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Migratory birds excel in phenotypic flexibility, adapting physiologically as their life histories and environments require. Discerning the metabolic processes underlying migrants' physiology, an emergent property of multiple continuous and dynamic organism–environment interactions, is therefore challenging, particularly under natural conditions. Accordingly, analyses of snapshot‐sampled serum‐circulating metabolites, versatile and readily applicable for migrating birds, have increasingly become the method of choice for such physiologic inference. However, the atemporal nature of single sampling might obscure the links between observed metabolite concentrations and the processes producing them, necessitating an analytical decoupling of focal processes from their broader biochemical background.In the present study, we examined how variation in combined fat and muscle fuel stores, traits pivotal in migratory context, relates to the serum‐circulating metabolomes of spring‐migrating Eurasian blackcaps stopping‐over. Our analyses accounted for potential spatiotemporal influences in the form of time past night's fasting and random local conditions across three sites within the Negev Desert. We shifted the focus from compound‐level analysis of preselected metabolites towards the level of inclusive metabolome, quantifying serum‐circulating lipophilic and polar molecules via UHPLC–MS/MS untargeted metabolomic technique.Our results indicated a general relationship between fuel stores and the metabolome, comprising 16 326 lipophilic and 6923 polar compounds, among which 918 and 44 were annotated, respectively. By applying generalized latent‐variable linear modeling (GLLVM) upon concentrations of annotated metabolites, we identified several candidate biomarkers, some novel in migratory context, notably the fuel‐associated increase in serum ceramides likely derived from circulating very low‐density lipoproteins (VLDLs). Relying on estimated metabolite links with fuel and foraging time and on modeled residual covariations among metabolites, we demonstrate fuel–metabolite associations generally consistent with higher fat‐ and lower protein mobilization in birds having greater stores and with decreased fuel utilization as ingested nutrients accumulate over time, thus introducing a novel approach for the physiological study of migrating birds. [ABSTRACT FROM AUTHOR]

Abstract Avian nests provide a location for incubation, and in many cases rearing of nestlings. These energetically demanding activities have meant that nest insulation has been the subject of many studies but few to date have dealt with how variation among species in nest construction materials could affect nest insulation. This study investigated the insulation of nests constructed by three species of Old Word warblers (Sylviidae), which vary in size and composition. Insulatory values, i.e. difference in cooling rate of temperature loggers placed inside and outside a nest, and internal cooling rates within the nest cup were determined using temperature loggers under still-air and moving-air conditions. Insulatory values determined in still-air conditions of a laboratory were significantly different among nests of the different species but not when the values were determined within the smaller volume of a wind tunnel. Moving-air increased insulatory values by an order of magnitude but also increased internal cooling rates in all species. Insulatory values were positively correlated with the nest base thickness. Moving-air increased the cooling rate of the external temperature logger much more than the internal logger, which inflated the insulatory value of a nest wall in moving-air. Reasons for these results may reflect the thermal properties of the materials individually or in combination. Future testing of nest insulation should be under standard conditions that limit air movement but the role of the nest location in situ should be investigated in future research. Highlights • Insulatory values correlated with nest mass and the nest base thickness, but not wall thickness. • Warbler nests have differing patterns of thermal insulation that reflect their compositions and varying wall structures. • Moving-air increases internal cooling rates by increasing convection from the nest surface but the increase in insulatory value is largely associated with the increased cooling rate of the external temperature logger. [ABSTRACT FROM AUTHOR]

Despite the fact that the structure of a forest, its vegetation composition and the species diversity in its tree stands are among the key factors shaping avian communities in forests in general, there are few studies on this topic relating to the deciduous forests of Central and East-Central Europe. The aim of the present study was therefore to investigate the relationship between the forest structure and the occurrence of common chaffinch Fringilla coelebs, wood warbler Phylloscopus sibilatrix, common chiffchaff Phylloscopus collybita and Eurasian blackcap Sylvia atricapilla, and also investigate habitat occupancy as expressed by territory size, in certain areas of NW Poland. The hypothesis tested was that if a habitat is rich, then the territory should be smaller. The mean territory size was 0.704 ha in the case of F. coelebs, 0.307 ha for P. sibilatrix, 0.148 ha for P. collybita and 0.312 ha for S. atricapilla. The use of a generalised linear mixed model demonstrated statistically significant relationships between the environmental variables and the territory size of the target bird species, the number of trees being the most significant environmental variable positively correlated with the territory size of birds. With regard to the canopy, a statistically significant negative relationship was demonstrated between the environmental variables and the territory size, whereas in the case of shrubs it was positive. The obtained results indicate need to restore the diversified structure of beech forests by ensuring the heterogeneity of forest stands, to increase avian diversity in managed forests. [ABSTRACT FROM AUTHOR]