Tuesday, 22 November 2016

Coral Cay Island Birds – Great Barrier Reef – Part 5 Other bird species.


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.

While at Lady Musgrave Island and lagoon we recorded a total of 18 bird species. The Part 2 - 4 posts covered 8 of these species and this post covers the remaining 10 species.

Lady Musgrave Island lies about 60kms offshore from the Town of Seventeen Seventy with no islands in between, so it was not surprising that no land birds were recorded there. Although National Park information signs on the island indicted Silvereyes may be present – we did not hear or see any Silvereyes. No doubt vagrant land birds turn up on offshore islands such as Lady Musgrave Island from time to time however they do not become established as permanent residents.

Three species of migrant shorebirds were seen.

Wandering Tattler (Tringa incana)

Due to the difficulties of separating the Wandering and Grey-tailed Tattlers I may be wrong with my ID of the bird in the following two photos (both photos are of the same bird on different days in different locations and light). I came to my ID based on checking the field guides, the overall dark grey appearance, the bird was alone on rock platforms of a coral cay island plus the Warden on Lady Musgrave said she had seen the bird and also thought it was a Wanderer (she has had a lot of experience with both Tattler species and told me that the Wanderer has become quite common along the Queensland coast in recent years). 

Please click on photos to enlarge.

My first encounter with the Tattler.

Second encounter in different location and light.

Ruddy Turnstone (Arenaria interpres)

Each time I visited Lady Musgrave Island I came across Ruddy Turnstones in various locations around the shoreline, both resting and actively feeding on coral platforms at other times. I think there were six altogether.

It is always a delight to find Turnstones.
 
Bar-tailed Godwit (Limosa lapponica)

I found a Bar-tailed Godwit on two occasions – it is possible that there were two birds on the island though one bird is more likely to be the case.

Lone Bar-tailed Godwit feeding among coral rubble on Lady Musgrave Island.

Eastern Reef Egret (Egretta sacra)

Reef Egrets are common along the tropical East coast of Australia and on the Great Barrier Reef islands. About 12, including both white (light morph) and dark grey birds, were present on Lady Musgrave Island. The white birds outnumbered the dark by about 3 to 1. They rested in trees on Lady Musgrave Island during high tides and became active at low tide feeding on the reef around both the island and on the fringing reef around the lagoon.

A white and dark morph Reef Egret resting together in a casuarina.

White morph Eastern Reef Egret.

White morph Reef Egret in flight.

Dark morph Reef Egret

Bird from the photo above in flight.

I saw one Reef Egret looking for food in the Pisonia Forest.

In addition to insects and spiders, eggs and in time, chicks falling from Black Noddy nests would provide food opportunities for the Egrets.

Buff-banded Rail (Gallirallus philippensis)

Dozens of Buff-banded Rails foraged on the Pisonia jungle floor – no doubt the supply of nutrients via Black Noddy droppings supported many insects and other life forms living in and on the forest floor which the Rails were exploiting. In addition, they would take any eggs and chicks that fall from the thousands of Black Noddies nesting above.

Two Buff-banded Rails foraging on the floor of the Pisonia forest on Lady Musgrave Island.

Both species of Oystercatchers were on Lady Musgrave Island.

Australian Pied Oystercatcher (Haematopus longirostris)

One of two Pied Oystercatchers I found on Lady Musgrave Island.
  
Sooty Oystercatcher (Haematopus fuliginosus)

One of two Sooty Oystercatchers I found on Lady Musgrave Island. This one is trying to open a small mollusc prized from the reef.
 
Coral cay islands due to their isolation from mainland Australia have been relatively free of predators and so many sea birds have evolved to use the islands to breed. Certainly humans until recently were no threat to the islands. Mainland avian predators such as many of the raptor and owl species did not visit the islands and terrestrial animals such as dogs, cats and large reptiles, including the monitors (goannas) and snakes, did not reach the islands.

However, we did see a number of predatory bird species at Lady Musgrave Island, including about thirty Silver Gulls. In small numbers gulls can provide a clean-up role and provide an important part of the ecological balance around a large colonial nesting event such as the Black Noddy event on Lady Musgrave Island. However, with the Silver Gull population increasing in Australia as a result of our waste food and rubbish, they can and have had a serious negative impact on some nesting birds (note the experience of bird surveyors with Brown Boobies nesting on Fairfax Island mentioned in the Part 4 post).

Silver Gull (Chroicacephalus novaehollandiae)

Silver Gull looking to pick up Black Noddy eggs under the Pisonia trees.

Silver Gulls have become so common around humans that we tend to overlook their beauty.

Another sea bird that could be regarded as a predator or indirect predator on coral cay island nesting birds, are Frigatebirds. There are three species of Frigatebird found in Australian tropical waters - the Great, Lesser and Christmas Island Frigatebirds.

Lesser Frigatebird (Fregata ariel)

One afternoon I observed five Lesser Frigatebirds lazily riding the updraft of a sea breeze above Lady Musgrave Island. At times the birds hung in the sky almost motionless, certainly at no time did I see them flap their long slender wings.

Lesser Frigatebird above Lady Musgrave Island.

Frigatebirds have poorly developed oil glands, so unlike many other sea bird species their feathers do not allow them to enter the water in pursuit of food or to rest on the sea surface. If they did enter the water their feathers would become waterlogged and they would be unable to fly – they would eventually drown.

Frigatebirds snatch food from the sea surface. Flying fish and squid, young birds and carrion are listed as their main foods. Part of their food supply is obtained by forcing other seabirds to drop or even disgorge their food. Frigatebirds are supreme aerialists and often harass other seabird species in order to force them to give up food. Hence Frigatebirds have been called pirates. The technical term for this behaviour is kleptoparasitisim. To the extent that the unfortunate birds are only deprived of some food and not their life, the Frigatebird is not strictly a predator. The Brown Boobies nesting on nearby Fairfax Island possibly provided opportunities for the Frigatebirds to obtain some easy meals as the Boobies returned to their young with food.

Unfortunately I was not able to capture all five Frigatebirds in the frame at once.
 
White-bellied Sea-Eagle (Haliaeetus leucogaster)

A White-bellied Sea-Eagle was the only raptor species I saw at Lady Musgrave Island. No doubt Eastern Osprey and possibly Brahminy Kites also visit Great Barrier Reef islands such as Lady Musgrave from time to time.

White-bellied Sea-Eagle.
 
This was the last post in the Coral Cay Island Birds series.


End note:

We were very privileged to be able to visit the Bunker Group on the Southern GBR and Lady Musgrave Island. Coral cay islands are special places. A small number of seabird species have adapted to living and breeding on these unique islands.

Rising sea levels and temperatures and sea water acidification due to CO2 and other greenhouse gas emissions will impact Lady Musgrave Island and the birdlife that depends on it over the course of this century. Even a moderate sea level rise could/will destroy the perched freshwater table on Lady Musgrave Island which in turn will kill the Pisonia trees that are so important for breeding birds such as the Black Noddy. More widely the destruction of coral and the disruption of marine micro-organisms such as plankton will alter the food chain and the coral reef ecosystem.

It is hard to contemplate this wonderful World Heritage area, that has taken thousands of years to evolve, being put at risk of destruction during this century by the Earth’s human population, especially considering we humans have brought about this state of affairs in less than a century of industrialisation and exponential growth!