It is one of the smallest birds we have in Europe. Well linked to the riparian forest, the male takes advantage of the flower of the poplars (Populus alba) to begin to weave several nests at the same time, and once he has completed them, it is the female who chooses the one which will be built the entrance tube.

In many places in the plain of Lleida they are known as “shoes”, because after the nest is finished, it has a shape and texture that is reminiscent of the wool booties that are often put on babies.