Tosefta על פאה 4:11

An ear of grain that is among the standing grain, behold, it belongs to the homeowner. [An ear of grain] that is among the harvested [grain], behold, it belongs to the poor. [If] half is among the standing grain, and half is among the harvested [grain], he takes it and throws it behind him, because [in a case of] doubt [as to what is considered] gleanings, [the doubt is resolved in favor of its status being] gleanings (see also Peah 6:4 re: forgotten sheaves).

[With respect to grain found in] ant holes (see Peah 4:11), it is forbidden [to the poor] under [the laws of] stealing, but if the homeowner declared them ownerless, they are permitted [under the laws of] stealing [and thus, the poor may take them]. Rabbi Shimon ben Elazar says, "If they were [intentionally] stored there, they are forbidden under [the laws of] stealing."