Terns

Black-naped tern/ Sterna sumatrana / Family - Laridae

Terns are the most widespread group of seabirds, covering all the world's oceans and major inland lakes.

Their bodies are typically graceful, with long pointed wings, finely tapering bills, deeply forked tails and buoyant flight.

Some mariners refer to the members of this family as 'sea swallows.'

All terns are spectacular divers.

Habitat

Terns are one of the seabirds mostly commonly seen on the Great Barrier Reef.

They are often seen from ships, close to coastlines and harbours, frequently hovering over schools of small fish, plunging one after the other with a splash as they capture their pray.

The majority of terns are sedentary and favour warm or temperate waters. However, the Arctic tern migrates between the poles and has the longest migration route of any bird on Earth. It leaves its breeding grounds north of the Arctic Circle in late northern summer or early autumn and follows the sun to sub-antarctic latitudes for the southern summer.

Most terns nest on the ground on stretches of sand, but several species spend all their lives inland on rivers, lakes or marshes. Terns often nest very close together in simple bare hollows that may be lined with different plant materials found close to the nesting area. Others nest in trees or on rocky ledges.

Reproduction

Terns share incubation of the newborn for less than a full month. Both parents feed the chicks, with the major growth period being 4 to 5 weeks. A juvenile tern may fly at this stage, but take much longer to become fully independent. Terns will fiercely attack intruders during this time, human or animal. Their colonies are often very large and are sited in places least vulnerable to predators.

Tern colonies can be so immense and their crèches so packed with young birds that it would seem impossible for the parents to recognise their chicks - yet somehow they are able to find them by voice recognition.

Feeding

Most terns feed by diving on small fish at the surface, but some prefer not to submerge.

Some terns feed on the scraps of fish and offal discarded from commercial fishing vessels.

Threats

Great care should be taken when visiting known seabird breeding grounds. Walking or sitting carelessly can destroy eggs or chicks. Some birds are easily frightened and may abandon their eggs and chicks.

Apart from human disturbance, natural pressures such as storms and cyclones also affect seabird numbers. The effects of these natural events can be considerable, but can be tolerated because they are irregular. Unfortunately careless human activity is much more likely to delay or prevent a colony's recovery from natural disasters.

There are many ways we can protect birds and their habitats:

• During the breeding season, some islands of the Great Barrier Reef are closed to all visitors. For example, the Brook Islands are completely off limits during summer to protect the thousands of Pied Imperial Pigeons that migrate from Papua New Guinea to nest there.
• Special fire regimes are in place to manage vegetated islands and cays.
• Preservation of the mangrove forests is vital, not only for birds and other animals, but also to maintain the natural tidal flows and to offset the destructive effects of cyclones.
• Pollution control is necessary to protect the Reef from excessive sediment, rubbish and waste that affect critical mangrove, mudflat and inner reef habitats, and alter food supplies.
• Controlling feral animals will help to reduce predation on nesting birds and young.
• Control of introduced plants will allow native vegetation to regrow.
• Controlling beach access and vehicles on sand dunes will help to maintain these features and protect vulnerable ground-nesting birds. Dunes are a natural part of beaches and are our first line of defence from coastal erosion due to rising sea levels.