In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.

Passage: The Perijá tapaculo is a small bird, 10 to 12 cm (3.9 to 4.7 in) in length with an average mass of 17 to 18 grams (around 0.6 oz). The bill averages 6.8 millimetres (0.27 inches) long, 2.9 mm (0.11 in) wide, and 3.5 mm (0.14 in) high. The legs are about 21 mm (0.83 in) long. The Perijá tapaculo's tarsus averages 21.1 millimetres (0.83 in) long. The wings measure 57.4 mm (2.26 in) on average and the tail is about 40 mm (1.6 in) long with between 8 and 12 rectrices.The forehead, lores, crown, mantle, and scapular area are a neutral grey colour. There is a brown spot on the nape. The top of the tail is brown, and the bottom is faintly striped brown. The bird's back and rump are striped brown-sepia, and the throat, breast, and belly are grey-white. Its lower belly and flanks are tawny. The iris is dark brown. Male specimens are distinguished by having less sharp brown spots on their napes, and the bottom of their breasts are mixed with a pale buff colour. The legs are brown on the back and whitish on the front. Young birds have a yellowish appearance with striped brown flanks.The bird's plumage colouration is most similar to the pale-bellied tapaculo. The S. g. morenoi subspecies of the pale-bellied tapaculo can be differentiated from the Perijá tapaculo by its entirely brown back and nape, and its different calls. Juveniles of this subspecies have a dull ventral plumage, while the Perijá tapaculo has a more yellow plumage. It also resembles the Caracas tapaculo but has a duller ventral colour.
How many inches long is the average bill of the Perijá tapaculo?