Question for game biologists

[Brutus]

At night while walking near hardwood trees, sometimes I hear a small mammal(?) making a peeping sound when I am with X amount of feet of a hardwood tree.

My question is this: Am I hearing a small songbird announcing its presence or is this a bat trying to echo locate me?
Often it's one small peep. Other times, and less often I hear 2 or 3 peeps.

Just curious......
Thank you

 

[9.3mauser]

Without knowing exactly what it sounds like its hard to make a guess, but my WAG would be some sort of tree frog:

 

[DBeato]

Agree, tree frog. was watering the front flower bed the other night and every time I sprayed the one bush I got a very loud response, chirping type sound. Was sure it was some kind if bird, took a closer look to find this guy: