> The fact remains that animals do seek out and get drunk on various fruits.
I
> remember reading of birds in suburban areas of the US falling down dead
> drunk after eating rotting glossy privet fruit.

maybe it happens to birds in cities as they feed on crap ,in that case they
will have the same problems than humans .seeking stimulants
i never seen a wild bird getting drunk on wild foods . we have many animals
here grazing in orchards with tons of fruits on the ground in season ,
animals used to their natural diet don't seek to ingest them to the point of
getting drunk .
>
> The amount of fruit required is not large: 2 normal sized apples will make
1
> standard drinks' worth of cider.

i live in the real world , 2 apples fallen from the tree don't transform
thenselves in a glass of cider .at the most where the fruit have been
bruised , you will have a brownish part containing a tiny amount of alcohol
and vinegar. But when i harvest an apple like that i have no desire to eat
that part as it tastes generally not thast great
alcohol is an acquired taste .childrens and peoples like me who never drank
it don't like it .

> turning into vinegar requires aerobic fermentation which would not occur
> under the skin, likewise for mold development.  In the case of
blackberries
> perhaps the very high tannin content keeps them stable.

again i live not in text book , moldy and vinegar tasting berries are just
very  very common ( it occur very frequently in blackberries , raspberries ,
thimble berries , especially ).rarelly on salmon berries as they are gone
before fully ripe ( being the first fruit to happen,  now ) salal berries
are quite stable as they are less juicy , red huckleberries are not sweet
enough to spoil easelly .

>
> BTW, have you eaten wild crab apples?

yes i do and dry them to for the winter .we have also a wild one native from
here "pacific crab apple " that commes in bunches of 1 cm diameter size
fruits for the biggest .they are very sour unless after the first frost  .in
that case they are sweet.i love them sour or sweet .
jean-claude