title: Ecological specialization to fluctuating resources prevents long-distance migratory raptors from becoming sedentary on islands.
abstract: BACKGROUND
  The adaptive transition between behavioral strategies, such as the shift from migratoriness to sedentariness, remains an outstanding question in evolutionary ecology. Density-dependent variation in the age of first breeding has been proposed as a feasible mechanism through which long-lived migratory birds with deferred sexual maturity should become sedentary to persist on islands. Although this pattern seems to hold for most raptors and herons, a few exceptions have been identified. One of these exceptions is the Eleonora's falcon, a long-distance migratory bird, which shows one of the most peculiar adaptations in the timing of reproduction and food requirements among raptors.
  
  
  RESULTS
  Here, we compiled data concerning demography, banding recoveries and satellite tracking of Eleonora's falcons to discuss likely explanations for the exceptional behavior of this insular long-distance migratory species.
  
  
  CONCLUSIONS
  New data reveal that Eleonora's falcons do return to the natal colonies in their first year and young birds are able to breed. However, in contrast to previous hypothesis, the highly specialized strategy of this and other ecologically similar species, as well as the virtual lack of food during winter at breeding areas prevent them from becoming sedentary on islands. Although the ultimate mechanisms underlying the process of sedentarization remain poorly understood, the evidence provided reveal the existence of important trade-offs associated with ecological specialization that may become particularly relevant in the present context of global change.
authors.affiliation: Department of Wetland Ecology, Estación Biológica de Doñana, CSIC, Seville, Spain. laurag@ebd.csic.es
authors.forename: Laura
authors.initials: L
authors.lastname: Gangoso
authors.forename: Pascual
authors.initials: P
authors.lastname: López-López
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Grande
authors.forename: Ugo
authors.initials: U
authors.lastname: Mellone
authors.forename: Rubén
authors.initials: R
authors.lastname: Limiñana
authors.forename: Vicente
authors.initials: V
authors.lastname: Urios
authors.forename: Miguel
authors.initials: M
authors.lastname: Ferrer
mesh_terms: D000220:Adaptation, Biological; D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D004463:Ecology; D046093:Falconiformes / Q000502:physiology*; D005260:Female; D020387:Food Chain; D062312:Islands; D008297:Male; D011157:Population Dynamics; D012098:Reproduction; D012621:Seasons