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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 nonbreeding 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.

Aim Investigate whether birds use vegetation green‐up, a measure of spring arrival, as a cue to shift their migration speed in response to climate change by examining: (1) how green‐up moves in the landscape, (2) how bird migratory speed responds to green‐up, (3) how species traits affect migratory speed and (4) how migration speed affects arrival time at breeding sites. Location Eastern North America. Time Period 2002 to 2017. Major Taxa Studied Fifty‐five species of eastern North American Passerines. Methods We calculated speed at the migration front using arrival dates derived from 16 years of eBird data with a linear regression. Similarly, we calculated the advancement speed of forest vegetation green‐up using satellite data. Green‐up effects on bird speed were tested using generalised additive models. Results On average, songbirds migrate northward during spring at a mean speed of 63 km/day. We observed strong non‐linear effects of latitude, with bird migration speed accelerated and green‐up speed slowed as the distance from the equator increased. Annual and spatial variation in bird migration speed depended on the local green‐up date and how quickly green‐up was advancing northward: years with earlier and faster green‐up were associated with higher migration speeds. Bird arrival relative to green‐up was strongly influenced by two variables: how early green‐up was and how fast birds were migrating. Main Conclusions The variation of bird migration speed with green‐up suggests birds can shift migration speed to ‘catch up’ with earlier springs. However, the stronger effect of green‐up date compared to migration speed suggests that birds do not fully compensate for arrival time by simply migrating more quickly. Climate change will likely outpace birds' ability to speed up their migration and adapt to new phenological regimes.

There are more than 1500 road segments, where large amphibian mortalities are recorded in Slovenia. One of such road-kill hotspots is at Vinogradniška pot in Razvanje (NE Slovenia), where censuses of migrating amphibians have been carried out in spring of 2019, 2020, 2021 and 2024 alongside actions to prevent road death that have been taking place since 2018, but irregularly. Here, the first data from those censuses are presented. Four amphibian species have been recorded migrating over the road, namely common toad (Bufo bufo), common frog (Rana temporaria), agile frog (R. dalmatina) and Italian crested newt (Triturus carnifex). The most numerous was B. bufo, of which 500–1000 individuals migrated over the road annually and represented about 99% of individuals of all recorded amphibian species. Male B. bufo outnumbered females by 4–12:1 and species mortality was fairly low (between 5 and 12%), however, it was deliberately artificially reduced. Amphibian activity was lower later in the evening and had a significant moderate positive correlation with the air temperature. The data presented indicates the importance of amphibian spring migration monitoring also over low-traffic roads, which are rarely the focus of similar studies. V Sloveniji je trenutno registriranih več kot 1500 odsekov kjer prihaja do množičnih povozov dvoživk. Ena od takšnih črnih točk je cesta na Vinogradniški poti v Razvanju (SV Slovenija), kjer smo popise selečih se dvoživk opravljali v letih 2019, 2020, 2021 in 2024, v sklopu akcije prenašanja dvoživk čez cesto, ki jo v lastni režiji izvajamo od leta 2018, a ne redno. Tukaj predstavljamo prve podatke iz popisnih let. Na lokaciji smo zabeležili štiri vrste selečih se dvoživk, in sicer navadno krastačo (Bufo bufo), sekuljo (Rana temporaria), rosnico (R. dalmatina) in velikega pupka (Triturus carnifex). Najštevilčnejša je bila navadna krastača, s 500–1000 selečimi se osebki letno, ki so predstavljali okoli 99 % osebkov vseh zabeleženih vrst dvoživk. Samci so v populaciji prevladovali nad samicami v razmerju 4–12:1, smrtnost pa je bila relativno nizka (med 5 in 12 %), a se v sklopu akcije ta namerno zmanjša. Aktivnost dvoživk je skozi večer upadla in je korelirala zmerno pozitivno, a statistično značilno s temperaturo zraka. Podatki prikazujejo pomen monitoringov spomladanskih selitev dvoživk tudi čez manj prometne ceste, ki so redko vključene v podobne raziskave.

Species that make long-distance migrations face changes in the phenology of natural processes linked to global climate changes. Mismatch between the onset of resources and arrival on breeding grounds or changes in the conditions faced during migration such as early snowmelt in northern environments could have severe impacts on migrant populations. We investigated the impact of local weather and broad-scale climate and of the availability of forage resources on timing of spring and fall migrations of migratory caribou (Rangifer tarandus) from the Rivière-George and Rivière-aux-Feuilles herds in northern Québec and Labrador, Canada. We tested the effect of local weather using data provided by the Canadian Regional Climate Model, a large-scale climate index, snow and ice cover, and the Normalized Difference Vegetation Index on departure and arrival dates of 377 spring migrations and 499 fall migrations of female caribou. Since 2000, except for the spring arrival, migrations tended to occur earlier. Spring arrival was delayed when caribou encountered mild temperatures and abundant precipitation during migration, as early snowmelt may increase cost of movements. At greater population sizes, caribou seemed to limit the time spent on summer range by arriving later and departing earlier, possibly to limit competition for summer forage. During fall, caribou adjusted their migration to conditions en route because they arrived earlier if November was snowy and mild, possibly to limit the costs of moving through deep snow. Like numerous migrant species, most caribou herds are declining, and it is crucial to assess which environmental factors affect migrant populations. Our study contributes to the understanding of the impact of local weather conditions and climate change on migratory land mammals.

Migrating birds are expected to fly at higher airspeeds when minimizing time rather than energy costs of their migratory journeys. Spring migration has often been suggested to be more time selected than autumn migration, because of the advantage of early arrival at breeding sites. We have earlier demonstrated that nocturnal passerine migrants fly at higher airspeeds during spring compared to autumn, supporting time-selected spring migration. In this study, we test the hypothesis that seasonal airspeeds are modulated differently between short- and long-distance migrants, because of a stronger element of time selection for autumn migration over long distances. In support of this hypothesis, we demonstrate that the seasonal difference in airspeed is significantly larger (spring airspeed exceeding autumn airspeed by a factor of 1.16 after correcting for the influence of altitude, wind and climb/descent on airspeed) among short-distance compared to long-distance (factor 1.12) migrants. This result is based on a large sample of tracking radar data from 3 years at Falsterbo, South Sweden. Short-distance migrants also tend to fly with more favourable winds during autumn, indicating relaxed time constraints (being able to afford to wait for favourable winds) compared to long-distance migrants. These results indicate surprisingly fine-tuned seasonal modulation of airspeed and responses to wind, associated with behavioural strategies adapted to different levels of time selection pressures during spring and autumn migration.

Migrating birds have to incorporate migration into their annual cycle, next to breeding and moult. This presents the challenge to arrive at the right place at the right time at any given moment during the year to maximize fitness. Although many studies have investigated the timing of specific (life-history) activities of migrating birds, it is poorly studied how the timing and duration of these activities depend on each other and, ultimately, how they affect fitness. Therefore, we investigated variability and dependencies in the timing and duration of successive activities throughout the annual cycle and assessed their fitness consequences in hoopoes (Upupa epops), a long-distance migratory bird, using geolocator and breeding phenology data of five consecutive years. We found that the timing and duration of seasonal activities generally depended on the timing and duration of the preceding activity; yet, the strength of these dependencies and the degree of variability varied between activities. The strongest dependencies were found between the end of breeding and departure from the breeding grounds as well as between the arrival in the breeding grounds and the onset of breeding. We also found fitness consequences of timing and duration but only for specific activities: spring migration and particularly the duration of the pre-breeding period influenced the quality of the territory acquired as well as the total number of fledglings. Consequently, we suggest that our study species has the flexibility to adjust the timing and duration of activities but to varying degrees. This is a step forward in understanding the time-constraints that migratory animals face and in identifying their fitness consequences.

Migratory behaviour allows individuals to inhabit areas with optimal environmental conditions throughout the year. To reduce energy expenditure and the risk of mortality while migrating, birds may schedule their departures basing on environmental cues that provide seasonal and/or local information. In this study, we aimed to identify the possible effect of environmental factors on the spring migration of 30 Eurasian teal Anas crecca tracked between 2014 and 2018 from Italian wintering areas. We used Cox proportional hazard and generalized estimating equation models to evaluate the environmental cues that affect teal's decision to start migratory movements from the wintering grounds and continue migration from stopover sites. Apart from the anticipated effect of photoperiod, the onset of spring migration was not substantially influenced by environmental variables, whereas the speed of migration seemed to be influenced by both seasonal (increased ground temperature, an indicator of spring advancement) and local (low cloud cover and northward blowing winds, which support migratory flight) environmental cues. The slow migration observed in teal may favour a strategy in which migratory timing is modulated mainly by the conditions encountered during the journey rather than at the start of the migration. This suggested low impact of local environmental variables on the onset of spring migration could have important consequences both for the management of this species for hunting purposes and for the way the species might respond to the ongoing climatic change.

Climate factors shape the spring phenology of migrant birds in Europe. We examined carry-over effects of temperature and rainfall in four regions of Europe on the spring migration timing of a medium-distance migrant, Eurasian Wren, at the southern Baltic coast over 60 years. We modelled the effects of these climate factors on the timing of the start (10%), median (50%) and end (90%) of wrens’ spring passage at the bird ringing station Hel (N Poland) during 1964–2023. The dates of start and median of spring passage have not changed, but the end shifted earlier by 5.7 days over these 60 years. The start, median and end dates of wren passage on the Baltic coast were early after warm autumn, winter or spring, but delayed after high autumn and winter rainfall in central and northern Europe. Analogous climate conditions in southern and south-western Europe had the opposite effect on wrens’ timing of passage. High spring rainfall in central and southern Europe delayed spring passage at Hel. High rainfall in early summer in northern Europe was related to early wren passage the following spring, but such conditions in late summer resulted in a delay of spring passage. We assume that temperature and rainfall in these regions influence the timing of wren spring passage through their effect on food availability, individual fitness, migration distance and proportion of immatures among migrants. We suggest that varied humidity, which caused different insect abundance for wrens, explains the varied effects of rainfall in various regions of Europe on the timing of wren spring passage at Hel. We show that wrens’ spring migration phenology in the Baltic region is shaped by a combination of carry-over effects of many environmental factors. They affect wrens in regions of Europe where they stay previously, even months before their spring migration.

Since the 1980s, earlier European springs have led to the earlier arrival of migrant passerines. We predict that arrival is related to a suite of climate indices operating during the annual cycle (breeding, autumn migration, wintering, spring migration) in Europe and Africa over the year preceding arrival. The climate variables include the Indian Ocean Dipole (IOD), Southern Oscillation Index (SOI), and North Atlantic Oscillation (NAO). Furthermore, because migrants arrive sequentially from different wintering areas across Africa, we predict that relationships with climate variables operating in different parts of Africa will change within the season. We tested this using daily ringing data at Bukowo, a spring stopover site on the Baltic coast. We calculated an Annual Anomaly (AA) of spring passage (26 March–15 May, 1982–2024) for four long-distance migrants (Blackcap, Lesser Whitethroat, Willow Warbler, Chiffchaff). We decomposed the anomaly in two ways: into three independent main periods and nine overlapping periods. We used multiple regression to explore the relationships of the arrival of these species at Bukowo. We found sequential effects of climate indices. Bukowo is thus at a crossroads of populations arriving from different wintering regions. The drivers of phenological shifts in passage of wide-ranging species are related to climate indices encountered during breeding, wintering, and migration.

Migratory birds may either upregulate their immune system during migration as they might encounter novel pathogens or downregulate their immune system as a consequence of trade‐offs with the resource costs of migration. Support for the latter comes not least from a study that reports a positive correlation in autumn migrating birds between fuel stores and parameters of innate and acquired immune function, that is, energy‐exhausted migrants appear to have lowered immune function. However, to our knowledge, no study has tested whether this pattern exists in spring migrating birds, which may face other trade‐offs than autumn migrants. Here, we investigate if in spring there is a relationship between fuel stores and microbial‐killing ability, a measure of innate immune function, and total immunoglobulin (IgY), a measure of acquired immune function, in four migrating bird species: chaffinches (Fringilla coelebs), dunnocks (Prunella modularis), song thrushes (Turdus philomelos) and northern wheatears (Oenanthe oenanthe). Our findings indicate no significant correlation between fuel stores and either microbial killing ability or IgY levels when considering all species collectively. When analysing species separately, we found a significant negative correlation between fuel stores and microbial‐killing ability in chaffinches and a positive correlation between fuel stores and IgY levels in wheatears. In song thrushes, but not in any of the other species, there was a significant negative correlation between relative arrival date and microbial‐killing ability and between arrival date and IgY levels. Sex did not affect immune function in any of the species. Our study suggests that the relationship between immune function and fuel stores may be different during spring migration compared to autumn migration. Differences in the speed of migration or pathogen pressure may result in different outcomes of the resource trade‐off between investment in immune function and migration among the seasons. Constitutive immune function is not linked to fuel stores in spring migrating birds. However, there is a negative relationship between immune function (% Escherichia coli killed) and arrival date. This suggests that there are seasonal variations in pathogen pressures and migratory speed which could impact the resource trade‐off between investment in immune function and demands of migration.