Justification of Red List Category
This species breeds in the limited suitable habitat of just one area of a very small island, and it has a small population which has declined rapidly owing to the effects of past habitat clearance. Recent die-back of some of the breeding habitat indicates that habitat quality continues to decline, although it is unclear whether this die-back has been caused by introduced yellow crazy ants. Because of the significance of even minimal declines in habitat quality within the limited breeding habitat of this booby, it is listed as Endangered.
Following an estimate of 2,500 active pairs in 1991, the total number of mature individuals has been put at c.6,000, equating to c.9,000 individuals in total. It should be noted that only a proportion breed in a given year owing to a 15-18 month breeding cycle and the possibility that some unsuccessful pairs take 'rest years' rather than breed in successive years. Despite a helicopter survey in 2002, the 1991 survey is considered the most accurate and comprehensive.
The species's population is estimated to have declined by 30-49% over the last 90 years based on its disappearance from much of its former breeding range in the Indian and Pacific Oceans. However, it seems that the breeding population was more or less stable between 1991 and 2002 (Commonwealth of Australia 2004, P. Green per D. James and M. Jeffery in litt. 2005) and so the current trend is now tentatively assessed as stable.
Papasula abbotti breeds only on Christmas Island, Indian Ocean (to Australia), though it once had a much wider distribution in the Indian and probably Pacific Oceans. One female was recently observed on Rota Island (Northern Mariana Islands to USA), though it is not known whether it is vagrant or a solitary resident (Pratt et al. 2009). The population was estimated at 2,300 pairs in 1967, declining to 1,900 pairs by 1983. The breeding areas discovered on Christmas Island in 1997 brought the total to an estimated 2,500 active pairs following a survey in 1991 (Yorkston and Green 1997), which is regarded as the most accurate and comprehensive to date (James 2007). A helicopter survey in 2002 recorded about 1,500 active nest sites (Commonwealth of Australia 2004), but the results were not verified by ground-based surveys (James 2007). Overall, it seems that the breeding population was more or less stable between 1991 and 2002 (Commonwealth of Australia 2004, P. Green per D. James and M. Jeffery in litt. 2005), but the survey techniques are not directly comparable (D. James in litt. 2005, 2007, James 2007). The species's breeding cycle takes 15-18 months, meaning that successful pairs nest once every two years whilst unsuccessful pairs may breed in successive years or take 'rest years', thus only a proportion of the breeding population breeds in a given year, and this is dependent on nesting success in the previous year (James 2007). Thus, in 2000, following on from the 1991 survey, the total population of mature individuals was estimated at c.6,000. It disperses within the Indian Ocean (Clark 2016). Recent records from the Banda Sea may indicate either part of its distribution range or unknown breeding colonies.
It nests in tall rainforest trees at 160-260 m elevation in the western, central and northern areas of Christmas Island (Commonwealth of Australia 2004), and lays one egg. Successful parents can only breed biennially. It may first breed at eight years of age, and its average lifespan may be c.40 years. It feeds at sea on squid and fish. The at sea distribution of this species is poorly known. It was previously thought that cold water upwellings south of Java could be important feeding areas for breeding boobies (Commonwealth of Australia 2004, Olsen 2005), however tracking studies showed that chick-rearing adults forage relatively close to Christmas Island, on average about 60 km off the island, and show no association with oceanographic features (Hennicke and Weimerskirch 2014a,b).
Loss and degradation of habitat due to mining and road building has represented a significant threat to this species. During 1965-1987, phosphate extraction resulted in the destruction of approximately one third of nesting habitat. More recently, in 2007, significant patches of mature secondary forest were cleared for mining (D. James in litt. 2005, 2007). Some trees in nesting areas have degenerated, but the extent of this is unquantified (D. James in litt. 2005, 2007). In addition, exotic plants that have been introduced to, and subsequently colonised, old mine sites may invade existing forest and threaten habitat rehabilitation (Commonwealth of Australia 2004, Department of the Environment and Heritage 2004). Also in 2007, a new application to mine a 250 ha area of rainforest (P. Green in litt. 2007) was turned down (J. Hennicke in litt. 2007), but has subsequently gone to appeal (D. James in litt. 2005, 2007). Future habitat loss is possible through clearance for mining (S. Garnett in litt. 2003). Plans for a satellite launch pad on the island are not proceeding at present (T. Low in litt. 2006). The effect of satellite launches on this species is unknown (Commonwealth of Australia 2004, Department of the Environment and Heritage 2004). In wind-affected areas, increased turbulence causes higher adult mortality and reduces fledging success. Artificial forest clearings, e.g. for roads and buildings, also cause wind turbulence and, as such, may represent a threat to the boobies' reproductive success.
The introduced Yellow Crazy Ant Anoplolepis gracilipes, which formed super-colonies during the 1990s and spread rapidly to cover 28% of the forest on the island, is also thought to pose a significant threat to the booby. Control efforts have been successful (P. Green and D. O'Dowd in litt. 2003); at the beginning of 2005 there were an estimated 300 ha with A. gracilipes present on Christmas Island, representing around only 2% of the island's area, with densities considerably lower than prior to control (D. James and M. Jeffery in litt. 2005). Despite the successes, in 2006 the ants were regarded as widespread and patchily common (T. Low in litt. 2006). It is possible that ant super-colonies may prey directly on nestlings or cause nest abandonment, however, there have been no observations of ants preying on the species, and comparison of ant distribution and densities with P. abbotti distribution showed no sign of nest abandonment in ant-infested areas (D. James and M. Jeffery in litt. 2005). Super-colonies alter island ecology by killing the red crab, Gecaroidea natalis, one of the dominant species on the island and by farming scale insects which damage trees. Anoplolepis gracilipes occurs from below ground-level to the canopy where P. abbotti nests. There are signs of forest die-back in a small area of breeding habitat, which may be indirectly caused or exacerbated by A. gracilipes, but its impact is unlikely to be severe (D. James and M. Jeffery in litt. 2005).
Climate change may threaten the species through changes to sea surface temperatures, rainfall patterns and El Niño Southern Oscillation (Commonwealth of Australia 2004, Department of the Environment and Heritage 2004). Breeding boobies are vulnerable to extreme weather events, as shown by the destruction of a third of monitored fledglings and nest-sites by a cyclone in 1998. Increased sea surface temperatures and decreased marine productivity have been shown to affect the chick-rearing of Abbott’s Boobies due to impacts on the foraging ecology, including trip duration, dive depth and prey composition (Hennicke and Weimerskirch 2014b). The species is unlikely to be affected by sea level rise though as it nests above 100 m above sea level (D. James in litt. 2005, 2007). At sea, birds suffer from direct hunting (Hennicke 2012), and potentially also from bycatch, but the latter has not been confirmed (Commonwealth of Australia 2004, Department of the Environment and Heritage 2004).
Conservation Actions Underway
CITES Appendix I. A national park was created in 1980, which has since been extended to cover more than 60% of the island (D. James in litt. 2005, 2007; Low 2016) and includes most breeding areas. A lease agreement with Christmas Island Phosphates Pty Ltd prevents clearance of primary rainforest and requires permits to clear regrowth. A monitoring programme was in place between 1982 and 1993. Since 1984, c.20% of mined areas adjacent to nesting areas have been planted in an ongoing restoration programme. A control programme for A. gracilipes has been successfully initiated since 2000 and effectively eliminated the ant from 2,800 ha of forest (95% of its former extent) (P. Green and D. O'Dowd in litt. 2003). Monitoring of the problem continues and hand-baiting measures have been ongoing. Aerial baiting was carried out in September 2002, 2009 and 2012 and proved to be successful against major colonies (Olsen 2005), eliminating over 98% of ants (D. James in litt. 2005, 2007). However, the ants have since recovered (D. James in litt. 2005, 2007). The ants remained persistent in 2006, and it was thought that perpetual baiting would be the only means of controlling them (T. Low in litt. 2006). The bait used so far is known to be toxic to invertebrates, including crabs, and although alternatives have been trialled, an effective replacement has not been found (D. James in litt. 2005, 2007). Control of the scale bugs by parasitoid wasps which parasitise the scale insects that the ants tend for their sugar secretions has been suggested, in order to reduce this food supply (T. Low in litt. 2006; D. James in litt. 2005, 2007). This bio-control programme is in its final test phase before implementing it large scale on Christmas Island (J. Hennicke in litt.). In 2004, 2005 and 2006, surveys were carried out to assess the impact of the construction of an immigration centre on a breeding colony adjacent to the site (James 2007). Since 2004 ground surveys have been carried out and in 2009 an areal survey was conducted to determine population dynamics and breeding activity (J. Hennicke unpubl. data). Since 2004, the foraging ecology, reproduction as well as immunology and genetics of adults and juveniles has been investigated to identify threats and pressures and their effects on the species (e.g. Quillfeldt et al. 2011, Morris-Pocock et al. 2012, Hennicke and Weimerskirch 2014 a,b).
Conservation Actions Proposed
Monitor the abundance and spread of A. gracilipes (Commonwealth of Australia 2004), whilst continuing to implement control measures. Develop and implement appropriate monitoring techniques (Commonwealth of Australia 2004). Monitor the impact of rehabilitation efforts on trends and distribution. Continue to investigate the foraging ecology of adults and juveniles (e.g. by tracking studies) (Commonwealth of Australia 2004, Olsen 2005). Negotiate with the mining company to ensure protection of all breeding habitat and appropriate buffers. Minimise and monitor effects of developments such as the launch pad (Commonwealth of Australia 2004). Develop a wind turbulence model to guide habitat restoration (Commonwealth of Australia 2004). Continue to implement weed management strategy (Commonwealth of Australia 2004). Monitor likely impact of developing fisheries around Christmas Island (Commonwealth of Australia 2004). Address threats from global climate change at national and international levels (Commonwealth of Australia 2004). Monitor the possible effects of climate change on the species (Commonwealth of Australia 2004). Protect all existing and potential future breeding habitat, i.e. protect all remaining primary rainforest on the island’s plateau as well as the adjacent secondary growth forests.
79 cm. Black-and-white booby. Dark eye and dark-tipped bill, pale grey in male, pink in female. White head, neck and most of underparts. Black upperwing with white flecking on coverts and narrow white leading edge. Black thigh patch and tail. Black patch on mantle and back continuous with wings, remainder white. Blue-grey legs and feet. Juvenile similar to adult male. Similar spp. Confusion unlikely. At sea, adult Masked Booby Sula dactylatra has white upperwing-coverts, yellow bill and black facial mask.
Text account compilers
Garnett, S., Benstead, P., Calvert, R., Harding, M., Hermes, C., Martin, R., McClellan, R., Crosby, M., Moreno, R., Fjagesund, T., Taylor, J.
Garnett, S., Green, P., Hennicke, J., James, D., Jeffery, M., Low, T. & O'Dowd, D.
BirdLife International (2023) Species factsheet: Papasula abbotti. Downloaded from http://www.birdlife.org on 25/03/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/03/2023.