Complex nest decorations of a small brown bird in the Pampas

Abstract

If one travels through the Pampas region in east‐central South America, it is common to observe large piles of sticks on trees, shrubs, and electricity poles. These structures are the nests of a small brown bird, the aptly named firewood‐gatherer (Anumbius annumbi, family Furnariidae; Figure 1a). During their life, these birds build multiple nests (Delhey et al. 2010), which accumulate throughout their territory and are often used by other species to roost and breed (Turienzo and Di Iorio 2007). The mounded nests are sturdy enclosed structures constructed from sticks and twigs, with an entrance tunnel that spirals down to the brood chamber (WebFigure 1). Their outer walls and entrance contain many curious objects that do not serve any obvious structural purposes and the presence of such “decorations” makes these oversized nests one of the more puzzling expressions of animal building behavior.