building a pendulous nest
• (n.) A European titmouse (Parus, / Aegithalus, pendulinus). It is noted for its elegant pendulous purselike nest, made of the down of willow trees and lined with feathers.
Pen'du`line noun [ French See Pendulum .] (Zoology) A European titmouse ( Parus, or Ægithalus, pendulinus ). It is noted for its elegant pendulous purselike nest, made of the down of willow trees and lined with feathers. 
penduline Applied to birds that build pendulous nests. Pendulous nests are described as those that are suspended so they swing or sway.