Peter Adamík

Barrier crossing in small avian migrants: individual tracking reveals prolonged nocturnal flights into the day as a common migratory strategy

Over decades it has been unclear how individual migratory songbirds cross large ecological barriers such as seas or deserts. By deploying light-level geolocators on four songbird species weighing only about 12 g, we found that these otherwise mainly nocturnal migrants seem to regularly extend their nocturnal flights into the day when crossing the Sahara Desert and the Mediterranean Sea. The proportion of the proposed diurnally flying birds gradually declined over the day with similar landing patterns in autumn and spring. The prolonged flights were slightly more frequent in spring than in autumn, suggesting tighter migratory schedules when returning to breeding sites. Often we found several patterns for barrier crossing for the same individual in autumn compared to the spring journey. As only a small proportion of the birds flew strictly during the night and even some individuals might have flown non-stop, we suggest that prolonged endurance flights are not an exception even in small migratory species. We emphasise an individual’s ability to perform both diurnal and nocturnal migration when facing the challenge of crossing a large ecological barrier to successfully complete a migratory journey.

Nest losses of cavity nesting birds caused by dormice (Gliridae, Rodentia)

Mammals are common predators on bird nests. However, their species identity frequently remains unknown. Here we present long-term data (1975–2005) from a central European woodland on the predatory effect of three dormice species (Rodentia, Gliridae) on cavity-nesting birds. Dormice are mostly frugivorous during the active late-summer season, but shortly after they terminate hibernation, they frequently depredate cavity-nesting-bird nests. The seven bird species studied, lost on average between 2.9 to 18.4% of their broods. MigratoryFicedula flycatchers suffered the highest brood losses, while the residentParus titmice and the nuthatchSitta europaea had much lower brood losses. The three dormice species differed significantly in their predatory effect during different avian breeding stages. The edible dormouseGlis glis (Linnaeus, 1766) depredated both eggs and nestlings equally, while the common dormouseMuscardinus avellanarius (Linnaeus, 1758) and the forest dormouseDryomys nitedula (Pallas, 1778) destroyed more nests during egg laying and the incubation period. Among adult birds, females were taken more frequently by dormice than males. Among avian species, adultFicedula flycatchers were more often depredated than the titmice and nuthatch. Our study provided further evidence, that among the traditional studies on the costs of reproduction, parental mortality at the nests needs to be considered and that incubating or brooding females might be under higher predation risk than the males.

Cyclicity and variability in prey dynamics strengthens predator numerical response: the effects of vole fluctuations on white stork productivity

Theory predicts that optimality of life-long investment in reproduction is, among other factors, driven by the variability and predictability of the resources. Similarly, during the breeding season, single resource pulses characterized by short periods and high amplitudes enable strong numerical responses in their consumers. However, it is less well established how spatio-temporal dynamics in resource supplies influence the spatio-temporal variation of consumer reproduction. We used the common vole (Microtus arvalis)—white stork (Ciconia ciconia) resource—consumer model system to test the effect of increased temporal variation and periodicity of vole population dynamics on the strength of the local numerical response of storks. We estimated variability, cycle amplitude, and periodicity (by means of direct and delayed density dependence) in 13 Czech and Polish vole populations. Cross-correlation between annual stork productivity and vole abundance, characterizing the strength of the local numerical response of storks, increased when the vole population fluctuated more and population cycles were shorter. We further show that the onset of incubation of storks was delayed during the years of higher vole abundance. We demonstrate that high reproductive flexibility of a generalist consumer in tracking the temporal dynamics of its resource is driven by the properties of the local resource dynamics and we discuss possible mechanisms behind these patterns.

Cold spell en route delays spring arrival and decreases apparent survival in a long-distance migratory songbird

BackgroundAdjusting the timing of annual events to gradual changes in environmental conditions is necessary for population viability. However, adaptations to weather extremes are poorly documented in migratory species. Due to their vast seasonal movements, long-distance migrants face unique challenges in responding to changes as they rely on an endogenous circannual rhythm to cue the timing of their migration. Furthermore, the exact mechanisms that explain how environmental factors shape the migration schedules of long-distance migrants are often unknown.ResultsHere we show that long-distance migrating semi-collared flycatchers Ficedula semitorquata delayed the last phase of their spring migration and the population suffered low return rates to breeding sites while enduring a severe cold spell en route. We found that the onset of spring migration in Africa and the timing of Sahara crossing were consistent between early and late springs while the arrival at the breeding site depended on spring phenology at stopover areas in each particular year.ConclusionUnderstanding how environmental stimuli and endogenous circannual rhythms interact can improve predictions of the consequences of climate changes on migratory animals.

Effect of climatic change on the duration of the breeding season in three European thrushes.

Capsule Evidence for extension of breeding seasons in Song Thrushes and Blackbirds (multiple‐brooded species) and shortening in Fieldfares (a single‐brooded species). Aims To analyse breeding data from central Europe during 1964–2006 in relation to climatic conditions operating at breeding and wintering grounds, and to compare breeding phenology in urban and rural habitats. Methods Using chick ringing data we evaluated long‐term changes in breeding phenology of Fieldfares Turdus pilaris, Song Thrushes T. philomelos and Common Blackbirds T. merula. Changes in phenology were analysed for the 5th percentile, median, 95th percentile, inter‐quantile range (IQR) and brood size. Results All thrushes showed consistent trends towards earlier onset of breeding. However, there was a contrasting pattern in the later phenological characteristics (median, 95th percentile and IQR) that were associated with single‐ versus multiple‐brooded species. The single‐brooded Fieldfares revealed an advancing trend in all phenological phases, which caused shortening of its breeding period. In contrast, the multiple‐brooded Song Thrushes and Blackbirds delayed both medians and the 95th percentiles of breeding dates leading to extension of their breeding seasons. Temperatures at both wintering and breeding grounds were generally negatively associated with the onset of breeding. Urban birds bred significantly earlier than their rural conspecifics, but brood sizes did not differ. Conclusion Multiple‐brooded species may respond differently to increasing spring temperatures than single‐brooded species.

Impact of Nesting Mortality on Avian Breeding Phenology: A Case Study on the Red-Backed Shrike (Lanius collurio)

The seasonal timing of avian reproduction is supposed primarily to coincide with favourable feeding conditions. Long-term changes in avian breeding phenology are thus mostly scrutinized in relation to climatic factors and matching of the food supplies, while the role of nesting mortality is largely unexplored. Here we show that higher seasonal mean daily mortality rate leads to a shift in the distribution of breeding times of the successful nests to later dates in an an open-nesting passerine bird, the red-backed shrike Lanius collurio. The effect appeared to be strong enough to enhance or counteract the influence of climatic factors and breeding density on the inter-annual variation in mean hatching dates. Moreover, the seasonal distribution of reproductive output was shifted to larger, or smaller, broods early in the season when the nesting mortality increased, or decreased, respectively, during the season. We suggest that population level changes in timing of breeding caused by a general advancement of spring and of the food supplies might be altered by the seasonality in nesting mortality. Hence, we argue that consideration of nesting mortality is of major importance for understanding long-term trends in avian phenology, particularly in species capable of renesting.

Rapid Decline of Common Cuckoo Cuculus canorus Parasitism in Red-Backed Shrikes Lanius collurio

Several 19th and 20th century studies on Common Cuckoo Cuculus canorus brood parasitism suggest that Red-backed Shrikes Lanius collurio used to be one of its common hosts in central Europe. However, since the late 1960s parasitism ceased to occur in Red-backed Shrikes in Hungary. Using data from bird ringing records in the Czech Republic and Slovakia we evaluate whether this finding holds on a broader scale. We found a rapid decline in the parasitism rate, expressed as the frequency of Common Cuckoo chicks encountered in Red-backed Shrike nests, during 1964–2006. During the first decade of the study, on average 2.19% of Shrike nests contained a Cuckoo chick, while in the last decade Cuckoos occurred in 0.37% of the nests only. This suggests a six-fold decline over the study period. Parasitism rates showed strong regional variations which were positively related to the size of regional host populations. In addition to the high ability of Shrikes in discriminating Cuckoo eggs, as found in previous studies, we suggest that decreases in regional host population numbers might lead to host abandonment within a few decades. Whether these two factors work in tandem, or independently, remains to be answered.

Red-spotted Bluethroats Luscinia s. svecica migrate along the Indo-European flyway: a geolocator study

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.

Linking events throughout the annual cycle in a migratory bird—non-breeding period buffers accumulation of carry-over effects

Annual cycles of animals consist of distinct life history phases linked in a unified sequence, and processes taking place in one season can influence an individual’s performance in subsequent seasons via carry-over effects. Here, using a long-distance migratory bird, the collared flycatcher Ficedula albicollis, we link events throughout the annual cycle by integrating breeding data, individual-based tracking, and stable-carbon isotopes to unravel the connections between different annual phases. To disentangle true carry-over effects from an individuals’ intrinsic quality, we experimentally manipulated the brood size of geolocator-tracked males prior to tracking. We did not find unambiguous differences in annual schedules between individuals of reduced and increased broods; however, in the following spring, the latter crossed the Sahara and arrived at the breeding grounds earlier. Individuals with higher absolute parental investment delayed their autumn migration, had shorter non-breeding residency period but advanced spring migration compared to individuals with lower breeding effort. Neither the local non-breeding conditions (as inferred from δ13C values) nor the previous breeding effort was linked to the timing of the following breeding period. Furthermore, while on migration, collared flycatchers showed a pronounced “domino effect” but it did not carry over across different migration seasons. Thus, the non-breeding period buffered further accumulation of carry-over effects from the previous breeding season and autumn migration. Our results demonstrate tight links between spatially and temporally distinct phases of the annual cycles of migrants which can have significant implications for population dynamics.Significance statementTiming is everything! This holds true also for migratory animals which must time their annual movements, breeding and non-breeding seasons according to the environment they live in. However, perfect timing of a particular event can be hampered by past events. We studied connections between spatially and temporarily distinct annual phases in collared flycatchers, a small bodied bird which twice a year migrates between Europe and sub-Saharan Africa. We found tight links between individual’s parental investment and timing of autumn migration, but not spring migration. Similarly, the timing of autumn migration did not translate to influence the timing of spring migration. Thus, our results demonstrate that the non-breeding period may serve as a buffer to overcome high energy expenditure during the previous breeding season and prevent further accumulation of carry-over effects in migratory birds.

Characterizing the mammalian hair present in Great Tit (Parus major) nests

Capsule Many birds are known to incorporate mammal hair into their nest lining, but the frequency with which they use hair from different mammals is unknown. We performed one of the first detailed examinations of mammalian hair from 54 Great Tit nests. We identified 5317 hairs belonging to 21 mammal species. Almost all of the examined nests contained hair from Roe Deer (Capreolus capreolus), but hair from Wild Boars (Sus scrofa), European Hares (Lepus europaeus) and Red Foxes (Vulpes vulpes) was also common.