Trap-lining or trap line refers to a feeding strategy amongst certain families of birds, notably hummingbirds and woodpeckers. These birds visit a circuit of specific plants, trees, or other feeding sites, much as trappers check their lines of traps.
In the case of sapsuckers, entrapped insects in sap are an essential source of food. For hummingbirds the relationship is to the seasonally flowering species providing nectar.