Ḥadj is a particular kind of travelling litter; naʿsh supplies a raised supporting frame; mukhayyam marks the covered or tent-like appearance. Together they outline the bird’s conspicuously elevated head.
Yatbaʿna is a third-person feminine plural imperfect verb, referring back to the young ostriches. The agreement is worth noticing: grammar is tied to the bird-group being pictured.