Nutrition in Raptors

Raptors include birds of prey from many genera. Most medium to large raptors consume whole vertebrate prey. Commonly fed items include mice, rats, day-old chicks, quail, and pigeons, depending on the raptor species. Smaller species prefer day-old chicks, for example, whereas adults of larger species generally prefer rats and pigeons. Captive-bred prey should be fed to help prevent spread of disease. Kestrels generally consume insects. Fish are the natural diet of piscivorous raptors, such as ospreys and sea eagles.If raptors are fed fish as their predominant diet, daily thiamine supplementation (30–35 mg/kg feed), as well as daily vitamin E (100 mg/kg), is commonly advised (1).

Commercial diets for birds of prey are available and consist mostly of a mash of several different prey items with a specific amount of vitamins and minerals.

Small raptors (100–200 g) eat as much as 20–25% of their body weight per day; raptors weighing 200–800 g eat 15%, raptors weighing 800–7,000 g eat 6–10%, and raptors > 7,000 g eat 3.5% of their body weight per day. Captive raptors should be weighed regularly, and food volume adjusted as needed to prevent both emaciation and obesity. If weighing is not possible, the breast-comb (keel bone) can be checked: if it feels sharp, the animal is emaciated; if it is covered in palpable fat, the bird is obese.

The best foods for birds of prey are mature mice and rats, because they contain a more complete nutrient profile than many other prey items; however, day-old chicks and other whole birds or mammal species also are adequate. Although breeders regularly remove the egg yolk sac before feeding because it can cause hygienic problems when it breaks, the egg yolk of day-old chicks should not be removed when fed. The yolk contains a substantial amount of vitamins and minerals; through yolk extrusion, vitamins A and E are lost, calcium:phosphorus ratio becomes unbalanced, and protein levels and energy content are seriously depleted. Feeding animals from the wild (eg, rats, pigeons, rabbits) is not advised, because these animals carry potential diseases, toxins, and poisons. Food items should not be thawed in warm water or they may grow undesirable bacteria; instead, food items should be thawed slowly in a refrigerator. Just before feeding, thawed foods should be taken out of the refrigerator and allowed to come to environmental temperature.

Although whole prey, including organs, should be a complete, nutrient-sufficient feed, adding a small amount of a balanced vitamin and mineral supplement is advised, especially when birds are under stress. Prey with relatively large bones must be avoided because of the potential to cause obstruction in the gizzard, which prevents casting (regurgitation of the undigestible parts of prey). Birds < 12 days old should not be fed too many bones, because they cannot digest them and metabolic bone diseases can result. Metabolic bone diseases can also result when chicks grow too fast and their calcium needs are not met. Birds of prey should not be fed before traveling because doing so increases the chances for crop impaction and digestive upset.

If an organ meat–based diet is fed to raptors, vitamins and minerals should be supplemented; calcium supplementation should be offered at 10 g of calcium carbonate/kg of fresh meat. In general, Harris's hawks, common buzzards, golden eagles, northern goshawks, red-tailed hawks, gyrfalcons, saker falcons, peregrine falcons, kestrels, bald eagles, and African fish eagles should be fed day-old chicks daily, as well as mouse, quail, or rats. African fish eagles and bald eagles also should be given fish. Some vultures (eg, griffon vultures) can consume approximately 40% of their body weight at once; however, feeding approximately 10% of their body weight twice a week is suggested. Owls should be fed day-old chicks, rats, or mice daily.