Re: La Jolla Cove, Sunday Sep 21, 2020: early migrating surf scoter[s] et al.
Stan et al.,
Checking my notes, I had a few small groups of Surf Scoters, mostly moving north, but two were headed south, off La Jolla, in late August. So, I don't think it is safe to say that southbound birds are necessarily "migrating."
As for Heermann's Gulls, anecdotally I want to say they had a decent year in Mexico given a good number of scaly juveniles here on San Clemente Island (10 juveniles with 11 adults on 4 August, 22 juveniles on 17 August, etc.). In poor years (recent, previous years) we've seen very few, if any, juveniles. Curiously, I'd heard the Brown Pelicans in Mexico did NOT do well, and those two species generally have parallel success/failure.
San Clemente Island
Source: SanDiegoRegionBirding Latest Reports