DISENTANGLING THE EFFECT OF GENETIC AND ENVIRONMENTAL COMPONENTS ON MOVEMENT BEHAVIOUR DURING THE POST-FLEDGING DEPENDENCE PERIOD: A CROSS-FOSTERING STUDY ON EAGLE OWL (BUBO BUBO)

Family resemblance in animal movements is well documented for several species of vertebrates, however, this similarity may be due either to common genetic origins and/or to the fact that siblings share a common rearing environment. In birds, the post-fledging dependence period (hereafter, PFDP) is known to represent a critical period in the life-history of individuals, and may considerably shape individual movement behaviour during the successive phases of its life. Previous studies conducted on the population of eagle owls (Bubo bubo) located in the Sierra Norte of Seville (Spain) suggest that movement patterns of siblings during both PFDP and natal dispersal (hereafter, dispersal) show a certain similarity to each other, and this may indicate the presence of a ¿family effect¿ on movement behaviour in this species. It remains unknown, however, if this family resemblance is a consequence of either the common genetic origin of siblings or the fact that they share the same rearing environment, or if it is the result of a combination of the two. To be able to separate these two sources of similarity (common genetic origin vs. common rearing environment) and to experimentally assess if genetics plays a main role in shaping movement behaviour of juveniles during PFDP, we conducted a cross-fostering experiment and investigated movement patterns of 21 owlets (9 cross-fostered and 12 controls, from 8 nest sites) followed by radio-tracking during their PFDP. Our results revealed that cross-fostered owls behaved more similarly to their foster siblings, rather than their biological ones. Treatment (i.e. cross-fostering) did not show to influence any of the movement parameters considered, except for the area explored by the owlets. This results suggest that genetics does not affect movement behaviour in eagle owls during this phase. As expected, age only showed to be an important factor affecting most of the movement parameters, and this may be easily explained by the fact that, during PFDP, young owls are still developing both their flight and cognitive abilities, and thus, the way they move around the natal area changes over time. We therefore propose that similarity in movement behaviour during this phase is not due to the common genetic origin of siblings, but rather originates from factors related to the common rearing environment, such as association and interaction within siblings and between young and parents and the fact that owls share the same area during their PFDP.