Not Alcatraz, of course, but a rocky island of Columbia River Basalt south of Yaquina Head. Newport, Oregon is in the distance. You can't really tell at this scale, but that rock is literally covered with wall-to-wall nesting seabirds (Open the photo for full size; they're much more apparent in a larger version). The only thing remotely similar I've seen is penguin colonies in Antarctica. There- my vision wasn't good enough to tell, here- the spacing is determined by how far the birds can crane out and peck while sitting in their nests. The nests will be far enough apart that any two that are occupied will be far enough apart that their residents can't quite reach each other. This is a great example of how differential weathering and erosion- physical processes- have a profound influence on and benefit to biological processes.