Only bird which can fly backward?

The Hummingbird has a unique muscle and wing structure that gives them a level of flight control that other birds envy (or at least we do). You can think of a hummingbird as a miniature helicopter. Like a helicopter, the hummingbird can hover, fly right to left, left to right, diagonal, forwards, even backwards. The hummingbird has the ability to rotate its wings in circles making a figure eight. Based on the configuration of the figure eight, the hummingbird can change directions at will. With great speed and grace, hummingbird fly backwards. With great speed and grace, hummingbird can fly backwards with a speed of up to 30 mph! One can ever their quickness that their wings move so quickly that they are just a blur. This effect is a result of their wings flapping between 15 to 100 times per second to maintain the kind of agility to allow them to fly backwards.

Why do woodpeckers peck the trees?

A woodpecker is a bird which gets its name as it pecks the wood of trees, looking for insects to eat. The woodpecker is a great help to the trees because quite often, the insects and worms are harmful for the trees. These grubs and insects remain hidden deep in the crevices of the bark of trees. The woodpecker can find them instinctively  even when they cannot be seen outside. Then he drills a deep hole and straight gets down to them. Sometimes woodpeckers make two openings, like a front and back door. The woodpecker has a chisel like beak which can drill holes into dead or unhealthy trees. The structure of the head and neck of a woodpecker is adapted for driving its beak powerfully forward into the tree bark and absorbing the shock of the blow. It then uses its long tongue to capture and eat worms and insects. They can bore holes in the trees. Most woodpeckers next in large holes that they dig in the branches or tree trunks.