POST-FLEDGING DEPENDENCE PERIOD OF OSPREYS PANDIONHALIAETUS RELEASEDINCENTRALITALY: HOME RANGES, SPACE USEANDAGGREGATION PERÍODO DE DEPENDENCIA DURANTE LA FASE DEVOLANTÓN ENÁGUILAS PESCADORAS PANDIONHALIAETUS LIBERADAS EN ITALIA CENTRAL: ÁREAS DE CAMPEO, USO DEL ESPACIOYAGREGACIÓN Flavio MONTI 1 , Andrea SFORZI 1,2 * and Jean Marie DOMINICI 3 SUMMARY.—Space-use strategies are essential behavioural skills during the fledging-to-dispersal period, when physical capabilities and the ability to explore the external world are developed. Here we describe the space-use strategies of 13 radio-tagged ospreys Pandion haliaetus, released as part of a reintroduction project in Central Italy, during their post-fledging dependence period. The ospreys remained within a radius of about 1 km of the hacking tower for about twenty days after release. Later theybegantoexploremoreoftheirsurroundings.Theoccurrenceandfrequencyofexplorationsfurther than 1 km from the release point generally increased with time, even though juveniles continued to frequent the vicinity of the release pens. The translocated ospreys showed marked aggregation perhaps because the period spent at the hacking tower could have reinforced the feeling of belonging to the same brood, promoting a consequent strong association among the young. Also, the absence of parents may have led juveniles to aggregate as a compensation behaviour for the lack of parental care. These explanations, which are not mutually exclusive, may have resulted in more time being spent in intra- specific interactions, accounting for the long pre-dispersal phase that we observed in the present study. Keywords: osprey, space-use, radio-telemetry. RESUMEN.—Las estrategias de uso del espacio resultan esenciales durante la fase que abarca desde elabandonodelnido(volantón)aladispersión,cuandosedesarrollantantolascapacidadesfísicascomo la habilidad para explorar el mundo externo. Aquí describimos las estrategias de uso del espacio de 13 águilas pescadoras Pandionhaliaetus marcadas con radio-emisores y liberadas como parte de un pro- yecto de reintroducción en Italia central, durante su fase como volantones. Las águilas permanecieron durante los 20 días posteriores a la suelta en un área de casi 1 km alrededor del sitio de crianza cam- pestre.Conposterioridad,empezaronaexplorarmáslosalrededoresdistantes.Laocurrenciayfrecuencia de exploraciones a más de 1 km del sitio de suelta se incrementó por lo general a lo largo del tiempo, incluso aunque los juveniles continuaron visitando la vecindad del sitio de crianza. Las águilas pesca- doras translocadas exhibieron una marcada agregación, tal vez porque el período pasado en la torre de Ardeola 59(1), 2012, 17-30 1 Parco Regionale della Maremma, via del Bersagliere 7/9, 58010Alberese (GR), Italy. 2 Museo di Storia Naturale della Maremma, Strada Corsini 5, 58100 Grosseto, Italy. 3 Rèserve Naturelle de Scandola, Parc Naturel Règional de Corse, 20245 Galeria, France. * Corresponding author: direzione@museonaturalemaremma.it