Order: Passeriformes (Suboscines) - Family: Furnaridae
The Wren-like Rushbird is a resident passerine at Costanera Sur. Its unmistakable call gives it away, though it is not easy to find and follow. Its voice resembles a starting scooter followed by a quick and sustained clicking sound sometimes interrupted by a long buzz.
The nest is big compared to that of other birds of the same size. It is almost 30 cm and is built at half meter above water. It is almost rounded with an entrance. Both adults build the nest. They weave the nest attached to rushes (Juncus) using the stalks as a warp. These stalks are easily leaned by the wind. So, the nest must be very flexible to bear the strain it is subject to. Ii is most protected in the middle of the clump. They use plant fibers or vegetal material collected from the surroundings. Once the nest is finished they put feathers on the base.
The nest is supported by columns, formed with stalks tied together. The Rushbird circles around the stalks winding the fibers and hooking the ends in the weave. Some are neatly covered with threads, others more roughly grouped. As they progress upwards in the cone they interweave other stalks as part of the structure. They render the weave more compact by adding long fibers and small bits of material to stuff open spaces. These bits are fixed "screwing" with the bill. All the work is done from the inside to the outside of the nest. They are very meticulous. Before leaving for more new material, they always check for loose ends to be corrected or adjusted. In the video this little bird can be seen pulling a fiber to tighten it.
They work very diligently. It is an incessant coming and going. They do not work at the same time on the nest. One comes in, the other goes out. Each one weaves the materials gathered nearby. Sometimes they leave the nest to have a break or feed. On one occasion the nest was left unattended and some curious male Chestnut-capped Blackbirds, which also breed nearby, came closer to investigate.
The time which lasts the construction of the nest (almost a week judging by the film) are days of mutual stimulation exhibited by displays. This species does not present sexual dimorphism, which prevents the differentiation of activities by sex. Nevertheless, some repeated patterns of behaviour let guess who was who.
Video November 2009 © Roberto Ares