EN
Golden White-eye Cleptornis marchei



Justification

Justification of Red List Category
This species has a very small range, occurring on three very small islands. The largest population on Saipan is inferred to be declining as a result of habitat loss caused by commercial and residential development. The introduction of Brown Tree Snake (Boiga irregularis) to the species's range islands could result in very rapid elimination of the subpopulations on the islands and therefore, the species has very few locations. For these reasons, the species is listed as Endangered.

Population justification

The species is considered to be abundant and widespread on Saipan, but less abundant on Aguiguan (MAC Working Group 2014).

On Saipan, surveys in 2007 provided an estimate of 71,997 individuals (95% CI 47,586 – 106,535), with a density of 711.8 ± 112.1 birds/km(Camp et al. 2009). Analysis of population densities indicated a decline between 1982 and 2007 (Camp et al. 2009) and analysis of data from roadside surveys from 1991-2010 indicated that the population decreased between 2001 and 2010 (Ha et al. 2018). Assuming that this trend has continued, the population on Saipan may now be expected to be smaller than in 2007. Based on the relative population densities recorded in 1997 (995.5 birds/km2; Camp et al. 2009) and 2007 (711.8 birds/km2; Camp et al. 2009), the abundance estimate from 2007 and assuming a constant rate of decline, the current population is estimated to be within the range 30,767 - 68,882 (best estimate: 46,551) individuals.

On Aguiguan, surveys in 2008 estimated 15,499 individuals (95% CI 10,383 - 22,277), with a population density of 2,433 ± 466 birds/km2 (Amidon et al. 2014). Analysis of population densities indicated an increase between 1982 and 2008 (Camp et al. 2012, Amidon et al. 2014). Assuming that this trend has continued, the population on Aguiguan may now be expected to be larger than in 2008. Based on the relative population densities recorded in 1995 (1,901 birds/km2; Amidon et al. 2014) and 2008 (2,433 birds/km2; Amidon et al. 2014), the abundance estimate from 2008, and assuming a constant rate of increase, the current population is estimated to be within the range 13,039 - 27,975 (best estimate: 19,463) individuals.

A third population was established on the uninhabited island of Sarigan through translocations of 24 and 50 individuals in 2011 and 2012, respectively, with breeding detected within the first year (Radley 2012, MAC Working Group 2014). There is no more recent population data for the population on Saigan at the time of assessment.

Based on the population sizes described above, the current total population on Saipan and Aguiguan is estimated to be within the range 43,806 - 96,857 (best estimate: 66,014) individuals, which roughly equates to 29,204-64,571 (44,009) mature individuals. There is now an additional small population on Sarigan. The total population size is therefore placed in the band 29,000 - 70,000 mature individuals.

There are three subpopulations, one on each range island.



Trend justification

On Saipan, surveys by Engbring et al. (1986) in 1982 using point-transect methods estimated the population at 55,500 individuals. Further surveys were carried out in 1997 (USFWS 1998) and 2007 (Camp et al. 2009). The 2007 survey provided an estimate of 71,997 individuals (95% CI 47,586 – 106,535; Camp et al. 2009). Despite the larger population estimate in 2007, the population density was found to have declined from 1,287.3 ± 191.0 birds/km2 in 1982 to 995.5 ± 160.0 birds/kmin 1997 and to 711.8 ± 112.1 birds/kmin 2007 (Camp et al. 2009). The difference between the population estimates in 1982 and 2007 was attributed to a difference in the statistical methods used to estimate population size (Camp et al. 2009). Analysis of data from roadside surveys from 1991-2010 indicated that the population has increased from 1991-2000, then decreased between 2001 and 2010 (Ha et al. 2018).

On Aguiguan, surveys using point-transect methods in 1982 resulted in a population estimate of 2,300 individuals (Engbring et al. 1986). The transects were resurveyed in 1992 (Craig et al. 1993), 1995, 2000 (Cruz et al. 2000), 2002 (Esselstyn et al. 2003) and 2008 (Camp et al. 2012, Amidon et al. 2014). All surveys followed standard point-transect methods. The 2008 surveys estimated 15,499 individuals (95% CI 10,383 - 22,277; Amidon et al. 2014). Density estimates were as follows: 1,094 ± 196 birds/km2 in 1982; 1,901 ± 382 birds/kmin 1995; 2,224 ± 396 birds/kmin 2000; 1,693 ± 275 birds/km2 in 2002, and 2,433 ± 466 birds/kmin 2008 (Amidon et al. 2014). The population density increased significantly between 1982 and 2008 (Camp et al. 2012, Amidon et al. 2014). 

A third population was established on the uninhabited island of Sarigan through translocations of 24 and 50 individuals in 2011 and 2012, respectively, with breeding detected within the first year (Radley 2012, MAC Working Group 2014).

Although the population size appeared to be increasing on Aguiguan (Camp et al. 2012, Amidon et al. 2014), and a new population has been established on Sarigan (Radley 2012, MAC Working Group 2014), the largest subpopulation, on Saipan, was found to be decreasing (Camp et al. 2009, Ha et al. 2018) and overall, the species is inferred to be undergoing a continuing decline in population size.

Based on the relative population densities recorded in Saipan in 1997 and 2007, the relative population densities recorded in Anguiguan in 1995 and 2008, the abundance estimates from 2007 (Saipan) and 2008 (Aguiguan), and assuming that the population on Sarigan has no more than 100 individuals, and that rates of population change have remained constant, the total population is suspected to have undergone a reduction of 10-19% over the past ten years. Assuming the trend continues over the next decade, the population is also suspected to undergo a reduction of 10-19% over the next three generations.

Distribution and population

Cleptornis marchei is endemic to the Commonwealth of the Northern Mariana Islands (to USA), occurring on Saipan (115 km2) and on the uninhabited Aguiguan (7 km2). The species is now also found on Sarigan (4.5 km2) after translocations of individuals from Saipan took place in 2011-2012, with breeding taking place in the first year (Radley 2012, MAC Working Group 2014). Observations of unbanded birds were made on Sarigan in 2015 and 2016, indicating that these were not translocated individuals (L. Berry in litt. 2016). Prehistoric evidence has indicated that the species was once found on Tinian and Rota (Steadman 1999).

Ecology

On Saipan, the Golden White-eye occurs in all wooded habitats, including the native limestone forest (which is restricted to steep slopes and cliffs and covers c. 5% of the island), secondary forest and introduced tangan tangan (Leucaena leucocephala) thickets on flat lowlands and plateaus (c. 28% of land cover), and also agricultural and urban areas (Pratt et al. 1987, Craig 1990, A. Tieber in litt. 2008, 2010). However, it is decidedly more common in limestone forest than in disturbed areas (Craig 1996), and higher nesting densities are recorded in limestone forest than tangan tangan thickets (Sachtleben 2005, Peiffer 2017). It forages predominantly in the foliage of trees, particularly Cynometra ramifolia, feeding on invertebrates, flying insects, nectar, fruit and flowers and also taking insects from tree bark (Pratt et al. 1987, Craig 1990) and is typically seen in small groups of 2-4 individuals, thought to be family groups (A. Tieber in litt. 2008, 2010). Mean clutch size is 1.85 eggs (n = 39) (Peiffer 2014). Nest predators include the native Mariana Kingfisher, and the introduced Emerald Tree Skink and rats Rattus spp. (Peiffer 2014).

Threats

The most serious current threat is considered to be habitat loss (L. Berry in litt. 2016). Although the species has been recorded in urban areas, it is most frequently recorded in forest (Craig 1996, Sachtleben 2005). Habitat loss is thought to have been the main cause of the species's past reduction and the cause of the decline on Saipan (Camp et al. 2012). Since the 1980s, a significant amount of forest on Saipan has been degraded or lost as a result of residential, commercial and touristic development, and invasive species (Camp et al. 2009, G. Wiles in litt. 2020). In contrast, on uninhabited Aguiguan, where agricultural land has been reverting back to forest, the population is increasing (Camp et al. 2012, Amidon et al. 2014).

The threat that could have the most devastating consequences is the potential introduction of Brown Tree Snake (Boiga irregularis) to the species's range islands (Rodda and Savidge 2007). If the snake were to become established on Saipan, it would likely lead to extremely rapid declines, as has been the case amongst the endemic avifauna of Guam (to USA) (A. Saunders in litt. 2003, Wiles et al. 2003, Williams 2004). Roadside surveys on Guam indicated a 90% decline in most bird species within 8.9 years (Wiles et al. 2003). Accidental introduction via cargo ships and planes has been the primary mechanism for the spread of the species from Guam to other islands, and all goods received in the Northern Mariana Islands are shipped through Guam, with the majority arriving in Saipan (Colvin et al. 2005MAC Working Group 2014). There have been over 70 reports of Brown Tree Snake on Saipan, including sightings away from port areas (Rodda and Savidge 2007, MAC Working Group 2014), and the island was previously thought to have an incipient population (Colvin et al. 2005). However, surveys have not demonstrated the establishment of a breeding population on the island (Rodda and Savidge 2007) and there have been no confirmed records of the species on Saipan for 20 years (L. Berry in litt. 2020). There have been no reports of predation on Golden White-eye (A. Tieber in litt. 2008, 2010)The population decline of Golden White-eye recorded on Saipan is not attributed to Brown Tree Snake and did not follow the geographic pattern that would be expected if an expanding population of snakes was the cause (Camp et al. 2012). Nevertheless, the risk of the establishment of Brown Tree Snake on Saipan remains high. Although efforts are being made to prevent the introduction of the species, it is not possible to detect all snakes in cargo. Sightings of Brown Tree Snake on Aguiguan have been very rare. Aguiguan is uninhabited and difficult to access and it is unlikely that snakes will be accidentally introduced there (J. Lepson in litt. 1999).

Other invasive non-native species may also threaten the Golden White-eye. The invasive vine Scarlet Gourd (Coccinia grandis) was probably introduced to Saipan in 1998 and has led to degradation of the forest habitat on the island (Camp et al. 2009). Saipan supports high densities of the Black Rat (Rattus rattus), whilst the species is absent in Aguiguan, which may contribute to the different trends in Golden White-eye population seen on the two islands (Amidon et al. 2014). Rats have been observed predating Golden White-eye nests on Saipan (Peiffer 2017). Feral goats (Capra hircus) and the invasive plant Lantana camara may also lead to long-term degradation of the species's habitat; little tree recruitment has been observed on Anguiguan (Engbring et al.1986, Amidon et al. 2014).

Having a distribution on relatively low-lying islands, this species is potentially susceptible to climate change through sea-level rise and increased typhoon frequency and/or intensity (BirdLife International unpublished data). However, analysis of roadside survey data on Golden White-eyes on Saipan found no link between population density and typhoon frequency or severity (Ha et al. 2018). The species may also be impacted by a shift in suitable climatic conditions; both wet and dry seasons are predicted to be wetter and warmer in the western Pacific, including the Marianas. Saracco et al. (2016) suggest that such conditions could have negative consequences for the Golden White-eye, which appears to exhibit higher reproductive output in years with a relative contrast in greenness.

The population on Sarigan could also be threatened by volcanoes (P. Radley in litt. 2020).


Conservation actions

Conservation and Research Actions Underway
Extensive efforts are underway to prevent the accidental introduction of Brown Tree Snake (Boiga irregularis) on Saipan (Colvin et al. 2005). Cargo arriving at sea and air ports in Saipan is checked for snakes and traps have been installed to catch any snakes that are missed (MAC Working Group 2014). Barriers have been constructed at docks on Saipain to allow any introduced snakes to be contained (MAC Working Group 2014). Sniffer dogs have been trained to detect Brown Tree Snakes at Saipan airport (MAC Working Group 2014). Port officers from Saipan have been sent to Guam to receive training on prevention of Brown Tree Snake invasion and a programme has been carried out on Saipan to increase awareness among the general population of the importance of reporting Brown Tree Snake sightings (MAC Working Group 2014).
Efforts are also underway to develop captive breeding techniques for the species. The MAC Project brought 24 Golden White-eyes into captivity in 2007 and another 24 in 2008, with successful breeding reported from four institutions (MAC Working Group 2014).  All institutions have developed captive breeding protocols but chick mortality a problem among all holders.  In April 2011, 24 Golden White-eyes were captured on Saipan and translocated to Sarigan (Radley 2012). A second cohort of 50 Golden White-eyes were captured on Saipan and released on Sarigan in May 2012 (Radley 2012).
Several protected areas have been established on Saipan (Berger et al. 2005).
Roadside surveys to track species populations began on Saipan in the 1990s  (Ha et al. 2018). A regular monitoring programme known as Tropical Monitoring of Avian Productivity and Survivorship (TMAPS) was established in 2008 and is ongoing (Saracco et al. 2015,  P. Radley in litt. 2016). Its intent is to investigate the seasonal components of demographic rates of Golden White-eyes and other species on Saipan, and how these vital rates relate to temporal variations in local habitat quality (Saracco et al. 2016).

Conservation and Research Actions Proposed
Continue to monitor population trends through systematic surveys. Continue to monitor the translocated population on Sarigan. Continue to develop techniques for maintaining a captive population (F. Amidon in litt. 2007, Liske-Clark 2015). Monitor habitat trends, especially on Saipan. Maintain monitoring to detect the presence of any Brown Tree Snake individuals on the species's range islands.
Continue to implement measures to prevent the establishment of a Brown Tree Snake population on Saipan. Carry out public awareness programmes on Saipan to raise awareness of conservation issues (MAC Working Group 2014). Establish further protected areas and control development to protect remaining habitat, particularly forest, on Saipan (Liske-Clark 2015, Peiffer 2017). Continue to expand the captive population. Future translocations are planned to establish a population on the island of Alamagan in 2029-2030 (MAC Working Group 2014).

Identification

14 cm. Medium-sized, bright, warbler-like bird. Golden-yellow or peach-coloured, browner above, with bright orange bill, legs, and feet. Yellowish-white eye-ring. Voice Flock calls a rasping schik and a loud whistle. Song a rolling warble SEE-ME-can-you-SEE-ME-I-can-SEE-YOU-can-you-SEE-ME ...

Acknowledgements

Text account compilers
Wheatley, H.

Contributors
Amidon, F.A., Benstead, P., Berry, L., Bird, J., Davis, R., Derhé, M., Hawley, N., Lepson, J., Mahood, S., North, A., O'Brien, A., Radley, P., Saunders, A., Shutes, S., Stattersfield, A., Symes, A., Tieber, A., Westrip, J.R.S., Wiles, G. & Wright, L


Recommended citation
BirdLife International (2021) Species factsheet: Cleptornis marchei. Downloaded from http://www.birdlife.org on 02/12/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 02/12/2021.