Ecological specialization to fluctuating resources prevents long-distance migratory raptors from becoming sedentary on islands

[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. [Methodology/Principal Findings]: 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/Significance]: 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.

L.G. is supported by the FP7-REGPOT 2010-1 EcoGenes Project (Grant No. 264125). P.L.-L. is supported by a ‘Juan de la Cierva’ postdoctoral grant from the Spanish Ministry of Economy and Competitiveness (reference JCI-2011-09588). U.M. is supported by a FPU grant from the Spanish Ministry of Education (reference AP2008-0947). R.L. has a postdoctoral grant (reference 10/12-C) co-funded by ‘Consejería de Educación y Ciencia’ (JCCM) and the European Social Fund.

Peer Reviewed