Trumpeter Swan

{W}{W}
Creature -- Bird
1/2
Flying

: Untap target creature. That creature gets +1/+1 until end of turn. Play this ability only once each turn.
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This card was designed to fit the name. Don't get me wrong, I like the slew of fantastical creatures that Magic harbours, but sometimes, I like to see a mundane creature too. The abilities followed rather closely from the name and from there, it was obvious that this had to be a white creature.
I am not entirely certain how I want to cost this. I don't think I want it to cost just three mana, because then it begins to horn in on other cards that I like (Ghost Warden and Angelic Page.) I have created several cards recently that cost 3C, so I don't know if I want this to go there either. 2CC may be a little costly for this effect, but I am also wary of making the creature bigger because it doesn't seem sensible that a swan should be as formidable as a griffin. Any advice in this matter would be appreciated.
The restriction on the ability that allows it to be played only once each turn is to keep this creature from untapping itself infinitely, giving itself +1/+1 each time.
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Current Wording:
Trumpeter Swan
{W}{W}
Creature -- Bird
1/3
Flying
: Untap target creature. That creature gets +1/+1 until end of turn. Play this ability only once each turn.