More than half of the birds are cavity-nesters.

A cavity is a sheltered chamber where cavity-nesting birds build a nest to lay eggs and raise their young ones.

The species of cavity-nesting bird is diverse ranging from woodpeckers to owls, parrots and sparrows. Tree cavities provide shelter to the birds and protect their young ones from predators.

There are two types of cavity nesters; primary cavity-nesting bird and secondary cavity-nesting bird.

Primary cavity nesters and those birds who create their own cavities. Only a few birds are competent at excavating their cavity nests like woodpecker, chickadee, barbet and nuthatches. Some birds drill out chambers and some dig burrows in the ground. This process requires intense labour and may take several days to weeks according to the nesting requirements of the bird. They are considered as ecological keystone species, as their presence in nature enables many other birds to use the interiors of trees as nesting space and roosting habitats.

Secondary cavity nesters are those birds that use pre-existing cavities made by primary excavators. The natural cavities formed during the tree decay are also used by some species.

  Majority of the birds are secondary cavity nesters like owls, sparrows, ducks, wrens and  parrots.These birds usually have beaks specialized for gathering seeds or hunting insects, they use pre-existing cavities made by other birds like woodpeckers.

Earlier there were numerous trees where secondary cavity nesters found shelter but unfortunately this is not the case now.

Increase in population has led to afforestation, industrialists and urbanization. Man’s greed has turned the natural clean and green area into anthropogenic structures. Cities have become densely populated and at the same time they are expanding geographically at a high speed and as a result even the avifauna is threatened by anthropogenic factors.

Lack of trees means lack of nesting cavity and lack of nesting cavity means no lack of nesting space for the birds for both primary and secondary cavity nesters. Therefore, various ornithologists and environmentalists are creating awareness among people about the importance of birdhouses.

We ourselves are the culprit. Now it is our duty to atone for the heinous crime we have committed by providing our feathered friends a safe and secure shelter that they can call home.