50 CFR 14.172 - Primary enclosures.
(a) A primary enclosure for birds shall have ventilation openings on two vertical sides that comprise at least 16 percent of the surface area of each side and are positioned so as to decrease the likelihood of creating a draft.
(b) Perches shall be provided for birds that rest by perching. The diameter of the perch shall be sufficient to permit the birds to maintain a firm, comfortable grip. Perches shall be placed so that droppings do not fall into food or water troughs or onto other perched birds. There shall be enough head room to allow the birds to move onto and off the perches without touching the top of the enclosure.
(c) An enclosure used to transport one or more birds that rest by perching shall be large enough to ensure that sufficient perch space is available for all birds to perch comfortably at the same time. No more than 50 birds that rest by perching shall be transported in one primary enclosure, with the exception of large birds (longer than 23 cm, or 9 inches), which are limited to a maximum of 25 per primary enclosure.
(d) A primary enclosure used to transport a raptorial bird shall be large enough to transport the bird comfortably and to permit it to turn around without stretching its wings to the fullest extent. Only one raptorial bird shall be contained in a primary enclosure.
(e) A primary enclosure containing nonraptorial birds that do not rest by perching shall be large enough for the birds to turn around, to lie down, to stand erect, and to change posture in a normal manner.
(f) Nectar-feeding birds shall either be transported in a primary enclosure equipped with feeding bottles accessible from outside the enclosure for replenishment or hand-carried and fed in accordance with the written instructions of the shipper.
(g) Birds transported in the same primary enclosure shall be of the same species and be compatible with one another. Birds that are incompatible shall be placed in individual primary enclosures and these enclosures shall not be stored or transported in visual proximity to one another.