Data Zone
Justification of Red List category
Although this species has a large population, it qualifies as Near Threatened because of its tiny range and fears that the Brown Tree Snake Boiga irregularis could become established on its main range island (that hosts >99% of the global population), which could result in a moderately rapid population reduction. The risk of more rapid population reductions is mitigated by the presence of a Brown Tree Snake barrier at Tinian Port, with all planes, vessels and cargo subject to inspections, as well as snake traps maintained on fence lines surrounding ports of entry, and a taskforce able to respond to reports of snakes.
Population justification
The most recent estimate of the Tinian Monarch population on Tinian is 91,420 (95% CI 74,593-110,822) in 2013 (Naval Facilities Engineering Command, Pacific 2014). This is an increase from the last estimate in 2008 of 56, 305 (95% CI 43,343-70,909); however, the long-term trend for the Tinian Monarch population has been stable between 1982 and 2013 (Naval Facilities Engineering Command, Pacific 2014) and these differences are likely born from a difference in survey methodology. A second population was established on Guguan. Although no population estimate has been made of this population since its introduction, the size of the island means that it is unlikely to exceed a few hundred individuals when at carrying capacity, thus is unlikely to exceed 1% of the global population. The global population is placed in the band of 50,000-99,999 individuals, or perhaps approximately 33,000-66,000 mature individuals.
Trend justification
The population is believed to be stable in absence of an acting threat. A five-year monitoring programme, which included surveys and survival studies, was undertaken from 2006 to 2010 as part of the removal of this species from the U.S. Endangered Species List; the study apparently indicated a continuing decline in monarch populations on Tinian (USFWS 2005, Marshall & Amidon 2009, F. A. Amidon in litt. 2012, P. Radley in litt. 2012), although the most recent surveys in 2013 revealed that their numbers are comparable to earlier estimates (Naval Facilities Engineering Command, Pacific 2014).
This species is endemic to Tinian in the Northern Mariana Islands (U.S.A.). The northern two-thirds of the island are leased to the Department of Defense who previously used it only intermittently, allowing the regeneration of vegetation. In 2015 and 2016 it was introduced to Guguan for conservation purposes and has successfully bred on this island.
It inhabits all types of forest, including introduced tangan-tangan Leucaena leucoephala thickets. Although it appears to be adaptable to patches of recovering forest habitat, limestone forest remains crucial. Surveys in 2013 estimated the following densities per habitat: limestone forest: 11.188 birds/ha ± 1.357 SE (95% CI 8.786-14.221); secondary forest: 11.005 birds/ha ± 1.314 SE (95% CI 8.657-13.711); tangan tangan: 10.147 birds/ha ± 1.159 SE (95% CI 7.984-12.465); herbaceous scrub: 5.047 birds/ha ± 1.051 SE (95% CI 3.085-7.234). Annual survival rates from 2006 to 2009 were 82% for males and 64% for females (Marshall & Amidon 2009). Surveys in 1995 found over 60% of nests in native tree species with far greater nesting success in remnant native forest, probably due to the greater availability of insects and greater protection from fire and damage from storms (USFWS 1996). However, this may have been an artifact of the study occurring within a particularly bad year for storms, and the fact that the remaining native forest on Tinian is restricted almost exclusively to cliff lines which may have been responsible for protection from storm damage, rather than the habitat type itself (L. Zarones in litt. 2016). A broader study over multiple seasons and using replicate plots per habitat type is recommended (L. Zarones in litt. 2016). Although the species has been shown to breed year-round, there appears to be distinct seasonality in nesting activity and success, with less nesting occurring during periods of low rainfall (USFWS 1996).
The Tinian Monarch is regarded as a Species of Greatest Conservation Need by the CNMI Division of Fish and Wildlife, due to threats from commercial, agricultural and residential development, invasive vines, military expansion, typhoons, and the potential for establishment of the Brown Tree Snake (Liske-Clark 2015).
By 1945, native forest had been reduced to 5-7%, owing to development for sugarcane production and the construction of infrastructure to support military activities in Second World War (USFWS 1996, Lusk et al. 2000). Native limestone forest currently only remains on around 5% of Tinian (USFWS 2009), mostly on rugged limestone slopes (J. Lepson in litt. 1999, Camp et al. 2012). However, this species appears very resilient to habitat loss and degradation, occurring widely in scrub and second growth habitats. Forest clearance for cattle farming and (possibly) tourism developments are also considered threats (P. Radley in litt. 2012).
The potential introduction of the exotic Brown Tree Snake Boiga irregularis from the nearby island of Guam is a concern, although robust biosecurity measures currently reduce the likelihood of this causing rapid declines or extirpation. Pox-like lesions were found on some birds captured and banded in 2006 and 2007, but none captured during 2008 showed symptoms, indicating that avian disease may threaten the species (Amidon and Marshall 2008), however testing of samples of the lesions proved inconclusive (Marshall and Amidon 2009).
Conservation Actions Underway
The northern two-thirds of Tinian are leased to the Department of Defense who previously used it intermittently, allowing the regeneration of much of the vegetation, albeit primarily introduced tangan-tangan (Leucaena leucocephala), which has undoubtedly benefited the species (USFWS 1996, Lusk et al. 2000). Future actions of the Department of Defense on this land through forest clearing and building construction (P. Radley in litt. 2016) may however have negative environmental impacts. In 2013, a petition to relist the species on the Endangered Species List was created and was signed by Guam Audubon and various other groups and individuals in the Marianas and elsewhere (P. Radley in litt. 2016). A Brown Tree Snake barrier is now operational at the Tinian port to assist with interdiction efforts (N. Hawley in litt. 2007, F. A. Amidon in litt. 2012). A Department of Defense-funded research project at the University of Washington to study the life history of the Tinian Monarch on Tinian has been issued CNMI permits. As part of the MAC project 48 Tinian Monarchs were successfully translocated in 2015 to the island of Guguan, and an additional 54 monarchs in 2016. All translocated birds were colour-banded and in 2016, three unbanded adults were observed by CNMI Division of Fish and Wildlife biologists, indicating that breeding had successfully occurred (P. Radley in litt. 2016). A captive breeding programme for Tinian Monarchs in AZA zoos was initiated as part of the MAC program. These efforts have experienced only modest success and captive breeding is no longer a priority focus of the programme.
Conservation Actions Proposed
Continue to regularly monitor population trends through detailed censuses (L. Zarones in litt. 2016). Continue to monitor the translocated population on Guguan. Preserve the remaining limestone forest habitat on Tinian (USFWS 1996). Preserve secondary forest (L. Zarones in litt. 2016). Attempt to increase the amount of native forest (J. Lepson in litt. 1999). Continue biosecurity measures to prevent the introduction of the Brown Tree Snake.
15 cm. Small, dull-coloured flycatcher. Buffy-tan sides of face, bold eye-ring, and most of underparts, grey crown and nape. Brown-chocolate back, black wings and tail, with white tail tip, two narrow wing-bars, and edges of tertials. White rump and undertail-coverts. Similar spp. Rufous Fantail Rhipidura rufifrons has rufous rump, dark underparts and white throat. Voice Loud, raspy scold and short two-note call that sounds like a dog's squeaky toy. Song a loudly whistled tee-tee-wheeo. Hints Found in any brushy areas on the island.
Text account compilers
Berryman, A.
Contributors
Amidon, F.A., Camp, R., Derhé, M., Dutson, G., Hawley, N., Khwaja, N., Lepson, J., Mahood, S., North, A., O'Brien, A., Radley, P., Shutes, S., Stattersfield, A., Wiles, G. & Zarones, L.
Recommended citation
BirdLife International (2024) Species factsheet: Tinian Monarch Metabolus takatsukasae. Downloaded from
https://datazone.birdlife.org/species/factsheet/tinian-monarch-metabolus-takatsukasae on 25/12/2024.
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 25/12/2024.