Raptors Introduction

The term raptor refers to birds of prey, including eagles, hawks, buzzards, falcons & vultures. Less commonly, the term also includes owls. Sometimes "diurnal raptor" is used to distinguish eagles, hawks, etc. (which predominantly hunt during the daytime) and "nocturnal raptor" is used for owls (which predominantly hunt during the night). (It should be noted that both diurnal & nocturnal raptors may hunt at any time of day or night, depending on species & conditions). The word comes from the Latin word "rapere", meaning to seize & carry off, from which came "raptor" meaning plunderer, robber or ravisher.

One recent comprehensive book (Ferguson-Lees & Christie) recognises 313 separate species of diurnal raptor.

(In the following descriptions, I have loosely split the raptors into 4 categories. The first three categories are Owls, Vultures, Falcons. All other raptors [eagles, buzzards, true hawks, kites, etc] I have grouped together as hawks, this is purely for brevity in the text.)

With the exception of the vultures (which have evolved into scavengers) all of the raptors have adapted to using their feet to catch & kill their prey. Falcons tend to kill with the aid of speed, often by dropping from a great height (stooping) & striking the prey with their feet, either killing the prey outright, or, if not killed, the prey is dispatched by a twist of the beak to the spine. Many falcons have an elongated middle toe, which they wrap around the prey whilst still in flight. Hawks & owls tend to capture their prey in the feet, often on the ground, & kill the prey by crushing. Hawks feet have a ratchet-like mechanism to aid capturing & keeping their prey without too much exertion, allowing them to concentrate on any other possible predators. The hawk clenches her muscles, tightening the toes around the prey (gripping it with the talons), when the muscles are released, the toes & talons remain locked in place. Further clenching of the muscles tightens the grip on the prey (finally crushing it to death). The foot remains locked in this position, keeping a good hold on the prey, until the bird has fed itself, it is only then the muscles are released. occasionally, this can cause problems if the feet become locked on struggling prey & another predator decides to attack. There have also been sightings of sparrowhawks & marsh harriers drowning their prey.

Raptors are completely carnivorous and/or insectiverous (well nearly, the Burrowing Owl will eat fruit & seeds & the Palm Nut Vulture or Vulturine Fish Eagle (Gypohierax angolensis) is virtually vegetarian), obtaining all of their required nutrients from their prey. The nutrients which normally come from vegetable matter are often found in the stomachs of their prey. A lot of the water required for survival will also be extracted from the prey. Raptors will devour the prey entirely, regurgitating (casting) the indigestible matter in pellet form, once or twice a day. Raptors play an important part in population control in nature, preying on the weakest members of the prey population. This weeds out the sick, infirm, starving & often, genetically unsuitable members & thus helps keep a viable, healthy prey population.

All of the raptors have hook-tipped beaks, which are used for ripping the dead prey. Falcons have a notch on each side of the upper beak, forming a tooth-like projection (known as the nook) which, it is believed, aids breaking the spinal cord of the prey by biting. Lacking the nook of falcons, some hawks have a more pronounced hooked tip to the beak, probably for a similar reason. Vultures have developed a much larger, stronger beak well suited for tearing the hides of dead animals & cracking their bones.

Other features that raptors have in common are :

Sight :

All raptors are able to see in much more detail than people, enabling them to see small objects (ie their prey) from a greater distance than a person could. The central region of the retina, called the fovea, is adapted to seeing detail, the sensors involved in seeing in detail are called cones. Inside the fovea of hawks (including falcons), the cones are packed between 4 to 8 times more densely than in humans, which gives them up to 8 times the resolution of detail compared to a human. In addition to high density of cones, they have two fovea, compared to the human's single fovea. One of these is dedicated to forward vision (as in people), the other is dedicated to lateral (i.e. sideways) vision. The area of vision of the forward facing fovea overlap & working in conjunction, these improve the birds visual resolution even further. The fovea form a small pit within the retina & act like a telephoto lens. Outside of the fovea, the region which is more sensitive to movement, the cones are packed at least twice as densely as humans. In practical terms, this means they can see much smaller things from much further away, and detect movement far more easily. Owls are similarly advantaged, though, because of the positioning of the eyes, they only need a single fovea. In addition, they are adapted to vision in low light conditions (contrary to popular myth, they cannot see in total darkness).

Smell :

Apart from the Turkey Vultures, birds of prey are generally accepted as having a minimum sense of smell, if any at all. There have been tests done, with birds offered good meat & rotting meat, where the rotting meat is refused, but there is no firm evidence that this is due to smell. Turkey Vultures feed solely on carrion & they have a highly developed sense of smell, able to detect sources of food from several miles away.

Size :

With the exception of vultures & Secretarybirds, almost all raptors exhibit reversal sexual size dimorphism - females being bigger than males. In some vultures, both sexes can be similar in size, or even the male slightly larger than the female. In falconry, the term for a male bird is tiercel, an old french term roughly translated as 1/3rd smaller. One possible reason for size difference is that the females need to be larger to defend the nest, whilst incubating & fledging the young. Another is that it gives an advantage in diversifying food that can be feed to the young, males being smaller & more agile are able to catch faster moving prey, while females can catch larger prey. It also means that while not breeding, sexes are not directly competing for food source.

The sex of raptors is often determined by size, females significantly larger than males. With some females (especially owls) laying very late on in life, a small female can be mistaken for a male for a long while. It is definitely a female if it lays eggs, it might be male if not. Until recently, the main alternative was surgical, which involved some risk to the bird. A new technique involving similar techniques to DNA profiling is currently becoming more available, requiring a feather or very small blood sample, involving no risk to the bird.

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