Abstract
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.
Highlights
The geographic range of species is dynamic, often contracting, expanding, or otherwise changing its limits in relation to multiple environmental and demographic drivers (Gaston, 2003)
| 4243 of the original population nucleus in terms of nesting substrate and breeding habitats. We test these ideas by analyzing nesting habitat selection by the Bonelli’s eagle, using territories established in southern Portugal from 1990 to 2014 and that were still active at the end of the study period
Our results suggest that during the 25-year expansion of Bonelli’s eagles in southern Portugal, the nesting habitat characteristics and selection patterns remained very similar to those of the initial population nucleus, albeit with some changes over time
Summary
The geographic range of species is dynamic, often contracting, expanding, or otherwise changing its limits in relation to multiple environmental and demographic drivers (Gaston, 2003). Tree nesting behavior had an important role in this expansion, by allowing new pairs to establish in cliffless areas in a wide range of landscape types (Palma et al, 2013) It is uncertain, whether this expansion was associated with innovation in terms of new habitats occupied and increasing tolerance toward humans, or rather it was conservative by largely retaining the characteristics. | 4243 of the original population nucleus in terms of nesting substrate and breeding habitats We test these ideas by analyzing nesting habitat selection by the Bonelli’s eagle, using territories established in southern Portugal from 1990 to 2014 and that were still active at the end of the study period. Results were used to discuss the importance of innovative versus conservative behavior for the conservation management of Bonelli’s eagles and other species of concern
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