Collared Flycatcher Research Articles

Niche divergence mechanisms of closely related hybridising bird species. Modeling approach based on remote sensing data of forest habitats

Describing mechanisms that ensure stable co-occurrence of sympatric species is fundamental to understanding the complexity of ecological community dynamics. In this study, the Pied flycatcher and the Collared flycatcher were used as model species for the analysis of co-occurrence patterns of closely related hybridising species that inhabit overlapping forest habitats. I hypothesise that spatial niche partitioning between species emerges as a vital adaptive response to interspecific competition and manifests itself in significant shifts in habitat preferences in syntopic areas but not in the allotopic ones. The study leverages a comprehensive dataset that includes species density in 372 randomly selected 1 km² grid cells across the territory of Poland. The analysis of habitat preferences was performed with linear mixed-effect modeling, whereas a contrast analysis was used to investigate changes in habitat preferences resulting from the presence of a competitor. The findings indicate that both species modify their habitat preferences when transitioning between syntopic and allotopic sites. Remarkably, in regions without competitors, such shifts are significantly less pronounced, as demonstrated by the Pied flycatcher that prefers the same habitats both in allopatric regions and allotopic sites. When these results are compared with other studies on closely related hybridising and non-hybridising species, it turns out that what influences the degree and number of niches subjected to competition is the time that passes from species divergence. This study highlights the imperative need to incorporate co-occurrence parameters of closely related species into niche and species distribution models to enhance their ecological realism.

The Pied and the Collared Flycatcher do not compete for microhabitats in the Białowieża Forest

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Parental provisioning is weakly age‐dependent and heritable in a small passerine

Parental care in birds encompasses many behaviours, from selecting nest‐sites and supplying eggs with nutrients to incubation and offspring provisioning. Unlike the early stages, where offspring are passive receivers of care, chicks actively solicit care after hatching. This may lead to either parent–offspring conflict or coadaptation, or both, if there is genetic variance in both parental provisioning and offspring begging. However, given that parental provisioning is highly responsive to brood size and age, its genetic determination is questioned. In this study, we used a multigenerational pedigree and 11 years of provisioning data to dissect the variation in this trait in the Collared Flycatcher Ficedula albicollis, and to examine whether offspring provisioning changes as parents age. We found that the parental provisioning rate was weakly repeatable (r = 0.088–0.213) and heritable (h2 = 0.052–0.158). Higher values were obtained when calculated based on within‐individual averages rather than individual measurements, and after adjusting for fixed effects. Older parents provisioned offspring at a lower frequency than younger ones. An additive genetic component in provisioning indicates potential for the evolution of parental care, parent–offspring coadaptation and indirect genetic effects on offspring traits. Future studies employing new tracking technologies, including accelerometers, radars and radio‐frequency identification readers, may help to determine whether senescence or increased experience causes the lower rate of offspring provisioning observed in older parents.

Plumage color degradation indicates reproductive effort: an experiment

Plumage color has traditionally been regarded as a static ornamental trait, but evidence is accumulating for significant color changes without molt that typically reduce the conspicuousness of ornamentation. In some species, the social partner seems to increase its reproductive investment if the color trait is experimentally enhanced, suggesting that color change could act as a signal. However, the information content of this signal is so far unclear. For example, birds in poor condition or making greater effort may deteriorate more severely. We used brood size manipulations to alter the reproductive effort of male and female collared flycatchers Ficedula albicollis. Both sexes showed less severe decline in some reflectance attribute of their white breast when their brood was experimentally reduced. In each sex, greater deterioration of the reflectance trait affected by the manipulation was accompanied by increased feeding rate by the partner. These feeding patterns do not prove, but are consistent with, a compensatory response by the partner to induced degradation. The manipulation effects on color change we detected confirm for the first time that plumage color deterioration can indicate current reproductive effort, thereby providing a potential fitness advantage to social partners that react to such deterioration.

Heterogeneity in song rates in the Collared Flycatcher (Ficedula albicollis) explained with the availability parameter in generalized N-mixture models: Its importance for abundance estimates in avian aural counts

Binomial N-mixture models are commonly applied to estimate abundance unaffected by imperfect detection, but are known to be sensitive to violations of assumptions. One of the model's assumptions, the independence of detections has rarely been tested. It requires that during a survey, detection of one individual does not affect detection of another individual. This assumption can be frequently violated in passerine birds, which exhibit territorial behaviour by singing, since neighbouring individuals are likely to motivate each other to vocalize, leading to non-independence in singing activity and in the following detection rate. Here, we explored this phenomenon with the generalized, binomial version of the N-mixture model, where detection probability is decomposed into availability probability φ – which can be interpreted as per capita song rate or the probability of vocalising – and actual detection probability p, given vocalisations take place. Using repeated counts of the Collared Flycatcher (Ficedula albicollis) as a case study, and treating the maximum observed counts Cmaxi at a site i as an explanatory covariate for φ, we showed that per capita song rates increased with observed counts at a site. Hence, if song rates vary due to local abundance, including Cmaxi as an explanatory variable for song rate addressed with φ, helps to explain this variation (which otherwise goes undetected) and improves inferences under the model. This had strong effects on the resulting abundance estimates: if this relationship was ignored in the models, total estimated population sizes were consequently lower by as much as 22–27%, compared to when this effect was included. Since it is likely that song rates may commonly be density-dependent in birds manifesting territorial behaviours by singing, further tests addressing violations of independence assumptions in these models are needed. As suggested by Kéry and Royle (2016), despite some form of circularity likely being involved, modelling heterogeneity in the detection process with the help of Cmaxi in standard N-mixture models (which, given availability, conflate availability with detection in a single parameter) should be applicable as well.

Effects of elevated nest box temperature on incubation behaviour and offspring fitness-related traits in the Collared Flycatcher Ficedula albicollis

Ambient temperature experienced by an animal during development or subsequently as an adult can affect many aspects of its behaviour and life-history traits. In birds, egg incubation is a vital component of reproduction and parental care. Several studies have suggested that environmental factors (such as nest microclimate) can influence the ability of incubating parents to maintain suitable conditions for embryo development. Here, we manipulated the developmental conditions of embryos through a modification of nest box thermal microclimate to investigate female incubation behaviour and its impact on offspring fitness-related traits in a wild population of the Collared Flycatcher (Ficedula albicollis). The temperature in experimental nests was increased using a heat-pack placed under the roof of a nest box, resulting in an average temperature increase of 2.5 ºC, which corresponds to projected climate change scenarios. We demonstrated that females from nests with elevated temperature spent less time in the nest box during egg incubation and had more off-bouts than females from control nests. Moreover, we found that offspring from the experimentally heated nests had larger body mass at fledging in comparison to the control ones. Our study indicates that nest microclimate during the incubation period affects female incubation behaviour and offspring quality, indicating that environmental variation in nest temperature early in ontogeny can have important and long-lasting fitness consequences.

The role of introductory alarm calls for song discrimination in Ficedula flycatchers

Assortative mating depends on species distinctiveness in mating traits and preferences, which can be challenging to maintain when traits and/or preferences are learned. This is because learning may cause individuals to copy heterospecific signals. Juvenile songbirds possess innate sensory biases favouring them to learn and to prefer conspecific songs, but the effectiveness of these biases relies on consistent and sufficient differences between the songs produced by different species. However, mating signals, including learned songs, sometimes converge in sympatry, and the species-specific cues that individuals use to shape their preferences are often unknown. In Ficedula flycatchers, a stereotyped and highly species-specific alarm call is often incorporated as the first syllable of their songs. However, where the two species co-occur, pied flycatchers, Ficedula hypoleuca , learn to incorporate the introductory calls of the closely related collared flycatcher, Ficedula albicollis , into their songs. In this study, we investigated the role of introductory alarm calls for song discrimination in collared flycatchers, using playback experiments of both manipulated and unmanipulated songs on adults and nestlings within the hybrid zone of Öland, Sweden. We predicted that the introductory alarm call would be sufficient to trigger song responses, such that adults and nestlings would respond similarly to song phrases including the call, whether it is followed by conspecific or heterospecific notes. Our results provide evidence that the introductory alarm call is sufficient to trigger song discrimination in nestlings, but not in adult males, potentially due to their greater experience with songs and, therefore, subtler discrimination. Altogether, this study highlights the often-overlooked importance of calls within or associated with songs. • Collared flycatchers often start their songs with an alarm call. • The alarm call seems sufficient to drive song responses in nestlings. • We argue that the call could guide learning onto appropriate songs. • However, the call alone is unlikely to be sufficient for discrimination in adults. • We discuss the broader implication of incorporation of calls into songs.

Inter-individual variation in provisioning rate, prey size and number, and links to total prey biomass delivered to nestlings in the Collared Flycatcher (Ficedula albicollis)

BackgroundIn bird species where offspring growth and survival rely on parents’ food provisioning, parents can maximise their fitness by increasing the quantity and/or the quality of preys delivered to their offspring. Many studies have focused on inter-individual variation in feeding rate, yet this measure may not accurately reflect the total amount of food (i.e. energy) provided by parents if there is large variation in the quantity and quality of preys at each feeding. Here, we explored the relative role of individual (sex, age, body condition), breeding (hatching date, brood size) and environmental (temperature) factors on feeding rate, prey number, size and quality, and their contribution to total prey biomass delivered to the nestlings of 164 Collared Flycatcher (Ficedula albicollis) parents in 98 nests.ResultsPreys delivered to the nest were mainly larvae (53.6%) and flying insects (45.6%). Feeding rate increased with brood size and age, and was higher in males than females. Mean prey number decreased, but mean prey size increased, as the season progressed and parents feeding their brood with primary larvae brought more preys per visit. Relationships between feeding rate, mean prey number and size remained when taking into account the provisioning quality: parents brought either a large number of small prey or a small number of larger items, and the force of the trade-offs between feeding rate and mean prey number and size depended on the quality of the provisioning of the parents. Whatever the percentage of larvae among preys in the provisioning, the variance in total prey biomass was foremost explained by feeding rate (65.1% to 76.6%) compared to mean prey number (16.4% to 26%) and prey size (2.7% to 4%).ConclusionsOur study shows that variation in feeding rate, prey number, size, but not quality (i.e. percentage of larvae), were influenced by individual factors (sex and age) and breeding decisions (brood size and timing of breeding) and that, whatever the provisioning strategy adopted, feeding rate was the best proxy of the total biomass delivered to the nestlings.

Density-Dependent Adaptive Topography in a Small Passerine Bird, the Collared Flycatcher.

AbstractAdaptive topography is a central concept in evolutionary biology, describing how the mean fitness of a population changes with gene frequencies or mean phenotypes. We use expected population size as a quantity to be maximized by natural selection to show that selection on pairwise combinations of reproductive traits of collared flycatchers caused by fluctuations in population size generated an adaptive topography with distinct peaks often located at intermediate phenotypes. This occurred because r- and K-selection made phenotypes favored at small densities different from those with higher fitness at population sizes close to the carrying capacity K. Fitness decreased rapidly with a delay in the timing of egg laying, with a density-dependent effect especially occurring among early-laying females. The number of fledglings maximizing fitness was larger at small population sizes than when close to K. Finally, there was directional selection for large fledglings independent of population size. We suggest that these patterns can be explained by increased competition for some limiting resources or access to favorable nest sites at high population densities. Thus, r- and K-selection based on expected population size as an evolutionary maximization criterion may influence life-history evolution and constrain the selective responses to changes in the environment.

The meaning of purely structural colour: white plumage reflectance indicates feather condition

White plumage areas are widespread among birds but the mechanisms generating individual differences in white feather reflectance are poorly known. Additionally, the proximate mechanisms of within‐season feather colour changes in general are also poorly known. Here we explored within‐individual changes in macrostructure and reflectance of the white wing‐patch of female Collared Flycatchers Ficedula albicollis using data from three stages within a breeding season. Changes in brightness and UV chroma were related to changes in the neatness and size of reflective surfaces, respectively. This suggests that white feather reflectance traits may act as indicators of feather intactness and preening activity.

Automatic bird song and syllable segmentation with an open-source deep-learning object detection method – a case study in the Collared Flycatcher (Ficedula albicollis)

Abstract The bioacoustic analyses of animal sounds result in an enormous amount of digitized acoustic data, and we need effective automatic processing to extract the information content of the recordings. Our research focuses on the song of Collared Flycatcher (Ficedula albicollis) and we are interested in the evolution of acoustic signals. During the last 20 years, we obtained hundreds of hours of recordings of bird songs collected in natural environment, and there is a permanent need for the automatic process of recordings. In this study, we chose an open-source, deep-learning image detection system to (1) find the species-specific songs of the Collared Flycatcher on the recordings and (2) to detect the small, discrete elements so-called syllables within the song. For these tasks, we first transformed the acoustic data into spectrogram images, then we trained two deep-learning models separately on our manually segmented database. The resulted models detect the songs with an intersection of union higher than 0.8 and the syllables higher than 0.7. This technique anticipates an order of magnitude less human effort in the acoustic processing than the manual method used before. Thanks to the new technique, we are able to address new biological questions that need large amount of acoustic data.

“Ficedula”: an open-source MATLAB toolbox for cutting, segmenting and computer-aided clustering of bird song

Qualitative and quantitative assessments of bird song repertoires are important in studies related to song learning, sexual selection and cultural evolution. Despite methods for automatic analysis, it is still necessary to engage in manual cutting, segmenting and clustering of bird song elements in many cases. Here, we describe a program, the Ficedula Toolbox, which has been made available for free to the bird song research community and has recently come into extensive use. The main advantages of this package are the opportunity to conduct all processing steps in one framework and the option of carrying out computer-aided manual clustering. Output files are ready for further analyses, such as estimation of repertoire size, sequential analysis and repertoire overlap calculation. With this program, findings based on empirical data from the Collared Flycatcher (Ficedula albicollis) song show high inter-observer similarity, and thus, reproducible results. The toolbox may be especially applicable to the analysis of song in species with moderately high repertoires.

When to measure plumage reflectance: a lesson from Collared Flycatchers Ficedula albicollis

Sexually selected colour traits of bird plumage are widely studied. Although the plumage is replaced only at one or two yearly moults, plumage colour has long been shown to change between moults. Nevertheless, most studies measure colour weeks to months after the courtship period, typically at nestling rearing, and it is unclear whether these measurements yield relevant data concerning the primary process of sexual selection. Here we analyse repeated spectrometric data taken from male Collared Flycatchers during social courtship and nestling rearing. We show that some spectral traits are not correlated between the two measurements and that within‐individual correlation declines significantly with the likely exposure of the plumage area to damage and soiling. There is an overall decline in spectral trait exaggeration during breeding, but trait decline is not closely related to measurement latency, especially not in the damage‐exposed areas. Finally, sexual selection estimates differ depending on whether they are derived from spectra measured during courtship or during nestling rearing. These results suggest that, contrary to current practice, measurements of plumage reflectance should be made during the primary period of sexual signalling. Spectral trait decline during breeding could also be studied as a possible signal for mates and neighbours.

Structure of the community of nesting birds in a ravine oak wood in the valley of the Oskol river

This investigation was carried out in a forest on the southern borders of the Central-Russian Upland, on the Prioskolsky plateau, in the Srednedonskoy subprovince of the Pontic steppe province. The aim of this work is to identify the peculiarities of structure and ways of formation of the breeding population of ravine oak forests on the border of two geographic zones. The objectives of the work were to describe quantitative and qualitative characteristics of the population of the nesting birds of ravine oak forests, as well as provide an analysis of the faunogenesic structure of the nesting bird population. To obtain data on the species composition and density of nesting birds we used the line transect method by D. Hayne – Y. Ravkin. The surveys were carried out in 2011–2015 three times per season (April to June). The indicators of the breeding density of each bird species and the totals for each year were calculated. The Polydominant Simpson index was used to characterize species diversity. To evaluate the uniformity we used the calibrated version of G ‘Alatalo index F’. The calculations were performed using the program PAST. In total we observed 34 species of birds over the 5 years of research. The dynamics of the total density of breeding birds in the period researched (2011–2015) showed a maximum in 2013 (1,711 pairs/km2); the average index for the 5 years was 1,288 ± 133 pairs/km2, which is similar to the characteristics of the populations of birds forests of the steppe zone (Donetsk Ridge, Azov Upland). The dominant and subdominant species comprised 32.2–54.7% of the population, indicating a balanced community, in spite of the insular nature of the forest. The absolute dominant in all years was the Chaffinch (an average of 21.2% of the population); subdominant species were the Robin (11.2%), Great Tit (10.5%) and the Collared Flycatcher (10.3%). Over a third of the total number of birds are the hollow-nesting birds (37.1%); species nesting in the crown were 32.3% and ground-nesting species 25.3%. The geographical and genesis structure of the communities of nesting birds are characterized by predominance of species from Nemoral and Ancient-Nemoral faunal assemblage (in some years up to 90.9% of the population). The species from the forest-steppe faunistic complex of the European type of fauna account for 3.6% to 9.48% of the population of nesting birds, and most of these have the status of third-degree (rare species). The composition of the group of third-degree species is highly diverse: in addition to the elements of Nemoral, Ancient-Nemoral and forest-steppe complexes, it includes species from the tropical and boreal groups. Among third-degree species there is a tendency to decrease in some species from the Nemoral faunal complex with a simultaneous increase in the forest-steppe faunistic component and increase in the homogeneity of the geography-genesis structure as a whole. The significant share of the population from the Nemoral and Ancient-Nemoral species complex, which formed in deciduous forests, is evidence of the origin of the researched ravine oak wood as a remnant of the once vast oak-forest areas.

Mutual ornamentation and the parental behaviour of male and female Collared Flycatchers Ficedula albicollis during incubation

One of the benefits of mate choice based on sexually selected traits is the greater investment of more ornamented individuals in parental care. The choosy individual can also adjust its parental investment to the sexual signals of its partner. Incubation is an important stage of avian reproduction, but the relationship between behaviour during incubation and mutual ornamentation is unclear. Studying a population of Collared Flycatchers Ficedula albicollis, we monitored the behaviour of both sexes during incubation in relation to their own and their partner's plumage traits, including plumage‐level reflectance attributes and white patch sizes. There was a marginally positive relationship between male feeding rate during incubation and female incubation rate. Female but not male behavioural traits were associated with the laying date of the first egg and clutch size. The behaviour of the two sexes jointly determined the relative hatching speed of clutches and the hatching success of eggs. Females with larger white wing patches spent less time incubating eggs and left the nestbox more frequently. Males with larger white wing patches fed females less frequently, whereas males with brighter white plumage areas visited the nestbox more regularly without feeding. Females tended to leave the nest less often when mated to males with larger wing patches, and females spent less time incubating when males had more UV chromatic plumage. The behaviour of both partners during incubation therefore predicted hatching patterns and was correlated with their own and sometimes with their partner's plumage ornamentation. These results call for further studies of mutual ornamentation and reproductive effort during incubation.

Aggressive behaviour of Robins Erithacus rubecula (Passeriformes, Muscicapidae) at watering places in the forest steppe zone of Ukraine

283 The purpose of this research was to study interspecific and intra-specific aggressive reactions of Robins (Erithacus rubecula L.) at watering places in natural and anthropogenically pressured areas. The study took place in Kaniv Nature Reserve, Cherkassy region, in May-June 2010, 2012 and 2014 and the state dendrology park “Oleksandriya” of the National Academy of Science in Bila Tserkva. The observation of the birds’ behavior was performed using the ethological methods of “total observation” and “continuous logging”. In order to calculate the critical distance at which a bird shows aggression, the watering areas studied were divided into 1 x 1 m squares. It was found that aggressive intersspecific actions of Robins were more frequent in the natural habitat of Kaniv Reserve while intraspecific aggression was more frequent in the dendrology park. It was noticed that Robins responded aggressively to 12 species of birds in the Kaniv Natur Reserve site. Those species were: Song Thrush (Turdus philomelos), Blackbird (T. merula), Great Tit (Parus major), BlueTit (P. caeruleus), Marsh Tit (P. palustris), Chaffinch (Fringilla coelebs), Hawfinch (Coccothraustes coccothraustes), Icterine Warbler (Hippolais icterina), Wood Warbler (Phylloscopus sibilatrix), Blackcap (Sylvia atricapilla), Collared Flycatcher (Ficedula albicollis) and Spotted Flycatcher (Muscicapa striata). Most often, aggression was directed to individuals that were already at a watering place rather than birds which arrived after the Robins. Besides, Robins frequently initiate aggressive relations. An inverse correlation of aggressive acts and the size parameters of the species, which were objects of Robins’ aggression, was observed. A success rating of Robins’ defence and attack in aggressive relations in Kaniv Nature Reserve was established: Robins were always successful in protecting its territory or attacking an Icterine Warbler and Chiffchaff, and always fails in defending agianst or attacking a Blackbird. The rating in contact with Spotted Flycatcher was zero. The critical distance of aggressive behaviour in intraspecific contacts at watering places was 40–50 cm, while for interspecific contacts it varied from5 cm to2 m. Our research emphasizes the importance of long-term research and multivariate approaches for understanding the complexity of dominance relations in birds.

A test on within-individual changes in risk-taking behaviour due to experience to predation in the Collared Flycatcher (Ficedula albicollis)

Summary Different experiences from the past may have influence on individual’s behaviour through feedback mechanisms that can weaken or preserve the within-individual consistency of behavioural traits. Here, we aimed to find evidence for such feedback mechanisms that may operate on risk-taking behaviour via the effect of former experience to potential predation events in male Collared Flycatchers (Ficedula albicollis). We predicted that risk-taking of males would decrease after experiencing a predator’s attack in previous breeding seasons (negative feedback). We assessed risk-taking by flight initiation distance (FID) that is the distance at which an individual flees from an approaching predator, which was estimated for 234 individuals from different breeding seasons. Information on predation experience (i.e. occurrence of nest predation, the incidence of capture by human observers) was available from our long-term database on individual life histories. In a horizontal approach, we found no difference in FID when comparing males with former experience to predation with males naive to predators. A longitudinal approach relying on the repeated tests of the same individuals from different years yielded analogous results, we could not show a significant change in the risk-taking behaviour of the males as a consequence of experience to predation in past years. However, we found that individuals systematically took less risk over the years, which might be a consequence of acquiring general experience with age.

Mammal hair in nests of four cavity-nesting songbirds: occurrence, diversity and seasonality

ABSTRACTCapsule: The diversity of mammal hair found in nest linings varied between bird species and with season.Aims: We examined mammal species composition in the guard hair material of four cavity-nesting songbirds, focusing on their numbers and occurrence, nest predation and seasonality.Methods: We surveyed 219 nests of four cavity-nesting songbirds breeding in a Central European woodland and identified hairs from 28 mammal species.Results: Roe Deer Capreolus capreolus hair was the most commonly used hair type in the nests of all four songbird species. This was especially the case in Blue Tit Cyanistes caeruleus nests, which may suggest a preference for Roe Deer hair. The greatest diversity of hairs was found in the nests of Great Tits Parus major, while the lowest was found in the Collared Flycatcher Ficedula albicollis. In flycatchers, 59% of females used only plant material for nest construction. Interestingly, we found a strong seasonal effect in hair use. Flycatcher nests that were initiated early in the season were more likely to contain mammal hair than those initiated later in the season. Similar, albeit weaker, negative seasonal effect was detected in Great and Blue Tit nests. There were no significant effects of any potential anti-predatory functions of mammalian hair in nests.Conclusion: Our study showed a clear prevalence of Roe Deer in the hair material of all bird species and certain preferences of birds for particular mammal species. When the aim is to detect a wide range of mammal species, for example, during biodiversity surveys, we advise to consider sampling effort and to focus on early breeding birds.

Context dependence of maternal effects: testing assumptions of optimal egg size, differential, and sex allocation models.

If offspring develop in adverse conditions, the maternal component of their phenotypic variation might increase due to the stronger dependence of offspring traits on parental investment. This should result in increased parental investment to individual offspring, as assumed by the model of optimal egg size. The opposite pattern, i.e., stronger dependence of offspring fitness on parental investment and consequently larger parental investment under good conditions is assumed by both the theory of differential allocation if attractive males provide material benefits, and reproductive compensation if they invest less into paternal care. Another influential idea is the Trivers-Willard model, which assumes sex-specific dependence of offspring fitness on parental investment. Here we tested these ideas by examining the effects of egg size on offspring fitness across many postnatal contexts in the Collared Flycatcher Ficedula albicollis. We employed a cross-fostering design that generated variation in egg size within nests and used brood means of fledgling mass as a functional measure of the quality of rearing conditions. Effects of egg size on three offspring traits, including lifetime reproductive success of recruits, were more pronounced in low-quality broods. These results support the assumption of the model of optimal egg size. Based on female preference for males providing material benefits, this pattern could support differential allocation, if attractive males invest less in paternal care, or reproductive compensation, if they invest more. By comparison, we did not find any evidence for sex specificity of fitness returns that might explain sex monomorphism of egg size in this species. The challenge for future studies will be the integration of components of parental investment and offspring fitness into their global measures and testing how the former affects the latter across gradients of postnatal conditions.

From Mediterranean to Scandinavia—timing and body mass condition in four long distance migrants

In spring, long-distance migrants are considered to adopt a time-minimizing strategy to promote early arrival at breeding sites. The phenology of spring migration was examined and compared between two insular stopover sites in Greece and Sweden for Icterine Warbler, Wood Warbler, Spotted Flycatcher and Collared Flycatcher. All of them migrate due north which means that some proportion of birds that pass through Greece are heading to Scandinavia. The Collared Flycatcher had the earliest and the Icterine Warbler the latest arrival time. The differences in median dates between Greece and Sweden were 3–4 weeks and the passages in Sweden were generally more condensed in time. The average overall speed estimates were very similar and varied between 129 and 137 km/d. In most of the species higher speed estimates were associated with years when birds arrived late in Greece. After crossing continental Europe birds arrive at the Swedish study site with significantly higher body masses compared to when they arrive in Greece and this might indicate a preparation for arriving at breeding grounds with some overload.