I've had rosemary, lavender, sweet bay, oregano, thyme, dwarf
blueberries, a raspberry, strawberries, and some of my temperate orchids
outside for a year with no problems. This winter, I went on a bit of a
spree, and added a bunch of plants, many of which have been completely
destroyed.

Here's what happened:
First, I added hyacinths and primroses. A few days in, the hyacinth
flowers had been taken off the inflorescences, and the primrose petals
and some leaves had been mostly ripped off.

So I dumped the primroses, kept the hyacinths because I
was hoping they'd return next year anyway, and replaced them with dutch
irises and narcissus. Within a few days, the irises have had all their
flowers bitten off, and one bulb has been uprooted. A few flowers of the
narcissus have been partially eaten, but no severe damage yet.

Meanwhile, I set out a parsley plant that has been
bitten down to the roots, while the plants I put out with it, mint,
sage, a new oregano and thyme, have been left completely alone.

I repotted my bletilla (hardy orchids) and the next
day, someone had dug up and sampled one of the bulbs, but I moved the
table they were on, and no one has been at them again... yet...

Also, the lily of the valley pips I planted were partially nibbled on, but perhaps unsurprisingly they don't seem popular.

Helleborus and my carnivorus plants are all completely fine, as well as the original plants.

I'd chalk this all up to squirrels, which are well known to do this
where I'm from, except for this: I live on the third floor of an
apartment complex in the city. All these plants are out on a big
terrace, which does have access to my neighbours' terraces, but wouldn't
be easily accessible from the ground. And I've never seen squirrels
anywhere when I've taken my dog out on walks.

I had a
bit of an issue last summer with the neighbours letting their cat out on
my terrace, and she was chewing on some of the plants, but they moved
out in November. Whatever is doing this seems to only come when it's
dark, so I doubt it can be birds... so what do you think? Mice, rats?
Another plant-loving cat? Both?

Thanks for your help! I can take pictures of some of the damage if it's helpful.