Under my wing: lesser kestrels and jackdaws derive reciprocal benefits in mixed-species colonies

In mixed-species assemblages, antipredator benefits for a timid species nesting close to a more pugnacious one are often reported. Advantages for the protected species are usually manifested in terms of higher reproductive success than conspecifics nesting remote to the protector species. Whether the protector species also accrues any benefit remains untested, and the species-specific behavioral traits underlying enhanced reproductive output in mixed-species associations remain poorly documented. We studied associations between lesser kestrels (Falco naumanni) and jackdaws (Corvus monedula) nesting in rural buildings in the Gela Plain (Italy). We tested for interspecific interactions of jackdaws and lesser kestrels by comparing single- and mixed-species colonies in terms of: 1) vigilance, nest attendance, and intra- and interspecific interference and 2) defensive responses shown by each species when confronted with potential predators or competitors. In both species, nesting in mixed associations was accompanied by decreased vigilance. Diminished vigilance, however, was associated with decreased defensive effort for lesser kestrels, whereas jackdaws increased alarm calling, but only in small colonies. Our results reveal a reciprocal influence on behavior of lesser kestrels and jackdaws nesting within the same colony, whereby both species experience decreased energetic expenditures associated with vigilance, but only lesser kestrels appear to benefit via reduced nest defense effort. We discuss our results in light of the possible asymmetrical information transfer triggered by a common set of nest predators that favors the exchange of interspecific information regarding predator detection and defense.