Food for birds: Nectar
Nectar is bird food mainly for hummingbirds, though orioles also like nectar. Orioles visit our yard generally only one or two days a year, though. Even though I put out orange halves and grape jelly, they just didn't stay around, so I don't do anything special to attract them anymore.
Sap could also fall into this category, but I haven't noticed birds, such as the yellow-bellied sapsucker, in my yard.