This video from the USA says about itself:
27 January 2016
A Blue-gray Gnatcatcher tends its nest in Arkansas. Both sexes cooperate in building the neat, open, cuplike nest, which takes up to two weeks to build. The nest is 2–3-inch wide and is held together and attached to a branch with spider webbing and decorated with lichen.
The nest’s high walls are built in flexible layers. The main structural layer is built of fibrous materials like plant stems, bark strips, and grasses, all held together by spiderweb or caterpillar silk. Inner layers become progressively finer, and the roughly 1.5-inch-wide cup is lined with plant down, paper, cocoons, hair, or feathers. The outside is covered with webbing or silk decorated with bits of lichen or bark flakes.