Archived 2020 topic: Glow-throated Hummingbird (Selasphorus ardens): revise global status?

BirdLife species factsheet for Glow-throated Hummingbird

Glow-throated Hummingbird (Selasphorus ardens) is endemic to Panama, where it occurs in the Serranía de Tabasará and in the highlands of the Azuero Peninsula. The species is mostly recorded above 1,200 m altitude (G. Angehr in litt. 2020). The species and its ecological requirements are not well known (Stiles and Sharpe 2020). It inhabits shrubby growth in clearings and forest borders, but is not thought to survive in areas where forest has been fully cleared (G. Angehr in litt. 2013, 2020). Apart from forest clearance, the species is potentially threatened by the impacts of climate change, as its range may shift upslope and contract in size close to mountaintops (G. Angehr in litt. 2020).

The population size has not been quantified directly. Based on the recorded population densities of congeners (Selasphorus calliope and S. platycercus: 15-75 mature individuals/km2 [Santini et al. 2018]), the area of the species’s mapped extant range (1,625 km2) and assuming that around 10% of the range is occupied, the population is estimated to fall within the band 2,430-12,150 mature individuals. To account for uncertainty in the estimate, the species is here placed in the band 2,000-15,000 mature individuals. Given that the species appears to be rare (G. Angehr in litt. 2020), it is conceivable that the true population size is closer to the lower end of the estimate.

Glow-throated Hummingbird has been considered Endangered under Criterion C2a(i,ii) (BirdLife International 2020). However, new information regarding the distribution range and the population size and trend suggest that the species may warrant a change in Red List status. Therefore, we have fully reviewed the species here against all criteria.

Criterion A – The population trend has not been assessed directly. The species is threatened by habitat loss; however forests within the range are largely inaccessible and declines in tree cover are local and low (G. Angehr in litt. 2020, Global Forest Watch 2020). Given that the species is able to survive in degraded and secondary forests (G. Angehr in litt. 2013), forest loss is currently unlikely to drive population declines. As the species is confined to a small range close to mountaintops, it is potentially vulnerable to climate change-related range shifts (G. Angehr in litt. 2020). Precautionarily, it is assumed that the species may be undergoing population declines in the future as suitable habitat is contracting at mountaintops. The rates of habitat loss and population declines have not been projected, but it is unlikely that they will exceed 10% over the next ten years (one generation length being 2.0 years; Bird et al. 2020)*. Unless new information becomes available, the species qualifies as Least Concern under Criterion A. 

Criterion B – The newly calculated Extent of Occurrence (EOO) for this species is 10,800 km2. This meets the threshold for Vulnerable under Criterion B1. However, in order to be listed as threatened, a species needs to fulfil at least two further conditions.

Given the homogeneity and stability of forests within the range, Glow-throated Hummingbird cannot be considered severely fragmented sensu IUCN (IUCN Standards and Petitions Committee 2019) nor occurring at a limited number of locations**, thus, the species does not meet sub-criterion a. As suitable habitat is feared to decline due to climate change impacts, the species is projected to undergo a slow continuing decline in EOO, AOO, extent of habitat, and population size over the next ten years, meeting sub-criterion b(i,ii,iii,v). There is currently no evidence of extreme fluctuations in the species, so that sub-criterion c is not met. Overall, while the EOO meets the threshold for Vulnerable, the species fulfils just one out of two further conditions. It can therefore only be listed as Near Threatened, approaching the threshold for listing as threatened under Criterion B1b(i,ii,iii,v).

Criterion C – The global population size is preliminarily estimated to number 2,000-15,000 mature individuals. Assuming that the true population size is closer to the lower end of the estimate, this meets the threshold for listing as threatened under Criterion C. However, in order to do so, a species must meet further conditions.

Glow-throated Hummingbird is precautionarily projected to decline at a rate of <10% over the next ten years. The species thus does not meet the threshold for listing as threatened under Criterion C1, but approaches it. The species moreover forms at least two subpopulations (G. Angehr in litt. 2020); one to three very small subpopulations on the Peninsula de Azuero and a substantially larger one further north. Therefore, sub-criterion a(ii) is not fulfilled. Moreover, even under the assumption that the true population size is closer to the lower end of the estimate, it is highly unlikely that the larger subpopulation numbers less than 1,000 mature individuals. Sub-criterion a(i) is therefore not fulfilled either; however under a conservative approach it can be assumed that the largest subpopulation only slightly exceeds this number and thus approaches this threshold. Overall, Glow-throated Hummingbird may be listed as Near Threatened, approaching the threshold for listing as threatened under Criterion C1+2a(i).

Criterion D – The global population size and range are too large to warrant listing as threatened under this criterion, and therefore Glow-throated Hummingbird is considered Least Concern under Criterion D.

Criterion E – To the best of our knowledge, there has been no quantitative analysis of extinction risk conducted for this species. Therefore, it cannot be assessed against this criterion.

Therefore, it is suggested that Glow-throated Hummingbird (Selasphorus ardens) be listed as Near Threatened, approaching the threshold for listing as threatened under Criteria B1b(i,ii,iii,v); C1+2a(ii).We welcome any comments to the proposed listing and specifically request up-to-date information on the population size and trend.

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).

**The term ‘location’ refers to a distinct area in which a single threatening event can rapidly affect all individuals of the taxon present, with the size of the location depending on the area covered by the threatening event. 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).

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: Selasphorus ardens. http://www.birdlife.org (Accessed 30 March 2020).

Global Forest Watch. 2020. Interactive Forest Change Mapping Tool. http://www.globalforestwatch.org (Accessed 30 March 2020).

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

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 Categoreis and Criteria. Version 14. http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

Santini, L.; Isaac, N. J. B.; Ficetola, G. F. 2018. TetraDENSITY: A database of population density estimates in terrestrial vertebrates. Global Ecology and Biogeography 27: 787-791.

Stiles, F. G.; Sharpe, C. J. 2020. Glow-throated Hummingbird (Selasphorus ardens), version 1.0. In: del Hoyo, J.; Elliot, A.; Sargatal, J.; Christie, D. A.; de Juana, E. (eds.). Birds of the World. Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi/org/10.2173/bow.glthum1.01 (Accessed 30 March 2020).

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6 Responses to Archived 2020 topic: Glow-throated Hummingbird (Selasphorus ardens): revise global status?

  1. Our organization has had permanent study plots in the Ngäbe-Bugle Comarca and in Veraguas since 2012.

    These study plots (15) have been measuring relative abundance (“timed species counts”) and species specific data (point counts combined with territory mapping) for (S. ardens). Moreover, we have been surveying habitat condition/change over time.

    We have measured a significant decline in S. ardens on these plots which we hypothesize is due directly to significant loss of habitat. Data to date is unpublished.

    We have been limited in a more precise and accurate survey of these areas due largely to the cost and difficulty in access. We do, although, have data from 2012 – 2020.

    I have been asked to contribute further on this … but time and funding is just problematic.

    *There has also been interest and concern for species mixing at the western territorial limit of S. ardens with S. scintilla. We have completed ad-hoc observational data which supports this concern. More investigation is required.

  2. Red List Team (BirdLife International) says:

    Global Forest Change data on tree cover loss up to 2019 have now been released and made available via Global Forest Watch. Based on these data, over ten years approximately 1.5% of tree cover with at least 30% canopy cover was lost from within the species’s range (Global Forest Watch 2020). This does not affect the above assessment under Criterion A.

  3. We confirmed the presence of a population of likely S. ardens in the Azuero Peninsula. Along with Dyer & Vallely’s (2017) intensive scrutiny on female description, we have reviewed the taxonomic status of Cerro Hoya specimens to accurately determine whether these specimens are conspecific to S. ardens in Comarca Ngabe-Bugle population of S. ardens. With the evidence available so far, we cannot assure that Azuero specimens and S. ardens are conspecific.
    In addition, the highlands of Azuero Peninsula include El Montuoso Forest Reserve, which is a place that has been surveyed and no individual of Selasphorus has been recorded.
    See below:
    https://bioone.org/journals/bulletin-of-the-british-ornithologists-club/volume-137/issue-2/bboc.v137i2.2017.a3/On-the-female-plumage-of-Glow-throated-Hummingbird-Selasphorus-ardens/10.25226/bboc.v137i2.2017.a3.full

    https://journals.sfu.ca/ornneo/index.php/ornneo/article/view/383

  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

    New information submitted during the Forum process is casting doubt on the validity of records from Azuero peninsula. Until these records are confirmed as being of S. ardens, we apply a precautionary approach: The range map has been adapted accordingly, with the species classified as ‘possibly extant’ on the Azuero peninsula. The assessment under Criteria A, D and E are unaffected by this change; under Criteria B and C the species is assessed as follows:

    Criterion B – The EOO is now calculated as 3,000 sqkm. As the species however does not fulfil enough conditions for a threatened status (see above), it is listed as Near Threatened under Criterion B1b(i,ii,iii,v).

    Criterion C – Based on the newly mapped range, the population size has been estimated as 2,235-11,175 mature individuals (see above for a description of the extrapolation method); it is here placed in the band 2,000-12,000 mature individuals. All individuals belong to one subpopulation. The species is projected to undergo a continuing decline of <10% over the next ten years. The species hence qualifies for listing as Endangered under Criterion C2a(ii).

    Based this information, our preliminary proposal for the 2020 Red List would be to list Glow-throated Hummingbird as Endangered under Criterion C2a(ii).

    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. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    The final categorisation for this species has not changed. Glow-throated Hummingbird is recommended to be listed as Endangered under Criterion C2a(ii).

    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.

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