Gleaning

Gleaning is the act of collecting leftover crops from farmers' fields after they have been commercially harvested or on fields where it is not economically profitable to harvest. Some ancient cultures promoted gleaning as an early form of a welfare system.

Bible

Old Testament

According to the Holiness Code and the Deuteronomic Code of the Torah, farmers should leave the corners of their fields unharvested, and they should not attempt to pick up that which was dropped or harvest any left-overs that had been forgotten when they had harvested the majority of a field. On one of the two occasions that this is mentioned by the Holiness Code, it adds that, in vineyards, some grapes should be left ungathered, an argument made also by the Deuteronomic Code.

These verses additionally argue that olive trees should not be beaten on multiple occasions, and whatever remains from the first set of beatings should be left. According to the Holiness Code, these things should be left for the poor and for strangers, and the Deuteronomic Code commands that it should be left for widows, strangers, and paternal orphans. The Book of Ruth features gleaning by the widow Ruth to provide for herself and Naomi, also a widow.

Gleaning (birds)

Gleaning is a term for a feeding strategy by birds in which they catch invertebrate prey, mainly arthropods, by plucking them from foliage or the ground, from crevices such as rock faces and under the eaves of houses, or even, as in the case of ticks and lice, from living animals. This behavior is contrasted with hawking insects from the air or chasing after moving insects such as ants. Gleaning, in birds, does not refer to foraging for seeds or fruit.

Gleaning is a common feeding strategy for some groups of birds, including nuthatches, tits (including chickadees), wrens, woodcreepers, treecreepers, Old World flycatchers, Tyrant flycatchers, babblers, Old World warblers, New World warblers, Vireos and some hummingbirds and cuckoos. Many birds make use of multiple feeding strategies, depending on the availability of different sources of food and opportunities of the moment.

Techniques and adaptations

Foliage gleaning, the strategy of gleaning over the leaves and branches of trees and shrubs, can involve a variety of styles and maneuvers. Some birds, such as the common chiffchaff of Eurasia and the Wilson's warbler of North America, feed actively and appear energetic. Some will even hover in the air near a twig while gleaning from it; this behavior is called "hover-gleaning". Other birds are more methodical in their approach to gleaning, even seeming lethargic as they perch upon and deliberately pick over foliage. This behavior is characteristic of the bay-breasted warbler and many vireos. Another tactic is to hang upside-down from the tips of branches to glean the undersides of leaves. Tits such as the familiar black-capped chickadee are often observed feeding in this manner. Some birds, like the ruby-crowned kinglet and red-eyed vireo of North America use a combination of these tactics.