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!
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