The semi circles are probably leaf cutter bees, but they won't be the ones completely decimating them. Wood pigeons will eat leaves, they are certainly partial to young leaves and buds on trees and hedges, but I suspect a number of culprits, bugs and birds, rather than just one for that number of trees and amount of damage. If you can stretch to it for 15 trees (I don't know how big they are and it depends where you get it from) you could consider a pyrethrum based spray for the bug pests (I'm not a fan of any spray, but this one is at least certified for organic use, based on naturally occurring compounds and safe on foodstuffs up to one day before harvest) and then something to scare the birds too. I feel for you, it's heart breaking to see all of your hard work going to serve as the local all you can eat buffet for the local pests.