In seeking to arrange the birds of the world into Common Name Groups the well known term “Birds of Prey” gives me some problems. Most people accept the term quite readily. They know which birds they would include (Falcons, Hawks, Eagles, Vultures etc) and don’t see a problem. Others will agree but will also include the Owls. A few may go beyond this and wonder about the inclusion of some other birds like the Corvids and Shrikes.
The phrase "Birds of Prey" is so well known to "birders" that there is no point in trying to develop a different name, but I do want to know exactly what I mean when I use the term. The only word in the phrase which helps me in this task is “prey”. Prey is the victim of the predatory instinct of the bird concerned but what is it?
What is their prey?
“Birders” use a variety of other words when talking about birds of prey:-
• Birds of prey are Carnivorous which means that they eat flesh which can be meat or fish. So it’s fair to say that “prey” in this case takes the form of flesh.
• Birds of prey are often called Raptors - they seize their prey or take it by force. This perhaps implies that the prey can move to evade capture and this is indeed true in many cases.
• Sometimes however the prey is already dead and we call this Carrion which means dead, putrefying flesh.
So we are talking about birds whose preferred food is flesh, which can be meat or fish and which can be alive or dead.
Where might prey be found?
Most prey is found on land or in inland or coastal waters. Another important source is smaller birds, which are caught in flight. Quite a few of these smaller birds are caught in coastal areas by various Falcons which are cliff nesters.
Predation on seabirds at sea or in the oceans is limited and opportunistic rather than systematic. Gulls which follow fishing boats in the seas and oceans attract the attention of aggressive and piratical birds (Frigatebirds, Skuas, Jaegers and some Petrels) which try to take prey from other birds or from the water surface. In fact most prey is snatched from the water surface with a minor amount being obtained by piratical behaviour.
Opening up the carcass of a victim is much more difficult when it is floating in the water, so most predation activities take place on land where the prey can be held against a firm support.
If we explore the way in which birds of prey find, catch and butcher their prey we can get a few more clues about which birds should be included.
How do they find prey?
Birds of prey are masters of the aerial environment. Their superb flying ability coupled with exceptional eyesight enables them to find prey over a very wide area. Some birds have a well developed sense of smell and are able to detect carrion over large distances. The Owls have good night vision and acute hearing and this, coupled with feathers which enable them to fly almost silently, makes them excellent night hunters.
So effective use of all the senses is key to finding food.
How do they catch and butcher prey?
Most birds of prey have strong legs and feet with talons which they use to capture their prey. Prey can be quite large, heavy animals which are taken back to the nest to eat.
Prey can be fish as well as meat. Some birds of prey, like Osprey and Fish Eagles, are adept at snatching fish from close to the surface of shallow water using their talons. Although one name for the Osprey is Sea Hawk these birds do not swim and are mainly found around inland waters.
Having caught their prey the birds use their strong, often hooked beaks to tear their prey apart in order to eat it. The prey needs to be held or pinned down on a firm surface while this takes place.
So talons and hooked beaks are key features.
There are surprises and exceptions.
Inevitably when we are talking about birds, there are exceptions to the points made in the above discussion. We tend to think of birds of prey as masters of the air using their senses to find potential prey on the ground below but some flesh eaters do it differently – so are they “birds of prey”?
The Secretary Bird can fly well but is nearly always seen on the ground where snakes are its main prey. They don't have hooked beaks or talons but they do have powerful feet which they use to kill their prey.
The Condor is a very powerful bird but its legs are quite weak so it can only carry small prey. Birds which can’t carry large prey and those which find prey using their sense of smell, eat carrion in situe.
The Palm-nut Vulture does not hunt live prey but it will take carrion which is usually dead fish.
The Marabou Stork is a large scavenger which feeds on animal carcases sometimes in competition with Vultures. It will also take live prey including small birds.
Frigatebirds (right) use their long, hooked beaks rather than talons to snatch prey from the ocean surface. They are piratical and rob other birds of their catch, using their speed and manoeuvrability to harass their victims. Their feet have only partial webbing between the toes and they don't swim. Part of each toe is free and presumably helps in the catching of prey. Because they spend much of their time on the wing they eat and swallow their prey in flight.
Skuas, Jaegers and some Petrels exhibit similar piratical behaviour.
Crows are omnivorous, and their diet is very diverse. They will eat almost anything, including other birds, fruits, nuts, molluscs, earthworms, seeds, frogs, eggs, nestlings, mice and carrion. They have very strong feet, especially the toes and claws. Large food items are held by the foot and torn with the beak. The Carrion Crow, at least in name, cries out to be included but I regard these birds as omnivorous, scavengers not hunters.
Gulls are highly adaptable, opportunistic omnivores. No gull species is a single-prey specialist. The food taken includes fish, both alive and dead, terrestrial arthropods and invertebrates such as insects and earthworms, rodents, eggs, carrion, offal, reptiles, amphibians, plant items such as seeds and fruit, and even other birds. I call them scavengers.
The Currawongs and Butcherbirds of Australasia have a hooked tip to their beaks and prey on small animals. The Pied Currawong (left) certainly looks the part. They don’t have talons and have difficulty in holding captured prey with their feet but they have learned wedge it in a tree fork or impale it on a thorn.
Shrikes and similar birds are well known for treating their prey in this way. I see no reason for applying any particular size limitation to a definition of which birds should be regarded as birds of prey. These hooked beak birds prey on frogs, lizards, rodents and other birds as large as them selves.
The Double-crested Cormorant (right) which has just caught a sand shark, looks quite aggressive and has a large hooked beak but I don't hear any "birders" saying that it is a bird of prey. The main difference here is that the Cormorants catch fish by diving and swimming. I list them with the Aquatic Birds.
Herons with their sharp "dagger" beaks, patiently and deliberately hunt and kill fish and are therefore flesh eating carnivores. Their hunting and feeding technique is totally different to that of the birds of prey so I treat them separately.
Penguins, Gannets and other Aquatic Birds are carnivorous, hunting their prey, mainly fish, by diving and swimming but don’t have sufficient characteristics for me to call them birds of prey. Again I treat them separately.
Birds of prey are primarily, almost exclusively, flesh (meat or fish) eaters. Prey can be alive or dead.
In addition to the obvious attributes like flying ability, the almost silent flight of the Owls, excellent eyesight, hearing and sense of smell, various observable characteristics justify inclusion in the following three groups:-
- Flesh eaters. Prey can be meat or fish, alive or dead.
- Birds which take fish from water surface but are not swimmers.
- Aggressive behaviour to other birds, some are positively piratical.
- Feet and talons play a major part in catching prey.
- Birds which don’t have strong legs and talons eat dead flesh (carrion).
- Strong, hooked beaks enable butchering of prey - note this needs a firm surface and is difficult on water.
Examples - New World and Old World Vultures, Condors, Caracaras, Falcons, Kestrels, Hobby, Merlin, Buzzards, Kites, Hawks, Harriers, Eagles etc. Osprey, Fish Eagles. Secretarybird.
- Flesh eaters - usually live meat.
- Good hearing, silent flight.
- Feet and talons play a major part in catching prey.
- Strong, hooked beaks enable butchering of prey - note this needs a firm surface.
Examples - Owls.
Opportunistic Small Hunters.
- Flesh eaters - usually live meat.
- Feet and claws play a major part in catching prey.
- Small birds of prey utilise thorns and spikes to hold dead prey.
Examples - Currawongs, Butcherbirds, Shrikes and similar birds.
Piratical Flesh Eaters.
- Flesh eaters, usually fish.
- Hooked beak used to snatch fish from water surface.
- Aggressive, piratical behaviour to other birds.
- Usually eat prey in flight.
Examples - Frigatebirds, Skuas, Jaegers and some Petrels.
Note - The important difference between Osprey / Fish Eagles and Frigatebirds / Skuas / Jaegers etc is that the Osprey / Fish Eagles take their prey back to the nest where they have a reasonably firm surface on which to butcher their prey. The Frigatebirds etc are at sea for much of their time so they don't have access to a firm surface to butcher their prey and they have to eat and swallow it on the wing. So the hooked beak only has to snatch the prey from the water surface - it does not need to do any tearing or butchering. These birds are piratical flesh eaters but are not considered to be birds of prey.
OTHER FLESH EATERS - omnivorous scavengers which I don't include as Birds Of Prey.
- Crows and other Corvids.
- Cormorants, Herons and other carnivorous fish eaters.