Bluethroat Research Articles

Thermal paper can replace typewriter correction paper in Emlen funnels

Emlen funnels are small funnel-shaped orientation cagesused to record the spontaneously directed migratory rest-lessness (Zugunruhe) of night-migratory songbirds (Emlenand Emlen 1966). Today, almost every group studying thecompass orientation capabilities of migratory songbirdsuses the Emlen funnel method (e.g., Sandberg et al. 2002;Wiltschko and Wiltschko 2003; Ritz et al. 2004; Muheimet al. 2006; Chernetsov et al. 2008). This method providesthe most reliable and cost effective tool to analyze thespontaneous directional preference of many migratorysongbirds during the migratory season. Results from Emlenfunnel experiments also play a key role in the current rushtowards understanding how the magnetic compass sense inmigratory songbirds works (e.g., Ritz et al. 2004; Mouritsenand Ritz 2005).When Emlen first invented the method (Emlen andEmlen 1966), he used an inkpad at the bottom of the cageand lined the walls of the funnel with blotting paper toscore the ink marks as a measure of the bird’s directionalchoice. Later, Rabol (1979) got the idea to use typewritercorrection paper on the walls instead of ink and blottingpaper to record the birds’ directional preferences. This wasa significant improvement for the birds, since ‘‘Rotkehl-chen’’ (Robin Erithacus rubecula) would no longer become‘‘Blaukehlchen’’ (Bluethroat Luscinia svecica) after severalnights hopping on the inkpad. The refined typewriter cor-rection paper version of the Emlen funnel was adopted byvirtually every study using Emlen funnels after 1980 (e.g.,Mouritsen and Larsen 1998; Sandberg et al. 2002;Wiltschko and Wiltschko 2003; Ritz et al. 2004; Muheimet al. 2006). However, over the last 10 years, researchersusing the Emlen funnel method have been challengedby the disappearance of typewriters, which has made itexceedingly difficult to find a reliable supplier of appro-priately sized rolls of typewriter correction paper needed todo Emlen funnel experiments.The Wiltschko-lab in Frankfurt (e.g., Wiltschko andWiltschko 2003; Ritz et al. 2004) were instrumental inconvincing one of the producers of typewriter correctionpaper to make a final production run, which helped manycolleagues stock up on paper for several years. Unfortu-nately, the chalk-like coating on typewriter correctionpaper tends to harden with time, which means that itbecomes more and more difficult to accurately scorescratches on the paper. In addition to this problem, ourstock ran out several years ago, which made us initiate asearch for an alternative solution, as going back to the inkmethod would not be acceptable for animal welfarereasons.First, we visited the local crime unit to see if fingerprintdetection dust could help us. It did not work because itsfunction is based on the fat on the fingers which the duststicks to. But the claws of birds are normally fat free andthus claw marks cannot be visualized with fingerprintdetection dust. Second, we got the idea that maybe thepaper used in trucks to record their speed (tachopgraphcharts, ‘‘Fahrtenschreiberpapier’’ in German) could also beused to record the scratches left in Emlen funnels bymigratory birds. As a result, we tested various such papersfrom several different producers with variable success untilwe received a sample of ‘‘Thermal paper’’ product number‘‘SC55’’ from the company ‘‘Blumberg Systempapiere’’,Kalkumerstrasse 46, 40885 Ratingen-Lintorf, Germany;

Alternative antipredator tactics in tree lizard morphs: hormonal and behavioural responses to a predator encounter

Most vertebrates respond to acute stressors with rapid plasma glucocorticoid elevations. Variation within species in this hormonal response should correlate with differences in physiological responses and behavioural tactics, yet this is rarely documented. We measured behavioural and hormonal responses of free-ranging male tree lizards ( Urosaurus ornatus ) during staged encounters with a collared lizard predator ( Crotaphytus nebrius ) or a control (stick). In our study population, males express alternate reproductive tactics that correlate with throat colour pattern: territorial males have a central blue patch on an orange background (OB males) and nonterritorial males lack the blue patch (O males). We also studied a previously uncharacterized male type with a mottled orange and blue throat (M males). A single encounter with an approaching predator initiated an elevation in plasma corticosterone that was similar among the male types (mean ± SE = 9.64 ± 3.17 (OB), 9.72 ± 2.49 (O), 10.19 ± 2.82 (M)). Despite this similarity, male types differed behaviourally. Compared to OB and M males, O males initiated flight when the predator was further away and stayed hidden longer after seeking refuge. The M males showed responses similar to OB males and may functionally be the same morph. Among individuals of all morphs, total corticosterone levels after the predator encounter correlated strongly with their flight initiation distance and hiding duration during the encounter. We conclude that male tree lizards with alternative reproductive tactics show alternative antipredator behavioural tactics, and that individual variation in escape responses is directly correlated with corticosterone levels.

Testosterone stimulates the expression of a social color signal in Yarrow's Spiny Lizard, Sceloporus jarrovii

The sex steroid testosterone has been shown to regulate the development of male-specific coloration in many organisms that exhibit sexual dichromatism, but the role of testosterone is less certain for species in which both sexes express bright coloration. Lizards in the genus Sceloporus possess bright blue patches on their throats and abdomens. These patches, which are used in social signaling, are often regulated by testosterone and are consequently expressed only in males of most species. However, Yarrow's Spiny Lizard (Sceloporus jarrovii, Cope 1875) exhibits a derived condition in which both sexes express bright blue ventral patches despite dramatic sexual differences in circulating testosterone levels throughout postnatal ontogeny. In this study, we used surgical castration and hormone replacement in juvenile males to test the hypothesis that testosterone stimulates the expression of blue ventral coloration in S. jarrovii. In two separate experiments conducted in captivity and the natural field environment, we found that surgical castration decreased the hue and saturation while increasing the brightness of blue throat and abdominal patches. Castration also decreased the amount of black pigment bordering the blue throat patch. Treatment of castrated males with exogenous testosterone restored all aspects of ventral coloration to values similar to those of intact control males. Early organizational effects of testosterone during prenatal development may lead to the expression of blue coloration in both sexes, but the results of our present experiments indicate that subsequent effects of testosterone during sexual maturation further enhance the coloration of males.

Seventy new microsatellites for the pied flycatcher, Ficedula hypoleuca and amplification in other passerine birds

The pied flycatcher (Ficedula hypoleuca) is a small migratory passerine bird commonly distributed across Europe which has been the focus of considerable ecological and evolutionary research. Here, we present details of 70 microsatellite markers for the species adding to the six which are currently available. Sixty-six markers were also polymorphic in the closely related collared flycatcher (Ficedula albicollis), while 54 were polymorphic in another related passerine, the bluethroat (Luscinia svecica), and 12 were polymorphic in the more distantly related Siberian jay (Perisoreus infaustus).

Importance of trophic information, simplification and aggregation error in ecosystem models

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 360:25-36 (2008) - DOI: https://doi.org/10.3354/meps07394 Importance of trophic information, simplification and aggregation error in ecosystem models S. J. Metcalf1,2,3,*, J. M. Dambacher2, A. J. Hobday1,2, J. M. Lyle3 1School of Zoology and QMS, University of Tasmania, Private Bag 5, Hobart, Tasmania, Australia, 7001 2CSIRO Marine and Atmospheric Research, GPO Box 1538, Hobart, Tasmania, Australia, 7001 3Marine Research Laboratories, Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, Private Bag 49, Hobart, Tasmania, Australia 7001 *Email: metcalfs@utas.edu.au ABSTRACT: Ecosystem models are becoming increasingly important as pressure from fisheries intensifies and ecosystem-based fisheries management becomes more widely used. Trophic webs often form the basis of ecosystem models and ecosystem-specific dietary information is crucial for optimal model performance. This is particularly the case if model predictions are used in management decisions. The Tasmanian live fish fishery for banded morwong was used as a case study to investigate the importance of trophic information, model simplification and aggregation error on ecosystem model results. Dietary analysis of 6 commonly captured reef fish was undertaken. Significant trophic overlap was found between blue throat wrasse Notolabrus tetricus and purple wrasse N. fucicola, and banded morwong Cheilodactylus spectabilis and bastard trumpeter Latridopsis forsteri. Marblefish Aplodactylus arctidens and long-snouted boarfish Pentaceropsis recurvirostris had significantly different diets from other species studied. Using this information, a detailed qualitative model was produced and then simplified through the aggregation of variables. Variables were aggregated using 3 methods: Euclidean distance, Bray-Curtis similarity, and regular equivalence for inclusion in 3 simplified models. Variable aggregation is undertaken in many studies and may create aggregation error. Each aggregation method produced a different proportion of incorrect model predictions as a result of aggregation error. The model simplified using regular equivalence produced the least aggregation error and a web structure aligned with the dietary analysis. More widespread use of these methods in fisheries management should be considered. KEY WORDS: Diet · Qualitative modelling · Model structure · Regular equivalence Full text in pdf format PreviousNextCite this article as: Metcalf SJ, Dambacher JM, Hobday AJ, Lyle JM (2008) Importance of trophic information, simplification and aggregation error in ecosystem models. Mar Ecol Prog Ser 360:25-36. https://doi.org/10.3354/meps07394 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 360. Online publication date: May 22, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Age‐related variation in primary sexual characters in a passerine with male age‐related fertilization success, the bluethroat Luscinia svecica

In passerine species with frequent extrapair mating, young (second calendar year) males often have a lower fertilization success than older (after second calendar year) males. This pattern might be explained by male‐ or female‐driven mechanisms, such as female preference for older males or higher competitive ability of older males. In this study we measured the size of the testes, the seminal glomera and the cloacal protuberance as well as the size and motility of the sperm, in individual bluethroats Luscinia svecica. In this species, nearly all extrapair fertilizations (EPFs) are obtained by older males. We found that the mass of the testes and the seminal glomera were highly positively correlated and that older males had significantly larger testes (38%), seminal glomera (15%) and cloacal protuberance (23%) than young males. In contrast, there was no difference between age groups in average sperm size or sperm motility. Our results are consistent with the idea that higher fertilization success by older males in this species is due to their higher rate of sperm production, allowing larger ejaculates and/or more frequent copulations. Unequal sperm production capacities by young and older males have important implications for the interpretation of paternity patterns in extrapair mating systems.

Population structure and migratory directions of Scandinavian bluethroats Luscinia svecica– a molecular, morphological and stable isotope analysis

Many species of birds show evidence of secondary contact zones and subspeciation in their Scandinavian distribution range, presumably resulting from different post‐glacial recolonization routes. We investigated whether this is the case also in the Scandinavian bluethroat Luscinia svecica, a species that has been suggested to consist of two separate populations: one SW‐migrating and long‐winged (L. s. gaetkei) breeding in southern Norway, and one shorter‐winged ESE‐migrating (L. s. svecica) in northern Scandinavia. We sampled males at eleven breeding sites from southern Norway to northernmost Sweden. There were no morphological differences or latitudinal trends within the sample, neither were there any genetic differences or latitudinal trends as measured by variation in AFLP and microsatellite markers. Stable isotope ratios of throat feathers moulted on the wintering grounds showed no, or possibly marginal differences between birds from southern Norway and northern Sweden. We also re‐measured old museum skins that in previous studies were classified as L. s.gaetkei, and found marginally longer wings in birds from the southern part of the Scandinavian breeding range. The difference, however, was much smaller than proposed in earlier studies. We conclude that there is no evidence of a genetic population structure among Scandinavian bluethroats that would suggest the presence of a zone of secondary contact. Finally we discuss whether the presumed subspecies gaetkei ever existed.

Blow fly Trypocalliphora braueri parasitism on Meadow Pipit and Bluethroat nestlings in Central Europe

The larvae of blow fly (Trypocalliphora braueri) are known to cause a subcutaneous myiasis in bird nestlings mainly in Nearctic species, while only a few records are available from the Palaearctic. Here, we report on infestations of this insect ectoparasite in two passerine species, Meadow Pipit (Anthus pratensis) and Bluethroat (Luscinia svecica), breeding in the Central European mountain range Krkonose. The infestation of T. braueri parasite was relatively low in studied bird species (3.0% of infested nests in Meadow Pipit and 4.2% in Bluethroat) but varied strongly between years (0–33% of infested nests/year/species). The presence of the parasitic blow fly larvae was apparently controlled by temperature; they were found only during warm summers. The combination of parasite infection and heavy rainfalls in a critical period significantly reduced nestling survival.

Expression of breeding coloration in European Green Lizards (Lacerta viridis): variation with morphology and tick infestation

According to the hypothesis of parasite-mediated sexual selection, for a communication system to work reliably, parasites should reduce the showiness of sexual signals of their host. In this study, we examined whether the expression of breeding coloration in free-ranging adult European Green Lizards ( Lacerta viridis (Laurenti, 1768)) is linked with infestation by their common ectoparasite Ixodes ricinus (L., 1758) (Acari: Ixodidae). We found that tick infestation was higher in males than in females. Males showing relatively heavier body for their tail length (predominantly males with regenerated tails) and relatively thinner tail base experienced higher infestation rates. In turn, relatively heavier females for their snout–vent length were less tick infested. Although some components of throat and chest coloration varied significantly with relative tail length, tail-base thickness, body mass, and head size, a measure of male throat and female chest color saturation seemed independent of lizard morphology. After correcting for the effects of morphology on skin coloration and tick load, the saturation of blue throat color in male lizards decreased with increasing level of tick infestation. In contrast, yellow chest color saturation increased with residual tick numbers in females. Considering presumably different signaling functions of male and female lizard coloration, our work suggests that tick infestation might represent a handicap for Green Lizards.

Do Displays Send Information about Ornament Structure and Male Quality in the Ornate Tree Lizard, Urosaurus ornatus?

AbstractDisplays can transmit information about ornament or male quality; however, few studies have simultaneously explored the relationship between displays, ornament and male quality within a single species. We quantified ornament morphology (five throat color morphs, throat area, and belly area), male quality (bite force, sprint speed, body condition, and body mass), display behavior [percent time displaying (PTD), number of pushups per display, and display duration], and movement behavior among males in a population of the ornate tree lizard, Urosaurus ornatus. Previous studies have shown that male U. ornatus are polymorphic in throat coloration and that morphs differ in behavioral aggression. Our study shows that blue throat morphs use 1.5 more pushups per display than other male color morphs, which suggests that throat color and display behavior act as backup signals for aggression. However, other data support the multiple messages hypothesis, and overall our data do not provide conclusive evidence for any one hypothesis. In addition, we show that body mass is positively related to both PTD and percent time moving and this relationship is independent of color morph. We also found that throat area, belly area, bite force, sprint speed, and body condition are unrelated to display behavior. This result highlights at least some discordance between display behavior, ornaments, and performance in U. ornatus and suggests that these traits may be evolving independently.

AvianClockgene polymorphism: evidence for a latitudinal cline in allele frequencies

In comparison with most animal behaviours, circadian rhythms have a well-characterized molecular genetic basis. Detailed studies of circadian clock genes in 'model' organisms provide a foundation for interpreting the functional and evolutionary significance of polymorphic circadian clock genes found within free-living animal populations. Here, we describe allelic variation in a region of the avian Clock orthologue which encodes a functionally significant polyglutamine repeat (ClkpolyQcds), within free-living populations of two passerine birds, the migratory bluethroat (Luscinia svecica) and the predominantly nonmigratory blue tit (Cyanistes caeruleus). Multiple ClkpolyQcds alleles were found within populations of both species (bluethroat: 12 populations, 7 alleles; blue tit: 14 populations, 9 alleles). Some populations of both species were differentiated at the ClkpolyQcds locus as measured by F(ST) and R(ST) values. Among the blue tit, but not bluethroat populations, we found evidence of latitudinal clines in (i) mean ClkpolyQcds repeat length, and (ii) the proportions of three ClkpolyQcds genotype groupings. Parallel analyses of microsatellite allele frequencies, which are considered to reflect selectively neutral processes, indicate that interpopulation allele frequency variation at the ClkpolyQcds and microsatellite loci does not reflect the same underlying demographic processes. The possibility that the observed interpopulation ClkpolyQcds allele frequency variation is, at least in part, maintained by selection for microevolutionary adaptation to photoperiodic parameters correlated with latitude warrants further study.

Functional infertility among territorial males in two passerine species, the willow warbler Phylloscopus trochilus and the bluethroat Luscinia svecica

Information about male infertility in free‐living birds is scarce, but anecdotal and circumstantial evidence suggests that it does occur regularly at a low frequency. In this paper we document three cases of azoospermia in two passerine species, the willow warbler Phylloscopus trochilus and the bluethroat Luscinia svecica at their breeding grounds in South Norway. In willow warblers, two males out of a sample of 50 territory holders had no sperm in their seminal glomera, the storage site of sperm ready for ejaculation. The two males also had very small testes. One out of 48 bluethroat males also had no sperm in the seminal glomera. This male had an extreme asymmetry of the testes, with the right testis being about twice as large as the left. He also failed to fertilize any eggs in his own nest, as well as in neighbouring nests, as revealed by microsatellite genotyping. Thus, the proportion of males without sperm seems to be at a magnitude of a few (2–4) percent in both species. These are among the first estimates of the frequency of azoospermia in wild birds. Our results indicate a significant risk for sexually monogamous females of laying unfertilized eggs, which could favour the evolution of extra‐pair copulation as a fertility insurance strategy in females.

Molecular and phenotypic divergence in the bluethroat (Luscinia svecica) subspecies complex

Subspecies complexes may provide valuable insights into the early stages of the speciation process. The bluethroat (Luscinia svecica) consists of many morphologically distinct subspecies that differ most strikingly in the ornamental colour pattern of the male throat. We investigated the genetic and phenotypic differentiation in this subspecies complex, using (i) microsatellite genotyping (11 loci) of a sample of 364 individuals from bluethroat populations in Europe and Asia, and (ii) spectrometric and morphological measurements of a sample of 131 museum skin specimens. Population genetic analyses, based on microsatellite allele frequency variation, revealed a slight but significant overall population differentiation (F(ST) = 0.042). There was a well-differentiated southern group of subspecies with white or no throat spots and a less-differentiated northern group of chestnut-spotted populations. Phylogenetic analyses indicated that the southern all-blue and white-spotted forms are ancestral to the chestnut-spotted subspecies. In addition to the qualitative variation in throat plumage pattern already described in the literature, we found significant quantitative variation among subspecies in hue, chroma and brightness of the ultraviolet (UV)/blue throat coloration, and this variation seemed to be unrelated to the phylogenetic distance between subspecies.

Non‐destructive ageing in Notolabrus tetricus using dorsal spines with an emphasis on the benefits for protected, endangered and fished species

Age estimates from clipped dorsal spines were compared to otoliths and scales in the blue throat wrasse Notolabrus tetricus. Dorsal spines provided accurate, non‐destructive ageing and are recommended in favour of destructive methods for conservation purposes.

北海道におけるオガワコマドリの記録

There have been five records of Bluethroat Luscinia svecica, from Hokkaido. All are capture records except for one that is unclear in detail. There has been no direct observation record. Among the four capture records, one was obtained in the latter half of September and three in early October. These occurrence records are markedly earlier than those in the southern half of Japan. There has been no record in winter seasons. It is highly probable that Bluethroat recorded in Hokkaido are accidental visitors while undergoing their autumn migration.

Numerical and functional responses of breeding passerine species to mass occurrence of geometrid caterpillars in a subalpine birch forest: a 30‐year study

In northern Fennoscandia, the geometrid moths Epirrita autumnata and Operophtera brumata have cyclicities in density with mass occurrence at 10‐year intervals. The larvae of Epirrita and Operophtera attain a size of 2–3 cm and 1.5–2 cm, respectively, and are nutritious food items for passerine birds. To examine whether these larvae have any numerical and/or functional influence on a passerine bird community (mountain birch forest in Budal, central Norway) during a 30‐year period (1972–2001), I estimated their abundance (number of larvae per 100 sweeps) in the birch canopy, and the densities of breeding birds in the passerine community. In addition, from 1972 to 1998, I monitored the nesting success of five of the bird species. The foraging pattern of the most abundant bird species and their gizzard contents (adults and nestlings) were examined in 1972–78 (covering population peaks of both the geometrids). Population peaks of Epirrita occurred in 1975–76, 1985–86 and 1996, and of Operophtera in 1976–77, 1986–87 and 1997–98. The passerine community consisted of eight species that were territorial in all 30 years, one species in 26 years, three species in 14–21 years and three species in 1–4 years. Only the Brambling Fringilla montifringilla population responded numerically to the fluctuations of Epirrita and Operophtera. Brambling was also the only species whose mean clutch size varied between years, and this correlated positively with the density of Epirrita. The mean annual nesting success of Willow Warbler Phylloscopus trochilus, Bluethroat Luscinia svecica and Common Redpoll Carduelis flammea tended to be higher in years with mass outbreaks of Epirrita, but was significantly so only for Reed Bunting Emberiza schoeniclus. The abundance of Operophtera larvae showed no influence on the nesting success of any bird species. The passerines foraged more frequently in the birch canopy in the Epirrita outbreak years (1975–76) than in the years before or after. Gizzard analyses of five adult passerine species and their nestlings showed that Epirrita was the main food item in 1974–76. Even though Operophtera occurred in large numbers in birch trees in 1976 and 1977, only a few larvae were found in the gizzards of the passerines. None of the passerines showed an increase in their population density in the year following the larval outbreaks, but the densities of Willow Warbler and Bluethroat increased in the succeeding year, indicating a higher return rate for these species. The study shows the existence of a dietary response and also indicates a reproductive response to the changes in the abundance of Epirrita in mountain birch forest. The lack of numerical response in the passerines (except the Brambling) to the fluctuation in Epirrita contrasts with the pattern described for passerine communities in northern temperate deciduous forests in North America, where Lepidoptera caterpillars periodically have mass outbreaks.

Inventering av fåglar i Rautasområdet 1978 och 2001 – populationsförändringar i ett fjällområde

The breeding bird fauna of the Rautas mountain area, south of Torne träsk in northern Sweden, was censused in 1978 and 2001. Sixtyseven 2x2 km squares were censused along 9.6 km transects within each square. Thirtyone of the 63 analysed species showed no significant population changes, 20 species had decreased significantly, and 12 species had increased significantly. Among the increasing species were: Short-eared Owl Asio flammeus, Long-tailed Skua Stercorarius longicaudus, Redpoll Carduelis flammea, and Whimbrel Numenius phaeopus. Among the 20 decreasing species were: Golden Plover Pluvialis apricaria, Red-throated Pipit Anthus cervinus, Bluethroat Luscinia svecica, and Lapland Bunting Calcarius lapponica. A Correspondence analysis revealed that a relatively large proportion of the species in alpine heathlands had decreased, while there was a mixture of stable, increasing and decreasing species at the woodland and wetland end of the gradient. A possible explanation to the observed population changes could be an increasing number of reindeer in the Swedish mountains since the 1970s, since overgrazing can affect both the availability of nest sites and food negatively.

Extrapair paternity and offspring immunocompetence in the reed bunting, Emberiza schoeniclus

Female promiscuity is widespread in birds, as well as in other taxa. It is often assumed that in bird species with a socially monogamous mating system, females engage in extrapair copulations to obtain indirect (genetic) benefits. ‘Good genes’ and ‘compatible genes’ models predict that extrapair young (EPY) should be of higher quality than within-pair young (WPY), but the empirical evidence for this effect is limited. A recent study, however, indicated an enhanced cellular immunity in EPY in a passerine bird, the bluethroat, Luscinia svecica. To assess the generality of that finding, we replicated the study using the reed bunting, a passerine with an extrapair mating system similar to that of the bluethroat. Using the same immune assay protocol, we found no indication of enhanced cellular immunity in EPY compared with WPY. Female reed buntings thus do not seem to engage in extrapair copulations to achieve the same type of genetic benefit as in bluethroats. Furthermore, EPY in mixed-paternity broods did not grow faster and were not in better body condition close to fledging than WPY. We conclude that our results do not support the hypotheses assuming indirect benefits to female extrapair copulations. It appears that the adaptive value for females of pursuing extrapair fertilizations varies, even between species with similar extrapair mating systems.

Age-related improvement of reproductive success in Bluethroats Luscinia svecica

Capsule Young birds are less likely to have high reproductive success compared with older ones because of a lack of several skills influencing breeding performance. Aims To test the ‘constraint’ hypothesis by investigating the effect of male and female age on reproductive performance of a Bluethroat Luscinia svecica population. Methods We compared two age-classes (yearling versus old), breeding for the first time at Guérande salt-pans, France, by evaluating arrival dates on breeding site, territory quality, laying dates, clutch size and egg size, delay before re-nesting, breeding performance, feeding rate at two different nestling periods (on days 4–5 and 10–11 after hatching) and nestling body condition. Results Our results clearly demonstrated an age effect on reproductive performance for both males and females: young breeders were less likely to fledge young. In older males, improvement of reproductive success was related to feeding rate during the first nestling period. For females, timing of breeding (laying date) and reproductive investment (such as clutch size, feeding rate in the whole nestling period, brood condition) were the main determinants. The presence of a yearling in a pair strongly decreased the number of young produced per breeding season. Conclusion Bluethroat supported the ‘constraint’ hypothesis, i.e. that behavioural and physiological maturation is needed for young breeders to enhance reproductive performance.

Sex‐specific patterns in body condition and testosterone level changes in a territorial migratory bird: the Bluethroat Luscinia svecica

The Bluethroat Luscinia svecica is a migratory passerine that exhibits a socially monogamous pair bond and a high level of parental care. Males are territorial both when wintering and breeding whereas females are territorial only in winter. We investigated changes in body condition and testosterone levels during successive life‐history stages and determined their relationships. Sex‐specific patterns were observed in the variation in body condition and testosterone level. Male body condition varied mainly during the winter. It peaked at the onset of the prenuptial moult and then decreased, whereas it remained stable throughout breeding. In contrast, female body condition varied mainly during the breeding season. It increased during the prelaying stage and then abruptly decreased until fledgling provisioning. As in other monogamous and territorial passerines, testosterone levels in Bluethroat males were low during winter, increased in late winter, peaked during the prelaying stage and then decreased when provisioning young. In wintering females, territorial competition caused testosterone levels to rise. These females were able to produce territorial vocalizations and exhibit aggressive postures. Females showed higher mean testosterone levels than males when wintering whereas the opposite was observed when breeding. Our data from wintering female Bluethroats support the ‘challenge hypothesis’ under which high testosterone levels are associated with periods of social instability, and testosterone can regulate female territorial behaviour during this period.