Brown sugar, honey, agave or any other kind of sweetener is not recommended for use in hummingbird feeders because they are more likely to grow bacteria.
These sweeteners also spoil more rapidly and can make the birds sick. You may not even realize that you are making the birds sick because they won’t die until several days after they have ingested the spoiled food.
Other animals may visit your humming bird feeder like bees, wasps and ants as they are attracted to the sugar water. This can deter hummingbirds from coming to the feeder to take a sip.
The pests may crawl into the feeder where they can become trapped and drown. You can help prevent ants from crawling into your feeder by using Vaseline on the wire it hangs from so they can’t get to the nectar. As for bees and wasps…sorry, can’t help you there.