park and shorebirds

Today when I went down to the park for the first time today, it was sunny and cold. When I was was walking out to the end of the breakwater, I saw a crow on one of the railings and it didn’t fly away when I walked past it. When I was out at the end of the breakwater, I saw some ducks out on the water. When I was in the park, I saw a raven in the trees. When I was nearing the battle site bench, I saw some Black oystercatchers and other shorebirds out on the beach by the water along with some crows. I stopped to take some photos of the black oystercatchers and after they flew off, I walked out onto the beach to see if I could get better photos of the other shorebirds. I walked out onto the beach sometimes stopping for a bit to get some photos of them just in case they flew off. I actually got really close to them and got some good photos of them, before I decided that I had gotten close enough and walked back to the trail scaring some crows that had flown in while I was taking photos of the birds. When I was on the trail by the river, I saw some mergansers. When I was on my way back home, I saw some juncos, chickadees, a song sparrow and some other sparrow.
Why did the shorebirds not fly away when I got close to them?
Why were there no ducks in the river?
What was that other sparrow?