Graphics Reference
In-Depth Information
Hummingbirds
The consequence of living on a diet of nectar means an almost constant
feeding pattern to meet the high energy demands of the hummingbird's
particular flying techniques. Hummingbirds have become such specialist
feeders that their location is limited to places where a ready supply of nectar
is constantly available. To access nectar, they have developed the ability to
hover using high-speed wing beats and beaks that are modified in both
length and shape to allow them to access nectar deep within flowers of
various kinds. Some have become such specialists that they are dependent on
a single species of flower. The beak of the sword-billed hummingbird
Ensifera
ensifera
is actually longer than the rest of its body, making it necessary to use
its legs to preen itself. Its beak is simply too long to reach the preen gland
while the bird is balancing on one leg.
Birds of Prey
The category of birds of prey covers a broad range of birds that are present
all over the world. Although they all depend on hunting live prey, they have
developed different diets that depend on availability. Some of them have
developed a highly specialized diet; others will take a far broader range of
prey animals—small mammals, other birds, fish, carrion. Many birds will take
live prey as part of a diet but fall outside the classification of raptor. Carrion
crows, as their name suggests, enjoy the delights of eating previously killed
animals; however, other birds—the vulture family—have become more
specialist in this regard. The diet of a meat eater allows for long periods
between hunting.
Birds that have become specialist meat eaters have developed physical
features such as sharp beaks and talons to deal with it. Shrikes have neither
the talons to catch their prey nor curved beaks to tear them apart; instead
they use the large thorns on bushes to assist in dismembering the lizards on
which they feed. Vultures have developed featherless heads and necks as a
result of the way they shove their heads into the bloody carcasses of dead
animals.
The methods of finding and hunting down their prey also vary. In some
cases the modes of flight have become an important aspect of predators'
success. The hobby is capable of great speed, allowing it to catch very
fast birds such as swifts, swallows, and martins; sparrowhawks' speed
and agility allow them to hunt small passerines through rather dense
hedgerows and woodland. For many raptors eyesight is a critical factor.
Forward-facing eyes allow for binocular vision, enabling distances to be
judged better; the large eyes of owls allow more light to fall onto the
retina, enabling them to hunt in low-light conditions. Although owls don't
distinguish color well, they are very sensitive to shape and movement;
luckily color is not a critical factor for nighttime hunting. Daytime hunters
are able to distinguish color and to locate their prey at great distances.
