The small burrowing ducktail

It's commonly called burrowing ducktail (Subsilvana tyrannocommensalis) and it's found exclusively in the Belgrano wetlowland.
This ducktail species can't create its own den, so it's forced to live in strict relation with large ground tyrants, living as commensal.
Ground tyrants are not bothered by the presence of this bizarre long-tailed bird and they happily share their tunnels; the presence of burrowing ducktails is actually beneficial for these large passerines, since this bird has a more robust body and can easily fend off their natural predators, like marters and sheardogs.
Burrowing ducktails use ground tyrants den for rest and defending themselves from the heat of the summer: because of the relatively high temperatures of Belgrano, this bird becomes crepuscular during summer, while in the rest of the year they are mainly diurnal. 

Burrowing ducktails are one of the smallest species of ducktail of the late Lentocene, weighing just 15 kg (33 lbs), like a big turkey.
Like the majority of its relatives, burrowing ducktails are herbivorous and feed on fresh plant stems and mosses.
Their food habit does not interfere with the feeding ecology of ground tyrants, which are more omnivorous (eggs, insects and other invertebrates can comprise half of their diet).