Bird's beak appearance is seen in:
Sigmoid volvulus often can be differentiated from cecal or transverse colon volvulus by the appearance of plain x-rays of the abdomen. Sigmoid volvulus produces a characteristic bent inner tube or coffee bean appearance, with the convexity of the loop lying in the right upper quadrant (opposite the site of obstruction). Gastrografin enema shows a narrowing at the site of the volvulus and a pathognomonic bird's beak. Ref: Schwaz's principle of surgery 9th edition, chapter 29.
Testicular torsion
Volvulus
Meconium ileus
Ileal atresia