Iiwi (Drepanis coccinea): Revise global status?

BirdLife International factsheet for the Iiwi.

The Iiwi is a species of Hawaiian honeycreeper, endemic to the Hawaiian Islands in the Pacific. It is a forest dependent species and inhabits a variety of native, disturbed and un-natural habitat (BirdLife International, 2020). The most recent population estimate places the global population between 572,670-638,374 individuals. If we assume two thirds of individuals are mature, this equates to 382,688-427,719 mature individuals. The total individuals on each island is estimated to be 1,789-3,520 on Kaua’i, 54,569-65,148 on Maui, and 516,312-569,706 on Hawai’i (Paxton et al. 2013).

The main threat to this species appears to be avian malaria, to which it is highly vulnerable. 50% of the global population is now restricted to an elevation band of 1,300-1,900m due to the prevalence of mosquito vectors at low and mid elevations. It is also predicted that this band will decrease further with climate change as warming temperatures allow the mosquitos to spread to higher elevations (Paxton et al. 2013).

This species has been considered Vulnerable under criterion B1ab(i,ii,iii,v) (BirdLife International, 2020). However, this listing was based on an Extent of Occurrence (EOO) that was calculated as the ‘area of mapped range’. The EOO is actually a measure of the spatial spread of the areas occupied by a species, not the actual area it occupies, and should be calculated using a Minimum Convex Polygon (MCP) (IUCN, 2012; Joppa et al., 2016). As such the current EOO value is no longer appropriate. The newly-calculated EOO exceeds the threshold required to maintain the species’s current listing, and consequently warrants a full Red List status review against all the criteria, which we have provided here.

Criterion A: Paxton et al. (2013) estimated projected trends for the Iiwi populations on Kaua’i, Maui and Hawai’i over a 25-year period, with mixed results. The rate of decline is measured over the longer of 10 years or 3 generation lengths of the species (IUCN Standards and Petitions Committee, 2019). The generation length for the Iiwi has been recalculated to 2.4 years (Bird et al., 2020)*. Rates of decline for the Iiwi are therefore calculated over a period of 10 years.

Iiwi populations on Kaua’i are projected to undergo the worst declines, at a rate equivalent to 54% over 10 years. On Maui, the population on one side of the island appears stable, but on the other side is projected to experience an equivalent 10-year decline rate of 15%. The combined projected trend for the declining populations on Hawai’i is a 53% decline over 25 years, equating to a 26% decline over a 10-year period. Populations on the leeward side of the island are projected to increase, but the authors state uncertainty about whether this is a genuine contrary population trend, or the result of a sparsely sampled area (Paxton et al, 2013).

According to IUCN guidelines, data representing declines from a few subpopulations can be projected onto the rest of the range if those subpopulations were by far the largest subpopulation three generations ago, or if it can be assumed that all the other subpopulations are declining at the same rate (IUCN Standards and Petitions Committee, 2019). Hawai’i represents the majority of the Iiwi population, containing an estimated 90% of the remaining individuals. Given the uncertainty about potential population increases on the island, and this species’s high vulnerability to avian malaria, it is suspected that the whole population will experience declines overall, placed here in the band of 20-29%. This rate of decline does not quite meet the threshold for Vulnerable under this criterion, however it is assumed that current declines could approach a threatened status in the future. Therefore, the species is considered Near Threatened, approaching a listing as threatened under criterion A3ce.

Criterion B: The newly-calculated EOO for this species is 45,000 km². This is too large to trigger the threatened threshold (EOO <20,000 km²) under this criterion. The Iiwi may therefore be considered Least Concern under criterion B.

Criterion C: The global population size estimate is too high to trigger the threatened threshold (< 10,000 mature individuals) under this criterion. The Iiwi may therefore be considered Least Concern under criterion C.

Criterion D: The global population size estimate is too high to trigger the threatened threshold (< 1,000 mature individuals) under this criterion. The Iiwi may therefore be considered Least Concern under criterion D.

Criterion E: To the best of our knowledge, no quantitative analysis has been carried out for this species. We therefore cannot assess this species against criterion E.

We therefore suggest that the Iiwi (Drepanis coccinea) be listed as Near Threatened, approaching a threatened status under criterion A3ce. We welcome any comments to 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.

BirdLife International (2020) Species factsheet: Drepanis coccinea. Downloaded from http://www.BirdLife.org on 18/05/2020

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. www.iucnredlist.org/technical-documents/categories-and-criteria.

IUCN Standards and Petitions Committee. 2019. Guidelines for using the IUCN Red List Categories and Criteria. Version 14. http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

Joppa, L. N.; Butchart, S. H. M.; Hoffmann, M.; Bachman, S. P.; Akçakaya, H. R.; Moat, J. F.; Böhm, M.; Holland, R. A.; Newton, A.; Polidoro, B.; Hughes, A. 2016. Impact of alternative metrics on estimates of extent of occurrence for extinction risk assessment. Conservation Biology 30: 362-370.

Paxton, E.H., Gorresen, P.M., and Camp, R.J., 2013, Abundance, distribution, and population trends of the iconic Hawaiian Honeycreeper, the ‘I‘iwi (Vestiaria coccinea) throughout the Hawaiian Islands: U.S. Geological Survey Open-File Report 2013-1150, 59 p.

This entry was posted in Americas, Hawaii and tagged , . Bookmark the permalink.

6 Responses to Iiwi (Drepanis coccinea): Revise global status?

  1. I would argue against changing the status of the Iiwi to Near Threatnened. The main for the change seems to be the failure to meet criterion B based on a recalculation of the species range. I would be interested in seeing a map of the newly estimated range and the methods used to derive it. Its not clear what the difference is in the new EOO: “The EOO is actually a measure of the spatial spread of the areas occupied by a species, not the actual area it occupies”. The primary threat to this species, mosquito-borne diseases, is expected to worsen quickly as a result of climate change, and I wonder if this has been adequately represented in the analyses.

  2. Joanna Wu says:

    It’s true that the review does not include this paper on modeled future ranges with climate change (Fortini et al. 2015; https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0140389). However, even with the future projected loss of 59% of its range, taking avian malaria’s expansion into account, the ‘i’iwi’s future potential range (743,000 km2) would still be higher than the threshold (20,000 km2).

    The conservation of island endemic species like the ‘i’iwi is of utmost importance, but it does not currently seem to fit well with IUCN’s criteria for Vulnerable.

  3. Eric VanderWerf says:

    This species is clearly threatened by mosquito-borne diseases and climate change. It was recently listed as Threatened under the USA Endangered Species Act. https://www.fws.gov/news/ShowNews.cfm?ID=991118D2-F9E8-6776-7B72B28610BC1433 I don’t know where your information came from, but it does not seem reasonable that the future potential range of the iiwi could be 743,000 km2. A quick Google search indicated that the land area of all the Hawaiian Islands put together is 16,636.5 km2, and the species occupies only a small fraction of that. In these days of proliferating misinformation and political division, proposing to downlist the iiwi would send a mixed message that could undermine efforts to protect it. If the Redlist criteria fail to recognize the threats to this species, then to me that indicates a flaw in the criteria.

  4. 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

  5. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2020 Red List would be to list Iiwi as Vulnerable under Criterion A3ce.

    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 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.

  6. Eric VanderWerf says:

    Under criterion B above, it says “The newly-calculated EOO for this species is 45,000 km²”. However, as I pointed out previously, all of the Hawaiian Islands put together have a total land area of only 6,423.4 square miles (16,636.5 km2), and the iiwi occupies only a tiny fraction of that area and is absent entirely from some islands. The information in the response above that its potential future range incorporating climate change is 743,000 km2 is even more nonsensical. The iiwi is a forest bird and does not occupy the ocean areas between the islands. Its range is already very small and is declining rapidly. As we all know, island endemic species are disproportionately at risk from all sorts of threats, it is surprising that IUCN cannot find a way to represent this risk in the criteria.

Leave a Reply

You have to agree to the comment policy.

All comments must follow the rules of usage.

This site uses Akismet to reduce spam. Learn how your comment data is processed.