Archived 2016 topics: Varied Tit (Parus varius) is being moved to the genus Sittiparus and split: list Izu Tit S. owstoni and S. olivaceus as Vulnerable?

This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for passerines

Lynx Edicions and BirdLife International will soon publish the second volume of the HBW-BirdLife Illustrated Checklist of the Birds of the World, building off the Handbook of the Birds of the World series, and BirdLife’s annually updated taxonomic checklist.

The new Checklist will be based on the application of criteria for recognising species limits described by Tobias et al. (2010). Full details of the specific scores and the basis of these for each new taxonomic revision will be provided in the Checklist.

Following publication, an open and transparent mechanism will be established to allow people to comment on the taxonomic revisions or suggest new ones, and provide new information of relevance in order to inform regular updates. We are also actively seeking input via a discussion topic here regarding some potential taxonomic revisions that currently lack sufficient information.

The new Checklist will form the taxonomic basis of BirdLife’s assessments of the status of the world’s birds for the IUCN Red List. The taxonomic changes that will appear in volume 2 of the checklist (for passerines) will begin to be incorporated into the 2016 Red List update, with the remainder to be incorporated into subsequent Red List updates.

Preliminary Red List assessments have been carried out for the newly split or lumped taxa. We are now requesting comments and feedback on these preliminary assessments.

Varied Tit Parus varius is being moved to the genus Sittiparus and split into S. varius, S. owstoni, S. olivaceus and S. castaneoventris, following the application of criteria set out by Tobias et al. (2010).

Prior to this taxonomic change, Parus varius (BirdLife species factsheet) was listed as Least Concern, on the basis that it was not believed to approach the thresholds for Vulnerable under any criteria. The pre-split species was characterised as common to abundant in southern Japan and the Kurils, uncommon in northern Japan, rare in northeast China and common in Korea. Occurs in lowland coniferous forests, open deciduous and mixed forests, in large gardens and urban parks in some parts of the range, and sometimes in coniferous plantations (Gosler and Clement 2016). Densities in the Izu Islands have been reported as 10-15 pairs/km2 (Gosler and Clement 2016), but this actually refers to a density derived from the number of pairs counted in a ‘certain area of 1 kilometer long and radial 50 metres’ along the main road (Higuchi 1976), suggesting that, if representative, the density extrapolated from here would be 200-300 mature inds/km2. Figures given in the same paper per hectare are 0.5-0.6 for the mainland and 0.8-1.2 for the island taxon (Higuchi 1976), or 50-60 pairs/km2 versus 80-120 pairs/km2.

Sittiparus owstoni is found on the three southern Izu Islands, namely Miyake, Mikura and Hachijo. S. olivaceus is restricted to Iriomote Island in the South Ryukyu Islands, while S. castaneoventris is found on Taiwan.

S. olivaceus has a very small single island range with an Extent of Occurrence of 368km2, but the area of land (taken as the maximum Area of Occupancy) is 292km2. However, population density appears difficult to apply given the discrepancy outlined above, and the fact that there do not appear to be any densities reported for the Ryukyu Islands. Given a population density of between 20-30km2 as reported to have been reported for the Izu Islands (per Gosling and Clements 2016), and assuming that 4/5 of the island area is suitable (given the very large area of remaining forest on the island), gives 4,672-7,008 individuals. Using the density actually reported from the Izu Islands between 1973 and 1975 (Higuchi 1976) gives a value of between 37,296 and 55,944 mature individuals. Clearly this is a problem, but it does allow an indication that the population is likely to considerably exceed 1,000 mature individuals, and is therefore unlikely to approach the threshold for listing as Vulnerable under criterion D.

Much of Iriomote is protected in some form, and there seems little to indicate that habitat loss is a concern for the species at present. Feral cats are present on Iriomote, but are not considered to pose a significant threat to the species given the presence of the native felid Prionailurus iriomotensis, and the absence of remains of the present species in a scat content study of felids on the island (Watanabe et al. 2003). In the absence of evidence of the impact of introduced species on Iriomote Tit the population is considered stable, hence the species is suggested to be listed as Least Concern.

Should there be evidence that the population of the species is actually much lower than suspected, due to a greatly divergent low population density in the species, or some unknown tragedy that has befallen this species in recent years, then it may warrant listing as Near Threatened.

S. owstoni has an EOO of 1,126km2, but a maximum AOO of approximately 130km2. The population has been estimated at 4,425-5,286 individuals (Fujita et al. 2011), which is considered equivalent to 2,900-3,600 mature individuals. Estimates for the three islands were 1.953-2,285 individuals on Miyake-jima, 1,077-1,453 individuals on Mikura-jima and 1,394-1,548 individuals on Hachijo-jima (Fujita et al. 2011), equivalent to 1,300-1,550, 700-1,000 and 900-1050 mature individuals respectively. The area of habitat considered suitable on each island was 24.7km2 on Miyake-jima, 18.2km2 on Mikura-jima and 25.8km2 on Hachijo-jima, of which 62.2km2 was natural forest (Fujita et al. 2011).

The species shares a range with Izu Thrush Turdus celaenops (BirdLife Species Factsheet) and Izu Leaf-warbler Phylloscopus ijimae (BirdLife Species Factsheet). For these species an ongoing population decline is suspected; for Izu Thrush the impact of introduced predators is thought to have caused an observed rapid decline and for Izu Leaf-warbler habitat loss and fragmentation are considered to be causing a moderate decline. Siberian Weasel was introduced to Miyake-jima in the 1970s and domestic cats are also widely present, additionally enhanced populations of Large-billed Crow as a result of the availability of food via poor human rubbish disposal. Large areas of natural forest have been replaced by Cryptomeria for timber. Road-building and the creation of tourist infrastructure have also been noted to have reduced the extent of natural habitat. In addition the impact of volcanic eruptions is a potential threat to populations in that these events can degrade large areas of habitat. The eruption in 2000 of Mt. Oyama is estimated to have degraded 60% of forest on Miyake-jima, however populations of birds reportedly recovered relatively quickly from this event. There does not appear to be any evidence of impacts from introduced predators on the taxon, although Sittiparus varius nameyei was noted to have very poor breeding success due to brood predation by snakes, but this appears specific to the island of Kozushima and is not seen in S. owstoni on Miyake-jima (Yamaguchi and Higuchi 2005).

From the threats outlined it is thought that Izu Tit S. owstoni, while tolerant of some habitat modification, has been negatively affected by the conversion of habitat within its range it is suspected of undergoing a minor, slow population decline.

Izu Tit S. owstoni is suggested as Near Threatened, on the basis that the species has a small population size that appears to be declining, and approaches the thresholds for Vulnerable under criterion C2a(i), given that on each island the population is close to 1,000 mature individuals.

If it is considered that the population is actually stable, then the species would be considered Least Concern.

S. castaneoventris is considered local on Taiwan, but is not believed to approach the thresholds for listing as Vulnerable under any criteria, and is therefore suggested to be listed as Least Concern.

Comments are invited on these proposed categories and further information would be welcomed.

*Note that the term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).

References:

Gosler, A. & Clement, P. 2016. Varied Tit (Poecile varius). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/59870 on 11 October 2016).

Higuchi, H. 1976. Comparative study on the Breeding of Mainland and Island Subspecies of the Varied Tit, Parus Varius. Tori 25 (99): 11-20.

IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. Gland, Switzerland and Cambridge, UK: IUCN Species Survival Commission.

IUCN. 2012. Guidelines for Application of IUCN Red List Criteria at Regional and National Levels: Version 4.0. Gland, Switzerland and Cambridge, UK: IUCN.

Tobias, J. A., Seddon, N., Spottiswoode, C. N., Pilgrim, J. D., Fishpool, L. D. C. and Collar, N. J. 2010. Quantitative criteria for species delimitation. Ibis 152: 724–746.

Watanabe, S., Nakanishi, N. and Izawa, M. 2003. Habitat and prey resource overlap between the Iriomote cat Prionailurus iriomotensis and introduced feral cat Felis catus based on assessment of scat content and distribution. Mammal Study 28: 47-56.

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One Response to Archived 2016 topics: Varied Tit (Parus varius) is being moved to the genus Sittiparus and split: list Izu Tit S. owstoni and S. olivaceus as Vulnerable?

  1. James Westrip (BirdLife) says:

    Based on available information, our preliminary proposal for the 2016 Red List would be to adopt the proposed classifications outlined in the initial forum discussion.

    There is now a period for further comments until the final deadline of 28 October, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from those in the initial proposal.

    The final 2016 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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