By Dr Don Sands,
Senior Principal Research Scientist, CSIRO, Division of Entomology,
Private Bag No.3, Indooroopilly. Queensland 4068
The birdwing butterflies are the largest and most spectacular butterflies in the world. About 30 tropical species occur from India, Southeast Asia to New Guinea, the Solomon Islands and eastern Australia. The birdwings depend on forest vines belonging to genus Aristolochia, the food plants for their larvae. Though there are many species of aristolochia vines, the larvae of the birdwing species are often only able to develop on one or a few species of the vines. These vines have a patchy distribution, usually occurring only in rainforest, where they have suffered from clearing for urban development, farming and forestry operations. Most species of the vines have declined in abundance, especially in the last 10 years, with some of the birdwings so dependent on them, now threatened with extinction.
Birdwing butterflies have always been popular with collectors for mounting in display cases or as specimens for study. In Papua New Guinea in 1966*, prices paid for good specimens took a leap when many of the rarer species were listed as protected species. This led to a lucrative trade in smuggled specimens which gained momentum when all species whether common or endangered, were listed by CITES as prohibited exports or imports. A single specimen of Queen Alexandra's birdwing fetched more than A$1,000 on the black market! Such protection from collecting has alone done little towards enhancing survival of these butterflies, since the numbers collected provide almost no threat when compared with destruction of their habitats. Birdwings protect themselves effectively by gliding well out of the reach of most nets! Sadly, the habitats for birdwings and their aristolochia food plant vines have gained no protection from clearing of forest except in a few national parks which are not always adequate for their survival.
Two threatened birdwing butterflies have attracted the attention of scientists, conservationists and members of the community by their dwindling populations. The Queen Alexandra's birdwing (Ornithoptera alexandrae) from Papua New Guinea and the Richmond birdwing (O. richmondia) from sub-tropical Queensland and New South Wales have, more than other birdwing butterflies, been faced with threats to their survival. This is due to both having relatively small distributions which are particularly prone to forest clearing, the loss of their food plants and their breeding grounds.
The Queen Alexandra's birdwing is the largest butterfly in the world, the giant females with a wingspan reaching 27.5 cm while the Richmond birdwing, one of the smallest birdwings, has a wingspan usually less than 15 cm. As with other birdwings belonging to the genus Ornithoptera,the sexes are strikingly different: in males the powder blue, green, gold and black of Queen Alexandra's birdwing and the iridescent green and black of the Richmond birdwing, contrasts with the dark brown, spotted with white and cream females of both species. Such large butterflies are adapted to extensive tracts of forest with occasional flowers providing sufficient nectar as food for their adults, while the males need certain tall trees for patrolling and as mating sites. The females are nomadic and disperse between patches of rainforest in search of certain vines on which they lay their eggs. For the Queen Alexandra's birdwing, larvae are adapted to feeding only on Aristolochia dielsiana, a plant widely distributed in Papua New Guinea but only abundant in the Oro Province. The reasons for this birdwing's rarity and limited distribution have remained a mystery but it now seems that it is dependent on relatively high densities of the food plant to support its huge, ravenous larvae, densities of this vine not found elsewhere in Papua New Guinea. This abundance of A. dielsiana is thought to relate to the volcanic soils close to Mount Lamington which are known to be very rich in phosphate.
For the Richmond birdwing, A. praevenosa is the only natural food plant for the larvae in lowland rainforests. At higher altitudes (above 800 m) on the border ranges of Queensland and NSW, the Richmond birdwing may also breed on another vine, A. deltantha var laheyana, in favourable seasons. Larvae of the Richmond and Queen Alexandra's birdwings are usually solitary on their vines since the soft leaves and terminal growth required when newly-hatched are in short supply and insufficient food for more than one. For the first meal larvae must find soft leaves or they will starve. Starving larvae readily turn to cannibalism on another individual when it is temporarily immobile or moulting, a process which takes place 5-6 times as it grows before reaching the pre-pupal stage. By contrast for the common Cairns birdwing, Ornithoptera euphorion, the main food plant Aristolochia tagala, has much softer leaves. Their often gregarious larvae may consume all leaves and stems without turning to cannibalism.
In the lowland parts of their distribution, larvae of both rare birdwings feed only on one species of aristolochia and females bird wings do not lay eggs on any others even when present nearby in the same forests. The development of tough, leathery mature leaves is a feature of the food plants and the only defence for the plants against the ravenous larvae. While some plants defend themselves against insect attack by concentrating certain chemicals in their leaves, the birdwings have evolved a tolerance to compounds which would be poisonous to most other insects. But this co-evolution of insect and plant cannot cope when they are tricked into lay eggs on exotic plants introduced by humans from other countries. The ornamental Dutchman's Pipe vine, Aristolochia elegans, originally from South America, attracts egg laying by most birdwing butterflies but the early instar larvae are poisoned when they feed on its leaves. For the Richmond birdwing the introduction of this vine has been a major disaster, speeding the extinction process particularly in National Parks and forested areas where Dutchman's Pipe has escaped from gardens to become a weed. Egg counts made over several years in Burleigh Heads National Park showed that the Richmond birdwing laid significantly more eggs on Dutchman's Pipe than on its own native food plant growing nearby. Curiously, in South America Dutchman's Pipe has its own suite of beautiful butterflies have co-evolved with this vine, and on which their larvae are dependent for their survival!
Community efforts are focussing on ways to prevent any further decline in the abundance and distribution of the two birdwing butterflies. Papua New Guinea led the way for the Queen Alexandra's birdwing by realising the importance of cultivating vines to enrich existing habitats and for planting the vines in gardens. In the early 1970's village conservationists like Russel Hauro, recognised the decline in Queen Alexandra's birdwings in the vicinity of Popondetta, Oro Province, where they were once seen visiting flowers in the suburbs. Russel found that the A. dielsiana was easily cultivated from cuttings, so he began planting cultivated vines in batches of several hundred in the bushland surrounding his village. Along with the other common birdwing butterflies which he encouraged by each particular species of aristolochia vine, Russel has coaxed the Queen Alexandra's birdwings to colonise the nearby bushland and visit flowers planted in the village. Some day he is hoping to develop this unique natural asset as a special attraction for visitors interested in natural history and conservation. Other village communities have since been inspired by the success of village people cultivating vines for encouraging the Queen Alexandra's birdwing. Students at the Popondetta Agricultural Training Institute began planting vines in the College grounds. Renewed efforts are now being made by the PNG Department of Conservation and Environment, and through a Company supported by AUSAID, to participate in preserving their special butterfly. Enthusiasm is gaining momentum throughout PNG, aided by the emblem selected for their flag - the male Queen Alexandra's birdwing!
The Richmond birdwing was once common and near Brisbane and occurred in great numbers in the streets of City in 1870, as reported by the early Queensland naturalist, Rowland Illidge. He also noted the decline in numbers in the early 1920's which has continued to the present day, where sightings in the vicinity of the City are extremely rare. Since about 1984, the nearby breeding sites at Mount Nebo and Bardon have been cleared, removing the last natural fragments of rainforest supporting the native aristolochia vines. Birdwings have become so scarce and their distribution has contracted to about two thirds of the original range. No natural breeding sites remain between Caboolture and Nerang in Queensland, while extinctions have occurred from Noosa to the Mary River and from the Richmond River to Grafton in NSW.
A project began in 1992, sponsored by officers from NSW National Parks and Wildlife Service and CSIRO, aimed at identifying practical conservation strategies for the Richmond birdwing. A plant nursery at Coraki, NSW was provided with 600 seedlings, seeds and cuttings of A. praevenosa to provide stocks for propagation. Several schools joined the project by planting vines to encourage the butterfly to breed in the school grounds. This concept of school involvement became so popular that CSIRO's Double Helix Science Club was approached to co-ordinate the educational and conservation project, which has now extended over the two States and involves more than 130 schools. Students began gathering valuable information about the seasonal growth of the vines. More than 15,000 vines have to date been distributed by retailers to community groups and schools between Grafton and Maryborough. Vines are being planted in gardens and reserves in areas where the birdwing and its vine have become extinct, to provide corridors between reserves which will enable the necessary genetic mix between otherwise isolated populations. With careful instruction, Dutchman's Pipe is being identified by students and conservation groups, then removed from gardens and bushland. The nursery trade has outlawed culture of the vine to protect the birdwing.
School students are participating in scientific studies on growth of the aristolochia vines and recording the influence of climatic variables on seasonal growth. A new device, a portable leaf penetrometer, is being trialled in a study to find out more about the role of leaf toughness on the survival of larvae. Community groups are identifying natural enemies such as bull ants and certain spiders which attack the immature stages of the birdwing. Larvae are moved from "overloaded" vines to healthier vines to enhance the chance of their survival. Queensland's first butterfly reserve has been designated on the Stanley River in a joint venture by the Department of Primary Industries and a Land Care group and the Southbank Corporation has donated a "Butterfly Island" where students have planted 100 A. praevenosa vines in the heart of Brisbane. Four years after the planting of vines, the first signs of breeding by the Richmond birdwing are apparent. At sites in both States the first larvae have completed development and adults have been seen investigating several other cultivated vines, intent on depositing their eggs. Several councils have shown interest in the project and are interested in enrichment planting of the birdwing's vine.
Butterfly conservation depends most of all on preservation of the natural habitats and the food plants supporting the larvae. The few specimens taken by collectors does not lead to rarity or extinction unless the habitat is threatened. However, where destruction of these habitats results from human activities, we must find other strategies to help the survival of threatened or endangered species. For the two threatened butterflies, the Queen Alexandra's and Richmond birdwings, their survival has been enhanced by cultivating the dwindling food plants and participating in the preservation of all remaining habitats.