Please note, the target is a cat.
I guarantee you seagulls have more to do with the decline of the plover population than a cat does.
These are omnivores like most Larus gulls, and they will scavenge as well as seeking suitable small prey. They frequently rob other seabirds of their catch. It can swallow a puffin or a small wild duck whole. http://en.wikipedia.org/wiki/Great_Black-backed_Gull
These basically weren't seen in the north New Jersey shore until they opened Arthur Kills landfill.