Parallax image sizing for mobile

Site URL: https://www.mellymooneyes.com/

Hey Guys! I've seen a lot of similar posts on here so I apologize if the answer has appeared because I still haven't seen one that works. 

Is there a code to insert to make your banner parallax images smaller on mobile?  I don't care if it disables the parallax function on mobile, I just don't want it to cut off SO MUCH of the visual field of the image.  

My site isn't active yet so here is what I'm referring to.  The lion image is on my homepage and the other image is on another page for reference both pages are index pages.  THANK YOU SO SO MUCH for your help!!