Birds have a natural advantage over their prey; their wings. This enables them to quietly observe their prey from above, form a plan of attack before surprising them and going in for the kill. This article touches upon the various forms of attack that birds choose to practice when stalking and catching their prey.
Ambush Strategy
The sparrowhawk (Accipiter nisus) feeds mainly on passerines weighing around 10 to 15 grams. These accipiters kill by ambush and their techniques are difficult to observe because of this fact and because kills often occur behind thick cover. The sparrowhawk utilises surprise and flying dexterity rather than speed alone, and chooses its prey with some care, flying low and fast. The more agile, aerial passerines such as the swallows are normally out of reach for the sparrowhawks, although male and female teamwork can enhance their range of prey. The prey is captured in the talons of the hawk which are held out whilst contact is made.
The sparrowhawk will generally ambush, by flying along a hedge or a line of trees before flicking over the top to surprise a foraging bird, often in the vulnerable open. It may also approach by flying low behind some form of cover, before dashing headlong into a flock of birds (usually sparrows). Such attacks will normally be planned from a distance rather than being opportunistic in nature. They can hear very well and will listen for the distress calls of other birds in the wood as well as the sounds of birds moving in the undergrowth.
There is very little time in which to focus on a victim during an ambush. An alarm call from one of the foraging birds will send all the small birds in the area scattering in many directions, they intend of course to confuse the sparrowhawk. The skill of the hawk therefore, lies in spotting and focusing on a prey animal without haste. If the alarm is issued it must then remain transfixed upon the prey whilst pursuing it through the wooded regions in which it hunts. Defensive flocking techniques can be successful in confusing the hawk. Scattering behaviour can leave the hawk undecided as to which bird was to be its intended prey. The longer the hunt goes on after such confusion the less chance the hawk has of catching its dinner. Starling flocks will also mob a hawk to confuse it still.
The northern goshawk (Accipiter gentilis) is larger than the sparrowhawk and like other accipiters exhibits similar hunting techniques, in areas that provide some form of cover (often found in forests and woodlands). They do however tend to have a more varied diet than the sparrowhawk and are faster, often out-flying a victim. The diet may include small mammals such as squirrels and rats as well as some large birds, like crows and wood pigeons. The brown goshawk (Accipiter fasciatus) fills the same ecological niche in the southern hemisphere, and is slightly smaller.
Hovers and Dives
The kestrel (Falco tinnunculus) is widely distributed in many rural areas. In Eurasia they have epitomised the ability to adapt to mankind’s intrusion. The European kestrel is often seen hovering by the roadsides. They hunt in such areas following the mice and vole populations that favour the deserted roadsides. The niche of the roadside is a widespread and very large one. In this situation the kestrel populations can soar as their prey are given more space to exist with every road built.
The long tail of the kestrel allows it to fly slowly whilst it scans the ground for prey. The wing tips quiver with great speed and its tail acts in three ways to aid the manoeuvre. The tail steadies the bird acting as a brake, and it also guides the bird, acting as a rudder against the oncoming wind, in this way added lift can also be achieved. The kestrel (and most hovering birds) can hover in such a way as to maintain the head in a fixed position whilst the tail wing and body move around to maintain the status quo in the face of changing breezes. The hover thus becomes an invisible perch from which to swoop. The kill normally follows a careful drop down in height to check the potential prey, before dropping down with haste to finalise the manoeuvre.
Low Level Attack
The Russian steppes are the home of the saker. This large raptor is another ‘hoverer’ but it additionally employs another hunting method. The saker will swoop at a height of only a few centimetres across the open grasslands of Russia. Occasionally a perch will be utilised to allow the prey to wander into the range before pouncing. This low level attack strategy occurs across the globe.
In Ethiopia the lanner employs the same technique, here the hunter is attempting to catch the rats at their burrow entrances. Golden eagles have been seen to utilise a similar strategy in hunting the American ground squirrel. These are very alert individuals, and so the intending hunter usually requires a planned attack to have any chance of success. In this case, the low level flying strategy has been observed. The golden eagle will sometimes spot a ground squirrel and then fly at low level for a long distance before attacking. Even in this situation the prey are often behind a bush or suchlike and are thus easier to catch because of such factors.
This article has been put together by the distance learning organisation Start Learning who are experts in home study.
If you want to find out more about Ornithology or many other distance learning courses please browse their website: http://www.start-learning.co.uk
Kerrana McAvoy
Academic Director – Start Learning
No comments:
Post a Comment