Identifying key habitats for the conservation of Bonelli's Eagle Aquila fasciata using radiotracking

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Natal or prebreeding dispersal is a key driver of the functioning, dynamics, and evolution of populations. Conditions experienced by individuals during development, that is, rearing conditions, may have serious consequences for the multiple components that shape natal dispersal processes. Rearing conditions vary as a result of differences in parental and environmental quality, and it has been shown that favorable rearing conditions are beneficial for individuals throughout their lives. However, the long‐term consequences of rearing conditions on natal dispersal are still not fully understood in long‐lived birds. In this study, we aim to test the following hypotheses to address the relationship between rearing conditions and certain components of the natal dispersal process in Bonelli’s eagle (Aquila fasciata): (1) The body condition of nestlings depends on the quality of the territory and/or breeders; and (2) the survival until recruitment, (3) the age of recruitment, and (4) the natal dispersal distance (NDD) all depend on rearing conditions. As expected, nestlings reared in territories with high past productivity of chicks had better body condition, which indicates that both body condition and past productivity reflect the rearing conditions under which chicks are raised. In addition, chicks raised in territories with high past productivity and with good body condition had greater chances of surviving until recruitment. Furthermore, birds that have better condition recruit earlier, and males recruit at a younger age than females. At last, although females in good body condition exhibited higher NDD when they recruited at younger ages, this pattern was not observed in either older females or males. Overall, this study provides evidence that rearing conditions have important long‐term consequences in long‐lived birds. On the basis of our results, we advocate that conservation managers work actively in the promotion of actions aimed at improving the rearing conditions under which individuals develop in threatened populations.

Section: Discussionmentioning

confidence: 99%

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

Azpillaga

Real

Hernández‐Matías

2018

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“…First, our study was conducted at relatively detailed spatial scales, with variables measured at most within 1 km from nests, whereas several other studies considered larger buffers (e.g., Carrete, Sánchez‐Zapata, Martínez, Sánchez, & Calvo, ; Di Vittorio, Sara, & López‐López, ; Gil Sánchez, Molino Garrido, & Valenzuela Serrano, ) or evaluated species presence/absence using 10 × 10 km squares (e.g., Carrascal & Seoane, ; Di Vittorio et al., ; Muñoz, Márquez, & Real, ; Real et al., ). This is important because different aspects of Bonelli's eagle habitat selection may become apparent at different spatial scales (López‐López, García‐Ripollés, Aguilar, García‐López, & Verdejo, ; Muñoz & Real, ; Real et al., ), with studies at smaller scales such as ours probably showing the requirements associated with nest sites, and studies at larger spatial scales probably revealing a combination of nesting and foraging habitat requirements. Second, our analysis was based on conditional logistic regression, matching nesting site conditions with those available within territories, whereas all other studies used unmatched comparisons between sites with and without Bonelli's eagles.…”

Section: Discussionmentioning

confidence: 99%

“…Reasons for the association of Bonelli's eagle nesting sites to the most rugged areas within territories may be related to the presence of suitable nesting trees and to less human disturbance (Palma et al., ; Real et al., ). For instance, large eucalypts are among the most used nest trees and they are most often found along waterlines at the bottom of valleys (Palma et al., ), which may be one of the factors attracting the eagles to rougher terrain.…”

Section: Discussionmentioning

confidence: 99%

“…For instance, large eucalypts are among the most used nest trees and they are most often found along waterlines at the bottom of valleys (Palma et al., ), which may be one of the factors attracting the eagles to rougher terrain. Also, rugged areas are probably less affected by forest management operations such as understory clearing for fire prevention (Real et al., ; Santana, Porto, Reino, & Beja, ) and they may be less often crossed by people. Whatever the reasons for the observed pattern, it is noteworthy that breeding habitat selection of tree nesting Bonelli's eagles in Cyprus was also affected by local topography and the availability of suitable nesting trees away from disturbance (Kassinis, ).…”

Section: Discussionmentioning

confidence: 99%

“…The buffers around nest sites and random points were characterized from 15 variables reflecting topography, human disturbance, land cover, and potential intraspecific interactions (Table , Table ), which were expected to influence Bonelli's eagles (e.g., Carrascal & Seoane, ; Di Vittorio, Sarà & López‐López, ; Muñoz & Real, ; Real, Bosch, Tintó, & Hernández‐Matías, ). All variables were extracted on a GIS from digital thematic layers, using ArcMap 10.1.…”

Section: Methodsmentioning

confidence: 99%

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The role of conservative versus innovative nesting behavior on the 25‐year population expansion of an avian predator

Dias

Palma

Carvalho

et al. 2017

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Species ranges often change in relation to multiple environmental and demographic factors. Innovative behaviors may affect these changes by facilitating the use of novel habitats, although this idea has been little explored. Here, we investigate the importance of behavior during range change, using a 25-year population expansion of Bonelli's eagle in southern Portugal. This unique population is almost exclusively tree nesting, while all other populations in western Europe are predominantly cliff nesting.During 1991-2014, we surveyed nest sites and estimated the year when each breeding territory was established. We approximated the boundaries of 84 territories using Dirichlet tessellation and mapped topography, land cover, and the density of human infrastructures in buffers (250, 500, and 1,000 m) around nest and random sites. We then compared environmental conditions at matching nest and random sites within territories using conditional logistic regression, and used quantile regression to estimate trends in nesting habitats in relation to the year of territory establishment. Most nests (>85%, n = 197) were in eucalypts, maritime pines, and cork oaks. Nest sites were farther from the nests of neighboring territories than random points, and they were in areas with higher terrain roughness, lower cover by agricultural and built-up areas, and lower road and powerline densities. Nesting habitat selection varied little with year of territory establishment, although nesting in eucalypts increased, while cliff nesting and cork oak nesting, and terrain roughness declined. Our results suggest that the observed expansion of Bonelli's eagles was facilitated by the tree nesting behavior, which allowed the colonization of areas without cliffs. However, all but a very few breeding pairs settled in habitats comparable to those of the initial population nucleus, suggesting that after an initial trigger possibly facilitated by tree nesting, the habitat selection remained largely conservative. Overall, our study supports recent calls to incorporate information on behavior for understanding and predicting species range shifts. K E Y W O R D SAquila fasciata, behavioral innovation, conditional logistic regression, conservation, habitat selection, quantile regression, range expansion

Individual variability in space use near power lines by a long‐lived territorial raptor

Marques

Palma

Lourenço

et al. 2022

Evaluating species responses to anthropogenic infrastructures and other habitat changes is often used to assess environmental impacts and to guide conservation actions. However, such studies are generally carried out at the population level, disregarding inter‐individual variability. Here, we investigate population‐ and individual‐level responses toward power lines of a territorial raptor, the Bonelli's eagle A quila fasciata . We used GPS‐PTT tracking data of 17 adult eagles to model space use as a function of distance to transmission and distribution lines, while accounting for other habitat features known to affect this species. At population level, eagles increased the intensity of space use in the proximity of power lines (up to 1,000 m), suggesting an attraction effect. At individual level, some eagles shared the general population attraction pattern, while others showed reduced intensity of space use in the proximity of power lines. These differential responses were unrelated to the sex of individuals, but were affected by the characteristics of the power grid, with a tendency for apparent attraction to be associated with individuals occupying home ranges with a denser network of transmission lines and transmission pylons. However, the study could not rule out the operation of other potentially influential factors, such as individual idiosyncrasies, the spatial distribution of prey availability, and the availability of natural perches and nesting sites. Overall, these results suggest that power lines may drive different behaviors and have differential impacts across individuals, with those attracted to the proximity of power lines potentially facing increased risk of mortality through electrocution and collision, and those avoiding power lines being potentially subject to exclusion effects. More generally, our results reinforce the need to understand individual variability when assessing and mitigating impacts of anthropogenic infrastructures.