Hi Flora May & welcome to GoY. Birds do peck yellow flowers off plants but it you have covered them with cloches and they are still being eaten then I suspect the good, or rather bad, old vine weevil. Remove the cloches as they are not doing anything to help the plants and treat with Provado Vine Weevil Killer. If you are organic you will need to go out at night with a torch and pick off the wretched bugs and stamp on them hard.

Hmmm. Vine weevils normally only chew round holes in the edge of the leaves rather than eat the flowers. I would be looking for either snails/slugs or possibly even earwigs.

Slugs and snails are likely culprits. Try some organic slug pellets (containing Ferric phosphate) or use your boots as MG suggests.