Today while watching the terns at Coulter Creek County Park I saw a
juvenile Caspian Tern "playing" with a stick. This evening, while going
through my photos I discovered I had photographed a Caspian Tern flying
with a stick which it dropped, and then dove into the water to retrieve.
It then carried it back to the group of terns.

Birds of the world has this to say:

Play
Two adults were observed on repeated occasions flying over a lake,
carrying small dark objects in bills; from time to time they dropped the
objects but retrieved them before they hit the water (132). Other
investigators have observed 2 adults playing with a stick (in 1 case
about 12 cm long) in a manner similar to that described by King (J.
Quinn pers. comm., FJC).

Curious if others have seen this. Some photos and eBird list here:

https://ebird.org/pnw/checklist/S95456745

--
John Riegsecker