#1. I would point out that snakes, and especially in my area, squirrels eat more birds. I also agree that cats are a problem, although I am not sure if they are killing baby birds or adults.
#2. I have crows in my neighborhood and in my backyard. I have no knowledge of where they are nesting. There is a marsh nearby. I would appreciate any tips on how to keep them from eating the plants in my garden. I have several bird feeders and they like to eat the seeds that fall on the ground. That's okay, but now they've started eating the plants.
#3. I believe I live near both species, but until I took this course, I couldn't distinguish them. Now I will pay more attention to behavior.
#4. As the video said, probably owls that use the nests that crows leave behind.