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Migratory strategies of animals are broadly defined by species’ eco-evolutionary dynamics, while behavioural plasticity according to the immediate environmental conditions en route is crucial for energy efficiency and survival. The Arctic tern Sterna paradisaea is known for its remarkable migration capacity, as it performs the longest migration known by any animal. Yet, little is known about the ecology of this record-breaking journey. Here, we tested how individual migration strategies of Arctic terns are adapted to wind conditions and fuelling opportunities along the way. To this end, we deployed geolocators on adult birds at their breeding sites in Svalbard, Norway. Our results confirm fundamental predictions of optimal migration theory: Arctic terns tailor their migration routes to profit from (1) tailwind support during the movement phase and (2) food-rich ocean areas during the stopover phase. We also found evidence for seasonally distinct migration strategies: terns prioritize fuelling in areas of high ocean productivity during the southbound autumn migration and rapid movement relying on strong tailwind support during the northbound spring migration. Travel speed in spring was 1.5 times higher compared to autumn, corresponding to an increase in experienced wind support. Furthermore, with their pole-to-pole migration, Arctic terns experience approximately 80% of all annual daylight on Earth (the most by any animal), easing their strictly diurnal foraging behaviour. However, our results indicate that during migration daylight duration is not a limiting factor. These findings provide strong evidence for the importance of interaction between migrants and the environment in facilitating the longest animal migration on Earth.

Nesting birds often respond to human disturbance as to a predatory act. In the case of the high Arctic, the disturbance of incubating birds may bring further complications due to egg cooling. In addition, it is assumed that birds in the high Arctic are not shy and do not respond to human presence fearfully. We tested how quickly the Arctic terns (Sterna paradisaea) nesting in two colonies in Svalbard return to the nest after human disturbance. One colony was situated inside a town where the terns were regularly harassed by human presence. The second colony was on a glacial foreland where breeding terns have limited experience with humans. We found that terns without frequent experience with humans returned to the nest about 5 min after disturbance, while urban terns habituated to human presence returned within a few tens of seconds. The urban terns in this way likely solve the risk of spending too much time off the nest, which could lead under the conditions of the high Arctic to the stopping of embryogenesis. Terns from a remote colony do not show lower hatching success of their eggs than the urban ones, however, incubation and the whole population of terns could be threatened when there is more frequent disturbance by researchers or tourists.

Currently, the deployment of tracking devices is one of the most frequently used approaches to study movement ecology of birds. Recent miniaturization of light‐level geolocators enabled studying small bird species whose migratory patterns were widely unknown. However, geolocators may reduce vital rates in tagged birds and may bias obtained movement data. There is a need for a thorough assessment of the potential tag effects on small birds, as previous meta‐analyses did not evaluate unpublished data and impact of multiple life‐history traits, focused mainly on large species and the number of published studies tagging small birds has increased substantially. We quantitatively reviewed 549 records extracted from 74 published and 48 unpublished studies on over 7,800 tagged and 17,800 control individuals to examine the effects of geolocator tagging on small bird species (body mass, + Publisher's Statement: This is the peer reviewed version of the following article: "Brlík, V, Koleček, J, Burgess, M, et al. Weak effects of geolocators on small birds: A meta‐analysis controlled for phylogeny and publication bias. J Anim Ecol. 2020; 89: 207– 220", which has been published in final form at https://doi.org/10.1111/1365-2656.12962. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.; Read Only Lizenz.

The origin and nature of seal carcasses scattered around the Ulu Peninsula, James Ross Island, is examined using robust and novel multidisciplinary analysis. Spatial distribution analysis indicates their predominance at low elevations and on surfaces with negligible slope. The seals died throughout the last century. Dental cement increments indicate that the seals died in late winter, and we interpret this to show an influence of the persistence and break-up of sea ice and the appearance of pools/cracks in the northern Prince Gustav Channel on death. Specifically, after being trapped by a late winter freeze-up the seals search for open water, become disoriented by snow-covered flat valleys and move inland. Carcasses from all age groups of crabeater seal are found on land, but inland movement is less notable for Weddell and leopard seals. Although most carcasses appear to have remained unchanged during the last 10 years due to the cold and dry conditions, a few carcasses that are located in sites of snow accumulation and subsequent melting have undergone enhanced decay. Decaying seal carcasses represent loci of nutrient release in a nutrient deficient environment and are colonized by algae, cyanobacteria, lichens and mosses. This research suggests further useful studies for the future.

Capsule Red-spotted Bluethroats Luscinia s. svecica from two European breeding populations spent the boreal winter on the Indian sub-continent. Aim Tracking the migration of Red-spotted Bluethroats from Europe to the hitherto unknown non-breeding areas and back. Methods Light-level geolocators were deployed on male Bluethroats at breeding sites in the Czech Republic (n = 10) and in Norway (n = 30). Recorded light intensity data were used to estimate the locations of non-breeding sites and migration phenology during the annual cycle. Results Bluethroats spent the boreal winter in India (n = 3) and Pakistan (n = 1), on average more than 6000 km from their breeding areas. Autumn migration started in August (n = 1) or early September (n = 2), and lasted for 26–74 days. Spring migration commenced on 8 and 9 April (n = 2) and lasted for about a month. During both autumn and spring migration, birds stopped over two or three times for more than 3 days. Conclusion This study for the first time showed where Red-spotted Bluethroats from European breeding populations stay during the boreal winter. This seems to be the first time that a passerine bird has been tracked along the Indo-European flyway. publishedVersion

Long-distance migratory birds are potentially exposed to a range of blood sucking arthropods that transmit avian blood parasites. Because of differential vector exposure, the parasite fauna may vary in different habitat types, among populations, or even within populations where individuals travel to different areas during migration. We applied PCR-based molecular techniques to determine patterns of blood parasite occurrence in adults of seven geographically isolated Bluethroat populations, belonging to three distinct subspecies differing in habitat preferences and wintering areas (Luscinia svecica svecica, L. s. cyanecula, L. s. namnetum). Moreover, to elucidate potential transmission of blood parasites on breeding sites, we tested adults of the relatively sedentary White-throated Dipper (Cinclus cinclus) from a Norwegian population. Across populations, we detected infection of at least one blood parasite genus in 68.5 % (139/203) of adult Bluethroats. The most common parasite genus was Plasmodium (10 lineages, 33.5 % of surveyed individuals), present in all seven populations, followed by Leucocytozoon (four lineages, 31.5 %) and Haemoproteus (two lineages, 4.9 %). We recorded multiple infections in 26.1 % of individuals. Leucocytozoon was found only in svecica inhabiting mountainous/subalpine areas with high abundance of blackflies, the main vector for this parasite. In Plasmodium, two lineages (BT6 and GRW4) were confined to specimens from svecica populations. In contrast, Lineage SGS1 was dominated by southern birds of the subspecies cyanecula and namnetum. Our data suggest transmission of Leucocytozoon on the breeding grounds in Norway as the same lineages were found in relatively sedentary White-throated Dippers as in migratory Bluethroats. We discuss these results in light of the ecological differences between the host populations, affecting their exposure to potential blood parasite vectors.

Spermatozoa are among the most variable animal cell types, and much research is currently directed towards explaining inter- and intraspecific variation in sperm form and function. Recent comparative studies in passerine birds have found associations between the level of sperm competition and both sperm length and sperm velocity. In species with sperm competition, postcopulatory sexual selection may shape the morphology of sperm as adaptations to the female environment. The speed of evolutionary change in sperm morphology at the species level is largely unknown. In this study, we analysed variation in sperm morphology among morphologically distinct and geographically isolated bluethroat subspecies in Europe. Consistent with previous studies, our analyses of mtDNA and nuclear introns suggest recent divergence and lack of lineage sorting among the subspecies. We found significant divergence in total sperm length and in the length of some sperm components (i.e. head and midpiece). There was a significantly positive relationship between pairwise divergences in sperm morphology and mitochondrial DNA, suggesting a role for genetic drift in sperm divergence. The magnitude of sperm length divergence was considerably higher than that in other geographically structured passerines, and even higher than that observed between several pairs of sister species. We hypothesize that the rapid sperm evolution in bluethroats is driven by sperm competition, and that strong postcopulatory sexual selection on sperm traits can lead to rapid speciation through reproductive incompatibilities.

Antarctic terns have to co-exist in a limited space with their major nest predator, the skuas. We conducted artificial nest experiments to evaluate the roles of parental activity, nest location and nest and egg crypsis in this simple predator–prey system. Predation on artificial (inactive) nests was higher in traditional nesting sites than in sites previously not occupied by terns, which suggests that skuas memorized past tern breeding sites. Predation on artificial nests in inactive colonies was higher than in active (defended) colonies. Parental defense reduced predation in colonies to the level observed in artificial nests placed away from colonies. This suggests that communal defense can balance the costs of attracting predators to active colonies. Within colonies, predation was marginally higher on experimental eggs put in real nests than on bare ground. Although it seems that the presence of a nest is costly in terms of increased predation, reductions in nest size might be constrained by the need for protective nest structures and/or balanced by opposing selection on nest size. Predation did not differ markedly between artificial (quail) and real tern eggs. A simultaneous prey choice experiment showed that the observed predation rates reflected egg/nest detectability, rather than discrimination of egg types. In summary, nesting terns probably cannot avoid being detected, and they cannot defend their nest by attending them. Yet, by temporarily leaving the nest, they can defend it through communal predator mobbing, and at the same time, they can benefit from crypsis of unattended nest and eggs.

The Antarctic Peninsula (AP) is experiencing rapid environmental change associated with warming and sea ice retreat, which is likely to affect locally breeding birds. Yet, contrary to the knowledge of bird biology along the maritime West coasts of the AP, there is a remarkable lack of data from the more continental East coast. We report on the distribution, abundance, and breeding of the Antarctic Tern at the James Ross and Seymour islands, the two largest snow-free areas in the NE part of the AP, where this species breeds under harsh climate conditions probably close to its limits. Terns were found breeding in most ice-free areas, with nests located up to 2.9 km from coastlines at altitudes up to 180 m a.s.l. While the large-scale density was relatively low (c. 450 pairs per 127 km2 of surveyed ice-free area), the local density (total colony area: 3 nests per ha; nest clusters: 100–140 nests per ha) was as high as elsewhere. Mean clutch size (1.21, n = 196) was smaller than in the west AP or in the maritime Antarctic. Daily nest survival rate during incubation varied between years and locations (mean = 0.977; 95 % CI: 0.966–0.985). While both predation and weather-caused mortality were locally important, the impact of skua predation might be lower in areas with alternative prey (penguin colonies). We suggest that the Antarctic Tern deserves attention as a species potentially suitable for monitoring of environmental impacts upon bird populations around the AP.

Differences in vocalization between subspecies of songbirds may influence intraspecific interactions including mate choice and territorial behavior, and contribute to their further divergence by strengthening pre-mating reproductive isolation. We have recently shown that songs of two Bluethroat subspecies, Luscinia svecica svecia and L. s. cyanecula, differ in spectral characteristics and structure. Here, in a first experimental test of whether these differences are biologically relevant, we compared responses of L. s. svecica males to both types of songs. Altogether 19 males from a subartic population in Abisko, Sweden, were exposed to playbacks of songs from the two subspecies, accompanied by display of a stuffed Bluethroat lacking subspecies-specific colour marks. These stimuli were presented in random order, separated by over 1 h. We evaluated two largely uncorrelated components of male responses: non-vocal territorial behavior, and singing activity. A significant difference in reaction to subspecies playbacks was observed in aggressive behavior: independently of the song order, males generally responded more strongly to playback of their own subspecies. In contrast, playback order rather than subspecies identity significantly influenced the singing activity, which usually increased in the second trial. A more detailed analysis nevertheless suggested that vocal responses of birds exposed first to playback of their own subspecies were stimulated in the subsequent trial but not vice versa. Our results show that Bluethroats clearly discriminate the two song types, indicating the potential for subspecies recognition. Further experimental work is needed to assess the general validity of these patterns.

Nest predation is a crucial factor influencing breeding success in birds. One possible way to protect nests is to modify parental activity in the vicinity of the nest. Here, we provide experimental evidence for an adjustment of incubation pattern during periods when there is an increased risk of nest predation in a small passerine. We compared the behaviour of incubating meadow pipit (Anthus pratensis) females during presentations of stuffed dummies of a nest predator (the magpie Pica pica) and a harmless intruder (the crossbill Loxia curvirostra) and during an undisturbed control incubation period. Females significantly decreased their activity in the presence of the nest predator. Specifically, after being flushed out, they returned to the nest later and moved to and from the nest less than when the harmless intruder was present. These results document the ability of birds to assess the nest predation risk and adjust their appropriate incubation strategy.

Age-related variation in breeding performance is well-known in birds. Similarly, plumage ornamentation as a signal of male quality may affect breeding performance. However, because of inter-correlation between age and plumage ornamentation, it is difficult to estimate the relative contribution of these factors on breeding performance in natural variation. In the current study, we examined the relationship between breeding characteristics, age and throat ornament size of bluethroat males (Luscinia s. svecica). The study was conducted on 96 males in the Krkonose Mountains, Czech Republic, in 2003-2011. The results show that older males had higher reproductive performance: they arrived earlier, were more likely to be territorial, had larger clutches and thus had more hatchlings. On the other hand, ornamentation had a few, inconsistent correlations with breeding performances: well-ornamented males had fewer mates but had more fledglings. Our results suggest that age rather than ornamentation size is the main correlate of variation in breeding performance.

Incubation behaviour of the Meadow Pipit (Anthus pratensis) was investigated in mountainous conditions in Central Europe (the Krkonose Mountains of the Czech Republic), in relation to the time of day and weather. Twenty-four-hour recordings of incubation behaviour were made with a time-lapse video recorder and mini-camera. The influences of year, nest, time of day, temperature, precipitation and previous bouts on session and recess duration were then analysed. The incubation behaviour of Meadow Pipits in general did not differ from the behaviour of other small female-only incubating passerines. Despite relatively cold climatic conditions in the study area, the mean length of sessions and recesses (19.69 and 5.53 min), as well as nest-attentiveness (77.19%), agreed with values which are most often found in other species. However, the Meadow Pipit incubation in the study area was, in terms of nest-attentiveness, more intensive than in other surveyed populations of this species. Incubation behaviour was strongly influenced by the time of day—incubating females increased nest-attentiveness during the morning and evening hours. After the time of day was filtered out, the influence of temperature was found only on sessions (not recesses). Sessions were the longest when the air temperature was approximately 12–16°C and shortened when the temperature was lower or higher. Precipitation forced female Meadow Pipits to take longer sessions and shorter recesses, which corresponds to their general tendency to give priority to the needs of the clutch ahead of their own temporary feeding needs.

The reproductive value hypothesis predicts that the level of nest defence is determined by the expected chance of offspring to survive until reproduction, and by the reproductive potential of the parents. Rates of survival from one breeding season to the next are low in small passerines, and their residual reproductive potential strongly declines as the current breeding season terminates. Therefore, we can expect that parents which have only one breeding attempt per season should defend their nests more intensively than parents with a possibility to renest. We studied nest defence in populations of meadow pipit (Anthus pratensis) breeding in Norway and the Czech Republic, differing in renesting potential. To simulate the threat from a predator, we placed a stuffed stoat (Mustela erminea) first 5 m and then 1 m away from a nest with nestlings. Parents increased or kept nest defence constant when the stoat approached their nests in Norway and, during a breeding season shortened by severe weather, in the Czech Republic (when renesting potential was limited). Parents decreased nest defence when the stoat approached the nest during “normal” breeding seasons in the Czech Republic (when renesting was common). These findings give support to the reproductive value hypothesis.

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.

Although mate guarding as prevention of extra-pair copulation is common among birds, evidence for aggressive behaviour involving physical contact related to mate guarding in passerines is scarce and cases of the presence of one partner directly influencing the aggressiveness of the other are lacking. We investigated the intra-specific territorial behaviour of male meadow pipits (Anthus pratensis; Passeriformes: Motacillidae) at the beginning of the breeding season by placing a pipit model accompanied by an intra-specific song playback in the territory of socially paired males and compared the responses of males whose mates were physically present during trials with those whose females were out of sight. The level of aggression of males was significantly higher in the presence of the female; half of the males in this group physically attacked the model (the most intense and risky aggressive behaviour). Physical attacks did not occur among males whose female was absent during the trial; response to the playback by most of these males was only weak. This pattern may be related to the prevention of extra-pair copulation; if the risks involved in the conflict are outweighed by potential loss of paternity, such aggressive mate guarding may pay off. The apparently overlooked effect on the territorial behaviour of a partner's passive physical presence during conflict should be further evaluated because it may be important for the design and interpretation of results of behavioural experiments.

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.

It has been suggested that the brood defence by parents of altricial birds should increase during the breeding attempt until the young depart from the nest. The two proximate hypotheses provide alternative predictions about the peak of brood defence intensity: (1) the vulnerability hypothesis predicts a rapid rise in brood defence after hatching of the chicks, with maximum defence intensity just before fledging and strong decline afterwards; (2) the feedback hypothesis predicts that brood defence intensity will, after a rapid rise, reach a plateau at the end of the nestling period and early after fledging and then slowly decline. I compared brood defence behaviour of altricial meadow pipit (Anthus pratensis) breeding in the Czech Republic during the late nestling stage and during the fledging time. A stuffed stoat (Mustela erminea) was placed 5 m from a meadow pipit nest and the defence behaviour of parents was recorded for 10 min from a hide. Brood defence intensity was higher during the fledgling time than during the late nestling stage, and this trend was more evident in males than in females. Regardless of the proportion of already fledged chicks and those still present in the nest, brood defence did not significantly decrease during the fledgling time in males or females. The results do not agree with the predictions of the vulnerability hypothesis and support the predictions of the feedback hypothesis.

Capsule Three similarly sized passerine species with various breeding strategies behaved differently in the presence of models of mammalian and avian predators. Aims We tested whether solitary breeders behave in the presence of a predator in order to avoid disclosing their nest site in: hole-nesting Pied Flycatcher Ficedula hypoleuca, shrub-nesting Blackcap Sylvia atricapilla and ground-nesting Meadow Pipit Anthus pratensis. Methods The behaviour of parents in response to two types of predator model (visually oriented Corvid birds and olfactory oriented Mustelid mammals) placed sequentially at 40, 5 and 1 m distance from the nest was recorded from a shelter. Results The hypothesis was supported in open-nesting species (Meadow Pipit and Blackcap), as parents did not approach the nest in the presence of a predator. In the hole-nesting Pied Flycatcher the parents disclosed the nest site in most cases (by entering the nest). The intensity of alarm calling increased with decreasing distance of a predator from ...

The feedback hypothesis has been proposed to explain variation in nest defence intensity in birds. In species in which the female builds the nest and incubates the eggs, this hypothesis predicts a higher level of nest defence initially for females, whereas males' responses should increase when they start feeding nestlings. We studied changes in nest defence by both sexes during the nestling period in meadow pipits, Anthus pratensis . We placed a stuffed stoat, Mustela erminea , 5 m from a meadow pipit nest with nestlings aged either 2–4 or 7–12 days and recorded the nest defence behaviour of both parents for 10 min. Males came closer to the predator and mobbed more intensely for older nestlings whereas females defended the nest at a high intensity from the beginning of the nestling period. This finding agrees with the predictions of the feedback hypothesis. We also discuss possible functions of alarm calls and number of mobbing birds during nest defence.

Distraction displays to a human were studied in the Meadow Pipit (Anthus pratensis) females in Central (Jeseniky Mountains-Czech Republic; 50 N1 7E) and Northern European mountains (Tydal area-Central Norway; 63 N1 2E) between 1995 and 1998. Three risk-dependent variables were scored and we found that flushing and settling distances of pipit females decreased with increasing intensity of display both in the Central and the Northern Europe locations. Paren- tal risk taking did not markedly diAer between studied populations, although, in particular, larger brood size and reduced opportunity to re-nest should contribute to a higher intensity of nest defence in the Northern than in the Central European mountains. Moreover, the level of risk taken was not significantly dependent on the air temperature, age of brood and brood size in both study areas, when com- pared separately. These results do not support the findings of most previous stu- dies on nest defence in birds. Possible causes of our contradictory results are discussed with respect to the reproductive value and the feedback hypotheses.

The harm to offspring hypothesis, which says that parental investment should be related to the harm that offspring without parental care would suffer, was tested on meadow pipits, Anthus pratensis. We placed a stuffed European weasel, Mustela nivalis, 5 m from seven nests with exothermic 1-3-day-old nestlings. We measured air temperature and the cloacal temperature of the nestlings at the start of the trial and the time elapsing between the removal of the weasel model and the parent's first entry into the nest. We compared pairs of trials at each nest when nestling condition was good (normal cloacal temperature) and when it was temporarily poor (reduced cloacal temperature). The hypothesis predicts a shorter elapsed time when nestling condition was poor. In all cases the females entered the nest before the males and entered more quickly when nestling condition was poor. The results thus supported the harm to offspring hypothesis.Copyright 1997 The Association for the Study of Animal Behaviour

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.