Early life movements and mortality of Egyptian vultures: Implications for transcontinental conservation

Abstract

Understanding the movements and mortality of individuals across different life stages is crucial for the effective conservation of wild populations. We used data from 32 Egyptian vultures (Neophron percnopterus) tagged with GPS transmitters as nestlings in three Iberian breeding areas to study their dependence period, migration routes, movements in Africa, and mortality at each stage. Our results show no significant differences in the timing of nest departure or the duration of the dependence period between individuals of different sexes or breeding nuclei. Most juveniles migrated to sub-Saharan Africa in their first year, but some (3 of 32, 9.4%) remained in the Iberian Peninsula. Individuals that migrated to Africa did so annually, while those remaining in Iberia never migrated to the Sahel, indicating distinct migratory and non-migratory strategies. Non-migratory individuals consistently moved northward during the breeding season to their natal territories. Siblings did not coordinate their migration strategy or timing. All juveniles showed extensive overlap in the vast areas used in Africa, where females arrived before males, and in the Iberian Peninsula. Our study also revealed that no juveniles died immediately after fledging, but that none of the tagged individuals lived more than 7 years or were recruited as breeders. Although most casualties occurred during the longer stay in the Sahel, the mortality rate was highest during the few days of the first migration. Our results show that despite small variations in movement patterns between breeding nuclei and sexes, Egyptian vultures face similar challenges during the years before recruitment as breeders, mostly determined by their migratory strategy. These findings are relevant for designing conservation strategies, both in breeding areas and, more importantly, in wintering areas and along migration pathways. Such strategies will significantly impact the entire Iberian population of this endangered species.

Keywords: Egyptian vulture; Iberian Peninsula; Sahel; dependence period; migration; mortality.

FIGURE 1

Movements across the Iberian Peninsula of GPS‐tagged juvenile Egyptian vultures Neophron percnopterus born in three Spanish breeding nuclei, namely, Arribes del Duero (orange symbols), Galicia (blue symbols), and Segovia (red symbols). Panels 1–3. Movements of individuals during the dependence period. The shaded area represents the KDE 95% area. Dots represent the different nests where the individuals were tagged and the different colors of the lines on these panels represent the movements of the different individuals.

FIGURE 2

Movements of GPS‐tagged juvenile Egyptian vultures Neophron percnopterus born in three Spanish breeding nuclei, namely Arribes del Duero (orange symbols), Galicia (blue symbols) and Segovia (red symbols). Triangles show the location where individuals presumably died. Polygons delineate the Sahel areas utilized by individuals born in the different Spanish breeding nuclei. The green shading represents the 95% KDE obtained using the positions of all individuals, regardless of their natal nuclei.

FIGURE 3

Movements of the three Egyptian vultures Neophron percnopterus born in Arribes del Duero that remained resident in the Iberian Peninsula throughout their lives (each color lines represent an individual). The polygons delineate the two core areas used by these individuals (blue, Salamanca; red: Cáceres), obtained as the 95% KDE of all their locations since they left their natal territories. Histograms on the right represent the monthly percentage of GPS fixes of each individual within each core area (blue, Salamanca; red: Cáceres). Green bars represent pooled data of movements of the three individuals outside the two core areas.

FIGURE 4

Temporal distribution of Egyptian vulture Neophron percnopterus that stopped transmitting GPS signals. Time zero represents the day of tagging of each bird. Above, the number of individuals (males and females) whose signal is normally received at each time is shown. The empty circles represent the time and stage (green: migration, blue: stay in the Sahel, red: stay in the Iberian Peninsula) at which each individual was lost, while the black circles indicate the age of the Egyptian vultures still emitting.