Tosefta על חולין 44:3

[What is] valid for the red heifer is invalid for the heifer whose neck is broken (Deut. 21:1-4), and what is valid for the heifer whose neck is broken is invalid for the red heifer (Hul. 1:6). And work [in the field] renders each of them unfit. B'nei yonah (young pigeons), once they are old enough to sip (see Hul. 22b:6), until their feathers become golden [are fit for sacrifice], [while] turtledoves, once they are able to fly, even if they are old [are fit for sacrifice], and consequently it is said, what is valid in turtledoves is invalid in b'nei yonah, and what is valid in b'nei yonah is invalid in turtledoves.