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Relation between observed flight time to FINO 2 and (a) expected time to FINO 2 (as calculated from the surface wind situation at departure, assuming a straight flight path), (b) fat score at release (estimated on a 0e9 visual scale; Appendix Fig. A1) and (c) degree of overcast at departure (0/8 ¼ clear sky, 8/8 ¼ total overcast; Table 4). The plots show residual times (min) after taking into account the effects of the complementary variables.
Source publication
Departure decisions of how and when to leave a stopover site may be of critical importance for the migration performance of birds. We used an automated radiotelemetry system at Falsterbo peninsula, Sweden, to study stopover behaviour and route choice in free-flying passerines departing on flights across the Baltic Sea during autumn migration. In ad...
Contexts in source publication
Context 1
... the GLM that best described factors affecting the observed flight time to FINO 2 according to the lowest AIC (Fig. 3, Table 4), fat score at release and degree of overcast were included in addition to the expected flight time to FINO 2; for factors included in the original model see Methods. We estimated the effect of wind by calculating the expected ground speed for each bird on the basis of surface wind conditions at departure time, and assumed that the ...
Context 2
... an expected flight speed of 10 m/s and a reduction in flight duration of 2.0 min per unit of fat score for song thrushes with the expected flight speed of 13 m/s. However, we observed a much larger reduction in flight duration in relation to increasing fat score, about 5.4 min per unit of fat score (based on the slope of the linear regression in Fig. 3b). Hence, it is likely that additional behavioural differences between lean and fat individuals, apart from the mass- dependent difference in airspeed, explain the observed pattern of flight durations in our study. Birds with the largest fuel reserves may be more risk-prone and depart straight and directly across the Baltic Sea, while ...
Citations
... The use of local cues to depart from stopover sites is welldocumented, particularly when birds need to cross ecological barriers and wait for the best possible weather conditions to aid their flight (Sjöberg et al. 2015, Kölzsch et al. 2016, Loonstra et al. 2019). However, even in the absence of an ecological barrier, as in our case, local cues that indicate good weather conditions are still important for making departure decisions (Sapir et al. 2011, Sjöberg et al. 2017, O'Neal et al. 2018, Le Rest et al. 2019. ...
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.
... Despite long-held predictions that songbirds should initiate migratory flights during a narrow window of time after sunset and their demonstrated ability to do so in captivity, observations of individual birds in the wild have repeatedly failed to match theory or captive studies. The general pattern observed in wild songbirds thus far is that although many individuals depart within the first four hours after sunset, departure can occur at any time between sunset and sunrise [16,20,21,[25][26][27][28][29][30][31][32][33][34]. Many factors have been hypothesized to account for variation in nocturnal departure time including age, sex, fuel load, parasite infection, the presence of ecological barriers, distance remaining to the migratory destination, and the type of movement initiated at departure [16,29,31,35,36]. ...
... The general pattern observed in wild songbirds thus far is that although many individuals depart within the first four hours after sunset, departure can occur at any time between sunset and sunrise [16,20,21,[25][26][27][28][29][30][31][32][33][34]. Many factors have been hypothesized to account for variation in nocturnal departure time including age, sex, fuel load, parasite infection, the presence of ecological barriers, distance remaining to the migratory destination, and the type of movement initiated at departure [16,29,31,35,36]. Nonetheless, why nocturnal departure times observed in the wild have been more variable than in captive studies or predicted by theory remains unclear. ...
... Upon departure, individuals may either recommence migration or relocate to another nearby stopover site through non-migratory regional movements, presumably to find better quality habitat (i.e., habitat with more food, fewer predators, etc.) [31,40]. Accordingly, individuals departing stopover sites likely vary in their need to maximize flight duration or observe celestial orientation cues and may subsequently depart at variable times of night [29,31,41]. Even among those birds continuing long-distance migration, individuals may show large amounts of variation in fuel load [39]. ...
Background
Each spring and fall billions of songbirds depart on nocturnal migrations across the globe. Theory suggests that songbirds should depart on migration shortly after sunset to maximize their potential for nightly flight duration or to time departure with the emergence of celestial cues needed for orientation and navigation. Although captive studies have found that songbirds depart during a narrow window of time after sunset, observational studies have found that wild birds depart later and more asynchronously relative to sunset than predicted.
Methods
We used coded radio tags and automated radio-telemetry to estimate the time that nearly 400 individuals from nine songbird species departed their breeding or wintering grounds across North America. We also assessed whether each species was most likely beginning long-distance migratory flights at departure or instead first making non-migratory regional flights. We then explored variation in nocturnal departure time by post-departure movement type, species, age, sex, and season.
Results
We found that 90% of individuals from species that were likely initiating long-distance migratory flights departed within 69 min of civil dusk, regardless of species, season, age, or sex. By contrast, species that likely first made non-migratory regional movements away from the migratory destination departed later and more asynchronously throughout the night. Regardless of post-departure movement type, 98% of individuals departed after civil dusk but otherwise showed no preference in relation to twilight phase.
Conclusions
Although the presence of celestial orientation cues at civil dusk may set a starting point for departure each night, the fact that species likely beginning long-distance migration departed earlier and more synchronously relative to civil dusk than those first making non-migratory regional movements is consistent with the hypothesis that departing promptly after civil dusk functions to maximize the potential for nightly flight duration and distance. By studying the onset of migration, our study provides baseline information about departure decisions that may enhance our understanding of departure timing throughout migration.
... By doing so, birds maximize the night time available for flying across the open sea and thereby minimize the exposure to the disadvantages of daytime flights, i.e. more turbulent air [18,71] and higher predation risk [72]. These findings highlight the importance of wind conditions in the context of barrier crossing [24,40,66], even of comparatively small ones such as the German Bight [39] or the Baltic Sea [73]. Although wind drift can cause substantial displacements in migratory birds [36], this passive effect is unlikely to be involved in this case, because (i) birds did not depart in strong winds, (ii) all Sedge Warblers were able to stay in close proximity to the coast, irrespective of the prevailing wind conditions and (iii) we simultaneously detected contrary routing decisions of different individuals. ...
Migrating birds flexibly adjust their individual migratory decisions, i.e. departing, routing and landing, based on intrinsic (e.g. energy stores) and extrinsic (e.g. landscape features and weather) factors modulating the endogenous stimuli. So far, these decisions have mostly been studied separately. Notably, we lack information on which factors landing decisions during active flight are based on. Therefore, we simultaneously recorded all three decisions in free-flying long-distance migratory songbirds in a coastal stopover area via regional-scale radio-telemetry and related them to the prevailing weather. Birds departed under favourable weather conditions resulting in specific nights with increased departure probability. Once departed, birds could either fly offshore or take a route along the coast, which was predicted by wind support. Radio-tracking revealed that departed individuals more likely interrupted their migratory endurance flight under overcast or headwind conditions. Studying departure, routing and landing decisions in concert, we highlight the importance of weather as a common driver across all migratory decisions. By radio-tracking individuals between stopovers, we provide evidence that avoidance of adverse weather conditions is an important function of stopover. Understanding how birds adjust migratory decisions and how they affect the timing of migration and survival is key to link migration performance to individual fitness.
... Additional endogenous factors, such as individual-specific traits (e.g. age, sex, body size, fuel stores), may impact the ability to compete for resources and influence the decision to engage in migratory flight (Ellegren 1991, Jakubas and Wojczulanis-Jakubas 2010, Smolinsky et al. 2013, Sjöberg et al. 2015, Zenzal et al. 2021. In contrast, exogenous factors, such as temperature or precipitation, can influence the decision to fatten and depart from the non-breeding area by directly affecting food abundance and, subsequently, an individual's ability to deposit fuel for long-distance flights (Wingfield 1983, Ramenofsky 2012, Tøttrup et al. 2012. ...
... Most studies investigating the departure decisions of migratory songbirds use data collected at stopover sites during passage (Dänhardt and Lindström 2001, Dierschke and Delingat 2001, Deppe et al. 2015, Sjöberg et al. 2015, Packmor et al. 2020 or from the breeding area in terms of stable isotope samples or tracking technologies (Woodworth et al. 2016, Cooper et al. 2017, Ouwehand and Both 2017. Few studies have directly examined departure from the nonbreeding area (Marra et al. 1998, Studds and Marra 2005, Gordo 2007. ...
... Interestingly, fuel load also had a strong inverse relationship with departure day in early departing kinglets, which may explain the lack of difference in fuel load between early and late departing individuals. The relationship between fuel load and the decision to migrate is no surprise as numerous other studies have also documented this relationship during the migratory and pre-migratory phases (Lindstrom and Alerstam 1992, Marra et al. 1998, Studds and Marra 2005, Deppe et al. 2015, Sjöberg et al. 2015, Zenzal et al. 2021; but see Zenzal et al. 2018). The difference in condition may suggest that early-departing migrants may be attempting to minimize time while late-departing migrants may be attempting to minimize the energetic cost of migration (sensu Alerstam and Lindström 1990, Lindstrom and Alerstam 1992, Alerstam 2011. ...
Migratory birds employ a variety of mechanisms to ensure appropriate timing of migration based on integration of endogenous and exogenous information. The cues to fatten and depart from the non‐breeding area are often linked to exogenous cues such as temperature or precipitation and the endogenous program. Shorter distance migrants should rely heavily on environmental information when initiating migration given relatively close proximity to the breeding area. However, the ability to fatten and subsequently depart may be linked to individual circumstances, including current fuel load and body size. For early and late departing migrants, we investigate effects of temperature, precipitation, lean body mass, fuel load and day of year on the initiation of migration (i.e. fuel load and departure timing) from the non‐breeding region by analyzing 21 years of banding data for four species of short‐ and medium‐distance migrants. Temperatures at the non‐breeding area were related to temperatures at potential stopover areas. Despite local cues being predictive of conditions further north, the amount variation explained by local weather conditions in our models differed by species and temporal period but was low overall (< 33% variation explained). For each species, we also compared lean body mass and fuel load between early and late departing migrants, which showed mixed results. Our combined results suggest that most individuals migrating short or medium distances in our study did not time the initiation of migration with local predictive cues alone, but rather other factors such as lean body mass, fuel load, day of year, which may be a proxy for the endogenous program, and those beyond the scope of our study also influenced the initiation of migration. Our study contributes to understanding which factors influence departure decisions of short‐ and medium‐distance migrants as they transition from the non‐breeding to the migratory phase of the annual cycle.
... Birds were trapped in the morning starting 30 min before local sunrise and ending at 11 am. Each bird was ringed and the mass (nearest 0.1 g, digital scale), wing length (mm), age, and fat score (0-9 according to a visual scale for fat classification; Pettersson & Hasselquist, 1985;Sjöberg et al., 2015) was recorded. All birds in the study were juveniles in their first autumn migration and had completed their post-juvenile molt. ...
Songbirds have evolved diverse strategies to cope with seasonality, including long‐, medium‐, and short‐distance migration. There is some evidence that birds with a longer migration distance deposit fuel faster. However, most studies focus on long‐distance migrants. Comparisons between species with different migration distances are necessary to broaden our understanding of fueling capacity in migratory birds. We present maximum fuel deposition rates of five songbird species migrating along the southeast coast of Sweden in autumn with migration distances ranging from long (neotropical migrant) to short (partial/irruptive migrant) (Willow Warbler Phylloscopus trochilus, Lesser Whitethroat Curruca curruca, Common Chiffchaff P. collybita, European Robin Erithacus rubecula, and Blue Tit Cyanistes caeruleus). The birds were fed ad libitum in captivity and were exposed to either extended or natural daylength. All species ceased to increase in mass when they reached a certain fuel load, generally corresponding to migration distance, despite unlimited access to food and ample time for foraging. Blue Tits, Willow Warblers, and Lesser Whitethroats had the highest fuel deposition rates with extended daylength (19%, 20%, and 20%, respectively), and about 13% with natural daylength, which is comparable to the highest rates found in migratory songbirds in nature. European Robins and Common Chiffchaffs that winter in the temperate Mediterranean had the lowest fuel deposition rates (12% and 12% with extended daylength, respectively). Our results suggest that the long‐ and short‐distance migrants in this study have developed an extreme capacity for rapid refueling for different reasons; speedy migration to distant wintering grounds or winter survival in Scandinavia. This study contributes to our current knowledge of maximum fuel deposition rates in different species and the limitations posed by daylength. We highlight the need for future studies of species with different migration strategies in order to draw broad conclusions about fueling strategies of migratory birds. Maximum fueling rates were measured in songbirds migrating along the Baltic coast. The effects of daylength were investigated, and species with different migratory distances were compared.
... The accumulation of energy reserves that many birds exhibit in preparation to their migratory flightstermed pre-migratory fuellingis promoted by increased food intake (hyperphagia) which, subsequently, leads to rapid and remarkable gains in subcutaneous fat stores (6)(7)(8)(9). Studies in different bird species sampled at stopover sites (i.e., where migrating birds temporarily suspend the migratory flight to rest and refuel) show that individuals with larger subcutaneous fat stores exhibit higher levels of migratory restlessness in captivity (10)(11)(12)(13)(14) i.e., the urge of captive birds to migrate at night (14) and can migrate faster (13). Thus, the physiological preparations occurring over the phase of pre-migratory fuelling are likely to be central in determining the success of the subsequent active phases of the migratory cycle. ...
... The accumulation of energy reserves that many birds exhibit in preparation to their migratory flightstermed pre-migratory fuellingis promoted by increased food intake (hyperphagia) which, subsequently, leads to rapid and remarkable gains in subcutaneous fat stores (6)(7)(8)(9). Studies in different bird species sampled at stopover sites (i.e., where migrating birds temporarily suspend the migratory flight to rest and refuel) show that individuals with larger subcutaneous fat stores exhibit higher levels of migratory restlessness in captivity (10)(11)(12)(13)(14) i.e., the urge of captive birds to migrate at night (14) and can migrate faster (13). Thus, the physiological preparations occurring over the phase of pre-migratory fuelling are likely to be central in determining the success of the subsequent active phases of the migratory cycle. ...
In both captive and free-living birds, the emergence of the migratory phenotype is signalled by rapid and marked increases in food intake and fuelling, as well as changes in amount of nocturnality or migratory restlessness. The metabolic hormone corticosterone and, as more recently suggested, the gut-derived hormone ghrelin have been suggested to play a role in mediating such phenomenal phenotypic flexibility given that they both regulate fuel metabolism and locomotion across vertebrate taxa. Here, using the Common quail (Coturnix coturnix) as our study species, we induced autumn migration followed by a non-migratory wintering phase through controlled changes in daylight. We thus compared plasma corticosterone and ghrelin concentrations between the two sampling phases and assessed whether these hormones might reflect the migratory state. While we found no differences in plasma corticosterone between the two sampling phases and no link of this hormone with changes in body mass, levels of food intake or migratory restlessness, the migratory birds had substantially higher levels of plasma ghrelin relative to the non-migratory birds. Furthermore, while ghrelin did not correlate with the gain in body mass over the entire pre-migratory fuelling phase (over an average of nine weeks preceding blood sampling), plasma ghrelin did positively correlate with the gain in body mass observed during the final fattening stages (over an average of three weeks preceding blood sampling). Again, variation in plasma ghrelin also reflected the amount of body mass depleted over both the long- and short-time frame as birds returned to their non-migratory baseline - lower levels of plasma ghrelin consistently correlated with larger losses in body mass. Thus, while our data do not highlight a role of the hormone corticosterone in sustaining pre-migratory fattening as shown in other bird species, they do add evidence for a potential role of ghrelin in mediating migratory behaviour and further suggest that this hormone might be important in regulating the transitioning of migratory states, possibly by promoting fuel mobilisation and usage.
... Broadly, sandpipers appear to prefer north/northwesterly winds of a low to moderate speed and high pressure for departure from the region. Juveniles used the same weather cues as adults, which has been seen in other species as well (Sjöberg et al. 2015). However, we noted that birds departed the Bay of Fundy under less variable wind conditions than on the Northumberland Strait, suggesting that they were more selective, and therefore may be extending their stay in the region waiting for ideal wind conditions. ...
Semipalmated Sandpipers (Calidris pusilla) are Arctic-breeding shorebirds that use staging sites in Atlantic Canada during their southbound migration to South America. The upper Bay of Fundy is recognized as a critical staging area, but hundreds of smaller sites outside the Bay of Fundy also host staging Semipalmated Sandpipers and have received comparatively little attention. Using the Motus Wildlife Tracking System, we tracked adult and juvenile Semipalmated Sandpipers and identified different staging strategies used by sandpipers tagged inside and outside the Bay of Fundy. Birds tagged in the Bay of Fundy remained there, while birds tagged along the Northumberland Strait, a tidal water body along the northern coast of New Brunswick and Nova Scotia displayed multiple strategies. Most birds tagged along the Northumberland Strait used sites outside the Bay of Fundy exclusively, while a smaller proportion moved to the Bay of Fundy. Length of stay was shorter for birds using only sites outside the Bay of Fundy compared to birds using Bay sites or transferring between them. Choice of departure conditions also varied; birds using the Bay were more selective of specific wind conditions, favoring north and northwesterly winds. We found juvenile sandpipers stayed 3 days longer in the region than adults and appeared to use a broader variety of sites. Our results highlight the importance of implementing conservation measures for smaller, lesser-known staging sites in Atlantic Canada, many of which are at an increased risk of loss and degradation due to climate change, coastal development, pollution, and human disturbance.
... In conclusion we would like to emphasize that our data and the data of other studies Taylor et al. 2011;Smolinsky et al. 2013;Mitchell et al. 2015;Deppe et al. 2015;Sjöberg et al. 2015;Dossman et al. 2016;Brown and Taylor 2017;Wright et al. 2018;Gesicki et al. 2019) show that before crossing ecological barriers and on coastal areas at least some songbird migrants perform regional-scale movements, not necessarily in the migratory direction. Involvement of migrants in such movements may strongly vary between the species, and also between age groups within the species, and also be conditiondependent. ...
... However, current data on the occurrence of such movements in different passerine migrants are very scarce. Ringing recaptures may help point to this intriguing topic, which obviously has serious implications for conservations of migrating birds, but serious research into this issue is not possible without large-scale radio tracking studies Taylor et al. 2011;Smolinsky et al. 2013;Mitchell et al. 2015;Sjöberg et al. 2015;Dossman et al. 2016;Brown and Taylor 2017;Wright et al. 2018). ...
Much evidence suggests that some passerines during seasonal migrations can perform regional-scale movements, both in the migratory and in the reverse direction. The scale of such movements exceeds the scale of typical stopover movements, but is usually smaller than most migratory flights. We studied regional-scale movements during autumn migration in short-distance migrants of three passerine species: European Robin (Erithacus rubecula Linnaeus, 1758), Goldcrest (Regulus regulus Linnaeus, 1758), and Long-tailed Tit (Aegithalos caudatus Linnaeus, 1758), by analyzing ringing and recapture data from 7 sites on the southeastern Baltic coast at a distance of 11-132 km from each other. The number of birds involved in regional movements varied significantly between species. Long-tailed Tits migrate during the day, and the proportion of birds performing regional-scale movements was one to two orders of magnitude higher than in European Robins (nocturnal migrants) or Goldcrests (migrants with a mixed migratory rhythm). In all three species, the average dates of their regional-scale movements over short distances did not differ significantly between individuals that moved in the migratory and the reverse direction. Regional-scale movements often occurred under headwinds, which suggests that these movements could be caused by aborting migratory flights and (or) by drifting in such winds.
... For some birds and insects, the timing of migration is often delayed until favourable wind conditions occur, so that the energetic costs of migrations are reduced [31][32][33][34]. However, hawksbill turtles simply departed from their island-nesting area without delay, as is commonly found in turtles tracked during their post-nesting migrations (e.g. ...
How animals navigate across the ocean to isolated targets remains perplexing greater than 150 years since this question was considered by Charles Darwin. To help solve this long-standing enigma, we considered the likely resolution of any map sense used in migration, based on the navigational performance across different scales (tens to thousands of kilometres). We assessed navigational performance using a unique high-resolution Fastloc-GPS tracking dataset for post-breeding hawksbill turtles ( Eretmochelys imbricata ) migrating relatively short distances to remote, isolated targets on submerged banks in the Indian Ocean. Individuals often followed circuitous paths (mean straightness index = 0.54, range 0.14–0.93, s.d. = 0.23, n = 22), when migrating short distances (mean beeline distance to target = 106 km, range 68.7–178.2 km). For example, one turtle travelled 1306.2 km when the beeline distance to the target was only 176.4 km. When off the beeline to their target, turtles sometimes corrected their course both in the open ocean and when encountering shallow water. Our results provide compelling evidence that hawksbill turtles only have a relatively crude map sense in the open ocean. The existence of widespread foraging and breeding areas on isolated oceanic sites points to target searching in the final stages of migration being common in sea turtles.
... The timing of migration has been long known to be predominantly controlled by genetic and intrinsic cues (Gwinner and Wiltschko, 1978;Gwinner, 1996), but also by external local conditions. These include photoperiod (Marra et al., 2005;Bradshaw and Holzapfel, 2008;Åkesson et al., 2021), wind assistance to reduce flight costs (e.g., Arizaga et al., 2011;Sjöberg et al., 2015) and environmental conditions, such as temperature, rain and different vegetation indices which can be used as a proxy for food availability at the pre-departure sites (Saino et al., 2004;Shamoun-Baranes et al., 2006;Tøttrup et al., 2012;Aharon-Rotman et al., 2021;Lawrence et al., 2021). The latter likely affect migration decision, the physical condition of the birds, their fattening rates, and hence the timing of departure (Marra et al., 1998;Arizaga et al., 2011;Aharon-Rotman et al., 2016;Aloni et al., 2019). ...
... Importantly, we show that for Lesser whitethroat, a species with northern breeding areas, temperatures at the stopover site were correlated to arrival timing, suggesting fine-tuning of stopover arrival to match conditions en-route. Clearly, there are many additional variables at multiple locations along the migration routes that potentially affect migration decisions (e.g., Saino et al., 2004;Arizaga et al., 2011;Sjöberg et al., 2015). Hence, a more comprehensive suite of variables may be more appropriate to make conclusions on the triggers to depart on migration. ...
Many migratory species have advanced their migration timing as a response to advanced breeding conditions. While data on arrival timing to breeding grounds in Europe is plentiful, information from the African departure sites are scarce. Here we investigated changes in arrival timing of four long-distance migratory passerines to a stopover site in Israel and potential links to Enhanced Vegetation Index (EVI) at the species-specific African pre-departure sites and local temperatures at the stopover site. We found that Lesser whitethroat (Curruca curruca) and Eastern Bonelli’s warbler (Phylloscopus orientalis) advanced arrival to the stopover site. The arrival timing of Thrush nightingale (Luscinia luscinia) and Olive-tree warbler (Hippolais olivetorum) did not change and was associated with mean EVI at the pre-departure site in Africa during the pre-migratory period. Additionally, temperatures at the stopover site affected the arrival timing of Lesser whitethroat only. This is probably because this species breed at higher northern latitudes and fine-tune their migration timing to match local conditions. Our results show that spring migration can be influenced by exogenous cues such as weather condition and food availability, and the level of response is species-specific. Moreover, some species show flexibility and fine-tuned migration speed in response to local conditions en route. While flexibility seems advantageous, dependence on multiple sites with varying conditions may ultimately limit advanced arrival to the breeding ground and result in mismatch with optimal conditions.
