Satellite telemetry reveals individual variation in juvenile Bonelli’s eagle dispersal areas

Abstract

Natal dispersal is the time elapsed between departing from the natal site and settling to attempt breeding for the first time. In long-lived species with deferred sexual maturity this period may last several years, making this process crucial for their survival and conservation. Here we present a large-scale outline of juvenile Bonelli's eagle's dispersal areas in the Iberian Peninsula. We describe the ranging and movement patterns of 14 juvenile Bonelli's eagles during their dispersal period, studied by satellite telemetry. Three distinct phases during the juveniles' first year of life were detected, namely, the dependence period, the departure from the parental territory, and the settlement in dispersal areas. In general, between-sex differences in relation to ranging behavior were not significant. Interestingly, there seems not to be a few, clearly delimited, overlapping Bonelli's eagle's juvenile dispersal areas within the Iberian Peninsula. A total of 17 dispersal areas were detected, with some animals using more than one. These areas were located in eight autonomous communities (Spanish administrative units), being the most important Castilla-La Mancha and Andalucía. Juveniles were more frequently located in cultivated man-managed areas, with non-irrigated herbaceous crops. This is probably due to higher prey availability and higher efficiency in prey capture in these open areas, as well as to the absence of breeding pairs. This has important management implications, suggesting that conservation efforts should focus on the whole landscape matrix of manmanaged ecosystems rather than in a few clearly delimited geographic areas.

Effects of rearing conditions on natal dispersal processes in a long‐lived predator bird

“…In territorial raptors, one of the most critical stages occurs when the parents expel their fledglings from their natal territory and young birds enter into a new transient nomadic phase—the dispersal period—which in Bonelli’s eagles implies long‐distance movements to dispersal areas and no territorial behavior (Cadahía et al., 2010; Real & Mañosa, 2001). Given that in our case, both territory quality and chick body condition are correlated, an explanation for our results might be that individuals with better body condition are better equipped to cope with short periods of food scarcity (Green & Cockburn, 2001; Hsu et al., 2017); alternatively, the greater concentrations of trophic resources near better territories may allow juveniles to improve hunting skills before leaving their natal territory (Sergio et al., 2009).…”

“…Our study species is threatened in Europe, and considerable conservation efforts are being undertaken to protect its remaining populations (Cadahía et al., 2010; Carrascal & Seoane, 2009; Hernández‐Matías et al., 2015; Real & Mañosa, 2001). This means that managers will need further scientific knowledge of dispersal processes as a tool for implementing conservation actions more efficiently.…”

“…The study and assessment of dispersal areas in management and conservation are vital as such areas may be heavily affected by human disturbance and so may be excluded from typical management plans (Cadahía et al., 2010; Carrascal & Seoane, 2009; Penteriani & Delgado, 2009; Rollan, Hernández‐Matías, & Real, 2016). In fact, reducing juvenile mortality in dispersal areas is a crucial conservation strategy for long‐lived species and may have an important effect on the viability of the reproductive fraction of a population (Fasciolo et al., 2016; Hernández‐Matías et al., 2015).…”

“…In fact, reducing juvenile mortality in dispersal areas is a crucial conservation strategy for long‐lived species and may have an important effect on the viability of the reproductive fraction of a population (Fasciolo et al., 2016; Hernández‐Matías et al., 2015). However, as these areas are often poorly known, difficult to detect and located in areas managed by more than one regional administration (each with their own particular jurisdictions), far less effort is generally devoted to their conservation than to breeding territories (Cadahía et al., 2010; Penteriani et al., 2015). So, better knowledge of natal dispersal processes is still needed if effective measures for conserving these dispersal areas are to be applied.…”

“…Bonelli’s eagle populations are composed of two fractions, nonterritorial and territorial birds that have markedly different lifestyles. Once the dependence period ends, Bonelli’s eagles enter a transient nomadic phase or dispersal period during which they perform long‐distance movements to dispersal areas (i.e., areas characterized by high prey abundance where nonadult individuals temporarily settle before recruitment) and show no territorial behavior (Cadahía, López‐López, Urios, & Negro, 2010; Real & Mañosa, 2001; Soutullo, López‐López, Cortés, Urios, & Ferrer, 2013). This period before recruiting into a territory may last for several years (Real & Mañosa, 2001) and typically ends by the third or fourth years of life (Hernández‐Matías et al., 2010).…”