Nests in trees are as good as or better than cliffs for two formerly persecuted, primarily cliff nesting eagles in Spain: a cautionary tale in defining the habitat of range‐restricted or threatened species

In the late‐20th century, golden and Bonelli's eagles suffered population declines on the Iberian Peninsula, partly due to human persecution. Habitat assessments – especially for Bonelli's eagles – always found or assumed strong associations with cliffs that provided nesting sites. However, in recent years these eagles have increasingly used trees for nests in this region. Using multi‐decadal surveys of golden and Bonelli's eagle fledglings at nests across Andalusia in southern Spain, we compared the number of young fledged in tree nests to the number reared in the more numerous cliff nests. We evaluated alternative hypotheses with an Information Theoretic approach to test whether increased use of trees resulted from growing populations relying on lower quality habitat or whether trees provide equivalent or higher quality nest‐sites that were previously unused. Reproductive rates of Bonelli's eagles were substantially higher in tree nests, while reproductive rates of golden eagles were similar between trees and cliffs. We found no difference in reproductive rates between trees and cliffs within territories that contained both types. Our results illustrate the difficulty in characterizing a species' habitat following a population decline or range restriction. Golden and Bonelli's eagles were intensively persecuted in Spain, which may have precluded them from nesting in trees that were easily accessed by humans. We should be cautious in making judgements about the quality or totality of habitat when we know a species no longer occupies the full extent of its former range. Overly narrow and inflexible definitions of a species' habitat in these cases may impede eventual recovery efforts for the species in question.