What Makes a Bird a Raptor?
All Raptors have a hooked beak, excellent eyesight, sharp talons, and strong legs and feet. Check out what makes a bird a Raptor and other nesting habits of Raptors!
A raptor's beak is one feature used to set them apart from other birds (see Curvy Beaks Activity Sheet). All raptors have the same beak design, curved at the tip with sharp cutting edges to tear apart prey that will easily fit into the mouth.
The beaks have evolved over time based on the type of prey eaten. For example, the American kestrel has a small beak for eating small prey, like mice and insects. Eagles have powerful, heavy beaks for tearing large pieces of meat, but snail kites have a highly specialized long, curved beak for probing inside snail shells.
Sharp Talons / Legs and Feet
Birds of prey have powerful leg and toe muscles that, when combined with their sharp talons, make their feet lethal weapons (see Sharp Feet Activity Sheet), perfectly designed to catch, hold, and carry prey. The length and size of a raptor’s toes, and the curvature and thickness of its talons are related to the type of prey it pursues.
Most birds of prey will have three toes pointing forward and one pointing backward. These toes can apply an extremely powerful grip on their prey, literally crushing it to death. The talons may also be used to pierce a vulnerable spot, such as the back of the neck, to quickly kill the prey. Eagles and hawks kill their prey by dislocating the neck.
Ospreys have two toes facing forward and two facing backward. This allows them to hold the fish they catch with four claws, two on each side for a secure grip. Ospreys also have spiny scales on their feet that help them hold the slippery fish more securely.
Owls also have four toes. However, one of the toes is very flexible, and
can be rotated forward or backward for a two plus two or a three plus one
Raptors are believed to have the keenest eyesight in nature because of the size of the eyeball and the eye muscles designed for rapid focus. Diurnal raptors have full color vision and two concentrations of cones (one directed to the side and one directed forward) in each eye, which control color perception.
The sharpest point of vision at these concentrations is called the fovea. When the fovea works in unison, they give raptors accurate depth perception, which is very important for birds of prey that must focus quickly when chasing moving objects.
The keenness of vision is related to the agility, size, and color of prey a raptor hunts. When a bird bobs its head, it is using its eyes like a range finder and focusing in on a specific area.
Nocturnal raptors, the owls, have an added advantage over other raptors with their remarkable sharp night vision. Owls have a concentration of more rods in their eyes that are essential for seeing under low light conditions. An owl's eyes are also located in the front of their heads, much like humans. By contrast, the night vision of diurnal raptors is no better than a human’s vision at night. Another thing that sets raptors apart from other birds is a special eyelid or nictitating membrane.
This special transparent eyelid closes laterally across the eye and is used to
- keep the eyes moist
- protect the eyes during flight
- protect the eyes when feeding themselves or their young
When humans close their eyes to blink and sleep the upper eyelid closes. Depending on the species, raptors have eyelids that close from either the bottom or top, for blinking and sleeping. WOW!
An additional form of eye protection in most raptors is a bony shield that
projects above the eye. The bony shield adds protection when raptors pursue
prey into brush, protects the eyes from injury while hunting, and also gives
raptors a menacing appearance.
Raptor Nesting Habits
A female raptor is often larger than the male. The reason for this size difference is really unknown, but scientists think that it is because the female lays the eggs and spends a lot of time incubating and protecting the nest.
Nesting habitats of raptors vary. A few examples of what raptors may do to help rear their young include:
- not building a nest, but using cavities and stick nests created by other birds (vultures, owls, and other raptors)
- nesting and laying eggs in sand or gravel, depressions, or scrapes
- nesting and laying eggs on the ground
- nesting and laying eggs on cliff faces or in treetops (eagles do this and are known to build very large nests)
- nesting and laying eggs in ground burrows of mammals (only burrowing owls do this)
For those raptor species that build nests, typically the female constructs while the male provides the material. Many raptors build a new nest each year, while others, particularly large raptors, reuse old nests or alternate between a number of nests.
Raptor eggs are typically large, rounded or oblong ovals, and vary in color. The number of eggs laid depends on their size. Large raptors lay fewer eggs than smaller raptors. It is believed that larger raptors live longer and need fewer eggs or young to sustain the viability of the species, while the opposite is true for smaller raptors.
Raptors have a two to three day lapse between laying each egg, and generally begin incubation after all of the eggs are laid for that nesting season (owls begin incubation immediately after the first egg is laid).
The female does the incubating while the male provides food. The period of incubation also varies with the size of a bird. For owls, hawks, and falcons there is usually a 26 to 35 day incubation period, while for eagles and vultures it is 36 to 50 days.
Raptors of temperate climates breed in spring and summer when warmer weather ensures rapid growth and survival of young. Other natural resources also aid in the success of a nesting season:
- growing plants that provide cover, nest sites, and nest material
- longer days that allow parents to gather more food
- the abundance of young prey species available during this time of year
After an eggshell is first cracked, it usually takes one to two days before hatching is complete. Raptor chicks grow quickly, doubling their birth weight in only a few days. The length of time a raptor spends from hatching until it is ready to fledge depends on size. Larger raptors stay in the nest from two to three months, while smaller raptors stay until they are three to four weeks old.
In temperate areas, like Idaho, raptors must grow rapidly in order to be
ready to migrate when the seasons change and become too warm.
Many thanks to the Bureau of Land Management for their partnership and assistance with the Birds of Prey information!
All of the information, activities, figures, and diagrams gathered for this site were compiled from the following:
U.S. Department of Interior, Bureau of Land Management, Lower Snake River District. 1998. Raptors In a Box Teacher Instruction Notebook. Boise, ID.
U.S. Department of Interior, Bureau of Land Management, Lower Snake River District. 1998. Raptors In a Box Traveling Trunk. Boise, ID.
Photographic Images were provided by the Bureau of Land Management and other individuals as indicated.