How are bird strikes tested in helicopters?
Do they happen as frequent as planes?


Here is a link to the Federal Aviation Administration's Wildlife Strike database. Here you can search all the recorded wildlife strikes in the USA, and filter them by various things, including Engine Type.

To get a good idea of how many helicopter bird strikes occur in comparison to other aircraft, we can compare how many bird strikes occurred in turboshaft (Engine Type F) engine aircraft to the total number of bird strikes. 

From January 1, 1990 to January 1, 2017...


  California
   - There have been 31 turboshaft engine wildlife strikes, accounting for 0.22% out of the total 13,698.
  
  Texas
   - There have been 46 turboshaft engine wildlife strikes, accounting for 0.30% out of the total 15,520.
  
  Florida
   - There have been 22 turboshaft engine wildlife strikes, accounting for 0.20% out of the total 11,119.


This data would suggest that roughly 0.25% of all wildlife strikes are on helicopters.

Taking another piece of data from the FAA, we find that the ratio of rotocraft to general aviation aircraft in 2015 is 9,766 to 199,927, meaning that helicopters account for roughly 4.66% of total aircraft. 



Combining these two pieces of data, we can see that since 0.25% of all wildlife strikes are on helicopters, but helicopters account for 4.66% of aircraft,  helicopters encounter wildlife strikes at a rate of ~18.64 times less than general aviation aircraft. 

(Disclaimer: Data used above is rounded and averaged. This is a ROUGH estimate!)