It's relatively easy to determine what has eaten a plant.

If the stem is gnawed off at a 45 degree angle, a rodent at it. This damage very much resembles your traditional pruning at 45 degree angles. Their teeth meet at that angle and their damage is characteristically that shape. This could be rats, mice, squirrels, rabbits, etc.

If the damage appears to be ripped off, it's likely deer, horse, cow, etc. They "chomp" and rip.

If it's chewed off like the bud you're holding, it's an insect like grasshoppers, Katydids, caterpillars, etc.

Might there be any bug poop around? It looks like little, dark pills, almost like pin heads.

Don't believe there is no way for a squirrel or rat to get up there. They climb VERY efficiently, right up the stems or trellis. You would be amazed what they can get in to easily and quietly. For the bug damage, there are many insecticides around, from "thermonuclear" types to organics, and are readily available at your local home improvement or garden center outlets. Just make sure they list the insects mentioned above as ones against which they are effective.

Rodents are quite a bit more difficult to deal with. Most often, the only way to protect the buds and plants is to put wire cages around them so they can't chew through and eat the plants and flowers. It's a "lot of fun", I know. I battle them all with my roses out back. Something has even found the front walled garden where I hoped my rose hips were safe. Nope. Some bugger has found them and ate them as quickly as I could harvest them. Welcome to gardening! Good luck. Kim

I won't say categorically that it CAN'T be a bird, but no bird gnaws off at the 45 degree angle, and I've not encountered one which leaves such a clean cut as the bud you're holding. Only rodents leave the perfect 45 degree cut and insects can chew off that prefect looking slice as your bud shows. Most birds I've encountered both in the chaparral in Newhall as well as the hills here in Encino, eat either bugs or seeds. The Twohees will dig up my seedlings and throw mulch everywhere looking for bugs, but they don't eat the plants. The female robins pull the flowers off the polygonum ground cover, but they are pulled off, not sliced or gnawed at the 45 degree angle.

Who knows why a bug or rodent chooses the precise flower or plant they eat? I have them ignoring hundreds of self set hips and targeting the hard to reach one with my paper tag on it. A friend suggested they like the "menus". Why won't they take the ripe, swollen red one instead of my developing green one I created? Perhaps the one they take is in an air path which helps them fly in? Perhaps it is more to their liking as far as temperature? Perhaps it affords them greater protection from birds flying in who might eat them? I dunno. Tis a puzzlement, but there is something about either where that rose is positioned, or about the rose itself which makes them prefer it. Otherwise the others with it should experience the same grazing. Fun, huh? Kim