To understand the answer, you have to hold three thoughts in your head at the same time. Ready?Lil' Birdy-
Ravens and Plovers have both been around for a very long time. how do you explain that there is only a problem now?
1. Plovers used to be more numerous on the coast. Large populations still suffered predation, but it didn't matter because the number killed was such a small percentage of the population that the breeding potential remained high.
2. Damage to habitat and disturbance by people, vehicles and pets reduced the areas suitable for plover breeding, feeding and rearing. This concentrated plovers to a few areas.
3. Predators like ravens and other corvids are attracted to areas where people leave trash, and when you concentrate predators in those few areas where plovers remain, the percentage killed exceeds the bird's breeding capacity.