Q.How does selective feeding affect the nutritional status of raptors?
A. Wild free-living raptors can, and do, practice selective feeding. As well as selecting the type of food item they wish to hunt and catch for food, the wild, free-living raptors can eat selective parts of the food item and discard others, once it has been obtained.

Raptor food items do not contain the 40+ nutrients that are regarded as essential for raptors, dispersed evenly throughout the food item. Different parts contain specific concentrations of certain nutrients. Raptors requiring specific essential nutrients will frequently eat certain body parts of their prey first... often leaving the less desirable parts.

In the case of wild, free-living raptors this normally involves caching the less desirable parts of the food item or discarding them completely. If the hunting is good, the cached items are ignored and further caught prey is again selectively eaten. If hunting is poor, the cached food items may be returned to for a later meal. However, in most cases, the cached food is either found and eaten by some other animal or subsequently ignored by the raptor.

Captive raptors, on the other hand, are not usually allowed to practice selective feeding. Normal feeding regimes entail the captive raptor eating all of the offered food items, with less food being subsequently offered if parts of the food items are left. Captive raptors are expected to "clear up" at every meal... leaving no opportunity for selective feeding. Unless the food items fed to captive raptors are accurately balanced with the correct amounts of essential raptor nutrients then nutritional deficiencies will occur.

A captive raptor will eat food to excess to obtain adequate amounts of specific nutrients that are contained within its food in less than the raptor's required amounts. By doing this, the raptor can obtain more of the limiting nutrient but has to convert the excess food that it has ingested into body fat. Eventually, body fat becomes excessive and the selective feeding for specific nutrients becomes inhibited as a general inhibition of food intake increases.

A captive raptor being fed an optimum supplemented diet that includes the opportunity to practice selected feeding is able to regulate its body fat deposition to regulate its body weight to an efficient ideal. Fat, captive raptors are not in an efficient (or healthy) body state... why should they carry lots of excess fat around when there is no need. Significant energy reserves are of little use to captive raptors.

Generally speaking, well-adjusted captive raptors that become obese if fed ad lib are probably eating extra to obtain sufficient quantities of the limiting nutrients in their diet. Captive raptors that are fed optimum supplemented diets will normally regulate their body fat in line with their muscle mass and daily energy expenditure, with inactive raptors in pens normally being at lesser weights than active, captive falconry raptors and their wild, free-living counterparts.