Predatory Bird Beaks: Featuring Tomial Teeth and Cranial Kinesis
Predatory Bird Adaptations for Dispatching Prey
When you hear the term "raptor", it sounds like something out of the movie Jurassic Park, but it's also another name for birds of prey. In Latin, rapere means to literally "seize or take by force", which is how they obtain their food. Birds of prey are apex predators and they eat other animals for their sustenance. Predatory birds include eagles, hawks, falcons, buzzards, harriers, kites, ospreys, true hawks, New World vultures (from North and South America), caracaras, secretary birds, and owls.
Raptors are adapted to catching, dispatching, and consuming their chosen foods. To be considered a bird of prey, they must have strong feet and curving talons for gripping prey, a curved beak for ripping apart their food and/or dispatching it, and strong eyesight (vultures are a special exception to most of these, but they are still categorized as a bird of prey due to genetic classification). Today I want to focus on the beaks of birds of prey; in particular, falcons, kites, and some accipiters (namely, sharp-shinned and Cooper's hawks). I also want to introduce you to some interesting avian terminology.
Raptor beaks, like all bird beaks, have an underlying boney support system for both the upper mandible (maxilla) and lower mandible (mandible), that is super light and hollow like their bones. These boney structures are covered in keratin, which is similar to your hair or nails. This keratin is "keratinized", or layered, to make it very hard. The keratinized layer of bird beaks is called the RHAMPHOTHECA (Ram-theka), which is thought to be a modified version of reptile scales. Many sea turtles that feed on vegetation also have rhamphothecia.
In the beak, there are both melanin and carotenoids which provide coloring. This is why some beaks are dark and some are light. Birds breathe through their NARES, or nasal openings, which are usually found on the top mandible. Falcons have a slightly tubular opening on their nares (see picture above), which is speculated to be to slow airflow into their nose and act as a foil when they are in a dive. Bird breathing is a very fascinating topic that I'll cover later because it's complex. It is very much like the circular breathing of didgeridoo players.
I'm not going to go into all the details about the boney structures and supports that attach the beak to the skull. You can read about that in more detailed ornithological texts (I particularly like Manual of Ornithology by Proctor and Lynch). However, I do want to focus on two key features of some raptor beaks that make them adapted for dispatching prey. The first adaptation is something called CRANIAL KINESIS. This is simply the movement between the upper jaw and the brain case through joints that are supported with tendons and muscles. Cranial kinesis is present in fish, reptiles, and birds of all kinds. It is not present in modern amphibians (though it was in ancient amphibians), crocodiles, turtles, and mammals. This means that reptiles, amphibians, and mammals don't hinge their jaws in the same way that birds do.
Most birds exhibit a form of cranial kinesis called PROKINESIS. This means that their upper beak hinges at the the base of the beak and at the naso-frontal hinge. The beak moves up and down from the brain case using a flexible set of ligaments. The advantages of this are that the birds can increase the angle at which their mouth opens, they can raise their upper jaw but keep their head and lower jaw still, and it provides a faster jaw closure on the hinge system. Parrots have the most extreme prokinesis because they have to use their beaks to crack very hard nuts.
Raptors use their prokinesis for a variety of functions ranging from ripping and tearing meat to dispatching prey. This leads me to the second feature of raptor beaks (found in falcons, kites, and accipiters) that I want to focus on. It is called the TOMIAL TOOTH (pl. mandibular tomia). The tomial edge of the upper mandible is the outer, or cutting, edge of the beak. The tomial tooth is the protrusion that extends from the tomial edge of the beak. It is thought to be used to deliver the killing blow to prey. The tomial tooth of the upper mandible is often matched by a mandibular notch, or divot, in the lower mandible. Look at the picture of the Cooper's hawk above to see these.
This tomial tooth system is important because not all raptors rely solely on their muscular feet and talons to dispatch their prey. Birds like falcons may grab their prey and then use the lever-powered beak to sever the spinal cord of the prey that they catch. They slide their beak over the neck of their prey and use the upper and lower mandible to sever the spinal column. This sounds cruel, but it's quite efficient and puts the prey out of discomfort very quickly.
I know this is technical jargon, but for naturalists, it's quite fascinating. The tomial tooth is found mostly in birds of prey that eat other birds or insects, and that needed to kill them quickly, perhaps, even in flight. Other birds of prey may show some slight tomial indentations but not to the extent that falcons, kites, and accipiters do. When teaching about raptors, this can be a fun talking point to engage students with raptor beaks and their associated adaptations.