# [Jelly][1], <s>13</s> 12 [bytes][2]

-1 byte thanks to @Luis Mendo (use `Ḃ` to replace `%2`)

    Œlf“aeiou”LḂ

All test cases are at **[TryItOnline][3]**

How?

    Œlf“aeiou”LḂ - Main link takes an argument - s
    Œl           - lowercase(s)
       “aeiou”   - string of lowercase vowels
      f          - filter - keep only the vowels
              L  - length - the number of vowels
               Ḃ - Bit (modulo 2)
      
---
**Non-competing, 5 bytes** (since I just added the function `Øc`)

    fØcLḂ

Test cases also at **[TryItOnline][4]**

Same as above, but `Øc` yields the English vowels, `'AEIOUaeiou'`


  [1]: https://github.com/DennisMitchell/jelly
  [2]: https://github.com/DennisMitchell/jelly/wiki/Code-page
  [3]: http://jelly.tryitonline.net/#code=xZJsZuKAnGFlaW914oCdTOG4ggrFvMOH4oKsS-KCrFk&input=&args=InRyZWVzIiwiYnJ1c2giLCJDQXRzIiwiU2F2b2llIiwicmh5dGhtIg
  [4]: http://jelly.tryitonline.net/#code=ZsOYY0zhuIIKxbzDh-KCrEvigqxZ&input=&args=InRyZWVzIiwiYnJ1c2giLCJDQXRzIiwiU2F2b2llIiwicmh5dGhtIg