Spatio-temporal migratory patterns, habitat crossing and within-individual movement repeatability of Central Mediterranean European Rollers Coracias garrulus

Abstract

Populations of long-distance migratory species may exhibit dissimilarities in the leeway of scheduled annual migration programs, the routes they follow and their convergence at ecological barriers. The aim of this study was to fill the current geographical gap, spanning over 1,100 km longitudinally between southern France and eastern Austria, in the pan-European assessment of the migration ecology of the European Roller Coracias garrulus, and contribute to completing the puzzle of spatio-temporal patterns of migration, stopover and wintering at the Western-Palearctic scale for this species. We utilized high-resolution GPS tracking data from adult Rollers breeding in Italy and Croatia, tracked on their intercontinental seasonal journeys between 2018 and 2022 and modelled the variation of migratory components both at individual and population levels. Rollers from the Central Mediterranean exhibited a clockwise spring migration loop, following a Central African migration route and wintering across a wide longitudinal belt spanning from Namibia to Mozambique. Northern savannah zones were used as long stopovers, both in autumn (Chad/Sudan) and spring (Central African Republic/Cameroon). The probability of movement was significantly higher during the night and in spring. Migration speed varied according to season (> in spring) and the habitat crossed (sea > desert > rainforest > savannah). Individuals tracked in successive years showed high consistency of key migratory parameters and partial winter home ranges overlap, in contrast with the large variability of migratory parameters at the population level. This work bridges the current geographical gap of Roller migration ecology at the European level and helps meet conservation needs at the scale of the species’ flyway, with new ecological information valuable for the implementation of International Single Species Action Plans (ISSAP) dedicated to the Roller.

Significance statement

Tracking studies help to disentangle intraspecific variation in migratory strategies and wintering destinations among populations, as well as investigate individual-level decisions taken en route across seasonal journeys. By GPS tracking the intercontinental migration of adult Rollers we found that spatio-temporal components of migratory and flight strategy largely depend on extrinsic factors such as daytime, season and the habitat they traversed, and vary at population level. In contrast, within-individual consistency in migratory and wintering patterns emerged across years. Our findings emphasize the need for effective conservation strategies at the flyway scale.