do i need an I/O shield for quadcopter motors
If the ESC accepts a signal that the Arduino can generate (i.e., 5V PWM) then no interfacing is required.

If the ESC is running from 3.7V (or similar) then some level shifting may be required to reduce the 5V signal to 3.7V, depending on the ESC. That may be built on a shield of some form or just with discrete resistors wired in manually to the leads.