Speciation in the stonechat (Saxicola torquata) inferred from nucleotide sequences of the cytochrome-b gene

The geographical differentiation and speciation in the stonechat (Saxicola torquata; Aves: Turdidae) was studied by sequencing a 300-bp fragment of the mitochondrial cytochrome-b gene. Stonechats from three different subspecies inhabiting three continents (S. t. rubicola, the European stonechat; S. t. maura, the Siberian stonechat; and S. t. axillaris, an African stonechat) and stonechats from seven European populations were examined. While variation within the populations of the European subspecies was less than 0.3%, the genetic distances between the subspecies were substantial (2.7-5.7%) in comparison with published data for subspecies of other birds. If speciation is indeed reflected in the cytochrome-b gene of stonechats, species status for the African stonechat, but also for the Siberian taxon, should be reconsidered, especially in the light of differences in distributions, morphology and habitat preference.     

Age-related changes in song repertoire size and song type sharing in the Whinchat Saxicola rubetra

In many oscine passerines males’ songs, the repertoire size increases with age. At the same time it often remains unknown when and where males learn new songs. To infer the Whinchat Saxicola rubetra song learning strategy, we described and catalogued song-type repertoire, revealed age differences and examined song sharing strategies among neighbouring and distant males. We recorded song vocalizations of 40 males in a limited (104 ha) study plot during four years. Whinchats produce short and discrete songs with clear intersong pauses. In total 45 song types were allocated, the individual repertoire size averaged 23.5 ± 7.6 song types (range 9–34 song types). The males’ age significantly influenced the song-type repertoire size. The second calendar year (first breeding) males had a lower repertoire size than the older males. The majority of song types were shared by less than half of males in our sample. The Jaccard similarity indexes varied from 0.5 to 0.7. We could not find a relationship between males’ song sharing and geographic distances between their nests. We assume that Whinchat males learned new songs in the local population before territory establishment.     

Seasonal changes in day-light intensity as a potential zeitgeber of circannual rhythms in equatorial Stonechats

Summary The annual rhythms of reproduction and molt of equatorial Stonechats in East Africa (Saxicola torquata axillaris) are controlled by an endogenous circannual rhythmicity. This has been demonstrated in previous experiments in which birds from Africa were kept in a seasonally constant environment: the annual cycles of gonadal size and molt were found to persist for up to 10 years. Since in such constant environmental conditions the period of the rhythms tended to deviate from 12 months, we postulate that seasonally changing factors in the normal environment of these birds normally synchronize the rhythms with the natural year. In the present study we examined the possibility that annual variations in daytime light intensity that occur as a result of changing cloud cover associated with the dry and rainy seasons may provide a circannual zeitgeber. An experimental group consisting of 6 male Stonechats was kept for 25 months in a light-dark cycle in which the light period had a constant duration of 12.5 hours and an intensity alternating between high and low in a 300-day rhythm. Changes in testicular size and molt of these birds were compared with those of a control group of 6 birds that were exposed to the same photoperiod but with bright daylight throughout the experiment. In the control group, only one bird went through 2 testicular cycles and two birds went through one cycle. All these birds showed a molt rhythm, but periods were highly variable among individuals. In contrast, all experimental birds went through two testicular cycles and exhibited rather synchronous molt rhythms (Fig. 1). These findings support the hypothesis that changing light intensity during daytime may provide synchronizing stimuli for circannual rhythms. Nevertheless, premature conclusions should be avoided; possible shortcomings of the experiment are discussed.

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Saisonale Änderungen der Tageslicht-Intensität als potentieller Zeitgeber circannualer Rhythmen bei tropischen Schwarzkehlchen

Zusammenfassung Die Jahresrhythmik der Fortpflanzung und der Mauser äquatorialer Schwarzkehlchen aus Ost-Afrika (Saxicola torquata axillaris) werden von einer endogenen circannualen Rhythmik kontrolliert. Dies zeigten frühere Versuche, in denen nachgewiesen wurde, daß der Rhythmik der Gonadengröße und der Mauser auch bei solchen Vögeln fortbestand, die über mindestens 10 Jahre in einer konstanten Umwelt lebten. Die Periode dieser Rhythmik wich unter solchen konstanten Versuchsbedingungen allerdings von 12 Monaten ab, was impliziert, daß es in der natürlichen Umwelt der Schwarzkehlchen jahresperiodisch schwankende Umweltfaktoren gibt, die die endogenen Rhythmen mit dem astronomischen Jahr synchronisieren. In der vorliegenden Arbeit untersuchten wir die Möglichkeit, daß jahresperiodische Änderungen der Tageslicht-Intensität, wie sie als Folge von Bewölkungsänderungen mit dem Wechsel zwischen Regen — und Trockenzeiten auftreten, einen solchen Zeitgeber darstellen. Eine Versuchsgruppe von 6 männlichen Schwarzkehlchen wurde 25 Monate lang in einer konstanten äquatorialen Photoperiode von 12,25 Stunden gehalten, in der die Tageslicht Intensität in einem 300-tägigen Rhythmus zwischen einer Phase mit hoher Lichtintensität und einer Phase mit niedriger Lichtintensität abwechselte. Die Zyklen der Hodengröße und der Mauser dieser Vögel wurden mit denen von 6 Kontrollvögeln verglichen, die 25 Monate lang unter derselben Photoperiode aber bei gleichbleibend hellem Tageslicht gehalten wurden. In der Kontrollgruppe durchlief nur ein Vogel zwei Gonadenzyklen und zwei durchliefen je einen Zyklus. Alle 6 Vögel gingen durch einen Mauserzyklus mit großen interindividuellen Unterschieden in der Periodenlänge. Im Gegensatz dazu zeigten alle 6 Versuchsvögel zwei Gonaden- und Mauserzyklen (Abb 1). Die Ergebnisse stützen somit die Hypothese, daß Änderungen in der Beleuchtungsstärke am Tage die circannualen Rhythmen dieser Vögel synchronisieren können. Vorsicht vor zu weitgehenden Schlußfolgerungen scheint allerdings angebracht und mögliche Mängel im Experiment werden diskutiert.

     

Evidence for senescence in survival but not in reproduction in a short‐lived passerine

Senescence has been studied since a long time by theoreticians in ecology and evolution, but empirical support in natural population has only recently been accumulating. One of the current challenges is the investigation of senescence of multiple fitness components and the study of differences between sexes. Until now, studies have been more frequently conducted on females than on males and rather in long‐lived than in short‐lived species. To reach a more fundamental understanding of the evolution of senescence, it is critical to investigate age‐specific survival and reproduction performance in both sexes and in a large range of species with contrasting life histories. In this study, we present results on patterns of age‐specific and sex‐specific variation in survival and reproduction in the whinchat Saxicola rubetra, a short‐lived passerine. We compiled individual‐based long‐term datasets from seven populations that were jointly analyzed within a Bayesian modeling framework. We found evidence for senescence in survival with a continuous decline after the age of 1 year, but no evidence of reproductive senescence. Furthermore, we found no clear evidence for sex effects on these patterns. We discuss these results in light of previous studies documenting senescence in short‐lived birds. We note that most of them have been conducted in populations breeding in nest boxes, and we question the potential effect of the nest boxes on the shape of age‐reproductive trajectories.     

Effects of changes in farming of subalpine meadows on a grassland bird, the whinchat ( Saxicola rubetra)

The increasing intensity of farming of meadows is supposed to be the major cause for strong declines of many meadow breeding birds. The whinchat, Saxicola rubetra, a Palaearctic migratory bird, is an indicator species of open grassland farmed at a low intensity. Originally widespread throughout Switzerland, it is now restricted to mountain and subalpine grassland. We document the changes in meadow cultivation in subalpine farmland from 1988 to 2002, and the breeding performance and density of the whinchat. We explored the impact of habitat degradation on the population dynamics of this meadow bird. The cultivation of hay meadows changed markedly within the 15 years: the onset of mowing was shifted forward by about 20 days, and farmers applied new techniques such as silage and irrigation. This shift was more pronounced in the favourable farmland in the valley bottom (Pradellas) than on the slopes (Vnà). The percentage of successful whinchat broods, ranging from 5% to 78% in different years, strongly depended on mowing date on both sites. In spite of earlier mowing, birds did not change their time schedule of breeding. Breeding success in Pradellas was too low to compensate for mortality (sink population), but because of immigration the number of breeding pairs did not decrease untill 2000. Population size may therefore be a misleading indicator of local population viability. Based on the breeding schedule of whinchats at different altitudes, we recommend mowing dates in agreement with the reproductive cycle of ground nesting meadow birds.     

Ecological traits influence the current distribution and range of an island endemic bird

Aim  The aim of this paper is to investigate the causes of the current restricted distribution of a narrow-range endemic bird species, the Canary Islands stonechat, Saxicola dacotiae .
Location  Eastern islands of the Canary Islands archipelago.
Methods  We compared climatic patterns (temperature and rainfall), habitat and microhabitat structure, food availability during a full annual cycle, and the abundance of native avian competitors and predators inside and outside the species' range. Three study areas, located in similar habitats on nearby islands, were studied: northern Fuerteventura, close to the northern border of the species' range; southern Lanzarote, 22 km from the nearest site occupied by stonechats; and the Lobos islet, 10 km from the nearest occupied site and 2 km from the coast of Fuerteventura.
Results  The cover of suitable habitats (slopes with high cover of large shrubs, stony fields and ravines) and microhabitats (shrubs and boulders) and the abundance of arthropods during the breeding period of Canary Islands stonechats were lower outside than inside the species' range. Temperature, rainfall and the abundance of competitors and predators inside and outside the species' range did not differ significantly.
Main conclusions  Ecological requirements explaining the distribution of the Canary Islands stonechat within its range seem to be the main factor hindering its settlement on nearby islands. Geological and palaeoclimatic processes, as well as past and current human impact, could also have constrained the distribution of this narrow-range endemic bird species.     

Gonadal status upon spring arrival in long-distance and short-distance migrating stonechats (Saxicola torquata)

Long-distance migration is often associated with relatively short breeding seasons and a start of reproductive activities shortly after arrival. The full activation of the reproductive system from the regressed state takes, however, several weeks and must, therefore, be initiated in the winter quarters or during spring migration. Hence, long-distance migrants face a potential conflict between the energetic and temporal requirements of migration and the preparation for reproduction. We studied long-distance migratory Siberian stonechats in northern Kazakhstan and short- distance migratory European stonechats in Slovakia. We hypothesized that migratory distance and gonadal status at the time of arrival are related. We found that males of both populations arrived with gonads that were not fully developed. However, the populations neither differed in gonadal state at the time of arrival, nor in the rate of testicular development to the fully active state at the time of egg laying. The rate of the last stages of gonadal development may be determined by physiological constraints rather than by a trade-off between migration and reproduction. Within populations, passage migrants and local breeders could not be distinguished on the basis of their testicular development. However, passage migrants showed higher variation in gonadal size than local breeders, which could relate to the differences in migratory distance and hence reproductive timing.     

Endogenous gonadal,LH and molt rhythms in tropical stonechats: effect of pair bond on period,amplitude, and pattern of circannual cycles

To investigate the effects of reproduction and associated stimuli on the circannual cycles of African stonechats Saxicola torquata axillaris birds were held for 29 months in aviaries under a constant equatorial (12.25 h) photoperiod, either singly (10 females and 10 males) or in 10 male/female pairs. The birds of all 3 groups went through circannual cycles in gonadal size, plasma LH and molt, but groups differed with regard to actual reproductive performance. During the second cycle, only one of the singly-held females laid eggs and incubated. In constrast, in the paired females egg-laying and incubation occurred in all but one bird. About 50% of the clutches from paired females contained fertilized eggs confirming the expectation of behavioral differences between the paired and unpaired birds. However, despite differences in reproductive performance there were no differences in either circannual period or duration of reproductive phases. Moreover, there was no correlation between number of broods produced per season and circannual parameters of the paired females. Therefore, the temporal course and, particularly, the period during which reproduction is possible is rigidly determined by an endogenous program that is not influenced by reproductive performance. A rigid program of this kind may be advantageous in the tropics because it prevents prolongation of the breeding season in years with favourable conditions which in turn could jeopardize optimal timing of breeding in the following year and thus reduce lifetime reproductive success.     

Foraging ecology and reproductive biology of the Stonechat Saxicola torquata: comparison between a revitalized, intensively cultivated and a historical, traditionally cultivated agro-ecosystem

An effective strategy to reintegrate biodiversity within otherwise intensively cultivated agroecosystems is to create set-aside and wildflower areas. It remains largely unknown, however, whether the ecological performance of an agroecosystem revitalized in this manner is comparable—from a species’ population biology perspective—to traditionally exploited farmland. To address this question we compared, during two successive years, the trophic ecology and breeding performance of an insectivorous, indicator passerine (the Stonechat Saxicola torquata) in a revitalized intensively cultivated farmland (RIC) and a traditional, extensively cultivated farmland (TEC) in southern Switzerland. The chicks' diet and prey abundance did not differ between the RIC and TEC, with orthopterans, caterpillars (Lepidoptera) and coleopterans predominating (approx. 80% of diet biomass). Although Stonechat pairs initiated more broods in TEC than in the RIC, reproductive success (number of fledglings/territory × year) did not differ significantly between the TEC and RIC. The chicks’ condition (body mass) was slightly better in TEC than in RIC, while no such effect could be shown for chick constitution (tarsus length) in either year. The inter-site (RIC vs. TEC) variation fell well within the inter-annual variation of breeding parameters, indicating that environmental stochasticity could be a greater determinant of reproductive output and young quality than agroecosystem type. Although in need of replication, these results suggest that incentives for setting aside farmland and creating wildflower areas within agroecosystems may not only enhance plant and invertebrate diversity, as has been demonstrated earlier, but can also support functioning populations of vertebrates situated at higher trophic levels along the food chain.     

Low ambient temperature increases food intake and dropping production, leading to incorrect estimates of hormone metabolite concentrations in European stonechats

Non-invasive methods to measure steroid hormone metabolites in bird droppings or mammalian feces have become very popular. However, the accuracy of these measurements may be affected by many factors. Here, we use the stonechat (Saxicola torquata) as a passerine bird model to test whether differences in ambient temperature affect food intake and dropping production and whether these changes lead to measurement artefacts in hormone metabolite concentrations. In addition, we tested for diurnal patterns in hormone metabolites. We held European stonechats in climate chambers and subjected them to two different long-term ambient temperature regimes, +5 degrees C and +22 degrees C. As expected, food intake and dropping production was higher at +5 degrees C than at +22 degrees C. Plasma concentrations of corticosterone and testosterone did not differ between different ambient temperature regimes. However, corticosterone and testosterone metabolite concentrations (in ng/g) were significantly lower at +5 degrees C than at +22 degrees C. When we measured the rate of hormone metabolite excretion (in picogram per hour) instead of the concentration, there was no difference between treatment groups. Thus, the measurement of hormone metabolite concentrations can be flawed because, depending on the treatment, similar amounts of hormone metabolites can be excreted into very different amounts of droppings. In conclusion, hormone metabolite concentration measurements are sensitive to changes in ambient temperature and probably any other factor that alters metabolic rates. Any study involving systematic changes in metabolism--i.e., during molt, migration, hibernation, egg production, or seasonal comparisons--needs to take these caveats into account.     

Cold weather events provoke egg ejection behaviour in open‐nesting passerines

We analysed 25 conspecific egg ejection events from a large sample of nests (n = 762) of three passerine species. In two species, most of the events could not be explained by intraspecific brood parasitism or nest sanitation behaviour. At least some of these cases were behavioural responses to unfavourable weather conditions in the spring of 2017. We conclude that clutch size adjustment through egg ejection may be more widespread among passerines than previously thought.     

Bird numbers in relation to grazing on a grouse moor from 1957–61 to 1988–98

Birds were counted before and after heavy grazing on a Scottish grouse moor. Oystercatchers Haematopus ostralegus, Lapwings Vanellus vanellus and Curlews Numenius arquata increased where high sheep stocks and grass seeding converted much ling Calluna vulgaris to smooth grass, but not where heath remained. A heathy part that held many gamebirds in 1957–61 but later became short grass had no Red Grouse Lagopus lagopus scoticus, Black Grouse Tetrao tetrix or Grey Partridge Perdix perdix in 1989–98. The study area held many Golden Plover Pluvialis apricaria in 1957–61 but none in 1988–98.     

Polymorphism at the Clock gene predicts phenology of long‐distance migration in birds

Dissecting phenotypic variance in life history traits into its genetic and environmental components is at the focus of evolutionary studies and of pivotal importance to identify the mechanisms and predict the consequences of human‐driven environmental change. The timing of recurrent life history events (phenology) is under strong selection, but the study of the genes that control potential environmental canalization in phenological traits is at its infancy. Candidate genes for circadian behaviour entrained by photoperiod have been screened as potential controllers of phenological variation of breeding and moult in birds, with inconsistent results. Despite photoperiodic control of migration is well established, no study has reported on migration phenology in relation to polymorphism at candidate genes in birds. We analysed variation in spring migration dates within four trans‐Saharan migratory species (Luscinia megarhynchos; Ficedula hypoleuca; Anthus trivialis; Saxicola rubetra) at a Mediterranean island in relation to Clock and Adcyap1 polymorphism. Individuals with larger number of glutamine residues in the poly‐Q region of Clock gene migrated significantly later in one or, respectively, two species depending on sex and whether the within‐individual mean length or the length of the longer Clock allele was considered. The results hinted at dominance of the longer Clock allele. No significant evidence for migration date to covary with Adcyap1 polymorphism emerged. This is the first evidence that migration phenology is associated with Clock in birds. This finding is important for evolutionary studies of migration and sheds light on the mechanisms that drive bird phenological changes and population trends in response to climate change.     

Observer variation in estimates of Meadow Pipit Anthus pratensis and Skylark Alauda arvensis abundance on moorland

Capsule Counts least susceptible to observer effects were those within 25 m of a transect and the total number along a transect, with observer effects greater for distance sampling.     

Evidence for declines in populations of grassland-associated birds in marginal upland areas of Britain

Capsule We report large declines among summer populations between 1968–80 and 2000.

Aim To assess changes in the status of breeding populations of birds in pastoral uplands.

Methods Volunteer observers revisited 13 areas of marginal upland in Britain where Common Birds Census data were collected during 1968–80. This allowed the status of 35 bird species to be examined over about 20 years and to make a comparison between grassland-based and woodland-based species.

Results For 12 species the decline in abundance was significant, particularly among passerines, such as Skylark Alauda arvensis, Wheatear Oenanthe oenanthe, Whinchat Saxicola rubetra, Yellow Wagtail Motacilla flava and Yellowhammer Emberiza citrinella, each of which declined by over 80%. Redshank Tringa totanus, Yellow Wagtail, Dipper Cinclus cinclus, Whinchat, Wheatear, Ring Ouzel Turdus torquatus and Yellowhammer were found on less than half the number of plots on which they were originally recorded. Most declining species were associated with grassland for nesting and foraging, compared to those species that increased (Wood Pigeon Columba palumbus, Pied Wagtail Motacilla alba, Carrion Crow Corvus corone, Jackdaw C. monedula and Goldfinch Carduelis carduelis) that were less specialized in their habitat requirements. Woodland or woodland edge species showed no significant change in status, suggesting that population declines among grassland species were not due to lower observer effort between recording periods.

Conclusion Long-term changes to grassland ecosystems in marginal upland areas of Britain may have influenced the status of bird populations.     

Ectogenesis and the case against the right to the death of the foetus

Ectogenesis, or the use of an artificial womb to allow a foetus to develop, will likely become a reality within a few decades, and could significantly affect the abortion debate. We first examine the implications for Judith Jarvis Thomson’s violinist analogy, which argues for a woman’s right to withdraw life support from the foetus and so terminate her pregnancy, even if the foetus is granted full moral status. We show that on Thomson’s reasoning, there is no right to the death of the foetus, and abortion is not permissible if ectogenesis is available, provided it is safe and inexpensive. This raises the question of whether there are persuasive reasons for the right to the death of the foetus that could be exercised in the context of ectogenesis. Eric Mathison and Jeremy Davis have examined several arguments for this right, doubting that it exists, while Joona Räsänen has recently criticized their reasoning. We respond to Räsänen’s analysis, concluding that his arguments are unsuccessful, and that there is no right to the death of the foetus in these circumstances.     

On the diversity of the Cladocera in the tropics

The mythical concept of an impoverished tropical cladoceran fauna is refuted. On a planetary scale, around half of the cladoceran species presently known occur exclusively in the tropics-subtropics, often with considerable restriction to particular geographical subzones. On a regional (political) scale, the situation is often unclear because of the continued fragmentary nature of studies, and because political units are not a good basis for biogeographical comparisons. At the finest level of resolution (lake-perlake comparisons), there appears to be an upper limit of c. 50 cladoceran species per individual lake. No significant difference between lakes in the temperate zone and in the tropics could be established here. Daphnia is largely absent from the tropics, but is replaced by more Sidids, Moinids, and Bosminids, such that the average cladoceran community in the limnetic zone of a tropical lake is not characterized by less species but rather by lower population densities. This, in turn, is considered a consequence of higher prevalent predation levels in the tropics.