The trans‐equatorial loop migration system of Eleonora’s falcon: differences in migration patterns between age classes, regions and seasons

Abstract

Internal factors such as experience (e.g. age) and motivation for breeding, and external ones such as environmental conditions (e.g. meteorology and landscape characteristics) can promote differences in migratory behaviour and routes among seasons, regions and populations. Using satellite telemetry we investigated whether such differences occur and which factors promote them among migrating Eleonora’s falcons breeding in the Mediterranean area (Spain and Croatia) and wintering in Madagascar. We found that during autumn migration no age differences occur when crossing the Sahara desert, but in the remaining African regions, juveniles were more prone than adults to fly at a slower and more tortuous rate, as well as exhibiting longer stop‐overs, particularly in the Sahel region. Such differences might be promoted by a lower foraging and pre‐migratory fattening efficiency in juveniles. During spring, routes were significantly more eastern than during autumn, resulting in a loop migration occurring in all studied populations. This could be accounted by seasonal variation in the distribution of trophic resources. Our results show that Eleonora’s falcons integrate spatially seasonal changing resources on a continental scale throughout their annual cycle, changing their movement patterns in response to internal (age) and external (habitat) factors. This loop migration pattern may prove to be widespread among other Palearctic trans‐continental migratory bird species.

Spring phenology of ecological productivity contributes to the use of looped migration strategies by birds

“…Which non-atmospheric factors are involved has not been determined. Results from studies of small numbers of individuals and species [5][6][7] travelling between Europe and Africa have similarly suggested but not yet clearly determined the extent to which non-atmospheric factors shape looped migration.…”

Terrestrial Bird Migration and West Nile Virus Circulation, United States

“…Although waterfowl follow regular paths bounded by mountains and rivers, terrestrial birds often follow looped routes that enable them to maximize tail winds, avoid head winds, and correlate with seasonal fluctuations in food availability ( 18 , 19 ). Although looped migration paths have been described for several species of birds ( Selasphorus rufus hummingbirds [ 20 ], Circus aeruginosus western marsh harriers [ 21 ], Falco eleonorae Eleonora’s falcons [ 22 ], Cuculus canorus common cuckoos [ 23 ]), the general flyways of terrestrial birds have been inadequately studied. However, in 2014, La Sorte et al provided a general description of terrestrial bird flyways in North America ( 18 ).…”

Solar/Argos PTTs contradict ring-recovery analyses: Woodcocks wintering in Spain are found to breed further east than previously stated

“…The TDR ranges from 0 to 1. Values closer to zero indicate long detours, whereas values closer to 1 indicate relatively straight, direct migration routes to the breeding grounds (Klaassen et al 2010;Mellone et al 2013).…”