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Journal of Ornithology (2021) 843-zORIGINAL ARTICLEMovements of Cyprus Wheatear Oenanthe cypriaca fledglings:evidence of a post‑fledging home range away from the natal site priorto first migrationP. Styles1 · R. Patchett1 · J. Robins King1 · W. Cresswell1Received: 16 April 2020 / Revised: 15 October 2020 / Accepted: 7 November 2020 / Published online: 25 November 2020 The Author(s) 2020AbstractDispersal to efficiently locate future breeding areas in young animals has important consequences for survival, life historyand future breeding success, and therefore population dynamics and evolution. Long-distance migrant birds that have littletime immediately pre-breeding may use the post-fledging period to locate their future breeding territory. We radio-tracked 37juvenile Cyprus Wheatears, Oenanthe cypriaca, a long-distance migrant passerine, to investigate movements for 10 weekspost-fledging. We measured how distance from the nest and distance of consecutive movements changed with age. We testedwhether distance from the nest stopped increasing and consecutive movement distance became similar to pre-dispersal distances, consistent with a fledgling adopting a post-fledgling home range that could reflect scoping out a future local breedingterritory. Fledglings had a very high survival rate. Directed movements away from the natal territory started at about 18 daysuntil about 45 days when individuals adopted a more fixed location on average about 600 m (range 0–1500) from their natalsite, and further movements were at a scale equivalent to movements within an adult-sized breeding territory. Our resultssuggest dispersal followed by settlement in a fixed home range prior to first migration that could function to identify thebreeding site location for the following year.Keywords Dispersal · Migration · Post-fledging period · Survival · Pre-migratory movementZusammenfassungOrtsveränderungen flügger Zypernsteinschmätzer Oenanthe cypriaca: Belege für Streifgebiete abseits desGeburtsortes zwischen dem Ausfliegen und dem ersten WegzugDismigration bei Jungtieren zur effizienten Suche nach zukünftigen Brutgebieten hat bedeutende Auswirkungen aufÜberleben, Biologie sowie späteren Bruterfolg und damit auf die Populationsdynamik und die Evolution. Langstreckenzieher,die unmittelbar vor der Brutsaison nur wenig Zeit zur Verfügung haben, können die Phase nach dem Ausfliegen nutzen,um ihr zukünftiges Brutrevier zu finden. Wir telemetrierten 37 juvenile Zypernsteinschmätzer, Oenanthe cypriaca, einelangstreckenziehende Singvogelart, um Ortsveränderungen während zehn Wochen nach dem Ausfliegen zu untersuchen.Wir quantifizierten, wie sich die Entfernung vom Nest und die Strecke der aufeinanderfolgenden Ortsveränderungen mitdem Alter wandelten. Wir prüften, ob die Entfernung vom Nest nicht weiter zunahm und ob sich das Ausmaß anschließenderOrtsveränderungen dem Niveau vor Einsetzen der Dismigration annäherte, wie dies für einen flüggen Jungvogel zu erwartenCommunicated by F. Bairlein.Electronic supplementary material The online version of thisarticle (https ://doi.org/10.1007/s1033 6-020-01843 -z) containssupplementary material, which is available to authorized users.* W. [email protected]‑and.ac.uk1Centre for Biological Diversity, University of St Andrews,St Andrews KY16 9TH, Fife, UK13Vol.:(0123456789)
340Journal of Ornithology (2021) 162:339–348wäre, der nach dem Ausfliegen ein Streifgebiet nutzt, welches ein Zeichen für die Suche nach einem zukünftigen Brutrevier imUmkreis sein könnte. Wir untersuchten, in wie fern sich der Abstand zum Nest sowie die nachfolgenden Ortsveränderungenmit dem Alter ändern. Flügge Jungvögel hatten eine sehr hohe Überlebensrate. Zielgerichtete Ortsveränderungen fort vomGeburtsort begannen nach zirka 18 Tagen bis nach etwa 45 Tagen, wonach sich die Vögel an einem konstanteren, im Schnittetwa 600 m (zwischen 0–1500 m) vom Geburtsort entfernten Ort niederließen und sich die weiteren Ortsveränderungenin einem mit dem Brutrevier eines Altvogels vergleichbaren Rahmen abspielten. Unsere Ergebnisse deuten auf eineDismigration, gefolgt von einem Niederlassen in einem festen Streifgebiet vor dem ersten Wegzug hin, das dazu dienenkönnte, einen Brutplatz für das folgende Jahr zu finden.IntroductionThe post-fledging period represents a time of intense selective pressure for birds with juveniles typically experiencinghigh mortality rates (Morton 1992; Grüebler et al. 2014;Naef-Daenzer and Gruebler 2016) as they develop and disperse into novel areas (Anders et al. 1997; Cox et al. 2014).Despite the fundamental importance of the post-fledgingdispersal period, it remains understudied in comparison tothe other stages of avian development (Cox et al. 2014).The main reason for this is the difficulty of tracking andobserving young after they leave the natal area (Kershneret al. 2004b) and the large spatial scale they can range over(Sutherland et al. 2000).The post-fledging period has been shown to be dynamicrather than a singular unified stage of life: as fledglingsdevelop, the selective pressures they experience change dueto increased mobility and knowledge of the foraging environment and predators (Raybuck et al. 2020). Fledglingsremain within the natal area within the first few weeks afterfledging and are at their most vulnerable to predation (Mooreet al. 2010; Ausprey and Rodewald 2011; Eng et al. 2011).However, as fledglings develop and their mobility increases,they are able to utilise different habitats that are potentiallydistant, which could represent a balance between predatorprotection (Morton 1991; Anders et al. 1998; King et al.2006) and optimal food availability (Vega Rivera et al. 1998;Vitz and Rodewald 2007). Reduction in the chance of predation as age increase may cause fledglings to shift their postfledging strategy from mainly predator avoidance towardsforaging (Streby et al. 2011) or locating future breeding territories (Mitchell et al. 2010).Mechanisms that allow the location of suitable breedingareas are likely to be under strong selection (Kokko 1999).This may be particularly intense in long-distance migrantswhich spend the non-breeding season far from their breedingareas (Lombardo 1987, e.g. Arlt and Part 2008). They thenlack the opportunity to locate breeding areas as adults exceptduring the short period after arrival back on the breedinggrounds in the spring, when early location and occupationof a territory increases fitness (Morrison et al. 2019, e.g.Aebischer et al. 1996, Currie et al. 2000, Velmala et al.2015). Therefore, there is likely to be strong selection for13potential breeding territories to be identified by juvenilesin the post-fledging period before first migration, and thismay be one of the reasons why juveniles also tend to migratelater than adults (Newton 2008). Location of future breedingterritories during this period may also allow the quality ofpotential future territories to be assessed through the breeding density, nesting site availability or success of conspecifics (Lombardo 1987; Nocera et al. 2006; Betts et al. 2008),or through food availability. If the post-fledging period oflong-distance migrants functions as a period for potentiallylocating a breeding site for the following year, we might thenexpect fledglings to disperse but then settle in fixed locationsaway from the natal site, but suitable for breeding.Processes other than locating future breeding sites mayalso lead to patterns of post-juvenile dispersal in migrantbirds. The migration commencement hypothesis suggeststhat movements by fledglings are orientated in the directionthat facilitates eventual autumn migration (Rappole and Ballard 1987). The habitat optimisation hypothesis suggests thatfledglings select areas to maximise access to food or to avoidpredators (Streby et al. 2011). The homing target formationhypothesis suggests that fledglings seek out large landscapefeatures that will help them recognise either their natal areaor dispersal area during their spring migration (Wiltschkoand Wiltschko 1978). Patterns could even be generated by arandom process of dispersal followed by home range formation, where individual fledglings have a random direction,distance and duration of dispersal, followed by feeding ina relatively small area up until migration. However even ifthis process is random, then selection should favour thoseindividuals that return to good areas to breed. It is likely thatseveral or all hypotheses may account for the movementsrecorded during the post-fledging period, acting at differentspatial and temporal scales.Here, we measure the post-fledging movements of CyprusWheatear, Oenanthe cypriaca, to determine whether theyare consistent with the prospecting for future breeding locations hypothesis. Cyprus Wheatears are widespread andcommon migrants (Randler et al. 2010) endemic to Cyprus(Randler et al. 2012) that winter in sub-Saharan East Africafrom southern Sudan to Ethiopia (Xenophontos et al. 2017).Measuring space use during the post-fledging period andterritory adoption the following year is much more tractable
Journal of Ornithology (2021) 162:339–348than in many systems. Most juvenile Cyprus Wheatears(92%) have been found to breed in the year after fledgingless than 1 km away from their natal site and to have annualsurvival rates that may exceed 35% (Xenophontos andCresswell 2016b), although recent work has suggested thatboth of these measures are likely to vary annually (Patchettunpublished data). Survival in the first 4 weeks post-fledging is particularly high ( 95%, Xenophontos and Cresswell2016a). Previous observations suggest that juveniles moveshort distances before settling in potentially suitable breeding habitat before their first migration.We measured how direction and distance from the nestsite varied with age over a 70-day period post-fledging todetermine if there was any evidence for adoption of a postfledging home range after initial dispersal during this period.We assumed that when juveniles begin moving distancesthat exceed the average diameter of a breeding territory thatthey are dispersing. We then examined the variation in thedirection and distance from their natal site, and distancebetween consecutive radio-tracked locations. This allowedus to determine whether distance from the natal site becamefixed, and daily movements became smaller as would beexpected with adoption of a post-fledging home range. Ifindividual juveniles disperse (leave their natal territory)completely randomly in terms of direction and distance,then distances from the natal site will inevitably decrease(because all movements initially must be away from the natalsite, whereas as an animal moves further away an increasing proportion of movements will be movements back tothe natal territory). Consecutive distances, however, willnot change. If individual juveniles disperse randomly withrespect to distance but not direction, they will continue toincrease in distance from their natal site, and consecutivedistances will remain similar. However, if juveniles adopta post-fledging home range, then distance from the natalterritory will level off, and then show smaller consecutivemovement distances. Post-dispersal movement distances arethen likely to be similar to those at the natal site if fledglings are restricting their movements to an area equivalentto an adult breeding territory. In practical terms, dispersalaway from the natal territory, followed by adoption of ahome range equivalent in size to the natal site, will lead toa sigmoidal relationship between distance away from thenest and age, and a quadratic relationship (with a maximumduring the dispersal phase) between consecutive distancesbetween locations (step lengths) and age. Furthermore, ifpost-fledging dispersal leads to home ranges corresponding to future breeding locations, we would expect birds tospread out rather than aggregate, and to settle in suitablebreeding habitat.Here, we first test whether individual juvenile CyprusWheatears disperse in a consistent direction and whetherthey ended spatially separated at a scale larger than an341individual adult territory, within potentially suitable breeding areas. Having established this, we then show that afterlarger-scale movements away from the natal site, individuals are likely to stop moving away from the natal area, andrestrict their movements to a smaller scale, equivalent tothem using adopting a home range similar in size to an adultbreeding territory. Finally, we determine the average duration of the dispersal phase and how long after leaving thenatal territory juveniles settle into a more fixed home range.MethodsThe study was conducted during the breeding season of2019 in a 130-ha area at Troodos National Forest Park (34 56011 N 32 51048 E: Fig. S1), at about 1800 m a.s.l. onCyprus. The study area was within an old, low-density coniferous forest, supporting one of the densest breeding CyprusWheatear populations on the island (Flint and Stewart 1992).The park covers an area of 9029 ha with its highest peak at1952 m. Habitats in the study area include Pinus nigra ssp.pallasiana forest, Juniperus foetidissima woodland and Serpentinophilous grasslands. Annual precipitation in the areais high but restricted to the winter period; summers are verydry and warm with afternoon temperatures reaching 35 C.From May through June 2019, we opportunistically foundCyprus Wheatear nests through close observation of adultbehaviour such as nest building and feeding chicks. Wemonitored nests every 3–4 days and every 1–2 days as fledging approached (fledging occurs at approximately 14 daysafter hatching). Cyprus Wheatear fledglings were capturedin mist nests or spring-traps within 25 days of fledging intheir natal territory: the average age at tagging was 13.5 days( 1.0 SE; range 1–25 days, where day 0 is the day of fledging). Only broods which were certain to have been producedwithin a territory, with attendant colour-ringed parents, weretargeted. Colour ringed parent birds were seen providingparental care to the fledglings in almost all cases so thattheir parentage was known at the time of capture, and wherebroods were targeted after the second week after fledgingthese were from the earliest few nests on the study site, withthe broods and their colour-ringed parents being confirmedas remaining within the natal territory before capture wasattempted.Each chick was ringed (with permission from the GameFund, Ministry of Interior and BirdLife Cyprus) with aunique combination of a single metal ring and three colourrings. It was not possible to ring Cyprus Wheatears in thenest, because access to the nest cavity would have destroyedthe nest site. Additionally, we attached a 0.42 g Ag379radio-transmitter (Biotrack, Wareham, UK) with a 13 cmwhip antenna and a battery life of c. 50 days. Tags wereattached using a modified leg-loop harness design (Rappole13
342and Tipton 1991; Streby et al. 2015). The harnesses wereconstructed of 0.5 mm elastic thread that would naturallydegrade over 3 months allowing the radio tag to fall off priorto migration. Birds weighed on average 15.82 g when ringedand the tags with harness on average weighed 0.49 g, whichequals 3.1% of body mass.We aimed to catch every chick in a brood (typical broodsize is 5, Xenophontos and Cresswell 2016b) with a ratio ofthree with radio-transmitter tags to two with colour ringsonly. In many cases, only some chicks from the brood couldbe caught because juveniles avoided nets or spring traps. Ininstances, where only four birds were caught, three fledglings were fitted with radio-transmitters and one with ringsonly. A single fledgling was tagged in seven broods, twofledglings were tagged in six broods, and three fledglingswere tagged in six broods. In total, there were 15 fledglingscolour ringed only from nine broods. There were no obvioustag effects in the study—no obvious mortality was recorded(see below). Birds fitted with tags flew off in the same manner as birds that had only colour rings. Birds with tags wereseen in subsequent days feeding and behaving identically tocolour ringed only birds from the same brood. Colour ringedonly chicks were also seen throughout the extended studyarea (see below) while locating the tagged chicks suggesting there was no obvious tag effect on dispersal distances.We had no evidence of chick mortality prior to the catchingperiod. For almost all of the broods we have complete nestinformation. The number of chicks present in the natal territory receiving parental care at the time of catching wasthe same as the number of chicks recorded prior to fledging.We defined an average natal territory size (for the purposeof classifying when juveniles started to disperse and moveaway from their natal territory) by calculating the mean distance between nests. We measured the distance between 12adjacent nests in the central area of the study site where allterritories were known and surrounded by other territories.We then used half the mean distance between the 12 neststo define an average natal territory size. This had a radius of175 m ( 1 SE 45.4 m).The study site was divided into sections based upontopography and local features. As juveniles began to disperse, a 300 m buffer was added to the central field sitewhere fledglings were tagged. A further 300 m buffer wasalso searched for any birds that we thought had dispersedfrom the central field site and that were not located in thefirst buffer zone. This occurred 5 weeks after the first tagwas fitted after it became apparent that at least four birdshad moved out of the first buffer area.Locations were collected daily but each section of thestudy site was visited only once every 3–8 days, resulting in15 discrete sampling events during the study covering theentire study site. Individual birds could be recorded in different sections during a sampling event, or not located, leading13Journal of Ornithology (2021) 162:339–348to greater than or fewer than 15 locations being recorded,respectively. The mean sampling interval per individual was5.8 ( 0.4 SE) days: there was no relationship between ageof an individual and sampling interval (0.0074 0.026 SE,t181 0.3, P 0.78; sampling interval age with individualidentity as a random effect). Because of this even pattern ofsampling with age, sampling interval was not considered asa confounding effect when examining distance from the nestor distance between consecutive locations.In each section, five or ten (to reflect the area of thesection) random sampling points were calculated usingthe QGIS v3.4 (QGIS Development Team 2019. QGISGeographic Information System. Open Source GeospatialFoundation Project, http://qgis.osgeo .org) random locationgenerator. Random points, rather than a regular grid, wereused to potentially sample all locations within the unevenlyshaped areas. For each observation day, new random pointswere created, if the random points were adjacent and therewas 5 m distance between them, the additional randompoint was removed from that day’s observations. At eachsampling point, we scanned for the radio frequencies of eachradio tag for a period of 10 s each. A programmable SIKAreceiver attached to a three-element Yagi antenna was usedto locate individuals and then their location was visuallyconfirmed and recorded using GPS. Where multiple signalswere detected, we located the first detected individual beforereturning to the sampling point to find the next detected bird.This was carried out until all detected frequencies werelocated.The average tracking time was 37.4 ( 12.3 SE) days,with a range of 1–70 days post-fledging tracked. An average of 6.9 ( 1.1 SE) locations were taken per individual.All tracked locations are mapped in Fig. S1. Of the 37 birdsfitted with tags (Fig. S2), 21 dispersed from their natal territory to settle within the study area but away from theirnatal territory, five moved from their natal territory andthen returned to it and two birds did not disperse from theirnatal territories. Five birds had their tags fail a few daysafter fitting giving limited data. In four out of five of thesecases which we classified as tag failure, tags transmitted adistorted signal in the days before the tag stopped transmitting, indicating an impending tag failure and the four birdswere then re-sighted carrying non-functional tags. The finalfour birds were tracked moving away from their natal areaand then were lost: these were assumed to have dispersedcompletely outside the study area. One bird that was thoughtto have dispersed in this way was then re-found outside theextended field site boundary 1.1 km from its natal territory,confirming this assumption. But we do not know for certain what happened with four individuals (one assumed tagfailure and three assumed dispersed out of the study area).For the assumed tag failure, the bird was not seen againafter the day of tagging and may have died. For the three
Journal of Ornithology (2021) 162:339–348assumed dispersed out of the study area, we do not thinkthe tags failed because there was no indication in the signal noise received on last detection that the tag was failing.Some tags stopped functioning near the end of the study astheir batteries were exhausted. We were able to discriminatebetween end of battery life and mortality because even afterthe battery of the tag had died, fledglings remained in thesame approximate area of the last transmission. For 13 birdswhere the tag functioned as expected but the battery ran outbefore the end of the study, 12 birds were resighted in thesame approximate location after their tag stopped transmitting and one that was not initially found in the same locationafter tag transmission ceased was resighted 4 weeks lateralive with the tag present.Statistical analysisFirst, we tested whether individuals dispersed in similar orrandom directions from their natal territory. Uniformity ofthe direction of each location of a juvenile from its nest site,after it left its natal area, was tested with a Rayleigh test todetermine if individuals dispersed in a consistent direction.We then tested whether the mean distance between birdsincreased with age to determine whether individuals dispersed to spatially separated sites. To do this without theconfounding effects of chicks within and between broods,we calculated the mean location of each bird in a brood,and then the mean of these within brood locations for eachbrood, for different ages of fledglings pooled into weeks.The mean of all possible distances between pairs of broodlocations (i.e. their average spacing) was then calculated foreach week.Second, we calculated distance moved with age. Forevery sampling event, the distance from the nest, and thedistance between it and the last location was calculated forevery individual tracked. All distances were calculated asgreat circle distances using the distHaversine function fromthe geosphere package in R. We then plotted these two distances with age and modelled the best fit function, expectingthat distance from the nest would take a sigmoidal function,and distance travelled between consecutive locations a quadratic function, if fledglings dispersed to a new home rangewithin the study area as if scoping out future breeding territories. We modelled distance with age on either raw data,with individual identity as a random factor in a mixed modelframework to control for uneven sampling across individuals, or, for visualisation, aggregated into one mean for eachindividual within a weekly period.Having established, with the analysis above, that therewas a pattern of dispersal where individuals moved a lot(dispersal) preceded by a period in the natal territory (predispersal) and followed by a period in a home range whenthey moved much less (post-dispersal), we then determined343the timing of these periods. We varied the relative durationof the three dispersal periods to determine which combination of durations best predicted variation in distance in asimple factorial model. The data were effectively subset intothe three different periods (pre-dispersal, dispersal and postdispersal). The end of the pre-dispersal period was variedfrom 10 to 25 days, and the end of the dispersal period from35 to 65 days. A model was then run for distance predictedby each range of period durations, and the model with thelowest AIC value was chosen. The process was iterative,varying relative duration of the periods until the lowest AICvalue was obtained. The model tested in each case was then:distance measure period, with period as a three-way factor; sample size was the number of individuals tracked, witheach individual contributing one mean value per period; birdidentity was added as a random factor because some individuals contributed a mean in all periods, and other only insome. Birds with only one record in a period were removedfrom the analysis. Within each period, the mean distancebetween locations, and its standard error, were calculatedfrom all possible pairwise distances between locations in aperiod, for each individual separately. Maximum distancewas calculated as the maximum possible distance betweenany pair of locations recorded in a period, for each individualseparately.Analysis was carried out using generalised linear mixedmodels (glmm), general additive models (gam), and nonlinear models (nls) using the libraries nlme, lmertest, MuMInand mgcv in R. Model fit was assessed by visual inspectionof residuals plotted against fitted values and quantile plotsand were reasonable in all cases, apart from models withdistance moved between consecutive locations as a dependent variable: these models had reasonable assumptions afterlog-transforming distance. Predicted values were plottedusing the lme4, AICcmodavg and ggplot2 packages in R;variance was partitioned into main and random effects inmixed models using MuMIn.ResultsSurvival rate was high. Survival rate of the 37 fledglingstagged varied from a minimum of 89.2% (assuming thefour individuals that could not be accounted for died) to amaximum of 100% (assuming the four individuals that couldnot be accounted for dispersed completely out of the studyarea). Individuals were tracked for approximately 35 dayson average, over a 2-month period after fledging, giving aminimum daily survival rate during this period of 0.997, anda maximum survival rate of 1.Fledglings showed consistency in direction from theirnest site, but they dispersed in different directions. The directions moved by individual fledglings was highly directional13
344(Rayleigh’s test P 0.001 in all cases). Fledglings (N 19broods) became more separated with age, rather than moreclustered, more than doubling their average distance apartover the 10-week study period (the increase in the meanvalue of all possible paired distances between averagelocations for a brood was 51.4 12.2 SE meters per weekt1,8 4.2, P 0.003: Fig. 1, Fig. S1). At least 16% of fledglings occupied territories where adults were still breedingafter dispersal within the main field site, and 20% of fledglings returned to their natal territory after initially dispersing several hundred meters away (Figs. S1, S2). All taggedindividuals moved to potentially suitable breeding areas inFig. 1 Average distance between all locations for individual broodmeans with week since fledging to show that that tracked fledglingsbecame increasingly spaced apart with ageFig. 2 Distance (m) moved byCyprus Wheatear fledglingsfrom their nest site with age.a Raw data, each location is apoint with individuals linkedby lines; fitted curve is a GAMof distance with age, withindividual as a random effect.b Data aggregated into weeks,the mean distance from the nestfor an individual in a week wascalculated and then the meanof all individual weekly meansare plotted: fitted curve is thebest fit sigmoidal function. Thehorizontal dashed line is themean radius of the natal territory, 175 m13Journal of Ornithology (2021) 162:339–348the sense that all areas were typical breeding habitat andwere part of breeding adult territories at least once duringthe longer term, ten year study (Fig. S1, Xenophontos andCresswell 2016a,b; Xenophontos et al. 2017).Distance from the nest increased with age before stabilising. A GAM with a single term of days since fledging, anda random effect of bird identity showed a sigmoidal patternand explained 43% of the deviance (F4.5 40.6, P 0.001,n 255: Fig. 2a). When aggregated into 11 week-long periods, a sigmoidal function with an asymptote of 594 51 SEmeters (t 11.7, P 0.001), and the highest rate of changeat 28.9 2.9 SE days (t 9.8, P 0.001, with an s value of0.12 0.04 SE, t 3.2, P 0.014) significantly explaineddistance from the nest with age (Fig. 2b). A sigmoidal function was a better fit than a straight line fit (change in AICwith a linear fit 2.51).Distances moved between consecutive locations increasedwith age before decreasing again. A quadratic function ofage explained some of the variation in distance moved byfledglings between successive locations, with individualidentity as a random effect [log distance (0.052 0.024SE age, t 181 2.1, P 0.033) ( 0.00098 0.0003SE age2, t181 2.7, P 0.007) (4.1 0.4 SE, t181 11.2,P 0.001): Fig. 3a] accounting for 13% of variance. Whendata were aggregated into 11 week-long periods the evidencefor a quadratic effect was stronger [distance (12.9 4.2SE age, t 3.0, P 0.018) ( 0.19 0.06 SE age2,t 3.1, P 0.016) (20.0 64.0 SE, t 0.3, P 0.76):Fig. 3b] accounting for 47% of the variance.The best-supported model for the timing of dispersalindicated that birds remained in their natal territory untilage 18 days (period 1), those that left their natal territorydispersed until 40–45 days (period 2) and adopted a morefixed location post 40–45 days (per
Überleben, Biologie sowie späteren Bruterfolg und damit auf die Populationsdynamik und die Evolution. Langstreckenzieher, die unmittelbar vor der Brutsaison nur wenig Zeit zur Verfügung haben, können die Phase nach dem
