P-'" 1" ELSEVIER PII: S0006-3207(96)00100-0 BiologicalConservation, 79 (1997) 5~66 Copyright O 1996 Elsevier Science Limited Printed in Great Britain. All rights reserved 0006-3207/97 $17.00 + .00 DEMOGRAPHY AND CONSERVATION OF WESTERN EUROPEAN BONELLI'S EAGLE Hieraaetus fasciatus POPULATIONS Joan Real & Santi Mafiosa Departament de Biologia Animal, Facultat de Biologia, Universitat de Barcelona, Avinguda Diagonal 645, 08028 Barcelona, Catalonia, Spain (Received 13 October 1995; accepted 15 May 1996) Abstract The basic demographic parameters of six Bonelli's eagle Hieraaetus fasciatus populations in Spain and France were calculated from field data obtained in the last 15 years. Average annual productivity ranged from 0.36 to 1.24 young/pair and average annual adult survival from 84% to 96%. Preadult survival (from fledging to recruit- ment) was estimated at 10%. All the populations were declining at annual rates ranging from -7.3 to -1.1%. Although no statistically significant disagreement was observed between the predictions of a Leslie matrix model fitted to the population parameters and the real trends, some populations declined faster and others more slowly than expected. These differences were interpreted as a result of differential emigration, recruitment rates or pre- adult survival not accounted for by the model. Since the intrinsic population growth rate was about four times less sensitive to changes in preadult survival than to changes in adult survival, and about ten times less sensitive to changes in fecundity and predispersal survival, con- servation efforts must be primarily directed towards increasing adult and preadult survival. Power line casual- ties and direct persecution must be eliminated in order to reduce mortality. Priorities on research should address dispersal, mortality and habitat relationships involving these two parameters. Monitoring should be extended to other populations. Copyright © 1996 Elsevier Science Limited Keywords: Accipitriformes, conservation, population dynamics, demographic models. INTRODUCTION Bonelli's eagle Hieraaetus fasciatus is an endangered raptor whose populations have experienced a marked decline in Europe, involving both a loss of range and numbers (Rocamora, 1994). The European population is estimated to be between 938 and 1039 breeding pairs, 75-93% of which are found in the Iberian Peninsula and south-eastern France (Real et al., in press). In spite of this situation, there is little information on detailed population trends, or on the most relevant life history parameters of this species. This information is essential for the proper design of conservation strate- gies. Using these data, demographic models can help to understand the factors involved in population decline (Lebreton & Clobert, 1991; McDonald & Caswell, 1993), or to evaluate conservation strategies (Ferret & Calderbn, 1990; Wootton & Bell, 1992; Wood & Col- lopy, 1993), and they may be also used as an alternative tool to detect population trends before it is too late (Taylor & Gerrodette, 1993). The aims of this paper are (1) to describe population trends of six Bonelli's eagle populations and to estimate their most relevant life his- tory parameters; (2) to build a demographic matrix model including these parameters in order to give addi- tional support to the observed population trends and (3) to use the model to show the value of different con- servation strategies and to suggest future trends in management and research. METHODS 59 Study areas and population change We studied the long-term population change of six Bonelli's eagle populations for 10-14 years up to 1994 in Spain and France, ranging from the northern limit of the species' distribution to southern Iberian peninsula (Fig. 1). The study included subpopulations located within the core distribution (El Vallrs-Penedrs in Cata- lonia, Murcia, Castellr), as well as some isolated sub- populations (Burgos, Navarra, Provence). Some areas held high eagle densities, such as Castell6 (0.48 pairs/ 100 km 2) and Murcia (0.40 pairs/100 km2), while others had only medium or low eagle densities, such as El Vallrs-Penedrs (0.32 pairs/100 km2), Provence (0.30 pairs/100 kin2), Burgos (0.25 pairs/100 km 2) and Navarra (0.13 pairs/100 kma). These densities were computed from the starting number of pairs and the area occupied on a 10x 10 km 2 UTM (Universal Trans- verse Mercator) grid.