It was a mindless act of violence and cruelty.

A fluffy little white-fronted tern chick in a specially constructed nest on an old abutment on the Hairini Bridge in Tauranga has been killed by a rock deliberately thrown from the bridge.

The nesting terns offer a fascinating up close and personal insight into life in the bird colony, but unfortunately, is also perilously close to people passing over the bridge.

Nigel McFadyen, who regularly cycles over the bridge, had been observing the grey chick every day.

'I have watched it grow.” But now the bird has been senselessly killed. 'I am really gutted that someone would do that. It is a low thing to do. A very low thing to do.”

When SunLive dropped by on Thursday, the stone and the bird carcass were still in the nest.

It's not the first time the tern colony has come under attack from both nature and people.

Fourteen months ago, three terns sitting on eggs on the bridge were killed in another attack. The mates kept visiting the nests and sitting with the dead birds.

It raised expert concerns about the future of the birds on the bridge. Entire colonies can be abandoned after such disturbances.

Then two years ago the old wooden framing on the bridge moved in a storm. The nesting habitat was specially reconstructed for the birds and the terns returned to breed. It was considered a remarkable success.

Because of their accessibility, the terns are visited by photographers from all over the country.