Approximately 215 species of birds have been recorded in the Great Barrier Reef. The islands and cays of the Great Barrier Reef are especially important to seabirds with some 1.4 to 1.7 million seabirds visiting them each year to breed. The birds of the Great Barrier Reef can be divided into three groups based primarily on their habitat use, shorebirds, land birds and seabirds. These are collectively known as coastal birds.

Ecological roles

The sooty tern is one of the 215 species of birds found within the Great Barrier Reef World Heritage Area. Seabirds play an important role in the Great Barrier Reef ecosystem, influencing the soils and plants present on islands and cycling nutrients through the deposition of guano and carrion.

Coastal birds play an important role in the Great Barrier Reef ecosystem. They are major consumers of marine organisms such as fish, squid and crustaceans, and form an integral part of the marine food web. Seabirds are also an important part of the nutrient cycle by linking reef and island ecosystems.^20,37 Seabirds enrich island soils by depositing guano and carrion and influence the growth of plants on coral cays. This in turn contributes to the cay’s stabilisation and development.³¹ Birds also transport seeds from the mainland to offshore islands, which contribute to the establishment of island plant communities.

Variability of bird populations

The number of birds present at a given site at any one time is highly variable. Seabirds may fly offshore to collect food and thus are only present on islands at certain times of the day. Severe weather events, such as cyclones or gales, can cause birds to leave islands or normal rookery sites for extended periods. Birds may also move between different areas or islands at different times depending on the availability of nesting sites, food or amount of disturbance.

Migration patterns and seasonal variation

Some bird populations are seasonal. Migratory shorebirds may travel large distances between their breeding and feeding grounds. For example, the Eastern Curlew (Numenius madagascariensis) makes a 7000 km migration from breeding grounds in Russia and China to Australia where they spend their non-breeding season.

Many seabirds are also highly migratory. The Common Tern (Sterna hirundo) and Little Tern are highly migratory species that visit the cays of the Great Barrier Reef in winter,³¹ and Wedge-tailed Shearwaters (Puffinus pacificus) migrate long distances to northern waters during the non-breeding season.³⁰ Recent research has determined that the majority of South-East Asia’s migratory population of Roseate Terns (Sterna dougallii) over-winter in the Swains Reefs of the Great Barrier Reef.³⁴ Recent studies also indicate that birds banded at Raine Island and other islands in the far northern Great Barrier Reef, such as the Brown Booby (Sula leucogaster), Masked Booby (Sula dactylatra) and Red-footed Booby (Sula sula), disperse across the western Pacific to countries including Indonesia, Papua New Guinea, Tuvalu and the Solomon Islands.¹²

Migratory shorebirds such as the Eastern Golden Plover (Pluvialis dominica) breed in Siberia and Alaska, and migrate down the East Asian – Australasian Flyway to Papua New Guinea, Australia and New Zealand between August and April. These wide-ranging movement present a major challenge to monitoring efforts.

These migration patterns demonstrate the importance of the Great Barrier Reef for migratory species, but also show that the abundance of birds in the Great Barrier Reef may be affected by impacts occurring in other areas of the bird’s migration paths.

The effect of variation on determining ‘Condition’

The large variations in the abundance and distribution of bird populations provide a challenge to monitoring because the number of birds counted at any one time will depend on the timing and location of the census. Consequently, bird monitoring programmes in the Great Barrier Reef identify ‘breeding effort’ which is represented by the number of breeding birds at major breeding sites. This provides a more accurate description of the overall health of the population. However, monitoring must still be conducted at multiple sites over a long period of time to accurately identify trends. Further, data about environmental conditions at the time may be required to interpret these trends.

Sources of information

Most of the information about coastal birds in Queensland is contained in the Coastal Bird Atlas³⁵ managed by the  Queensland Environmental Protection Agency (EPA). Since 2002, pre-existing archival records have been standardised and entered into the Atlas, increasing the database from 9000 to 60 000 records. Ongoing bird monitoring is conducted by EPA staff in accordnace with the Great Barrier Reef World Heritage Area Coastal Bird Monitoring Strategy⁴⁴ and this data is continually added to the Coastal Bird Atlas. Important information on coastal bird populations is also collected by independent research projects and by volunteer and community groups such as Birds Australia and the Australasian Wader Studies Group. Although comprehensive information is only available for a limited number of species and colonies, the data that has been analysed indicates significant declines in some of the most common seabird species.

Conservation status of coastal birds

Some coastal birds in the Great Barrier Reef are of significant conservation concern due to their limited numbers or distribution, or because their populations are seriously threatened. The Environment Protection and Biodiversity Conservation Act 1999 and the Queensland Nature Conservation Act 1992,  lists species such as the the Little Tern (Sterna albifrons) and the Yellow Chat (Dawson) (Epthianura crocea macgregori) as ‘Endangered’ or ‘Critically Endangered’ (Table 1). The Action Plan for Australian Birds 2000¹⁶ also assessed the status of a large number of birds and made recommendations for their conservation listings.

Table 1. The conservation status of selected birds in the Great Barrier Reef

*Note: The Great Barrier Reef’s Herald Petrel population is listed as ‘Endangered’ or ‘Critically endangered’ in Australia as the breeding population is less than 50 individuals and only breeds on Raine Island. The main Heral Petral breeding population is found further east in the Pacific.

More information about the conservation status of coastal birds in the Great Barrier Reef is available in the document Fauna and Flora of the Great Barrier Reef World Heritage Area (2005).

Condition: Seabirds

Seabird abundance, diversity and distribution

The islands and cays of the Great Barrier Reef are important breeding grounds for birds such as the Masked Booby (Sula dactylatra).

Between 1.4 and 1.7 million seabirds from at least 20 species breed on islands and cays in the Great Barrier Reef each year, representing more than 25 per cent of Australia's tropical seabird breeding population.²³ The population of non-breeding birds is estimated at 425 000 individuals, giving a total seabird population that may exceed two million.²⁹ Some of the more common seabird species found on the Great Barrier Reef include Boobies, Frigatebirds, Gulls, Noddies, Shearwaters, Terns and Pelicans. Many seabirds nest on the ground in shallow scrapes while others nest in open areas, under vegetation, in shrubs, trees or burrows.

At least 79 islands and cays have been identified as seabird rookeries with 56 of these considered to be key sites.²³ These sites are concentrated in the northern and southern regions of the Great Barrier Reef where islands with suitable nesting habitats are more common (Figure 1). The northern Great Barrier Reef has the greatest seabird diversity with 23 breeding species. ^23,27,28

Figure 1. Significant sites for coastal birds including Ramsar sites and major seabird rookeries.

Raine Island in the northern section has the greatest diversity of any island with 16 breeding species including the Herald Petrel, Red-footed Booby and Red-tailed Tropicbird, which are uncommon in Australia. Other important seabird sites in the northern Great Barrier Reef include Moulter Cay, Sandbank No. 7 and No. 8, and Michaelmas Cay (Figure 1).

In the southern Great Barrier Reef, some 22 islands support significant seabird colonies. Of these islands, coral cays in the Capricorn-Bunker group support 73-75 per cent of the Great Barrier Reef’s total seabird biomass (inset Figure 1), mainly because large numbers of the Wedge-tailed Shearwater and Black Noddy (Anous minutus) found in this area.^23,45 These two species are the most abundant seabird species found in the southern Great Barrier Reef. The Capricorn Bunker Group supports approximately 50 per cent of the global Black Noddy population and about 30 per cent of the global population of Wedge-tailed Shearwaters.¹⁴

Trends in seabird populations

Long-term monitoring programmes have been on-going at four of the most significant seabird rookery areas on the Great Barrier Reef and significant declines of several species have been observed. These declines are thought to be associated with a range of pressures including weather related phenomena (storms, cyclones and El Niño events), climate change, reduced food availability and increased human activity. (See Pressure: Natural pressures). Trends observed in these four seabird rookeries are summarised below.

Surveys at Raine Island have found significant declines in seabird numbers, including species such as the Red-footed Booby.

Raine Island

Since the 1980s, numbers of breeding seabirds on Raine Island have decreased by 70 per cent. The annual average population observed at Raine Ialnd decreased from 23 445 seen in 1979-1993, to an average of 7 098 in the years between 1993-2003 (Table 2). Declines were evident in 13 of the 16 surveyed species including the Common Noddy (Anous stolidus), Brown Booby and Lesser Frigate-bird (Fregata ariel)³ which are the most common species in the region. Between December 1995 and December 2000, a more detailed study was conducted on Wedge-tailed Shearwaters that suggested a population decline of over 40 per cent, based on the number of occupied burrows at Raine Island.¹³ No evidence of habitat loss or degradation has been observed and the cause of these declines is unknown. However, the absence of localised impacts suggests that the causes may be related to changes in climatic conditions and/or a reduction in the availability of suitable prey.³

Table 2: Species exhibiting the largest declines in abundance observed by long-term monitoring at Raine Island (Batianoff & Cornelius, 2005).

Michaelmas Cay

Michaelmas Cay is the most intensively monitored seabird site in the Great Barrier Reef due to its ecological importance, high tourism and recreational values and levels of use. The Queensland Parks and Wildlife Service have conducted monthly bird counts on Michaelmas Cay since 1984, providing reliable long-term data for detecting population trends.¹⁰ The Common Noddy and Sooty Tern (Sterna fuscata) are the two most abundant seabirds present on Michalemas Cay. Monitoring data show that the number of birds recorded at Michaelmas Cay decreased during the 1990s, reaching a low point in 1994. Recovery was observed for the Common Noddy in 2000, and more recent analyses indicate some signs of recovery in Sooty Terns.¹⁵ However, for the period up to 2001, the numbers of Sooty Terns and fully fledged young Common Noddies were still well below 1984 levels.

Long-term surveys revealed a 41 per cent decline in Brown Boobies in the Swain Reefs between 1986 and 1993.

Swain Reefs

Long-term monitoring in the Swain Reefs has shown significant declines in numbers of Brown Boobies and Silver Gulls (Larus novaehollandiae), but stable numbers (~1100 individuals) of Masked Boobies. In the seven years between 1986 and 1993, Brown Booby numbers fell by 41 per cent from 3200 to 1300.²⁰ The decline is thought to be a result of inadequate food supplies associated with increased sea surface temperatures (see Pressure). Monitoring in 2005 showed that the population has not recovered (P O’Neill 2005, EPA, pers. comm., May 2006). Masked Boobies feed further offshore than Brown Boobies and thus, may have been better able to find food.

Capricorn-Bunker Group

The coral cays of the Capricorn-Bunker Group are important seabird breeding sites that support 97 per cent of the Great Barrier Reef’s Black Noddy population (~302 000 breeding pairs) and the Pacific Ocean’s largest breeding population of Wedge-tailed Shearwaters (~560 000 breeding pairs).^14,22 Approximately 79 per cent of the Capricorn-Bunker population of Wedge-tailed Shearwaters breeds on North West Island, making the island an internationally important site. The Capricorn-Bunker Group also contains the Great Barrier Reef’s largest breeding population of Silver Gulls which elsewhere nest mostly in isolated pairs or small colonies of less than 20 pairs.²⁸

The islands of the Capricorn-Bunker Group are important seabird breeding sites. North West Island (pictured) is an internationally significant site for Wedge-tailed Shearwaters.

Monitoring programmes in the Capricorn-Bunker Group recorded declines in Black Noddies and variable trends in Wedge-tailed Shearwaters. The number of Black Noddies reached a low point in 1998-1999 on all surveyed islands. On Heron Island, the number of Noddy nests declined from 72 000 in 1996 to 23 000 in 1998-1999. While some recovery was observed in 2000, numbers are still well below 1996 levels.¹⁴ These declines have correlated with El Nino events and elevated sea surface temperatures (see Pressure).

Condition: Shorebirds

At least 32 species of shorebirds have been recorded in the Great Barrier Reef region, including both residents and migrants. Some shorebirds may form large aggregations such as those found in Shoalwater Bay and Bowling Green Bay. Many shorebirds are commonly found in coastal estuaries and tidal mudflats although some species also occur further inland. Resident shorebirds can usually be found throughout the year, but some shorebirds such as the Sooty Oyster Catcher and Beach Stone-curlew only breed in pairs on isolated islands or beaches and are less conspicuous.

Migratory shorebirds traverse the East Asian – Australasian Flyway that links breeding grounds in the northern hemisphere to non-breeding grounds in Australia and New Zealand. Image from DEH 2005

Migratory shorebirds may travel thousands of kilometres from their breeding grounds in the northern hemisphere to feed and rest in the southern hemisphere during their non-breeding phase. These birds migrate along the East Asian–Australasian Flyway that stretches from breeding grounds of Siberia and Alaska, through east and south-east Asia, to non-breeding sites in Australia and New Zealand.¹¹ Consequently, these species are usually only encountered during a few months of the year. There are two internationally recognised migratory shorebird areas (both listed as Ramsar sites) in the Great Barrier Reef World Heritage Area, Shoalwater Bay and Bowling Green Bay (see Fig 1). Shoalwater Bay contains the world’s largest aggregation of Whimbrels (Numenius phaeopus), and the second largest aggregation of Terek Sandpipers (Xenus cinereus).²⁹

There is very little information available to reliably assess the status and trends of shorebird populations in the Great Barrier Reef. The Australian Action Plan for Birds 2000 describes some shorebirds as stable while others show decreasing trends, but the variability in shorebird populations due to their seasonal patterns and wide distribution makes it very difficult to effectively monitor their condition or interpret trends.

The Capricorn white-eye, found on islands in the Capricorn Bunker Group, has been nominated as a new species.

Condition: Land birds

The land birds of the Great Barrier Reef inhabit the Great Barrier Reef’s coastal habitats, continental islands and coral cays. The bird communities on continental islands often resemble those found in adjacent habitats on the mainland. The Great Barrier Reef is particularly important to a number of land birds, including the Capricorn White-eye (Zosterops lateralis chlorocephalus), the Yellow Chat (Dawson) (Epthianura crocea macgregori), Pied (Torresian) Imperial Pigeon (Ducula bicolor), Bush Stone-curlew (Burhinus grallarius) and raptors such as the White-bellied Sea Eagle (Haliaeetus leucogaster).

The Capricorn White-eye is the only endemic bird found within the Great Barrier Reef. Recent research suggests that the Capricorn White-eye may be a distinct species.²⁶ Its distinctive morphology and genetic isolation from other forms of the White-eye support its nomination as a new and separate species ‘Zosterops chlorocephalus’.

The Yellow Chat (Dawson) is the most vulnerable land bird found in the Great Barrier Reef region. The Australian east coast population was previously thought to have been extinct but in the 1990s, QEPA officers discovered a small population on Curtis Island in Central Queensland. Recent surveys have located further individuals on the mainland near Rockhampton and the known population is now estimated to be over 250 individuals.³³ Nevertheless, the total population numbers are low and pressures from habitat degradation have resulted in the bird being classified as Critically Endangered under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act 1999).

The white-bellied sea eagle is one of the raptors occurring in the Great Barrier Reef region.

The Pied Imperial Pigeon is a migratory species that visits the Great Barrier Reef during summer and returns to Papua New Guinea during the winter. The greatest numbers of Pied Imperial Pigeons on the Great Barrier Reef occur between Cooktown and Cape York. In this region, Pied Imperial Pigeons make daily migrations from coastal islands to rainforests on the mainland to feed on rainforest fruits. After feeding, the Pigeons return to the islands in the evening to roost and in doing so, carry the seeds of rainforest plants to the islands. Over-hunting by early European settlers depleted populations resulting in their protection in the 1960s. This species has been monitored since the 1964, mostly by community groups with assistance from the EPA. Since protection was introduced the population has increased and stabilised. It is thought that numbers are unlikely to increase further as the population has stabilised and the available food and habitat resources are fully utilised. 

Three species of fish-eating raptors are found on islands in the Great Barrier Reef, the Osprey (Pandion haliaetus), Brahminy Kite (Haliastur indus) and White-bellied Sea Eagle.³¹ Although these species are also widely distributed along the Queensland coast, little is known about their population size and trends. A recently published study suggests that numbers of White-bellied Sea Eagles in coastal regions of north Queensland are declining but the cause for the decline is not clear.³⁹

Previous : Summary | Next : Pressure