In most animals, nests primarily aim to protect offspring, and are
presumably shaped by nat- ural selection. In some species, however,
nests are conspicuous and elaborate, thereby visible to predators. One
hypothesis to explain this apparent paradox is that nests could also
evolve through sexual selection. Here, we tested this hypothesis by
studying nest weaves across the weaver family (Aves: Ploceidae). We
hypothesized that scale-invariance, a measure of vi- sual regularity of
the weave, reflects the quality of the nest builder or activates
pre-existing preferences exploiting a sensory bias in the receiver. We
predicted a link between weave scale- invariance and two proxies of the
intensity of sexual selection: mating system and sexual size dimorphism.
Our results reveal that species under stronger sexual selection produce
more scale-invariant weaves. These results suggest a previously
unnoticed sexually selected signal associated with the evolution of some
of the most spectacular constructions observed in the animal kingdom.