I have a new hobby.

I keep track of all the wild birds I spot.

Which sentence uses parenthetical elements most effectively to combine the information in the sentences?

I have a new hobby, which is keeping track of all the wild birds I spot.
I have a (new) hobby, which is keeping track—of all the (wild) birds I spot.
I have a new hobby, keeping track—of all the wild birds I spot.
I have a new hobby—keeping track—of all the (wild) birds (I spot).