Structure and Function in Raptors




  • Integumentary system
    • Feathers
    • Beak
    • Talons
  • Musculoskeletal system
    • Respiratory system
    • Lungs
    • Air sacs
    • Inspiration
    • Expiration
  • Digestive system
    • Gastrointestinal tract
    • Liver
    • Pancreas
    • Cast and casting
  • Female reproductive system
    • Ovary
    • Oviduct
  • Male reproductive system
    • Testes
    • Ductus deferens
  • Urinary system
    • Kidneys
    • Ureters
    • Cloaca
  • Circulatory system
  • Brain and intelligence
  • Sensory system
    • Hearing
    • Vision


The knowledge of structure and function is essential for understanding raptors in health and diseases.

Integumentary system

Feathers are epidermal growths that form the distinctive outer covering, commonly called plumage, on birds. They are considered the most complex integumentary structures found in vertebrates and a primary example of a complex evolutionary novelty. There are two basic types of feather: vaned feathers which cover the exterior of the body, and down feathers which are underneath the vaned feathers. Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings and tail of a birds. Those on the wings are called remiges, while those on the tail are called rectrices. The primary function of the flight feathers is to aid in the generation of both thrust and lift, thereby enabling flight.

The beak of birds of prey includes the bones of the upper and lower jaws and their horny sheaths. The upper and lower horny sheaths are called the maxillary rhamphotheca or rhinotheca and the mandibular rhamphotheca or gnathotheca. Talons are the sharp, hooked claws at the end of the toe in birds of prey. Talons differ in shape and size depending on how the bird will use its talons.

Musculoskeletal system

The skeleton is a frame integrated by bones and joints supporting the body of a raptor. The skeleton of birds of prey is highly adapted for flight. It is extremely lightweight but, strong enough to withstand the stress of taking off, flying and landing. One key adaptation, in common with most bird species, is the fusing of certain bones into single ossified structures, including the notarium, the synsacrum and the pygostyle. Because of this, birds usually have a smaller number of bones than other terrestrial vertebrates.

Most birds have approximately 175 different muscles, mainly controlling the wings, skin and legs. The largest muscles in the bird are the pectorals, or the breast muscles, which control the wings and make up about 15 – 25% of the total body weight.

Respiratory system

Three distinct sets of organs perform respiration in birds in general, the anterior air sacs (cervicals, interclavicular, and anterior thoracics), the lungs and the posterior air sacs (posterior thoracics and abdominals. Typically, in most avian species, there are nine air sacs within the system.

Gastrointestinal system

The digestive system of raptors includes the cervical esophagus, crop (absent in Strigiformes), thoracic esophagus, proventriculus, ventriculus, pancreas, small intestine, large intestine, cloaca and vent. The proventriculus or true stomach is the glandular stomach where digestion primarily begins, while the ventriculus is the muscular stomach. This is not well developed in birds of prey. The liver is an accessory gland to the digestive system. A cast is the mass of undigested parts of food that some raptors throw up. The contents of a pellet depend on its diet, but can include bones, fur, feathers, bills, claws and teeth. In falconry terminology, the pellet is called a casting.

Female reproductive system

The female reproductive system consists of the ovary and the accompanying oviduct. While the female embryo in many species has two sets of reproductive organs, only one of these, the left survives and reaches maturity to produce eggs. The oviduct is integrated by five distinct anatomical structures including infundibulum, magnum, isthmus, uterus and vagina.

Male reproductive system

The male reproductive organs consist of two testes, each with a vas deferens or deferent duct that leads from the testes to the cloaca. The deferent duct transports the sperm from the testes, where they are formed, to the cloaca from which they enter the oviduct of the female when mating through the cloacal kiss.

Urinary system

Birds have paired kidneys, sub-divided into three lobes, connected to the lower gastrointestinal tract through the ureters. Unique to birds is the presence of two different types of nephrons both reptilian-like nephrons located in the cortex and mammalian-like nephrons located in the medulla. The urine collected by the kidney is emptied into the cloaca through the ureters and then to the colon by reverse peristalsis.

Cardiovascular system

Birds have a four-chambered heart, in common with mammals, and some reptiles (mainly the crocodilia). This adaptation allows for an efficient nutrient and oxygen transport throughout the body, providing birds with energy to fly and maintain high levels of activity.

Brain, intelligence

Birds in general use the medio-rostral neostriatum/hyperstriatum ventral, as the seat of their intelligence, and the brain-to-body size ratio of psittacines and corvids is actually comparable to that of higher primates.

Special senses

Hearing is the second most important sense and their ears are funnel shaped to focus sound. The ears are located slightly behind and below the eyes, and they are covered with soft feathers, the auriculars, for protection. The shape of a bird’s head can also affect its hearing, such as owls, whose facial discs help direct sound toward their ears. The confusingly named “ear tufts” of many owls and other birds of prey, however, have nothing to do with hearing.

Birds of prey have a very high density of receptors and other adaptations that maximize visual acuity. The placement of their eyes gives them good binocular vision enabling accurate judgement of distances. Nocturnal species have tubular eyes, low numbers of color detectors, but a high density of rod cells which function well in poor light.


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About the presenter

Jaime Samour has dedicated most of his professional life to falcon medicine. He graduated with Honors from the Faculty of Veterinary Medicine, Veracruz University, Veracruz, Mexico in 1978. In 1981, Jaime traveled to London to study and conduct research projects in reptile and avian medicine at the Institute of Zoology, Zoological Society of London. Immediately after earning a doctorate in Reproductive Biology from the Royal College of Veterinary Medicine in 1987, Jaime moved to the Middle East where he has worked ever since. His professional experiences include (but are not limited to) serving as the Director of Wildlife at the Wildlife Division of Wrsan in the United Arab Emirates (UAE) (2006-2020), Medical Director at the Falcon Specialist Hospital and Research Institute in Saudi Arabia (1998-2006), Head of the Veterinary Science Department at the National Avian Research Centre in the UAE (1993-1998), and the Senior Veterinary Officer at the Wildlife Park and Reserve in Bahrain (1987-1993)… [Learn More]


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Expert Q+A

Although Dr. Samour answered most questions during the live event, the remaining questions were answered by email and are posted below:



What is the normal digestion time of falcons when feeding a quail diet? 

The normal overall transit time in falcons used for falconry ranges from 90 minutes (if unhooded) to 180 minutes (if hooded).



In severe propatagium injuries, especially cases lost most of their propatagium, is there any chance for reconstruction of these patagium?

Reconstruction of the propatagial membrane would depend entirely of the nature and extent of the injury. Suturing and the use of hydrocolloidal dressings, mānuka honey dressings or the use of thrombocytes leucocytes rich plasma in liquid or, preferable, in gel format could all help.


The remaining questions posed to Dr. Samour were not directly related to anatomy or physiology

Have you had good outcome using alternative analgesic drugs for chronic pain clinical cases? 

I do not have experience using ketamine hydrochloride for pain management… I have used extensively ketoprofen in falcon medicine for many years. Ketoprofen is an NSAID anti-inflammatory agent widely used at the dose rate of 1 mg/kg SID. This should not be used in vultures.


…I [have] read/learned that bumble-foot in raptors was more frequently seen in falcons? Is there any specific reason for falcons to be more prone to this condition? Or to your knowledge that’s not been documented.

Bumblefoot is produced by several factors including lack, reduced or sudden cessation of exercising, the use of inadequate perching surfaces and nutritional deficiencies. Penetrating wounds may also cause bumblefoot but this is rare. Bumblefoot is the result of progressive avascular necrosis of the plantar skin and underlying structures.


Editor’s note:  The question below is a follow-up to Dr. Samour’s discussion of drug resistance.

What about anti-worm treatment in wild birds (raptors)? In general to treat on only when it shows clinical symptoms?  

Many birds of prey carry a certain degree of helminths in the gastrointestinal and respiratory system without showing any clinical sign of disease. The presence of parasitic ova or oocysts in the examination of a faecal sample does not necessarily translate into “parasitic infestation”. Having said this, the pathogenicity of protozoan parasites such as Caryospora spp., could be exacerbated under captive conditions producing severe gastrointestinal disorders leading to serious disease and even death.


What is your opinion on wing tip wing edema?

This is a syndrome almost exclusively to birds of prey caused by circulatory disorders related to trauma or, more likely in northern countries, to cold weather.


RACE approval

This program is approved for 1 hour of continuing credit for veterinarians and veterinary technicians in jurisdictions which recognize American Association of Veterinary State Boards (AAVSB) Registry of Approved Continuing Education (R.A.C.E.) approval.

To cite this page:

Samour J. Structure and function in raptors. Apr 26, 2021. LafeberVet website. Available at