Experimental evidence of non-random nest material selection in pied flycatchers.

•It is unclear if wild birds randomly or non-randomly collect nest materials.•We provided pied flycatchers with wool, feathers and deer hair close to their nests.•Nest building females collected the deer hair, whilst avoiding the wool and feathers.•Females thus showed strong preferences for some nest materials but not others.•Birds select nest material in a non-random manner from the wider environment.