Abilities » Fight Song
Is Altaria's "Fight Song" Ability stackable so attacks from Dragon type Pokemon can do an additional +20 damage for each Altaria in play?
Yes, it does.
Source: TPCi Rules Team (2012-08-23)

Relevant cards

Note: All applicable cards may not be listed below.
BW6_84
BWP_BW48
BWP_BW48