Adaptive latitudinal variation in Common Blackbird Turdus merula nest characteristics

Nest construction is taxonomically widespread, yet our understanding of adaptive intraspecific variation in nest design remains poor. Nest characteristics are expected to vary adaptively in response to predictable variation in spring temperatures over large spatial scales, yet such variation in nest design remains largely overlooked, particularly amongst open‐cup‐nesting birds. Here, we systematically examined the effects of latitudinal variation in spring temperatures and precipitation on the morphology, volume, composition, and insulatory properties of open‐cup‐nesting Common Blackbirds’ Turdus merula nests to test the hypothesis that birds living in cooler environments at more northerly latitudes would build better insulated nests than conspecifics living in warmer environments at more southerly latitudes. As spring temperatures increased with decreasing latitude, the external diameter of nests decreased. However, as nest wall thickness also decreased, there was no variation in the diameter of the internal nest cups. Only the mass of dry grasses within nests decreased with warmer temperatures at lower latitudes. The insulatory properties of nests declined with warmer temperatures at lower latitudes and nests containing greater amounts of dry grasses had higher insulatory properties. The insulatory properties of nests decreased with warmer temperatures at lower latitudes, via changes in morphology (wall thickness) and composition (dry grasses). Meanwhile, spring precipitation did not vary with latitude, and none of the nest characteristics varied with spring precipitation. This suggests that Common Blackbirds nesting at higher latitudes were building nests with thicker walls in order to counteract the cooler temperatures. We have provided evidence that the nest construction behavior of open‐cup‐nesting birds systematically varies in response to large‐scale spatial variation in spring temperatures.     

Breeding season weather determines long‐tailed tit reproductive success through impacts on recruitment

Productivity is a key demographic trait that can be influenced by climate change, but there are substantial gaps in our understanding of the impact of weather on productivity and recruitment in birds. Weather is known to influence reproductive success in numerous species, although such effects have not been reported in all studies, perhaps because they are masked by high nest predation rates or buffered by density dependence. Here, we use a 19‐yr study of a population of individually marked long‐tailed tits Aegithalos caudatus to quantify the impacts of weather on productivity in the nest (from eggs to fledging) and subsequent recruitment, while taking nest predation rates and density dependence into account. We find that weather has negligible effects on clutch size, hatching success, brood size, probability of fledging and number of fledglings. Annual variation in nest predation rates is a strong predictor of productivity, but we find no evidence that the magnitude of nest predation is determined by weather. Recruitment was strongly associated with breeding season weather, even when taking density dependence effects into account. This contrasts with the conventional view that first year survival of temperate passerines is primarily determined by winter weather. Recruitment was reduced when March temperatures were high, perhaps caused by earlier peaks in caterpillar abundance and thus reduced food availability at the time of fledging. Recruitment increased following high May temperatures, perhaps due to an improved thermo‐regulatory environment for young fledglings. These opposing effects of warm March and May temperatures highlight the importance of considering asymmetrical rates of warming in different months when predicting climate change impacts.     

Eggs in the freezer: energetic consequences of nest site and nest design in Arctic breeding shorebirds

Birds construct nests for several reasons. For species that breed in the Arctic, the insulative properties of nests are very important. Incubation is costly there and due to an increasing surface to volume ratio, more so in smaller species. Small species are therefore more likely to place their nests in thermally favourable microhabitats and/or to invest more in nest insulation than large species. To test this hypothesis, we examined characteristics of nests of six Arctic breeding shorebird species. All species chose thermally favourable nesting sites in a higher proportion than expected on the basis of habitat availability. Site choice did not differ between species. Depth to frozen ground, measured near the nests, decreased in the course of the season at similar non-species-specific speeds, but this depth increased with species size. Nest cup depth and nest scrape depth (nest cup without the lining) were unrelated to body mass (we applied an exponent of 0.73, to account for metabolic activity of the differently sized species). Cup depth divided by diameter(2) was used as a measure of nest cup shape. Small species had narrow and deep nests, while large species had wide shallow nests. The thickness of nest lining varied between 0.1 cm and 7.6 cm, and decreased significantly with body mass. We reconstruct the combined effect of different nest properties on the egg cooling coefficient using previously published quantitative relationships. The predicted effect of nest cup depth and lining depth on heat loss to the frozen ground did not correlate with body mass, but the sheltering effect of nest cup diameter against wind and the effects of lining material on the cooling coefficient increased with body mass. Our results suggest that small arctic shorebirds invest more in the insulation of their nests than large species.     

Substrate and structure of ground nests have fitness consequences for an alpine songbird

Songbird nests are an important life‐history component with multiple functions, including the creation of a suitable microclimate for offspring development. Thus, functional nest characteristics may influence fitness correlates, such as nestling size traits, and may co‐vary with prevailing environmental conditions. We investigated among‐ and within‐female variation in nest substrate, lining and decoration structures with associated fitness consequences (hatching success, nestling size traits, nest survival) across two breeding seasons for an alpine population of Horned Lark Eremophila alpestris. We combined these observations with explicit measures of nest temperature to address the influence of nest characteristics on microclimate. Nests in heather substrate had the coldest microclimates compared with grass and bare‐ground substrate, but also the greatest nest survival rates (68% versus 37–44% in other substrates), indicating the potential for substrate use decisions to reflect a trade‐off between microclimate and nest survival in response to prevailing weather and predation risk conditions. Furthermore, nest lining and nest decoration patterns indicated some support for a thermoregulatory function. Nests that were lined with willow (Salix sp.) seed‐down were associated with larger, heavier nestlings and the use of down lining decreased in frequency as the season warmed up. Nest decoration placed in front of the nest (e.g. stones or dirt clumps varying in mass from 5.3 to 186.6 g) was positively associated with warmer nest microclimates. Females demonstrated high phenotypic flexibility, as 61–94% of the observed variance in nest characteristics was explained by within‐female rather than among‐female differences. Such flexible nesting behaviour suggests the capacity to adjust to changing environmental conditions to maintain vital fitness correlates such as nest survival and nestling size development.     

Variation in laying date in relation to spring temperature in three species of tits (Paridae) and pied flycatchers Ficedula hypoleuca in southernmost Sweden

This study documents the advancement of laying dates in three species of tits (Paridae) in southernmost Sweden during recent decades, and the absence of a similar response in the pied flycatcher Ficedula hypoleuca. It is based on several different nestbox studies; the oldest one starting in 1969. During 1969 to 2012, mean spring temperatures in the study area increased by between 0.06 and 0.08°C per year, depending on the period considered. Great tits Parus major, blue tits Cyanistes caeruleus and marsh tits Poecile palustris, which generally start egg laying between the last week of April and the first week of May, all advanced laying date at a similar rate during the study period (0.25 d yr^–1). This indicates that these species were similarly affected by increasing temperatures. When accounting for mean spring temperature variation, we still found an advancement of laying date over the study period, mostly due to such relationships among marsh and blue tits. This result could reflect ongoing microevolution favouring earlier laying, but could also be a result of other factors such as increased intra‐ or inter‐specific competition for early breeding. Pied flycatchers, which generally lay during the third week of May, did not significantly advance the date of egg laying despite that the long‐term trend in the increase in ambient temperature during the 30‐d period preceding the start of egg laying was similar for pied flycatchers compared to the tit species.     

Incubation behavior adjustments,driven by ambient temperature variation,improve synchrony between hatch dates and caterpillar peak in a wild bird population

For organisms living in seasonal environments, synchronizing the peak energetic demands of reproduction with peak food availability is a key challenge. Understanding the extent to which animals can adjust behavior to optimize reproductive timing, and the cues they use to do this, is essential for predicting how they will respond to future climate change. In birds, the timing of peak energetic demand is largely determined by the timing of clutch initiation; however, considerable alterations can still occur once egg laying has begun. Here, we use a wild population of great tits (Parus major) to quantify individual variation in different aspects of incubation behavior (onset, duration, and daily intensity) and conduct a comprehensive assessment of the causes and consequences of this variation. Using a 54‐year dataset, we demonstrate that timing of hatching relative to peak prey abundance (synchrony) is a better predictor of reproductive success than clutch initiation or clutch completion timing, suggesting adjustments to reproductive timing via incubation are adaptive in this species. Using detailed in‐nest temperature recordings, we found that postlaying, birds improved their synchrony with the food peak primarily by varying the onset of incubation, with duration changes playing a lesser role. We then used a sliding time window approach to explore which spring temperature cues best predict variance in each aspect of incubation behavior. Variation in the onset of incubation correlated with mean temperatures just prior to laying; however, incubation duration could not be explained by any of our temperature variables. Daily incubation intensity varied in response to daily maximum temperatures throughout incubation, suggesting female great tits respond to temperature cues even in late stages of incubation. Our results suggest that multiple aspects of the breeding cycle influence the final timing of peak energetic demand. Such adjustments could compensate, in part, for poor initial timing, which has significant fitness impacts.     

Blue tits (Cyanistes caeruleus) respond to an experimental change in the aromatic plant odour composition of their nest

Although the use of olfaction by birds is now widely recognised, the olfactory abilities of passerine birds remain poorly explored, for historical reasons. Several studies however suggest that passerines can perceive volatile compounds in several biologically relevant contexts. In Corsica, recent findings suggest that cavity-nesting blue tits may use volatile compounds in the context of nest building and maintenance. Although they build their nests mainly from moss, female blue tits also frequently incorporate fragments of several species of aromatic plants in the nest cup. In field experiments, breeding female blue tits altered their nest maintenance behaviour in response to experimental addition of aromatic plants in their nest. In aviary experiments, captive male blue tits could be trained to detect lavender odour from a distance. Here I report results from a field study aimed to test whether adult blue tits altered their chick-feeding behaviour after an experimental change in nest odour composition. I experimentally added fragments of aromatic plant species that differed from those brought in the nests before the start of the experiment in a set of experimental nests and added moss, the basic nest material, in a set of control nests. Both male and female blue tits hesitated significantly longer entering the nest cavity after addition of new aromatic plant fragments, as compared to moss addition. This response was especially observed during the first visit following the experimental change in nest plant composition. Nest composition treatment had no effect on the time spent in the nest. This study demonstrates that free-ranging blue tits detect changes in nest odour from outside the nest cavity.     

Effects of experimentally imposed climate scenarios on flowering phenology and flower production of subarctic bog species

Climate scenarios for high‐latitude areas predict not only increased summer temperatures, but also larger variation in snowfall and winter temperatures. By using open‐top chambers, we experimentally manipulated both summer temperatures and winter and spring snow accumulations and temperatures independently in a blanket bog in subarctic Sweden, yielding six climate scenarios. We studied the effects of these scenarios on flowering phenology and flower production of Andromeda polifolia (woody evergreen) and Rubus chamaemorus (perennial herb) during 2 years. The second year of our study (2002) was characterized by unusually high spring and early summer temperatures. Our winter manipulations led to consistent increases in winter snow cover. As a result, average and minimum air and soil temperatures in the high snow cover treatments were higher than in the winter ambient treatments, whereas temperature fluctuations were smaller. Spring warming resulted in higher average, minimum, and maximum soil temperatures. Summer warming led to higher air and soil temperatures in mid‐summer (June–July), but not in late summer (August–September). The unusually high temperatures in 2002 advanced the median flowering date by 2 weeks for both species in all treatments. Superimposed on this effect, we found that for both Andromeda and Rubus, all our climate treatments (except summer warming for Rubus) advanced flowering by 1–4 days. The total flower production of both species showed a more or less similar response: flower production in the warm year 2002 exceeded that in 2001 by far. However, in both species flower production was only stimulated by the spring‐warming treatments. Our results show that the reproductive ecology of both species is very responsive to climate change but this response is very dependent on specific climate events, especially those that occur in winter and spring. This suggests that high‐latitude climate change experiments should focus more on winter and spring events than has been the case so far.     

Sea buckthorn berries Hippophae rhamnoides L. predict size and composition of a great tit population Parus major L

In seasonal environments variation in food abundance in the non‐breeding season is thought to affect songbird population dynamics. In a unique tit‐sea buckthorn berry system we can estimate the berry abundance and both the tit consumption and population dynamics. Six hundred nest boxes were available to great and blue tits Cyanistes caeruleus for breeding in spring and roosting in winter. We followed the dynamics including the recapture histories of individually marked great tits from 2008 to 2014. In each year we estimated 1) the winter sea buckthorn berry availability, 2) an index of berry consumption in December based on the colour of the faeces of roosting birds, 3) the number of breeding great and blue tits, 4) both recapture probability and the return rate of the great tits and 5) immigration rates. December berry abundance positively predicted the number of breeding pairs of both species in the subsequent season and great tit return rates in the second half of the winter. There was support for a sex specific berry effect on the adult return rate in the great tit: female return rate was associated less strongly to berry abundance than male return rate. This skewed the sex ratio of the local breeders in the following breeding season. Intriguingly, annual berry consumption in December was not related to berry abundance, and individuals consuming more berries tended to have slightly lower return rates. Reproductive rate was not related to berry abundance. There was hardly support for a relation between immigration rates of first year breeders and berry abundance. Taken together these results imply that berry stock not only affected population size but also the population composition through sex specific exchange with the surroundings. Since population density covaried with berry abundance, density dependent effects provide an alternative explanation for the patterns observed.     

Effect of air movement on the thermal insulation of avian nests

Capsule: Air movement over a nest increases the rate of cooling within the nest cup but the walls provide good thermal insulation.

Aims: This study compared nests of six bird species of the families Fringillidae and Motacillidae to investigate the insulative properties in still and moving air treatments. It was hypothesized that differences in nest size and moving air would differ between species and would have a significant effect on insulatory values of the nests.

Methods: Nest dimensions were measured for a total of 35 nests from six species. Thermal properties of the nests were recorded using temperature loggers within nests placed in a wind tunnel under still and moving air conditions.

Results: Insulatory values and internal nest cooling rates were significantly increased by moving air. There was no significant difference between species for the thermal properties of nests but nest mass correlated with greater insulatory values and a lower rate of cooling within the nest cup. Nest wall thickness had no significant effect on the thermal characteristics of the nests.

Conclusion: The use of a constructed nest mitigated the effects of air movement but the differences between species reflected difference in nest mass rather than wall thickness.     

Latitudinal trends in within-year reoccupation of nest boxes and their implications

Multiple brooding can substantially increase the annual reproductive output of birds, and the propensity for multiple brooding can vary geographically. Thus, studies attempting to understand the evolution of geographic variation in nesting success need to account for variation in re‐nesting potential. However, direct assessment of rates of multiple brooding requires individually recognizable breeding adults, which are not generally available. We explore the possibility of comparing relative indices of multiple broodedness across a latitudinal gradient from studies of un‐banded birds locally restricted to nest boxes. We analyzed nest box reoccupation by a multiple‐brooding species, the eastern bluebird Sialia sialis, reported by volunteers in a citizen‐participation project (1998–2002) in which nest boxes were monitored throughout much of the breeding range of the bluebirds. We found nest boxes in the southern portion of the bluebird range (30° latitude) had, on average 17–33% higher likelihood of repeated egg‐laying, brooding, and successful fledging events than boxes in the north (48° latitude). Latitudinal variation in the reoccupation of nest boxes may indicate that either (1) the number of broods per female varies with latitude, (2) female breeding dispersal/site fidelity varies with latitude, (3) the density, distribution, and/or availability of suitable nest sites varies with latitude, or (4) observer bias varies with latitude. Various lines of evidence suggest that nest re‐occupancy is a useful index of latitudinal variation in re‐nesting. During the time‐frame of second attempts, first‐time box occupancy was as likely as second occupancy and approximately 45% more likely in the south than north, suggesting that, despite considerable breeding dispersal, observed trends in box reoccupation conservatively reflect latitudinal trends in the number of nest attempts/broods per female. Furthermore, despite a compressed nesting cycle in the north (shorter incubation and re‐nesting interval), the shorter duration of the breeding season in the north restricted the potential number of broods. Studies of banded birds are necessary to confirm the behavior underlying the latitudinal trends in box reoccupation.     

Multiple responses to increasing spring temperatures in the breeding cycle of blue and great tits (Cyanistes caeruleus,Parus major)

Many bird species start laying their eggs earlier in response to increasing spring temperatures, but the causes of variation between and within species have not been fully explained. Moreover, synchronization of the nestling period with the food supply not only depends on first‐egg dates but also on additional reproductive parameters including laying interruptions, incubation time and nestling growth rate. We studied the breeding cycle of two sympatric and closely related species, the blue tit Cyanistes caeruleus and the great tit Parus major in a rich oak‐beech forest, and found that both advanced their mean first‐egg dates by 11–12 days over the last three decades. In addition, the time from first egg to fledging has shortened by 2–3 days, through a decrease in laying interruptions, incubation time (not statistically significant) and nestling development time. This decrease is correlated with a gradual increase of temperatures during laying, suggesting a major effect of the reduction in laying interruptions. In both species, the occurrence of second clutches has strongly decreased over time. As a consequence, the average time of fledging (all broods combined) has advanced by 15.4 and 18.6 days for blue and great tits, respectively, and variance in fledging dates has decreased by 70–75%. Indirect estimates of the food peak suggest that both species have maintained synchronization with the food supply. We found consistent selection for large clutch size, early laying and short nest time (laying to fledging), but no consistent changes in selection over time. Analyses of within‐individual variation show that most of the change can be explained by individual plasticity in laying date, fledging date and nest time. This study highlights the importance of studying all components of the reproductive cycle, including second clutches, in order to assess how natural populations respond to climate change.     

Colour composition of nest lining feathers affects hatching success of barn swallows,Hirundo rustica (Passeriformes: Hirundinidae)

Many bird species use feathers as lining material, and its functionality has traditionally been linked to nest insulation. However, nest lining feathers may also influence nest detection by predators, differentially affect reproductive investment of mates in a post‐mating sexual selection process, and affect the bacterial community of the nest environment. Most of these functions of nest lining feathers could affect hatching success, but the effect might vary depending on feather coloration (i.e. pigmented versus white feathers). This would be the case if coloration is related to: (1) thermoregulatory properties; (2) attractiveness of feathers in the nest for mates; (3) eggshell bacterial density. All of these hypothetical scenarios predict that feathers of different colours would differentially affect the hatching success of birds, and that birds should preferentially choose the most beneficial feather colour for lining their nests. Results from two different experiments performed with a population of Danish barn swallow, Hirundo rustica, were in accordance with these predictions. First, H. rustica preferentially selected white experimentally offered feathers for lining their nests. Second, the experimental manipulation of the feather colour composition of nests of H. rustica had a significant effect on hatching success. Experimental nests with more white feathers added at the beginning of incubation had a lower probability of hatching failures, suggesting differential beneficial effects of lining nests with feathers of this colour. We discuss the relative importance of hypothetical functional scenarios that predicted the detected associations, including those related to sexual selection or to the community of microorganisms associated with feathers of different colours. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 67–74.     

Parent birds assess nest predation risk: influence of cavity condition and avian nest predator activity

Skutch hypothesized that nest predators visually assess parental activities to locate a prey nest, whereas parents modify fitness‐related traits to reduce the probability of nest predation. We examined how cavity condition and parental activity interact with avian nest predators to shape the nest success of two coexisting parid species, marsh tits Poecile palustris and oriental tits Parus minor, breeding in nest‐boxes during the incubation period. Nest‐boxes were manipulated to create a prolonged risk of nest predation (entrance diameter 2.6 cm control vs 5.5 cm treatment) soon after clutch completion. To measure changes in parental behavior, we also simultaneously simulated a pulsed risk of nest predation, using sound playbacks of a coexisting control bird and an avian nest predator. We found that the parent tits merely responded the pulsed risk, presumably due to an environment with high avian nest predator encounters, compared to the prolonged risk. Instead, both species spent more time on vigilance at the nest, only under prolonged risk conditions. The activity of corvids near the nest‐box was higher in the marsh tit than that in oriental tits. This activity was also higher in the treatment nest box than that in the control nest‐box. Nest predation during the incubation period was higher in marsh tits than in oriental tits, presumably due to higher and more plastic vigilance in oriental tits, compared to marsh tits. Our results highlight that the differences in cavity condition and parental activities at the nests of two coexisting non‐excavators may contribute to differential nest predation by attracting avian nest predators.     

Latitudinal variation in parental energy expenditure during brood rearing in the great tit

The variation in time and energy allocation of female great tits, Parus major, was studied in five different European populations across a latitudinal gradient. Daily energy expenditure (DEE) was measured in females tending 12-day-old broods. The number of daylight hours used by the parents to collect food for the brood increased with latitude, while DEE and feeding rate per brood tended to level off with latitude. Individual variation in DEE could be explained by variation in ambient temperature (–), the duration of activity period (+) and area, but not by brood size, female body mass, brood mass or feeding rate. When the effect of ambient temperature and the duration of the activity period on the day of energy expenditure measurements were controlled for, female DEE still tended to level off with latitude. Temperature and activity alone can thus not explain the observed pattern. The present study suggests that parents at southern latitudes may be under a time constraint and do not increase energy expenditure because they have no more daylight hours available for foraging, while birds at northern latitudes may be under an energy constraint because they do not make full use of the long daylight period available. Received: 25 May 1999 / Accepted: 08 September 1999     

Rearing environment effects on immune defence in blue tit Cyanistes caeruleus nestlings

Rearing conditions may influence ontogeny and functioning of the immune system. Activation of different mechanisms involved in host disease resistance and their internal regulation can be affected by intrinsic and extrinsic factors influencing development. I investigated how rearing environment can influence associations between humoral and cellular constituents of immune defence in nestling blue tits (Cyanistes caeruleus). The ability to mount a cell-mediated immune response was estimated as a hypersensitivity reaction to phytohaemagglutinin, and the ontogeny of humoral immunity was determined by assessing circulating levels of total IgG in 15-day-old nestlings. Heterogeneity in rearing conditions was evoked by placing nest-boxes in areas differing in habitat structural characteristics, and examining natural variation in nest ectoparasite infestations, hatching date, brood size and brood sex-ratio. Habitat characteristics, parasitism and hatching date may shape associations between different components of the immune system in developing birds. I discuss the effects of rearing conditions on the interaction between different arms of the immune system and the implications for understanding negative correlations within the immune system at the individual and brood level.     

Food supplementation and predation risk in harsh climate: interactive effects on abundance and body condition of tit species

Food availability and predation risk can have drastic impacts on animal behaviour and populations. The tradeoff between foraging and predator avoidance is crucial for animal survival and will strongly affect individual body mass, since large fat reserves are beneficial to reduce starvation but may increase predation risk. However, two‐factor experiments simultaneously investigating the interactive effects of food and predation risk, are still rare. We studied the effects of food supplementation and natural predation risk imposed by pygmy owls Glaucidium passerinum on the abundance and fat reserves of tit species in boreal forests of north Europe, from January to March in 2012 and in 2013. Food supplementation increased the number of individuals present in a given forest patch, whereas the level of predation risk had no clear impact on the abundance of tit species. The stronger impact of food supply respect to predation risk could be the consequence of the harsh winter conditions in north Europe, with constant below‐zero temperatures and only few (5–7 h) daylight hours available for foraging. Predation risk did not have obvious effects on tit abundance but influenced food consumption and, together with food supplementation, affected the deposition of subcutaneous fat in great tits Parus major. High owl predation risk had detrimental effects on body fat reserves, which may reduce over‐winter survival, but the costs imposed by pygmy owl risk were compensated when food was supplemented. The starvation–predation tradeoff faced by great tits in winter may thus be mediated through variation in body fat reserves. In small species living in harsh environment, this tradeoff appeared thus to be biased towards avoidance of starvation, at the cost of increasing predation risk.     

Contrasting the seasonal and elevational prevalence of generalist avian haemosporidia in co‐occurring host species

Understanding the ecology and evolution of parasites is contingent on identifying the selection pressures they face across their infection landscape. Such a task is made challenging by the fact that these pressures will likely vary across time and space, as a result of seasonal and geographical differences in host susceptibility or transmission opportunities. Avian haemosporidian blood parasites are capable of infecting multiple co‐occurring hosts within their ranges, yet whether their distribution across time and space varies similarly in their different host species remains unclear. Here, we applied a new PCR method to detect avian haemosporidia (genera Haemoproteus, Leucocytozoon, and Plasmodium) and to determine parasite prevalence in two closely related and co‐occurring host species, blue tits (Cyanistes caeruleus, N = 529) and great tits (Parus major, N = 443). Our samples were collected between autumn and spring, along an elevational gradient in the French Pyrenees and over a three‐year period. Most parasites were found to infect both host species, and while these generalist parasites displayed similar elevational patterns of prevalence in the two host species, this was not always the case for seasonal prevalence patterns. For example, Leucocytozoon group A parasites showed inverse seasonal prevalence when comparing between the two host species, being highest in winter and spring in blue tits but higher in autumn in great tits. While Plasmodium relictum prevalence was overall lower in spring relative to winter or autumn in both species, spring prevalence was also lower in blue tits than in great tits. Together, these results reveal how generalist parasites can exhibit host‐specific epidemiology, which is likely to complicate predictions of host–parasite co‐evolution.     

Photoperiodically regulated cycle of locomotory activity and fat reserves during migration seasons in the irruptive bird species,the long‐tailed tit Aegithalos c. caudatus

In northern Europe the long‐tailed tit Aegithalos c. caudatus shows irregular outbreaks of migrating individuals in autumn. Therefore, this species is generally believed to be irruptive, moving in response to external environmental stimuli such as food limitation or overpopulation in the breeding area. We studied the locomotory activity of 24 young captive long‐tailed tits from August up to early May of the following year. All hand raised birds from the local population of Lake Ladoga region (NW Russia) exhibited a distinct seasonal pattern in their locomotory activity similar to birds trapped on migration. They showed a rise in activity both in autumn and spring period. Fat reserves did not peak in autumn but increased along with spring activity. The timing of increase in the locomotory activity and fat reserves, as well as daily pattern and maximum level of activity in autumn depended on photoperiod. Long‐tailed tits kept on the photoperiod, simulating late hatching, started to migrate at an earlier age and showed a significantly higher level of activity in autumn compared to their siblings kept on the photoperiod simulating early hatching. The present findings suggested that in the studied species there is an annual cycle of migratory restlessness that is exhibited in captivity and is influenced by photoperiod.