telomere biology may play a more important role in tropical compared to temperate birds. We measured mean telomere length of male stonechats (Saxicola spp.) at four age classes from tropical African and temperate European breeding regions. Tropical and temperate stonechats had similarly long telomeres as nestlings. However, while in tropical stonechats pre-breeding first-years had longer telomeres than nestlings, in temperate stonechats pre-breeding first-years had shorter telomeres than nestlings. During their first breeding season, telomere length was again similar between tropical and temperate stonechats. These patterns may indicate differential survival of high-quality juveniles in tropical environments. Alternatively, more favorable environmental conditions, that is, extended parental care, may enable tropical juveniles to minimize telomere shortening. As suggested by previous studies, our results imply that variation in life history and life span may be reflected in different patterns of telomere shortening rather than telomere length. Our data provide first evidence that distinct selective pressures in tropical and temperate environments may be reflected in diverging patterns of telomere loss in birds

Behavioural response of a migratory songbird to geographic variation in song and morphology

IntroductionSexually selected traits contribute substantially to evolutionary diversification, for example by promoting assortative mating. The contributing traits and their relevance for reproductive isolation differ between species. In birds, sexually selected acoustic and visual signals often undergo geographic divergence. Clines in these phenotypes may be used by both sexes in the context of sexual selection and territoriality. The ways conspecifics respond to geographic variation in phenotypes can give insights to possible behavioural barriers, but these may depend on migratory behaviour. We studied a migratory songbird, the Stonechat, and tested its responsiveness to geographic variation in male song and morphology. The traits are acquired differently, with possible implications for population divergence. Song can evolve quickly through cultural transmission, and thus may contribute more to the establishment of geographic variation than inherited morphological traits. We first quantified the diversity of song traits from different populations. We then tested the responses of free-living Stonechats of both sexes to male phenotype with playbacks and decoys, representing local and foreign stimuli derived from a range of distances from the local population.ResultsBoth sexes discriminated consistently between stimuli from different populations, responding more strongly to acoustic and morphological traits of local than foreign stimuli. Time to approach increased, and time spent close to the stimuli and number of tail flips decreased consistently with geographic distance of the stimulus from the local population. Discriminatory response behaviour was more consistent for acoustic than for morphological traits. Song traits of the local population differed significantly from those of other populations.ConclusionsEvaluating an individual’s perception of geographic variation in sexually selected traits is a crucial first step for understanding reproductive isolation mechanisms. We have demonstrated that in both sexes of Stonechats the responsiveness to acoustic and visual signals decreased with increasing geographic distance of stimulus origin. These findings confirm consistent, fine discrimination for both learned song and inherited morphological traits in these migratory birds. Maintenance or further divergence in phenotypic traits could lead to assortative mating, reproductive isolation, and potentially speciation

Diet Analysis of Wetland Passerine Nestlings Using Neck Collars or Faecal Sampling Produces Similar Results

Two methods are commonly used to study the diet of nestling passerines: the neck collar method and faecal sampling. Most studies apply either method, however, few methodological studies comparing both methods exist and are mainly limited to farmland birds. Furthermore, existing methodological studies only include high-level taxonomic diet categories. Here, we compared both methods using two wetland species, the Reed Bunting Emberiza schoeniclus and the Sedge Warbler Acrocephalus schoenobaenus, and included family level as a lower taxonomic prey level. We found no differences between the two methods in the dietary composition of high-level taxonomic categories (mainly orders) and only small differences in some orders at the family level. Hence, we recommend using the less invasive and easily accessible faecal sampling method rather than the use of neck collars in diet composition studies

Testosterone, territorial response, and song in seasonally breeding tropical and temperate stonechats

Abstract Background Testosterone facilitates physiological, morphological, and behavioral changes required for breeding in male vertebrates. However, testosterone concentrations and the link between its seasonal changes and those in reproductive behaviors vary greatly among species. To better understand the impact of tropical and temperate environments and life history factors on this variation, we have compared testosterone, territorial behavior and song performance across sequential stages of the breeding season in males of 16 closely related taxa of East African tropical and West European temperate stonechats (Saxicola spp), which all breed during a short breeding season, but differ in migratory behavior, seasonal territory-acquisition and pace of life. Results We found that generally, the profiles of testosterone and territorial behavior were similar across latitudes. African stonechats with a slow pace of life had equally high peak testosterone concentrations and responded as aggressively to an intruder as European stonechats with a fast pace of life. However, song performance at the beginning of the breeding season was lower in African than in European stonechats. The differences in song performance were not associated with variation in testosterone levels between tropical and temperate stonechats. Conclusions The results suggest a very similar role for testosterone as a mediator of high intensity territorial aggression during the fertile period of females in tropical and temperate stonechats, which all are highly seasonal, locally synchronous breeders. A potential explanation may be high risk of extra-pair copulations which has been associated with synchronous breeding. Interestingly, an association was not consistent for song performance. Our data suggest that song performance can be disassociated from peak testosterone levels depending on its role in breeding behavior. Despite similar testosterone levels, European males, which early in the breeding season acquire territories and mates, showed greater song performance than African stonechats, which maintain year-round territories and pair-bonds. Taken together, our study comparing related taxa of old world songbirds suggests that short breeding seasons may be a major selective force for high peak testosterone levels during breeding regardless of latitude and pace of life, but that particular behaviors, in our case song, can be uncoupled from peak testosterone levels

Additional file 1: Table S1. of Testosterone, territorial response, and song in seasonally breeding tropical and temperate stonechats

Datasets. (XLSX 99 kb

Habitat selection, diet and food availability of European Golden Plover Pluvialis apricaria chicks in Swedish Lapland

Fennoscandian alpine tundra habitats support large numbers of breeding waders, but relatively little is known about their breeding ecology despite the fact that this habitat is threatened by climate change. We studied habitat selection, diet and prey availability of European (Eurasian) Golden Plover Pluvialis apricaria chicks at the Vindelfj€allen Nature Reserve, Ammarn€as, Sweden. Information from 22 chicks tracked using radio-transmitters was analysed. By analysing 149 faecal samples, four main prey taxa were identified, Coleoptera (40%), Bibionidae (31%), Hymenoptera (13%) and Tipulidae (10%). We found that chicks switched from feeding on Tipulidae to feeding on Bibionidae as they grew, and that this switch coincided with a shift from the use of the habitat where Tipulidae were abundant (alpine meadow/heathland) to the use of the habitat were Bibionidae were abundant (Willow shrub). Although chicks track food availability to some extent, the link between prey availability and habitat use was not perfect, indicating that additional factors other than food abundance, such as shelter from predators, determine habitat selection. Bibionidae are an important prey for Golden Plover chicks as it is the only prey group that has a late summer flush in abundance, in contrast to the general decline of total arthropod biomass during the chick-rearing period. However, Bibionidae imagoes only occurred in 2011 and were virtually absent in 2013, which relates to the species’ ecology with 2- to 5-year cycles in mass occurrence. Extreme annual variation in an essential food source such as Bibionidae imagoes might have an important effect on the condition and survival of Golden Plover chicks, an important subject for future studies. The foraging conditions for Golden Plover chicks in Fennoscandia appear to be different to those in the UK, where the chicks rely mainly on a Tipulidae flush only