Many of the Great Barrier Reef’s coastal birds (shorebirds, land birds and seabirds) use the same habitats and are affected by the same pressures. Consequently, the pressures and responses discussed are generic to all coastal birds unless it is indicated that they apply to a specific group.

Coastal bird populations are affected by both naturally occurring pressures and pressures arising from human activities. Pressures associated with human activities include the direct disturbance of birds, and indirect pressures from habitat loss and deterioration.

Pressure: natural pressures

Coastal habitats, continental islands and coral cays are critical habitats for many coastal birds. These habitats are influenced by ongoing geophysical processes such as erosion and deposition, and are periodically affected by severe weather events such as cyclones.

Geophysical processes

Coral cays are the least stable type of island in the Great Barrier Reef as they typically do not protrude far above sea level and greatly affected by erosion and deposition. Consequently waves, winds and storms have a major influence over a cay’s shape, size and longevity.²¹ Strong winds, waves and storm surges can erode beaches and wash over the islands, damaging important nesting habitats on coral cays such as Pisonia forests, beaches and sand dunes. As a result, the availability of suitable nesting sites on coral cays may change dramatically over a short time.^4,28 For example, since the 1990s, erosion and sand movement at Sudbury Cay have resulted in the cay becoming completely submerged during high tide. Seabirds can no longer use Sudbury Cay as a permanent roosting site.

Cyclones may only temporarily displace adult seabirds from an area, as observed with crested terns (pictured) at Michaelmas Cay. However, chicks are more vulnerable to severe weather events than adults, and severe weather events can have devastating effects on breeding success and population size.

Storms and cyclones

The effect of cyclones and extreme weather events on seabirds may depend on the nature of the cyclone, the stage of the breeding cycle and the species involved.²³ In some instances, cyclones only temporarily displace adult birds. In 1986 and 1988, cyclones caused short-term reductions of 34 per cent and 47 per cent respectively in the breeding population of Common Noddies at Michaelmas Cay. Monthly monitoring by Queensland Parks and Wildlife Service staff suggested that these reductions were not caused by bird mortality, but by the birds avoiding the island during and immediately after the cyclones. Further, the cyclones did not affect all species equally with no observed decline in numbers of Sooty Terns (Sterna fuscata) and Crested Terns (Sterna bergii). In 1997, Cyclone Justin passed over Michaelmas Cay causing an estimated two-thirds of the seabird population to be displaced and burying 80 per cent of the island's vegetation under sand. Subsequent monitoring by the Queensland Parks and Wildlife Service showed that most of the adult seabirds returned after the cyclone passed.

The impacts of cyclones may be much more severe if they occur during sensitive periods of the breeding cycle, especially when large numbers of eggs or chicks are present. Severe weather can prevent adults from leaving nesting sites to search for food, and rough seas can make it more difficult for adults to capture prey or return to their nests to feed their young. This may lead to starvation of chicks. Furthermore, adults have been known to leave the nesting sites during severe weather events, exposing the chicks and eggs to wind, rain and lower temperatures.²⁸ In 1976, Cyclone David struck Heron Island and cyclonic conditions persisted for four to five days. While adults were able to return to the island after the cyclone had passed, many Black Noddy chicks were too weak to take food from their parents and large numbers died from starvation.²³

El Niño-Southern Oscillation events

El Niño-Southern Oscillation (ENSO) events may affect coastal birds, particularly seabirds, by reducing the availability of suitable prey. ENSO events typically result in major changes in current patterns and increased sea surface temperatures in the eastern tropical Pacific Ocean. These changes may affect the movement and behaviour of baitfish, and reduce the activity of pelagic predatory fish. This causes a flow-on effect as baitfish may become harder to locate, and the predatory fish stop driving them towards the surface where they become accessible to birds. The loss of available prey is known as ‘provisioning failure’. This may severely affect breeding success and chick growth, and in some cases may cause the death of large numbers of immature and adult birds.⁴⁰

El Niño events and subsequent rises in sea temperatures can result in provisioning failure. These events have been linked with poor breeding seasons of Black Noddies (pictured) in the Capricorn-Bunker Group.

Between 1982 and 1983, a severe ENSO event resulted in reproductive failure and high adult mortality of several seabird colonies in the Central Pacific.³⁸ In the Great Barrier Reef, periods of unusually warm water have been linked with poor breeding seasons observed in Black Noddy colonies¹⁴ in the Capricorn-Bunker Group, Brown Boobies in the Swains Reefs,²⁰, and Sooty Terns and Common Noddies on Michaelmas Cay.⁸ In 2002, abnormally high sea-surface temperatures in the Southern Great Barrier Reef coincided with the reproductive failure of the Wedge-tailed Shearwaters in the Capricorn Bunker Group, including the almost complete reproductive failure of the Shearwater population on Heron Island.⁴⁰

Pressure: disease

There are no known incidences of disease outbreaks causing widespread mortality or sickness in bird populations on the Great Barrier Reef. Nevertheless, disease remains a potential risk for coastal birds. The Avian influenza virus commonly occurs in birds, but most strains do not pose serious risks to either the birds or humans. Outbreaks of a highly pathogenic strain of avian influenza (H5N1) have occurred overseas including countries visited by migratory shorebirds and seabirds. There is a risk that either migratory birds or humans may introduce disease to the Great Barrier Reef. However, the risk of a virulent strain of avian influenza being introduced to Australia by migratory birds is considered to be small. Wild bird species involved in H5N1 outbreaks include ducks, geese and swans that feed in waterbodies, scavenging species such as crows and raptors, and species that scavenge in waterways such as gulls and herons. None of these species regularly migrate to Australia.⁵

Pressure: climate change

There is scientific consensus that climate change is occurring on a global scale, and that the evidence linking these changes to human activities is stronger than ever.^24,41 Over the 20th century, Australia’s average air temperature rose by 0.7 ºC while the average sea surface temperature has increased at a rate of 1-2ºC per century. It is predicted that the annual national average temperatures will increase between 0.4° and 2.0°C by 2030, and by 1.0° and 6.0°C by 2070.¹ These changes may have significant effects on Australia’s climate including changes in oceanic circulation patterns, more frequent ENSO events, increased frequency and intensity of severe storms, changes in rainfall patterns and rising sea levels.¹

Climate change may have a number of impacts on coastal birds, including an increase in the frequency and severity of severe storms and cyclones.

Climate change may cause ecological changes such as changes in the geographic range, movement and migration patterns, physiology, abundance and community composition of coastal birds.⁷ These changes may result from changes in the availability of prey and/or suitable habitats. Increases in the frequency and severity of ENSO events may reduce the abundance of prey in oceanic ecosystems. An increase in the frequency and intensity of severe storms associated with climate change could magnify the impact of these events on seabird populations.

Changing rainfall patterns could alter the productivity of coastal and estuarine systems as many coastal species, such as barramundi and mud crabs, have reproductive cycles linked to rainfall and river flow.^32,36 Consequently, changes in coastal productivity may change the availablilty of food for coastal birds. Changing temperatures and rainfall patterns may also lead to changes in island vegetation and could increase the spread of weed species that are unsuitable for birds.

The Great Barrier Reef’s breeding seabird populations are heavily dependent on coral cays as nesting sites. As most of these cays are less than 2.5meters above the high water mark, even slight increases in sea level and greater storm activity could have significant impacts through increased erosion, more frequent wave wash-over and increased storm damage. Seabirds nesting on the ground or in burrows could lose critical nesting habitat, and the loss of vegetation could affect the breeding success of birds that nest in trees.²³

Pressure: habitat degradation and disturbance

Habitat degradation and disturbance includes both direct and indirect pressures. Direct pressures usually arise from disturbance of birds from human visitation or use of an area, while indirect pressures are caused by the degradation or loss of nesting, foraging or roosting habitat sites such as islands or wetlands.

Habitat degradation

Queensland’s coastal wetlands (including mangroves, creeks and rivers, tidal mudflats and swamps) cover some 71 000km².¹⁵ While the extent of wetland habitat lost since European settlement is unknown, it is evident that large areas of the Queensland coast have been modified for human use, particularly for agriculture. Developments such as ports, marinas, expansion of coastal towns and aquaculture, may also result in habitat degradation.⁴³ For example, the clearing of coastal rainforest habitat in the Cardwell region is thought to be a limiting factor in the growth of the Pied Imperial Pigeon population (J Hicks 2005, pers. comm., September). Some islands and cays have been significantly degraded by activities such as guano mining. For example, Lady Elliot Island was extensively mined in the 1800s, resulting in the loss of almost all vegetation, nutrients and soil. For more information about islands and coastal habitats see Environmental status – water quality

Disturbance

Visitors to islands may disturb birds, resulting in chicks being more susceptible to predation.

Disturbance is a direct pressure and is of particular concern on islands with high levels of visitation or development. Disturbance can be caused by people walking near nesting areas, unrestrained pets that harass birds, noise and movement of boats, and aircraft activity such as take offs, landings and low level flights. These disturbances can disrupt feeding activity and displace birds from their natural habitats. At breeding sites, disturbance can cause nesting birds to abandon their nests and eggs, exposing eggs and chicks to heat stress and predators such as Silver Gulls and Egrets. Some birds are more sensitive to disturbance than others. Shorebirds are very easily disturbed by human activities whilst feeding on mudflats or beaches, and are particularly sensitive to disturbance at their high tide roosts. When shorebirds are disturbed and take flight, they use significant amounts of energy. Repeated disturbances could reduce the ability of migratory shorebirds to build up enough fat reserves to undertake their annual migration. Beach Stone-curlews and Roseate Terns are extremely sensitive to human disturbance tend to only breed successfully isolated sites with minimal human activity. Declines in the number of Pelicans breeding on islands in the northern Great Barrier Reef have also been attributed to human disturbance.²⁸ However, some bird communities may become habituated to human presence over time.¹⁸ In these instances, irregular human disturbance probably results in greater impact than regular visitation.

Michaelmas Cay is considered the second most important site for seabird breeding on the Great Barrier Reef. However, over the past decade there have been long-term declines in breeding populations of coastal birds. It has been suggested that tourism is a contributing factor to this decline, with visitation to Michaelmas Cay exceeding 70 000 people per year in the early 1990s.²² However, visitation is now tightly controlled (see Response) and the declines observed are thought to have been caused by a combination of factors, including human disturbance, El Niño events and a reduction in the size of Michaelmas Cay due to geophysical processes.¹⁸

Pressure: introduced species, pest animals and plants

Introduced species, pest outbreaks and feral animals have both direct and indirect impacts on coastal birds. Many islands in the Great Barrier Reef have evolved a delicate ecological balance of animal and plant communities that is easily disrupted by introduced animals and plants.   

Feral animals such as foxes, pigs and feral cats directly affect bird populations by eating eggs and chicks and/or the adults themselves. Birds that feed or nest on the ground such as Terns, Oyster-catchers and Curlews are especially vulnerable to introduced predators. Introduced black rats are a serious threat to island birds worldwide as they eat the eggs and chicks. Rats now occur on several islands in the Great Barrier Reef.

Feral goats were introduced on some islands as a source of food. Goats destroy vegetation by eating native plants, and accelerate soil erosion and help to spread weeds. These disturbances are a serious problem on many islands of the Great Barrier Reef. Weeds can over-grow and out-compete native species, reducing the abundance and diversity of native flora. The resulting loss of native vegetation reduces the availability of suitable nesting sites and food for coastal birds. Once established, introduced weeds reduce the ability of native plants to recover from disturbances such as storms and fires.

The defoliation of Pisonia forests results in the loss of critical nesting habitat for species such as the Black Noddy.

Outbreaks of scale insects on coral cays in the Capricorn-Bunker Group have been linked to the introduction of the pest African Bighead Ant. The ants feed off the sugary sucretion produced by the scale insects and carry them from plant to plant. Outbreaks of scale insects have caused Pisonia trees to lose their leaves and eventually die. This has altered the vegetation communities of some cays in the Capricorn-Bunker Group. The loss of Pisonia trees has reduced the amount of nesting habitat for tree nesting birds such as the Black Noddy. Pisonia die off can also lead to an increase in grasses and shrubs that grow thickly over the ground, reducing the amount of suitable nesting habitat for burrowing species such as Shearwaters.

Some islands that are important bird habitats have been identified as priority islands by the EPA for pest species management. These islands include Curtis Island, the cays of the Capricorn-Bunker Group,  Hinchinbrook Island, the Frankland Islands, the Barnard Islands and Magnetic Island.

Pressure: oil spills

Oil spills may have various impacts on coastal birds. Pelicans are one of the birds most likely to be at risk from an oil spill.

Shipping is a major commercial activity in the Great Barrier Reef region and the main threat posed by shipping to coastal birds is that of a major oil spill. Floating oil can have a number of direct impacts on seabirds. The oil can degrade the waterproof and insulating properties of feathers, causing hypothermia and subsequent loss of body weight. Sticky oils may cause feathers to stick together and add weight, causing oiled birds to drown and/or making them more vulnerable to predators. Birds may also ingest oils when attempting to preen and clean their feathers. Ingested oil is toxic and can result in altered behaviour and reduced feeding and breeding success.⁹ Severe poisoning can result in organ damage and death. Oil may also indirectly affect coastal birds by affecting their habitats. Oil can smother and contaminate important nesting or foraging sites such as mangroves, inter-tidal mudflats or seagrass beds. Collectively, these effects may result in significant long-term effects on coastal bird populations. In Queensland, the birds most likely to be at risk from oil spills are shorebirds and birds that swim through the water such as Cormorants, Boobies, Terns, Silver Gulls and Pelicans.⁹

Between 1987 and 2004, 33 significant shipping incidents were recorded. While none of these incidents resulted in the death of large numbers of birds, the accidental release of fuel or cargo resulting from grounding, collision or structural failure of a vessel has the potential to cause serious environmental damage. Consequently, management efforts are focused on reducing the risk of shipping incidents from occurring as much as possible, and ensuring that contingency plans, trained staff and equipment stockpiles are maintained and ready for rapid deployment should an oil spill occur (see Management status - Shipping and oil spills).

Entanglement and ingestion of marine debris is a significant risk to a variety of marine wildlife, and is listed as a Key Threatening Process.

Pressure: garbage and marine debris

Marine debris consists of a variety of objects and comes from a number of sources, but the main sources of litter and rubbish are vessels and coastal runoff. Most of the litter found on remote and sparsely populated areas appears to be from vessels.^19,25

A survey of twelve vegetated sand cays and three continental islands in the far northern Great Barrier Reef found over 2000 items of marine debris, most of which were plastics.¹⁹ Birds may mistake marine debris for food and ingest foreign objects, resulting in stomach and intestinal blockages. Entanglement in marine debris such as discarded fishing line may prevent birds from flying, swimming and feeding properly, and in some cases birds may become so entangled that they drown. Nesting birds and chicks may ingest or become entangled in debris washed up on beaches, resulting in decreased chick survival. The number of birds killed by marine debris in the Great Barrier Reef is unknown.

The disposal of garbage at sea may benefit certain species that are able to take advantge of garbage as a food source. It has been suggested that in the past, the dumping of garbage on islands contributed to an increase in numbers of silver gulls in some areas. This has lead to increased predation pressure on nearby seabird colonies, especially on colonies that experience human disturbance.²⁸

Pressure: hunting

The hunting or collecting of coastal birds is illegal in Queensland unless the birds are taken for traditional use. The hunting of coastal birds in the Great Barrier Reef is uncommon. However, there have been anecdotal reports of shooting occurring on islands with large populations of Pied Imperial Pigeons that may indicate some hunting by Indigenous communities. There are also anecdotal reports of bird egg harvesting throughout the Great Barrier Reef and Torres Strait, and Boobies are sometimes known to be trapped for pets and as food in some neighbouring countries.¹²

Pressure: fishing activities

Fishing activities can affect coastal birds by reducing the availability of prey species, by providing a supplementary food source for particular species, or by accidentally catching birds that dive for fish.

The reduction of prey and other fishes by fisheries has been identified as a significant pressure on seabirds in some areas of the world. In Peru, anchovy fishing directly affected seabirds by severly depleting the amount of prey available. In Hawaii, seabirds were indirectly affected by the depletion of tuna. The birds relied on schools of feeding tuna to drive baitfish to the surface where the birds could catch them and when stocks of tuna were depleted, the amount of baitfish near the surface declined.²³ The effects of prey depletion on seabirds in the Great Barrier Reef are unknown, but are probably minor compared to the effects of “provisioning failure” related to weather and climate factors.

Fishing activities may provide a supplemntary food source for some coastal birds in the form of bycatch. Prawn trawling generates large amounts of bycatch with as much as 10 kilograms of bycatch taken for one kilogram of prawns.⁶ Research suggests that trawl bycatch in northern Queensland may have supported a tenfold increase in the population of Crested Terns in the northern Great Barrier Reef, which in turn, has placed pressure on other seabirds through increased competition for nesting sites and food.⁶

Fishing may also directly effect seabirds when they are caught as bycatch. Seabird bycatch is a significant problem in some long-line fisheries where seabirds are accidentally hooked when they dive onto baited hooks. Long-line fishing does not occur within the Great Barrier Reef Marine Park (Marine Park) and is not considered to be a serious threat to seabird populations in the Great Barrier Reef.⁴² Nevertheless, some seabirds, particularly in the northern and southern Great Barrier Reef, may forage into waters where long-line fishing does take place. The impact of long-line fishing on these birds is not known.

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