The National Audobon Society states that “….birds have a remarkable ability to expand the mouth and stretch the oesophagus to swallow large prey…”

“The digestive tract is relatively short in birds that eat fruit, meat, and insects, and longer in those that eat seeds, other plant matter and fish. The basic oesophagus is a simple, narrow tube, which often widens into a sack-like crop, where food can be stored temporarily. The oesophagus can stretch considerably to accomodate large prey, such as when an egret swallows a large fish whole.”

The Sibley Guide to Bird Life & Behaviour. 2001, C. Elphick, J. Dunning Jr, D. Sibley eds.; Christopher Helm London, Chanticleer Press Ltd London, 1st ed.

“Waterfowl have a spontaeous tendencty to overfeed, a tendency which, at least for geeese, is probably related to the pre-migratory behaviour of their ancestors.”

“Based on the extra physiological use of a natural fattening phenomenon, foie gras has been recognised as a non-pathological and non-harmful product. ”

The Past, Present and Future of Force Feeding and “Foie Gras” Production. 2004, D. Guémené, G. Guy; World’s Poultry Science Journal, Vol. 60.

“[The] absence of pain indicators likely results from anatomical specificity of the waterfowl involved in foie gras production. For example, ducks and geese, like many other bird species, are able to swallow large preys. Consequently, the inside diameter of the upper part of the esophagus, which is essentially an expandable elongated pouch in waterfowl, the pseudo-crop sac, is comparatively larger than in mammals and is not circled by cartilaginous rings, explaining the capacity to swallow large objects.”

“Panting in ducks, which frequency is increased by the end of force-feeding period strikes many visitors of a force-feeding operation and is often misinterpreted as an indicator of discomfort. Panting originates from a thermo-regulatory reflex. Birds have no sudoriferous glands and their capacity to eliminate extra heat through contact with the air is limited by the insulating properties of their plumage. Thus, they open their beaks and pant to eliminate the latent heat associated with water losses. Panting constitutes an effective way “to burn” excessive calories. It is neither a voluntary nordeliberate action but a reflex controlled by the respiratory bulbous centers.”

“Globally, in absence of wound or pathology, force-feeding does not appear to induce pain and is not a major source of nociceptive information integrated by the nervous system.”

“…There are some species, however, in which the metabolic adaptations naturally result in hepatic steatosis. These include wild migrating birds and fish (e.g., cod), in which moderate hepatic steatosis occurs spontaneously as a consequence of energy storage before migration (Pilo and George, 1983). The process of hepatic steatosis is facilitated in these oviparous species, because the liver is the major site of de novo lipogenesis, which is not the case in mammals.”

Force Feeding: An Examination of Available Scientific Evidence. 2006, D. Guémené, G. Gérard, J. Servière, J. Faure; National Institute of Agronomic Research.

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