Archived 2020 topic: Seychelles Paradise-Flycatcher (Terpsiphone corvina): Revise global status?

BirdLife International factsheet for Seychelles Paradise-Flycatcher.

The Seychelles Paradise-Flycatcher is endemic to the Seychelles. This species inhabits native high canopy woodland, and there are currently successful populations on both La Digue and Denis Islands. A third population is in the process of being established on Curieuse Island.

The most recent census placed the population on La Digue at 294-441 individuals, of which 280-436 were mature (Bristol et al. 2018), while another 84 individuals were found on Denis Island, of which 70 were mature (Bristol & Gamatis, 2017). The lower population estimate for La Digue is conservative, and it is believed that the true population size is closer to the higher estimate (Bristol et al. 2018). A further population of 26 individuals was introduced to Curieuse Island in 2018-2019, and while they have bred successfully, it remains too early to tell whether that population is self-sustaining (R Bristol, 2020, pers. comm., 11 March). According to IUCN guidelines, introduced populations can only be included in assessments once they have bred successfully, or five years have passed since their introduction; whichever is longer (IUCN Standards and Petitions Committee, 2019). Here, the latter stipulation is not met, and so this population is not yet included in the new population or Extent of Occurrence (EOO) estimates. Therefore, the most current population size estimate for the Seychelles Paradise-Flycatcher is 350-506 mature individuals (Bristol et al., 2018; Bristol & Gamatis, 2017).

Populations of Seychelles Paradise-Flycatcher have been increasing over the last decade, from 143-190 pairs in 2007 (R Bristol, unpublished survey data) to 140-217 pairs in 2017 (Bristol et al. 2018). However, the species is still threatened by habitat loss for development projects, and the number of territories on the western plateau of La Digue continue to decline as a result (Bristol, 2016; Gamatis & Bristol, 2018).

The Seychelles Paradise-Flycatcher has been considered Critically Endangered under the criterion B1ab(iii). In light of the increase in population size and EOO from the successful reintroduction to Denis Island, this listing is no longer appropriate. This species had been placed under the five year rule, which has now come to an end, and its Red List assessment now merits review. We have therefore reassessed the Seychelles Paradise-Flycatcher against all the criterion below.

Criterion A: The population of the Seychelles Paradise Flycatcher is currently increasing, following a steady increase over the last 3 generations (11.1 years; Bird et al., 2020*). This species may therefore be considered Least Concern under this criterion.

Criterion B: The Extent of Occurrence (EOO) for this species has now increased to 160 km² following the successful reintroduction of a self-sustaining population to Denis Island. This meets the initial threshold for classification as Endangered (EOO <5000 km²) under criterion B1. The maximum Area of Occupancy (AOO), as calculated to IUCN guidelines, has been calculated at 32 km², which also meets the initial threshold for Endangered (AOO <500 km²). In order to fully qualify for this listing, other sub-criteria must be met.

This species is not considered severely fragmented, nor is it experiencing extreme fluctuations. It is however experiencing a continuing decline in habitat in one area of its range (Gamatis & Bristol, 2018). In order to fully qualify as threatened under this criterion, this species must occur in ≤10 locations. Location in this instance is defined as a geographically distinct area where a single threatening event can rapidly affect all individuals of the taxon present (IUCN Standards and Petitions Committee, 2019). The main threats to this species are habitat loss through development pressures, invasive species, and predation.

On the plateau on La Digue, the main threat is habitat loss resulting from development. Here, locations may be estimated based on the area where a single development project can severely reduce or eliminate the population over the longer of three years or one generation (IUCN Standards and Petitions Committee, 2019). The generation length for the Seychelles Paradise-Flycatcher has been recalculated to 3.7 years (Bird et al. 2020)*, so this is the figure that will be used when estimating locations. The exact rate of development is uncertain, but an estimate can be gleaned from examining the reduction in flycatcher territories, which is believed to be caused by development pressures (Gamatis & Bristol, 2018). Repeated surveys of the area bounded by the canal between 1999 and 2016 found that the number of territories decreased by 19 over the 17 year period. The territory size of the Seychelles Paradise-Flycatcher is estimated to be 1.04 ha (Currie et al., 2003), and so the number of lost territories equates to an area of 19.8 ha. Assuming that the rate of loss remains constant, this presents an annual loss of 1.16 ha. Over a single generation, 4.3 ha would be lost, which is roughly 4 territories. Over the whole plateau, there are currently 47 territories (Gamatis & Bristol, 2018), and the officially protected area of the Veuve Nature Reserve is large enough for 9 territories (Gamatis & Bristol, 2018). This leaves an estimated 38 territories at risk from development. If 4 territories are lost every generation, it would take 9.5 generations to completely eliminate the population on the unprotected plateau. Rounded, this would equal an estimated 10 locations. The area within the Veuve reserve is protected from development, and is not known to be under threat from invasive species or excess predation. It would therefore be considered as 1 location.

The hillsides of La Digue are relatively safe from development, but it is still important to consider the number of locations should the threat spread. The most recent population estimate for La Digue is 140-217 pairs (Bristol et al. 2018). Assuming this equates to 140-217 territories, minus the 47 on the plateau, this leaves an estimated 93-170 territories in the hillsides. Assuming development spread there at the same rate as above, it would take between 23 and 43 generations to eliminate the flycatchers. Therefore, there is estimated to be >20 locations on the hillside.

On Denis Island, the habitat has been restored, and it appears the main threat to the population there are invasive alien species. To date, rats (Rattus rattus), cats (Felis catus) and Common Myna (Acrotheres tristis) have been eradicated from the island (Bristol & Gamatis 2017). If these species were ever reintroduced, given the small size of the island, it is not unrealistic to estimate that in 3.7 years they could spread and have significant impacts on the flycatcher population. Denis Island is therefore estimated to be 1 location.

As the Seychelles islands sit in the Indian Ocean, they are at risk from cyclones. If one cyclone could cause a significant threat that would severely reduce the population, this may affect the number of locations considered here, and therefore the extinction risk applied under this criterion. We therefore ask: Do the islands of La Digue and Denis sit in the path of cyclones? How at risk from cyclone damage is the Seychelles Paradise-Flycatcher? Could one cyclone eradicate the population?

Based on the current information detailed above, in total, the number of locations for the Seychelles Paradise-Flycatcher is estimated to be >30. This is far too high to fully meet the ≤ 10 location threatened threshold. As such, the Seychelles Paradise-Flycatcher does not fully qualify as threatened under this criterion, and may therefore be considered Least Concern under criterion B.

Criterion C: Although the population size remains small, in order to be classified under criterion C, a species must be undergoing an observed, estimated, projected or inferred continuing decline. The population size of Seychelles Paradise-Flycatcher is increasing, and so it can be considered Least Concern under this criterion.

Criterion D: There are now at least 350-506 mature individuals of this species (Bristol & Gamatis, 2017; Bristol et al., 2018), which meets the threshold for classification as Vulnerable (<1000 mature individuals) under criterion D1.

Criterion E: To the best of our knowledge, no quantitative analysis has been carried out on this species, so it cannot be assessed against this criterion.

This species reached the threshold for a genuine change in Red List Category c.2015. It is therefore suggested that the Seychelles Paradise-Flycatcher (Terpsiphone corvina) be listed as Vulnerable under criterion D1. We welcome any comments for the proposed listing.

Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’ Red List status. Therefore, please make sure your comments are relevant to the species’ Red List status and the information requested. By submitting a comment, you confirm that you agree to the Comment Policy.

*Bird generation lengths are estimated using the methodology of Bird et al. (2020), as applied to parameter values updated for use in each IUCN Red List for birds reassessment cycle. Values used for the current assessment are available on request. We encourage people to contact us with additional or improved values for the following parameters; adult survival (true survival accounting for dispersal derived from an apparently stable population); mean age at first breeding; and maximum longevity (i.e. the biological maximum, hence values from captive individuals are acceptable).

An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.

References

Bird, J. P.; Martin, R.; Akçakaya, H. R.; Gilroy, J.; Burfield, I. J.; Garnett, S.; Symes, A.; Taylor, J.; Šekercioğlu, Ç.; Butchart, S. H. M. (2020). Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.

Bristol R. M. and Gamatis I., 2017, Seychelles paradise flycatcher population census on Denis Island, June 2017. Unpublished Report.

Bristol RM, Gamatis I, Onezia C., 2018, Survey of the Seychelles paradise flycatcher population on La Digue Island, 2017. Unpublished ETF funded project report.

Bristol, R.M., 2016, Seychelles paradise flycatcher population census on Denis Island, January 2016. Unpublished report.

Currie D, Bristol R, Millett J, Hill M, Bristol U, Parr SJ, Shah, NJ (2003b) Habitat requirements of the Seychelles Black Paradise Flycatcher Terpsiphone corvina: a re-evaluation of translocation priorities. Ibis, 145, 624-636.

Gamatis I, Bristol R.M., 2018, Seychelles paradise flycatcher (Terpsiphone corvina), census and territory mapping, La Digue western plateau, June 2018.

IUCN Standards and Petitions Committee, 2019. Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

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5 Responses to Archived 2020 topic: Seychelles Paradise-Flycatcher (Terpsiphone corvina): Revise global status?

  1. Rachel Bristol says:

    In response to your question “Do the islands of La Digue and Denis sit in the path of cyclones? How at risk from cyclone damage is the Seychelles Paradise-Flycatcher? Could one cyclone eradicate the population?”
    1. The islands of Denis and La Digue do not currently sit in the path of cyclones. i.e. they are outside the cyclone belt.
    2. They are therefore at LOW risk from cyclone damage.
    3. I very much doubt that (in the unlikely event that the granitic Seychelles was hit by a cyclone) one cyclone would eradicate flycatchers.
    I think they should be downgraded to ‘Vulnerable’ as suggested in the above assessment.

  2. Dave Currie says:

    I concur with Rachel Bristols’s comments

  3. Red List Team (BirdLife International) says:

    Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested by so many people in commenting. The window for consultation is now closed. We will analyse and interpret the new information and post a preliminary decision on this species’s Red List status on this page in early July.

    Thank you once again,
    BirdLife Red List Team

  4. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information, and the confirmation that the Seychelles Paradise-flycatcher is not at significant risk from cyclones, our preliminary proposal for the 2020 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 in mid-July, 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 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN. The final publication date will be publicised by IUCN here: https://www.iucnredlist.org/assessment/updates

  5. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    The final categorisation for this species has not changed. Seychelles Paradise-flycatcher is recommended to be listed as Vulnerable under Criterion D1.

    Many thanks for everyone who contributed to the 2020 GTB Forum process. The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.