Cabbage Tree Island Research Articles

A novel technique for estimating age and demography of long-lived seabirds (genus Pterodroma) using an epigenetic clock for Gould's petrel (Pterodroma leucoptera).

Understanding the demography of wildlife populations is a key component for ecological research, and where necessary, supporting the conservation and management of long-lived animals. However, many animals lack phenological changes with which to determine individual age; therefore, gathering this fundamental information presents difficulties. More so for species that are rare, highly mobile, migratory and those that reside in inaccessible habitats. Until recently, the primary method to measure demography is through labour intensive mark-recapture approaches, necessitating decades of effort for long-lived species. Gadfly petrels (genus: Pterodroma) are one such taxa that are overrepresented with threatened and declining species, and for which numerous aspects of their ecology present challenges for research, monitoring and recovery efforts. To overcome some of these challenges, we developed the first DNA methylation (DNAm) demography technique to estimate the age of petrels, using the epigenetic clock of Gould's petrels (Pterodroma leucoptera). We collected reference blood samples from known-aged Gould's petrels at a long-term monitored population on Cabbage Tree Island, Australia. Epigenetic ages were successfully estimated for 121 individuals ranging in age from zero (fledgling) to 30 years of age, showing a mean error of 2.24 ± 0.17 years between the estimated and real age across the population. This is the first development of an epigenetic clock using multiplex PCR sequencing in a bird. This method enables demography to be measured with relative accuracy in a single sampling trip. This technique can provide information for emerging demographic risks that can mask declines in long-lived seabird populations and be applied to other Pterodroma populations.

Movements, Home Range and Site Fidelity of Snapper (Chrysophrys auratus) within a Temperate Marine Protected Area.

Understanding the movement dynamics of marine fish provides valuable information that can assist with species management, particularly regarding protection within marine protected areas (MPAs). We performed an acoustic tagging study implemented within the Port Stephens-Great Lakes Marine Park on the mid-north coast of New South Wales, Australia, to assess the movement patterns, home range and diel activity of snapper (Chrysophrys auratus; Sparidae); a species of significant recreational and commercial fishing importance in Australia. The study focused on C. auratus movements around Cabbage Tree Island, which is predominantly a no-take sanctuary zone (no fishing), with an array of acoustic stations deployed around the island and adjacent reefs and islands. Thirty C. auratus were tagged with internal acoustic tags in November 2010 with their movements recorded until September 2014. Both adult and juvenile C. auratus were observed to display strong site fidelity to Cabbage Tree Island with a mean 12-month residency index of 0.83 (range = 0 low to 1 high). Only three fish were detected on acoustic receivers away from Cabbage Tree Island, with one fish moving a considerable distance of ~ 290 kms over a short time frame (46 days). The longest period of residency recorded at the island was for three fish occurring regularly at the site for a period of 1249 days. Chrysophrys auratus displayed strong diurnal behaviour and detection frequency was significantly higher during the day than at night; however, there was no significant difference in detection frequency between different hours. This study demonstrates that even small-scale protected areas can benefit C. auratus during multiple life-history stages as it maintains a small home range and displays strong site fidelity over a period of 3 years.

Ecological interactions between a common palmLivistona australisand a rare seabird on Cabbage Tree Island, Australia

Australia's most widespread palm, the Cabbage Tree Palm Livistona australis (R. Br.) Mart. has only a few offshore populations, but one of considerable significance is on Cabbage Tree Island on the mid-north coast of New South Wales. This island is also the principal breeding site of a threatened endemic seabird, the Gould's Petrel Pterodroma leucoptera leucoptera. This paper outlines some of the ecological interactions between this iconic palm and this enigmatic seabird. P. leucoptera nests in rock cavities, under fallen palm leaves, or in hollow fallen palm trunks. It takes to the air by climbing to the top of palms and is sometimes killed by colliding with them. The eradication of the European Rabbit Oryctolagus cuniculus from Cabbage Tree Island in 1997 was undertaken to remove one of the threatening processes endangering P. leucoptera. This action has in turn released the population of L. australis from 91 years of unsustainable grazing pressure, helping to restore the long-term integrity of this, and other, plant species on Cabbage Tree Island.

Establishment of a new breeding colony of Gould’s petrel ( Pterodroma leucoptera leucoptera) through the creation of artificial nesting habitat and the translocation of nestlings

Gould’s petrel ( Pterodroma leucoptera leucoptera) was restricted, essentially, to a single breeding locality – Cabbage Tree Island, Australia. As a safeguard against extinction, an additional breeding colony was established on nearby Boondelbah Island, where artificial nesting habitat was created by installing 100 plastic nest boxes. Over two years, a total of 200 nestling Gould’s petrels were translocated from Cabbage Tree Island to these boxes. Colonies on both islands were then monitored for a further four years. Selection of nestlings for transfer was based on prior knowledge of growth, plumage development and emergence from the burrow, and aimed to select only birds that were 11–28 days from fledging (DBF) in 1999 and 11–22 DBF in 2000. Of the first 100 nestlings translocated to Boondelbah Island (in March 1999), 95 fledged successfully 8–27 days after transfer (mean = 17.3 days). Of the second 100 nestlings translocated (in March 2000) all successfully fledged 9–22 days after transfer (mean = 15.1 days). The removal of young had no discernible effect on the subsequent breeding productivity of the donor pairs. In all, 41 Gould’s petrels have been recorded at the new colony on Boondelbah Island, where at least 27 nest boxes have been visited. Ten translocated fledglings (nine male, one female) have returned to the translocation site, taking up nest boxes that were, on average, 5.5 m from the box from which they fledged. An additional 27 non-translocated birds, of unknown origin, have also nested in nest boxes on Boondelbah, along with four birds previously known from Cabbage Tree Island. Two nestlings transferred to Boondelbah Island have returned to Cabbage Tree Island. Within five years of the first translocation, the newly established colony on Boondelbah Island has produced a total of 24 eggs and 14 fledglings. The translocation technique developed for Gould’s petrel has broad applicability, being readily adaptable for other burrow-nesting seabirds.

A trial translocation of Gould's Petrel (Pterodroma leucoptera leucoptera)

Aside from a few pairs recently discovered breeding on nearby Boondelbah Island, the Gould's Petrel (Pterodroma leucoptera leucoptera) is limited to a single breeding colony located on Cabbage Tree Island, New South Wales. The translocation of birds from Cabbage Tree Island to establish a new colony elsewhere, or to augment the small colony on Boondelbah Island, is an option currently being considered to aid the long-term conservation of this endangered species. We undertook a trial translocation of nestlings within their current breeding grounds on Cabbage Tree Island. This involved removal of the nestlings from the natal nest, denying them further parental care, relocating them to an artificial nest box and feeding them artificially. Thirty nestlings were translocated between gullies on Cabbage Tree Island after they had attained specific plumage characteristics thought to occur just prior to their first emergence from their nests. The translocated nestlings were confined to their adopted nest boxes for the first 3 days and artificially fed every third day until they fledged. The experimental translocation and the associated use of artificial feeding resulted in a small increase in fledging weight, but caused no reduction in fledging success, and had no effect on the timing of departure of the fledglings. Three translocated fledglings have returned to Cabbage Tree Island since their departure in April 1995; all returned to their adopted nest site, one being recovered only a few metres from the nest from where it fledged. This study demonstrated that translocations of Gould's Petrel nestlings can be achieved without any discernible detriment to the individual birds involved.

Eradication of European rabbits ( Oryctolagus cuniculus) from Cabbage Tree Island, NSW, Australia, to protect the breeding habitat of Gould's petrel ( Pterodroma leucoptera leucoptera)

The endangered Gould's petrel ( Pterodroma leucoptera leucoptera) nests, almost exclusively, in rainforest on Cabbage Tree Island, New South Wales, Australia. Since their introduction in 1906, European rabbits ( Oryctolagus cuniculus) have greatly changed the structure of the rainforest, threatening its existence and that of the petrel. Rabbits were eradicated by sequential epizootics of myxomatosis and rabbit haemorrhagic disease (RHD), and a single application of cereal-based bait (Talon® 20P) containing the anticoagulant brodifacoum. The effectiveness of these mortality agents was evaluated by monitoring 70 telemetered rabbits, half of which were vaccinated against RHD. A natural epizootic of myxomatosis from May to July 1997 reduced the rabbit population from about 250 to 100. RHD, released in August 1997, reduced the population by a further 55%, the rabbits dying within 4–23 days. No survivors tested positive to RHD antibodies. Aerial baiting in September 1997 eradicated all remaining rabbits within 13 days. Intensive monitoring over the next 6 months detected no survivors. Non-target deaths included two buff-banded rails ( Gallirallus philippensis) and one pied currawong ( Strepera graculina).

Conservation of the endangered Gould's Petrel Pterodroma leucoptera leucoptera

The only population of Gould's Petrel Pterodroma leucoptera leucoptera has declined substantially during the last few decades. Adult mortality has been high, and has exceeded potential recruitment. Breeding success has been low. Entanglement in the sticky fruits of the Birdlime Tree Pisonia umbellifera and predation by Pied Currawongs Strepera graculina and Australian Ravens Corvus coronoides have been the major causes of petrel mortality on land. Experimental management actions aimed at ameliorating these threats were implemented, and their efficacy assessed. The removal of Pisonia and the control of avian predators dramatically lessened the mortality of Gould's Petrels ashore on Cabbage Tree Island. Instigation of these management actions in 1993 was coincident with a 68% rise in the number of birds brooding eggs in mid-December. Further small increases in the breeding population occurred in subsequent years. Management of the colony was also coincident with a substantial increase in breeding success (up from 25% to 45%). Breeding success increased to 59% in the 1994?95 season, but declined to 26% during 1995?96. Prior to management of the colony, an average of 30 birds fledged per annum (range 23?40; n= 4); after management, this rose to 167 per annum (range 105?233; n= 3). Management of the colony appears the most likely cause of this turnaround, but the possibility of it being due to extraneous factors such as weather or oceanographic perturbations cannot be excluded. The threats posed by Pisonia umbellifera and avian predators were, together, sufficient to account for the decline of Gould's Petrel. The demonstration that these two threatening processes can be ameliorated successfully suggests a high potential for recovery of the species.

Mortality of Adult Gould's Petrels Pterodroma leucoptera leucoptera at the Nesting Site on Cabbage Tree Island, New South Wales

The remains of adult Gould's Petrels Pterodroma leucoptera leucoptera were recovered from the nesting site on Cabbage Tree Island, New South Wales. Entanglement in the sticky fruits of the Bird-lime Tree Pisonia urnbellifera was identified as a major cause of mortality. Removal of P. urnbellifera eliminated one cause of death but mortality of adult petrels continued at an unsustainable rate as the result of predation by the Pied Currawong Strepera graculina. Hunting and feeding behaviour of the Pied Currawongs were observed, including holding fast a petrel carcass while ripping flesh from the skeleton. Mortality of Gould's Petrels subsided immediately following the destruction of Pied Currawong nests and nestlings. Subsequent recurrences of predation were correlated with additional nesting attempts by Pied Currawongs but declined substantially following the instigation of a control program for Pied Currawongs on Cabbage Tree Island. Pied Currawongs take the eggs and nestlings of many species of birds, but losses of nesting adults or the decline of a seabird have not been attributed previously to currawong predation.

The status of Gould's petrel, Pterodroma leucoptera leucoptera, on Cabbage Tree Island, New South Wales

Gould's petrel, Pterodroma leucoptera leucoptera, breeds only on Cabbage Tree Island, New South Wales. Annual surveys to estimate the size of the breeding population and the reproductive output were conducted between 1989 and 1992. Annual estimates of the total number of pairs breeding in the two gullies containing the main population were between 122 +/- 20 (s.e.) and 202 +/- 26. Breeding success was less than 20% between 1989 and 1991, but rose to 24.7% in 1992. This marginal improvement may be the result of management action undertaken to reduce mortality of breeding adults and fledglings. The total population is estimated to have declined from 2004 (95% confidence limits: 1464,3185) in 1970 to 1479 (1250,1815) in 1992, a decline of 26% in 22 years. The reasons for this decline are unclear.

Buller's Shearwater on Cabbage Tree Island, New South Wales

Buller's Shearwater on Cabbage Tree Island, New South Wales

Cabbage Tree Island as an Artillery Target

Cabbage Tree Island as an Artillery Target

The Cabbage Tree Island Colony in the 1941–42 Season

The Cabbage Tree Island Colony in the 1941–42 Season

The Gould Petrel of Cabbage Tree Island

The Gould Petrel of Cabbage Tree Island