Prunus padus is the bird cherry (or hackberry) while prunus avium is the wild cherry (the gean).
Those look like geans. Bird cherries are wee black berries and they're generally sour as sour can be. Can you check the leaf stalks though? there should be a bump of two on them near the leaf. These are glands and sometimes not terribly obvious, but they will be there if it's a cherry.
Thing is though, the cherries, like apples, happily breed among themselves and produce hybrids. Some taste brilliant, some are really better left for the birds.
The stones aside, the one saving grace is that none of their fruits are poisonous....just make sure it's a cherry or one of the plum family (they can be confusing
) and folks don't always leave stems on to check when they get home) and it'll be fine.
Cherries and their relatives can identified by examining the base of the leaves. This is a googled image of the wee bumps on the leaf stalk (petiole) just below the leaf.
http://www.google.co.uk/imgres?imgu...vvUczbGsKg0QXGtoG4BQ&ved=0CDcQ9QEwAQ&dur=2553
cheers,
M
p.s. Sorry, just re-read Dwardo's post and this sounds as though I'm contradicting him, but I'm not really; the cherries really do interbreed and then only the botanists can manage to sort them out.
M