Sunday, 13 November 2016

Coral Cay Island Birds – Great Barrier Reef – Part 3 Terns

The background to our recent visit to Lady Musgrave Island on the Great Barrier Reef (GBR) was given in Coral Cay Island Birds – Great Barrier Reef – Part 1 Background.

We saw 6 species of terns on Lady Musgrave Island. The Black Noddy was covered in the Part 2 post. The other 5 tern species present on the island were Crested, Lesser Crested, Roseate, Black-naped and Bridled.

The Crested Tern is the most widespread and common tern to be found in Australian coastal waters. All of the other tern species we saw on Lady Musgrave Island are relatively uncommon and are more or less tropical species confined to tropical waters and therefore rarely found in southern Australia, particular along the coastline of my home State Victoria.

Bridled Tern (Onychoprion anaethetus)

Bridled Terns are similar to Sooty Terns and have a similar range in Australia. There were at least 20 pairs of Bridled Terns observed on Lady Musgrave Island in the early stage of breeding. Most birds were seen in pairs with many at nesting sites and courtship displays were also seen.

A pair of Bridled Terns resting together near a prospective nest site on Lady Musgrave Island. The distinctive white eyebrow is probably the feature that most obviously distinguishes this species from the Sooty Tern.

Pair of Bridled Terns courting. They rotated about one another with much graceful bowing and their wings held slightly away from the body. Holes under the tree stump behind contained three nesting pairs of Bridled Terns.

The Bridled Terns were nesting along the sandy beach not far above high tide level in a number of situations including under beach washed tree trunks and low dense shrubs and in long grass. This tropical tern breeds every six to seven months.

Bridled Tern above Tournefortia argentea (tree heliotrope) bush.

Same bird as above a second or two later.

Black-naped Tern (Sterna sumatrana)

This small elegant tern is exclusively tropical and marine, resting and breeding on coral reef cays and feeding mainly on small fish taken in adjoining tropical seas.

There were possibly 50 to 60 Black-naped Terns on Lady Musgrave Island when we were there. They did not show any signs of breeding however many gathered together at the top of the beach and at times fights broke out among some birds – perhaps this was a preliminary stage to forming pairs ahead of breeding which mainly takes place between October and December. One bird was seen carrying a small fish – fish flights and offerings to females are a part of courting for many tern species.

A small gathering of Black-naped Terns on coral rubble at the top of the beach on Lady Musgrave Island.
The pink blush visible on the birds in the above photo is mentioned in only the Pizzey and Knight field guide. While subtle it was quite obvious so it is somewhat surprising none of the other three popular Australian birding field guides mention this feature.

Periods of relative peace were punctuated by fierce squabbles among some birds.

The black napes show clearly on both the attacker and the attacked in this shot.

There was plenty of space for resting birds – this altercation most likely relates to competition for a mate and not roosting space on the beach?

In flight, the Black-naped Terns appeared a brilliant white against the intense blue tropical sky.

Roseate Tern (Sterna dougallii)

Roseate Terns are another tropical waters tern rarely seen down south. Only one pair was seen on Lady Musgrave Island. One of the Wardens on the island said more were expected to arrive shortly to breed there. I encountered the pair on a number of occasions, usually resting close to the shoreline among Crested Terns. They were very wary so I could only get a couple of long shots of them.

Based on the full black cap and red and black bill this pair in the photo below are in breeding plumage/condition. Non breeding birds have all black bills and a white forehead. The bird on the right has a silver band on its left leg.

Lesser Crested Terns (Thalasseus bengalensis)

Once again this is another tropical waters tern not found down south. The Lesser Crested Tern looks very similar to the much more common Crested Tern however it is easily identified by its noticeably smaller size and orange bill – the Crested Tern’s bill is yellow.

Only one pair were found on Lady Musgrave Island. They associated closely with the larger and closely related Crested Terns. The Lesser Crested could easily be overlooked among a large flock of Crested Terns so it is always a good idea to check carefully through a large flock of terns to see what other species might be lurking within their ranks.

One of two Lesser Crested Terns found on Lady Musgrave Island. Note the white flecks on the forehead – this bird is probably moulting to breeding condition, that is to a fully black cap.

While the Lesser Crested Tern on the left in this photo is a little fuzzy it does provide a good size comparison with the similar but much larger Crested Tern and also the bill colour difference shows well.

Crested Tern (Thalasseus bergii)

There were 200 to 300 Crested Terns on Lady Musgrave Island with most adults in breeding plumage. There were also a few juveniles and non-breeding adults. Some rested on the sand spit at the NE end of Lady Musgrave Island and others on a couple of defunct structures in the lagoon used in the past for tourists to view the underwater world of the lagoon without the need to enter the water.

A small section of a Crested Tern flock on the sand spit at Lady Musgrave Island. The two smaller terns in the foreground are White-naped Terns.

The black shaggy feathers at the back of the head on display here are not really a true crest. The dark bird is a Black Noddy.

For anyone wanting to see a range of tropical tern species in one place, a visit to a coral cay island on the Great Barrier Reef is a must.

Post No.4 will cover Wedge-tailed Shearwaters that were breeding on Lady Musgrave Island and Brown Boobies which were breeding on nearby Fairfax Island.

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