I am strongly against adding anything to the birds' water unless you also give them a source of clean, fresh, PLAIN water as well.
Putting a sugar -- any sugar, no matter how natural -- into the water in hot weather guarantees faster than usual bacterial growth. 
The reason that honey is antibacterial in it's pure form is that it's such a high concentration of sugar that bacteria can't grow in it. Plain white sugar would do the same -- and is actually used as a wound treatment in certain parts of the world where antibiotic ointments are not widely available.