I'm surprised the Pilot's Jargon series doesn't have this one...to 'squawk' something is to set an aircraft transponder to the frequency or code signal indicated. As an example, Mode C transponders (in the U.S.) squawk altitude, meaning that when they detect an air traffic radar signal, they respond with a signal into which is encoded the aircraft's current altitude. In an emergency, a pilot should squawk 7700 which means set his or her transponder to that set of digits so that it returns that code to Air Traffic Control. This indicates that the aircraft is in distress.

Squawk (?), v. i. [imp. & p. p. Squawked (?); p. pr. & vb. n. Squawking.] [See Squeak.]

To utter a shrill, abrupt scream; to squeak harshly.

Squawking thrush Zool., the missel turush; -- so called from its note when alarmed. [Prov. Eng.]

© Webster 1913.

Squawk, n.

1.

Act of squawking; a harsh squeak.

2. Zool.

The American night heron. See under Night.

Squawk duck Zool., the bimaculate duck (Anas glocitans). It has patches of reddish brown behind, and in front of, each eye. [Prov. Eng.]

© Webster 1913.