Update: My dad weighed in with 'pollarded plane trees.' This required a fairly lengthy explanation as to what pollarding is, but I think he's right.
The pier for the boat over to Alcatraz had changed since I was last in the city, and I didn't pay too much attention to where we were supposed to end up, and as a result we were among the last to board. Had we arrived earlier we might have taken the time to read the historical blurbs.
The boat ride over to Alcatraz for the night tour (which is a bit more extensive than the standard daytime tour and highly recommended if you're planning to go) was notable for two main factors: the rapid onset of some large clouds making the sun disappear and the rapid onset of some low-flying gulls...
.. which attracted quite a bit of attention from the assembled masses on the boat. Maybe they don't have seagulls where they came from? Is there such a place? Can I move there?