Raptor Biology

When one typically thinks of birds of prey, a few key characteristics instantly jump to the front of your mind. Keen eyesight, razor sharp talons, curved beak, and a general predation on smaller animals. While every single species of raptor share these things in common, what makes them so incredible is the differences between them.

Originally, the majority of your birds of prey fell into two main categories: Falconiforms and Strigiforms. Not too long ago, a new classification was added (Accipitriformes) breaking up the original order of Falconiform. For simplicity sake, we will lump them up into Diurnal raptors and Nocturnal raptors.

Diurnal Raptors

In our state, you can find 12 different species of diurnal raptor. They are easily categorized into four basic groups: Buteo, accipiter, falcon, and eagle. Buteos are classified as having large, broad wings that are meant for gliding and soaring. The Red-tail is an excellent example of this, often seen soaring in circles over fields. Accipiters on the other hand have shorter, rounded wings with a much longer, rudder-like tail. They are designed to hunt in dense forest, around brush and trees while at high speeds. Falcons are the aerial predators of the sky with their longer, pointed wings. Falcons also have small notches on either side of their beaks called a tomial tooth that is used for breaking bones. Eagles are easily the largest of the raptors in our state with a wingspan up to 6 feet and weighing as much as 10lbs.

ButeosAccipitersNative FalconsMigratory FalconsNative EaglesMigratory Eagles
Broad-wingSharp-shinnedAmerican KestrelGyrBaldGolden
Rough LeggedCoopersMerlin
Red-tailGoshawkPeregrine
Swainsons
Red Shoulder

Nocturnal Raptors

While not typically used in falconry, owls are still utilized by some individuals and boast their own merits. Pennsylvania has 6 different species of owls that reside here all year round, and 2 species that migrate down from the North. These birds are specially designed to use the cover of darkness to their advantage. Their large wingspan allow them to effortlessly glide through the woods while highly specialized feathers absorb sound. Despite not being the fastest birds out there, these adaptations allow them to silently ambush their prey. They have large eyes that collect as much light from the surrounding areas, making it possible for them to see at night. While the vast majority of owls are known to hunt at night time, it should be pointed out that not all are strictly nocturnal.

NativeMigratory
Saw-whetShort-eared
Eastern ScreechSnowy
Long-eared
Barn
Barred
Great Horned

Head and Eyes

One of the first things someone notices on any bird of prey is their eyes. If you have great vision, you can often be referred to as having “Eyes like a hawk.” However, it is no joke when you look into their eyes. Having proportionately larger eyes inside of their head, along with specially designed internals, allows most birds to see an average of 6x-7x greater than what we can now. A second Fovea (fine focus) in each eye means a greater area of clarity with the added benefit of spotting movement faster. This, in conjunction with being able to process images twice as fast as a human, allows these birds to fly perfectly in any situation. Some species of raptor, such as the Kestrel, are able to see a fourth color spectrum. This ultra-violet detection allows them to track Meadow voles via urine trails. The drawback to having such incredible vision and large eyes is a decreased space for other features. Due to this lack of space and a small boney ring, birds are not able to move their eyes inside of their heads. To compensate for this, they have developed more bones in their neck (sometimes twice as many as humans) to allow for a greater range of motion. Most diurnal raptors are capable of ~1/2 rotation while owls are able to do ~3/4 rotation. Birds also have a gyroscopic head which eliminates all head movement while either perched or in flight.

Wings and Feathers

Any bird’s wings are extremely necessary for their flight but it is what covers them that makes the whole process work. Those feathers that are responsible for flight are called primary feathers or primaries. They are the outer most feathers on the wing and do the majority of the lifting. Next down the wing are the secondaries. Shaping the wings are the covert feathers and finally the alula to redirect air over the top of the wing. Feathers on the various species of raptors are designed differently depending on the bird. Falcon feathers are much more stiff and rigid compared to your hawks. An owls feathers are going to be very soft to absorb the noise generated from flight. For the majority of birds of prey, there will be a noticeable difference in both feather color and length between adults and juveniles but not males versus females. After the birds first year, it will usually molt all of its old feathers starting in the spring and going through the summer into the early fall. After the second year, it may only molt out significant feathers or worn feathers as needed.

Feet and Talons

The number one most important tools in the bird’s arsenal is its feet. Despite their size, they are capable of generating a massive amount of force with specialized locking tendons. An average human can squeeze with close to 110psi where as the Great Horned owl can generate over 500psi and a Golden eagle can produce 2,500psi. Once locked in, those tendons hold that foot shut, requiring little effort to maintain that grip. The size of those feet are determined by the usual prey of that species. The Coopers hawk hunts small birds, therefore have small, skinny toes compared to the much beefier mammal based Red-tail. Falcons also tend to have longer, skinnier toes compared to a hawk or eagle. It is often believed that this is to provide a greater surface area in which to hit their target safely. On owls, the outermost toe is able to rotate backwards and provide a two-toe-forward, two-toe-backwards approach when catching smaller prey.

Tail

Despite the fact that it is made up of feathers, the significance of any raptors tail should be specially noted. In the world of birds of prey, no other species tail is more notable than that of an accipiter. While the Red-tail can be a considerably larger species, the Goshawk’s tail is much longer in comparison. This longer tail acts as a third wing to generate more lift while going through holes in cover. More importantly, it serves as a rudder to allow the hawk to turn on a dime and swiftly catch its prey. Consisting of a total of 12 feathers with the two centermost feathers being referred to as the Deck Feathers. This is often the location of many falconers equipment such as transmitters and bells. Located at the base of the tail is a small gland called the Uropygial gland, or preen gland for short. This gland produces the oil that is used to cover all of their feathers with a water proof coating. While all species of raptors possess this gland, an owl’s does not function as efficiently and provides almost no protection.