ELINT and SAR.

For the first one, just look at wikipedia lists of government says that fly as little triangular constellations, like Yaogan 9A, 9B, 9C on this list: https://en.wikipedia.org/wiki/Yaogan

Those are ELINT birds that use multilateration to spot emitters globally.

SAR can spot wakes far, far, larger than ships using the same techniques as SAR measuring ground erosion, etc.