Insularization effects on acoustic signals of 2 suboscine Amazonian birds

Environmental change may alter the communication systems of birds by imposing shifts in their acoustic signals. In tropical forests, vocally active species usually avoid overlapping signals in acoustic space by calling within narrow frequency ranges, whereas in forest islands a less saturated acoustic space may allow variation in acoustic signals. Some signals are also adapted to optimize its propagation in the prevailing habitat. Despite a growing understanding of what drives acoustic variation, it is unclear if human-induced insularization of natural landscapes can unleash alterations in avian communication systems. We investigated the variability of acoustic signal properties in 2 suboscines birds (Lipaugus vociferans and Tyranneutes virescens) in islands within an artificial lake created by the damming of the Uatuma River, in Brazilian Amazonia. We tested if signal variability was related to variation in acoustic community proxies (island area and isolation), and vegetation structure by surveying 13 variable-sized forest sites and 2 mainland continuous forest sites. Bandwidth variation in L. vociferans songs was related to island area and isolation (N = 67 inds), but these relationships were not observed in T. virescens songs (N = 69 inds). Additionally, the lowest and peak frequencies of songs of both species were higher in islands with greater tree basal area. In both species, temporal properties of songs were not associated with variation in island characteristics. Our study suggests that land-use changes may lead to alterations in particular traits of acoustic signals for species for which songs are innate.