Tattler

Noun

1. One who tattles (notifies authorities of illicit behavior) or is inclined to do so; a tattletale.

   "My sister is a big tattler; she always tells Mommy when I hit her!"

2. Either of two similar bird species in the shorebird genus Heteroscelus (Tringa in some taxonomies).
3. A device fitted to a vehicle to measure mileage etc.