Data Zone
Justification of Red List category
Although confined to just four small islands (one of which it was introduced to), this species remains very common and is not thought to be declining. However, it remains at risk from the accidental introduction of Brown Tree Snake Boiga irregularis from nearby Guam which caused the extinction of Zosterops conspicillatus. If the snakes were introduced to the island of Saipan, which hosts c.70% of the global population of this species, it may decline at a rate that qualifies it for being listed as threatened in a very short space of time. However, given the biosecurity measures on all four islands, a more rapid reduction capable of driving the species to Critically Endangered or extinction is considered very unlikely. It is consequently listed as Near Threatened.
Population justification
Among the commonest landbirds in its range (Pyle et al. 2010). The population was estimated to be 534,029 (95% CI: 427,858-650,667) individuals on Saipan in 2007 (Camp et al. 2009), 225,360 (95% CI: 192,080-283,200) individuals on Tinian and 3,388 (95% CI – 2,492-4,909) individuals on Aguijan in 2008 (Amidon et al. 2014). A total of 196 Saipan White-eyes, captured on Saipan, were translocated to northern islands in the chain with no permanent human populations; in 2008 and 2009 to the island of Sarigan (100 birds), and in 2015 and 2016 to the island of Guguan (96 birds) [K. Reininger in litt. 2021]. In June 2016, point transect surveys were conducted on Sarigan to evaluate the initial success of the translocation program. A population estimate of 8,239 birds from this survey (Amidon 2017) indicate the translocated birds had survived and were readily reproducing thus are considered in the population totals given here. A post-translocation survey of Guguan is planned, however given current uncertainty over whether they are reproducing, that they constitute a viable breeding population cannot be assumed and precautionarily this population is excluded from the totals given herein. The population size is not believed to have substantially changed since these estimates were made and therefore the population size is estimated at 630,000-950,000 individuals, or approximately 410,000-630,000 mature individuals.
Trend justification
A future decline of this species was formerly considered an inevitability due to the accidental introduction of Brown Tree Snakes Boiga irregularis. However, this threat has so far been kept at bay, principally due to biosecurity measures (see Yackel Adams et al. 2021). In the absence of additional threats acting on this species, the population is therefore considered to be stable while on the islands of its recent introduction (Sarigan and Guguan) it may be increasing until carrying capacity is reached.
Zosterops saypani is restricted to the Northern Mariana Islands (to U.S.A.) where it occurs naturally on the islands of Saipan, Tinian and Aguijan. One-hundred birds were introduced to the uninhabited island of Sarigan in 2008 and 2009; follow-up surveys in 2016 confirmed a thriving population of more than 8,000 individuals (Amidon 2017). Because this introduction was for conservation reasons, is close to the native range, has produced viable offspring and was done more than five years ago, it is here considered part of the species' range. Birds were also introduced to Guguan in 2015 and 2016, although follow-up surveys have not yet been undertaken; in the absence of these data, it is currently not considered part of the range.
The species is found in a wide range of habitats from native limestone forest to scrubby secondary growth of disturbed habitats and even urban areas. It is less common in swordgrass savannah (Craig 1996). It commonly forages in large flocks in the upper canopy of native limestone forest, but also feeds in other habitats (Engbring et al. 1982). Its food consists of insects, seeds, fruits, caterpillars and berries and it is not strongly nectarivorous (Engbring et al. 1982). It seemingly competes for food with the larger, dominant Golden White-eye Cleptornis marchei, probably because of the extremely high densities (Craig 1996). Breeding occurs in January, February and August, October; though on Saipan there is a distinct peak in February/March (Craig 1996, Sachtleben 2005). It nests predominately in Leucaena leucocephala thickets (Sachtleben 2005). It is not territorial but birds remain in the home range (Craig 1996).
The biggest threat to this species on all range islands comes from the hypothetical accidental introduction of Brown Tree Snake Boiga irregularis, which rapidly extirpated populations of Zosterops on Guam.
Conservation Actions Underway
Efforts continue to prevent the accidental introduction of the Brown Tree Snake Boiga irregularis into the Commonwealth of Northern Mariana Islands (CNMI). Inspections of planes, vessels and cargo are conducted at the airports and seaports on the islands of Saipan, Tinian and Rota as a first line of defence. Snake traps are maintained on fence lines surrounding ports of entry on all three of these islands. Rapid response action to reports of Brown Tree Snakes is coordinated between the CNMI Division of Fish & Wildlife (DFW), the USGS Rapid Response Coordinator and local volunteers.
Assisted colonisation efforts are underway as part of the Mariana Aviafauna Conservation Plan (MAC Working Group), a joint project of the CNMI DFW, USF&WS, the non-profit group Pacific Bird Conservation (PBC), and several Association of Zoos and Aquariums (AZA) zoos. A total of 196 Saipan White-eyes, captured on Saipan, have been translocated to northern islands in the chain with no permanent human populations; in 2008 and 2009 to the island of Sarigan (100 birds), and in 2015 and 2016 to the island of Guguan (96 birds) (PBC). In June 2016, point transect surveys were conducted on Sarigan to evaluate the initial success of the translocation program. A population estimate of 8239 birds from this survey (Amidon 2017) indicate the translocated birds had survived and were readily reproducing. A post-translocation survey of Guguan is needed. Public education efforts on Saipan, led by Pacific Bird Conservation and AZA zoos, include partnerships with the CNMI Public School System, Northern Mariana College, and the local conservation organization Mariana Islands Nature Alliance (MINA). Programs include: assistance with development of local ecology lesson plans to be formally incorporated into primary school curriculum; hosting Northern Mariana College students as field interns (with stipend); and supporting MINA’s the Bring the Trees Back Campaign. Additionally, educational outreach continues via public presentations at several community event venues and in primary school classrooms (K. Reininger in litt. 2021).
Conservation Actions Proposed
Continue to avoid the introduction of Brown Tree Snake on all islands using robust biosecurity protocols. Establish further protected areas and control development to protect remaining habitat, particularly forest, on Saipan (Liske-Clark 2015). Continue translocation efforts and update the strategic plan for future translocations (MAC Working Group 2014). Continue public awareness programmes on Saipan to raise awareness of conservation issues (MAC Working Group 2014).
12 cm. Small green and yellow warbler-like forest bird. Bright, olive-green upperparts, olivaceous ear-coverts, a white orbital ring and pale yellowish-white underparts. Voice Call a high-pitched tszeeip, often rapidly uttered and organized into a loose song.
Text account compilers
Berryman, A.
Contributors
Amidon, F.A., Hawley, N., Khwaja, N., Lepson, J., O'Brien, A., Radley, P., Reininger, K. & Saunders, A.
Recommended citation
BirdLife International (2024) Species factsheet: Saipan White-eye Zosterops saypani. Downloaded from
https://datazone.birdlife.org/species/factsheet/saipan-white-eye-zosterops-saypani on 23/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 23/11/2024.