You could start a niche website about a specific breed of cat. Another option could be a YouTube channel reviewing dog chew toys. Or you could start an authority site about caring for exotic birds. You could also go offline with your niche business by starting a pet sitting service. Pet owners in some cities are willing to pay up to $100 per day for reliable pet sitters.
I know what you’re saying. What if this idea sounds good to you, but you aren’t an expert? What if you haven’t ever even run a marathon before? Who cares! Share with others as you learn and just be honest with people that you are learning too, but you want to share what you learn. The Internet is full of self-proclaimed “gurus” so it’s refreshing to read a blog that is down-to-earth.