Practice makes perfect for the Botswanan Southern Masked Weaver, shown above weaving a complex nest of out grass. Weavers aren t born knowing how to build these structures, researchers reported today (Sept. 26, 2011) in the journal Behavioural Processess. Instead, the bird vary their technique from one nest to another, sometimes building left to right, sometimes starting from right to left. As the birds gain more experience building nests, they drop grass less often, suggesting that they improve at their art.