Heron Island is a member of a group of islands known as the Capricornia Cays that lie 70 km offshore of the city of Gladstone, Queensland on the Tropic of Capricorn and are part of the Great Barrier Reef. These islands are coral cays that are formed by sand building up on one end of a reef until it reaches above the high tide mark and becomes land. Unlike islands closer to shore, the coral cays have never been joined to the mainland and so are rather depauperate. Until the arrival of Europeans, they were not reached by any of Australia’s native mammals. Instead Heron Island is a refuge for an interesting variety of land and sea birds that have found their way to this unique habitat and made it their own.
The vegetation of the islands is quite different from the mainland, without the presence of Eucalyptus trees. Instead the majority of the island is covered in Pisonia forest. The Pisonia trees are adapted for life on windswept islands with only sand for soil and almost no organic matter. The roots are shallow and the trees easily blown over in the cyclones that periodically pass through, but the trees merely sprout from the fallen trunks and quickly fill in the canopy again. Around the edge of the forest Casuarinas and Pandanus palms grow but the middle of the island is the preserve of the Pisonia trees.
As the ferry approaches Heron Island, the first birds seen are gulls and terns, brown boobies and egrets. The Reef Egrets come in two colour phases: white and grey and the island was actually named for them by Captain Cook, who thought they were herons. Reef egrets stalk the shoreline, hunting in the shallows at low tide and resting on the beaches at high tides. On leaving the ferry and journeying up the wharf towards the resort and the research station, one is greeted by the most unusual birds on the island, the Banded Land Rails. These cheeky birds are found on most of the Capricornia group. Like many land birds that have made it to offshore islands, banded land rails are evolving towards flightlessness and are much less shy than mainland birds, probably due to the lack of predators. In fact these adaptable birds have become rather pesky because they recognise humans as a wonderful new food source and will do anything they can to invade kitchens and cabins in their relentless search for edible goodies. Their natural behaviour can still be observed in the Pisonia forest, where they scrape a living in the meagre soil, picking up the soil insects and beach hoppers (amphipods) that survive there.
Two other land birds have made Heron Island their home: Bar shouldered doves and Silvereyes. The rest of the avian fauna are seabirds. White breasted sea eagles are the top of the food chain and can often be spotted soaring in the winds above the island or roosting in the tallest of the pisonia trees but the most common seabirds on the island are White Capped Noddy Terns and Sooty Shearwaters, also known as Muttonbirds. These birds spend most of their lives at sea, fishing between the waves in the fish-rich waters of the Barrier Reef, but they come to Heron and other coral cays to breed and raise their young.
Muttonbirds dig burrows in the sand beneath and between the Pisonia roots. Their burrows are littered across the island and it is important to keep to the paths or the beaches when walking around the island, both for your own safety and the safety of the muttonbird chicks, as collapsing burrows can easily break a leg or smother a chick. Adult muttonbirds fly in at dusk, spend the night screaming like banshees at each other and then fly off to fish in the early morning. Their screams can be quite disconcerting at first and probably annoy many a wealthy patron of the resort, but the island is part of a national park and the birds’ rights come first. The muttonbird chicks have a great start to life, with a warm burrow and plenty of fish brought to them by their parents. But the parents abandon them before they can fly and the chicks are often seen, still covered in down, wandering forlornly around the island looking for a feed. Eventually they take off and fly out into the endless ocean all on their own to either learn how to fish or to die. It’s a tough strategy but obviously works as the species is both common and successful.
The white capped noddies nest in the branches of the Pisonia trees. These little birds are quite pretty, with long pointed wings, and the dark bodies and white caps that distinguishes them from other terns. They have webbed feet and look quite awkward when perched in the Pisonias or the Casuarinas, especially when the wind is howling. The females find a suitable location in the trees, usually where stems branch off from the main trunk. There are thousands of noddies here during the breeding season so competition for the best sites is fierce. The female guards her chosen spot while the male spends his hours bringing her fallen pisonia leaves to build her nest. She is fussy and rejects as many as she accepts but the males are patient and just keep bringing their mates more to choose from. If a leaf is acceptable, she glues it to her nest site with her droppings, making a rather messy excuse for a nest.
The Pisonias provide shelter for the young noddies and the muttonbird chicks but at a price. Because the soil is so poor in nutrients the Pisonias have evolved to provide their own sources. They produce sticky seeds that trap a certain number of chicks and even the occasional adult each year. These birds die slowly and it is painful to see them but the National Park policy is to let nature take its course because the bodies of the birds provide the nutrients that the trees need to survive and without the trees, the birds will have no place to nest.
Heron Island is also a major nesting site for Green Turtles. They can be seen in the waters around the island and from december onwards females can be seen laboriously crawling up the beach to dig great holes in the sand, lay their eggs and then drag themselves back to the sea. In February the babies begin to hatch and make their way from the safety of the burrow to the dangers of the beach, reef and open ocean. Probably only one in a thousand of these babies will survive to adulthood. Another tough strategy that has been successful over tens of millions of years. A few loggerhead turtles also use the beaches of Heron Island for nesting.
Most of the wildlife of Heron Island never leaves the sea. The reef around the island is much larger than the island itself and is home to a thousand species of fish plus countless invertebrate species. Diving on the Heron Reef and nearby Wistari Reef is a breath-taking experience. Parrot fish and clown fish, anenomes and endless varieties of plate, brain, massif and staghorn corals, wrasses and rabbit fish, sharks and rays, blennies, cod, eels, plus thousands of little iridescent green and blue fish like living jewels dazzle the eyes of the snorkellers. It would be impossible to do justice to the reef life of Heron Island in a single article. It has to be seen to be believed and yet it is only a small part of the whole Great Barrier Reef, a jewel in an immense crown. It is one of the wonders of the natural world and worth every penny of the money spent to visit it and protect it.