Migration distance affects stopover use but not travel speed: contrasting patterns between long‐ and short‐distance migrating ospreys

Abstract

The development of migratory behaviour is a continuous process which is not only determined by genes, but also moulded by individual differences based on life‐history variations occurring at each ontogenetic stage. Assessing consistency and plasticity in migratory traits between long distance (LDM) and short distance migratory (SDM) populations within the same species that may express dissimilarities in the leeway of annual schedules is essential to understand the evolution and ontogeny of migratory strategies. We studied the migration strategies in autumn regarding flight speed and the use of stopovers (number and duration of stop‐overs across the whole journey) at the intra‐specific level, by tracking with GPS loggers the intercontinental migration of 43 adult and juvenile ospreys Pandion haliaetus from both LDM and SDM populations. LDM ospreys travelled distances five times larger than SDM ospreys, but their total migration speed was 2.4 times slower. While daily distance travelled did not differ between populations, the reduced total migration speed by LDMs was due to higher stopover use compared to SDM birds. SDM birds used more direct routes, crossing open sea at higher flight speeds, even though both populations largely benefitted from wind assistance across their journey. Across populations, adult birds travelled longer distances per day and displayed less sinuous migratory paths than juveniles, suggesting that migratory capabilities improve with age and experience of the bird. Overall, the time constraint related to total migration distance was not the main driver of the total migration speed, and other factors such as physiological needs to rest and refuel at stopover sites may play an important role. Our study underlines the importance of investigating variability in migration strategies in partially migratory species, for a better understanding of avian migratory ecology.

Habitat availability influences migration speed, refueling patterns and seasonal flyways of a fly-and-forage migrant

“…We suggest that the loop migration pattern is most likely attributed to habitat availability and the need for refueling, in agreement with previous studies [39,40], yet, although long distance migrants are constraint by distance and time, and are thus expected to be less selective to wind conditions compared to short distance migrants [33], the effect of wind cannot be overlooked. Northerly tailwinds appear to aid the southbound Sahara Table 2 Significant results of binomial GLMMs from the best supported models showing in which ecological factors actual positions differ from random points generated within a 50 km buffer zone either side of the flying path.…”

“…As a strategy, nocturnal continuous flight with foraging during the day may result in shorter migration times [22]. Raptors, however, are not in general expected to fly at night [32] unless they are crossing large water bodies and need to extent their flight overnight [31,33]. Nevertheless, high resolution tracking data might reveal more about nocturnal flying activity [34].…”

Spatial and Temporal Variability in Migration of a Soaring Raptor Across Three Continents

“…Although we found marked differences in route choice between seasons, but inconsistent differences in performance, much more work is needed to determine how various innate and external factors contribute to the development of seasonal and population specific migration patterns, not only for Egyptian Vultures but all migratory species (Schmaljohann, 2018). Similar to other raptors, we also found some age-related differences in migration distance, duration, speed and timing (Sergio et al, 2014), with adults traveling faster along shorter routes, and departing earlier in spring, than younger birds (Monti et al, 2018), although the patterns were not consistent in all subpopulations. While our dataset did not allow a full assessment of changes in individual migratory performance with age (sensu Sergio et al, 2014), our findings are consistent with expectations that individual raptors must improve their migratory performance in early life to eventually be recruited into the breeding population (Sergio et al, 2017).…”

“…We found relatively high repeatability within subpopulations for distance and for straightness of travel, but much lower repeatability for duration and speed. The variation in duration and speed may be the result of varying environmental conditions and stopover use during each migratory journey (Vansteelant et al, 2015;Kölzsch et al, 2016;Vardanis et al, 2016;Monti et al, 2018) and, although multi-day stopovers are rare in Egyptian Vultures (López-López et al, 2014;Buechley et al, 2018b), further detailed investigation of both aspects is required. Greater speed during spring migration than fall migration has been hypothesized to be the result of a heightened drive to arrive on breeding grounds, and has been recorded in many species of soaring migrants (Alerstam, 2003;Nilsson et al, 2013).…”

“…Large soaring birds have been the subjects of many tracking studies, partly because their large size enabled the attachment of transmitters since early technical development (Shamoun-Baranes et al, 2003;Alarcón and Lambertucci, 2018;Sergio et al, 2019). However, while migratory patterns have been assessed for individuals from the same or proximate populations (Sergio et al, 2014;Vardanis et al, 2016;Schlaich et al, 2017;Vansteelant et al, 2017), and migratory connectivity has been evaluated for some raptor species (Martell et al, 2014;Trierweiler et al, 2014;Finch et al, 2017), relatively few studies have analyzed these patterns across large portions of a species' distribution (Mandel et al, 2011;Dodge et al, 2014;Monti et al, 2018).…”