Nest weave pattern in weaverbirds: a sexual signal selected through sensory drive?

Nests are primarily shaped by natural selection, but are also subject to sexual selection. Here, we investigated the potential role of sexual selection in shaping nest visual patterns, focusing on scale-invariance, a property describing how patterns remain similar across spatial scales. In humans, it has been documented that visual patterns are more attractive when their scale-invariance resembles natural habitats, likely because they are more efficiently processed. The underlying mechanism, called processing bias, extends the sensory drive hypothesis from colors to patterns. Applied to birds, processing bias predicts that nests whose scale-invariance matches natural habitats could be sexually selected. We tested this using a comparative analysis of weaverbirds. We quantified the deviation of nest scale-invariance from a range of putative selection optima, and then evaluated whether interspecific variation in this deviation is explained by mating system and sexual size dimorphism, two proxies for sexual selection. For both proxies, effect sizes were largest for the same putative optimum, aligning with scale-invariance values in natural habitats. Sexual selection may thus favor nest designs that are efficiently processed, such as those with habitat-like features. Our findings also highlight the challenge of designing a specific test for this hypothesis and call for further research linking pattern perception and sexual selection.