My first thought was that the Western Gull had stolen an egg, but it was pliable and flexible, certainly uncharacteristic for eggs. The Gull dropped its prey twice, but picked it up again, squeezing hard, releasing blood and fluids, and then finally swallowed it whole. Pictures following are in sequence. The Gull had flown in from the sea, I noticed it because it was pursued by another and both where squeaking excitedly.
The seagulls were trying to eat these. They were very excited about them.
These are everywhere on Coronado Beach this weekend. There are More at low tide but quite a few at high tide.