Archived 2020 topic: Gunnison Grouse (Centrocercus minimus): revise global status?

BirdLife species factsheet for Gunnison Grouse

Gunnison Grouse (Centrocercus minimus) is endemic to sagebrush habitats in western USA. Its historical range presumably included large areas in Colorado, Utah, Arizona, New Mexico and Kansas (Fjeldså and Kirwan 2020), but following intense habitat loss due to land-use change as well as hunting it is now confined to only 8% of its original range (Schroeder et al. 2004, Braun et al. 2014, Young et al. 2020). The population is estimated to number 4,800 mature individuals (Partners in Flight 2019). 85-90% of the population, i.e. 4,080-4,320 mature individuals, occur in one site in the Gunnison Basin, with a further seven small populations in the vicinity (USFWS 2019, Zimmerman et al. 2019). After severe declines in the past, the species now shows signs of recovery, with the population in the Gunnison Basin assumed to be stable since the late 1990s (Davis et al. 2015, USFWS 2019).

Gunnison Grouse is currently listed as Endangered under Criterion B2ab(i,ii,iii,v) (BirdLife International 2020). However, new information regarding the population size and trend and a review of the available data on the distribution range suggest that the species may warrant a change in Red List status. Therefore, it will be re-assessed against all criteria:

Criterion A – The species has been undergoing a large, significant decline over the last five decades; the rate of decline amounts to more than 50% between 1970 and 2017, equating to ≥ 22.6% over three generations (17.4 years; Partners in Flight 2019, see also Panjabi et al. 2019)*. It seems however, that these declines are historical, and the largest population in the Gunnison Basin is now assessed as stable (USFWS 2019). The seven satellite populations around Gunnison Basin are in more fragile states though: Declines are still ongoing, and under a worst case scenario, up to five of the satellite populations may be in critical condition or even extirpated by 2050 (USFWS 2019). The species is therefore projected to undergo a decline as satellite populations are declining, but the impact on the overall population is likely low, given that up to 90% of the population in the Gunnison Basin is presumably safe. The species is therefore estimated to decline at a rate of < 20% over three generations, which is projected to continue in the future. Hence, the species may be listed as Least Concern under Criterion A.

Criterion B – The species’s range is too large to warrant listing as threatened under Criterion B (Extent of Occurrence = 37,500 km2, maximum Area of Occupancy = 13,884 km2) and thus Gunnison Grouse qualifies as Least Concern under this criterion.

Criterion C – The global population numbers 4,800 mature individuals (Partners in Flight 2019). Studies have detected low levels of gene flow between sites; therefore the species is tentatively assessed as forming only one subpopulation (USFWS 2019, Zimmerman et al. 2019 and references therein). The species is projected to undergo a slow continuing decline. Hence, it qualifies for listing as Vulnerable under Criterion C2a(ii).

Criterion D – The population size and range are too large to warrant listing as threatened under Criterion D and thus Gunnison Grouse qualifies as Least Concern under this criterion.

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

Therefore, it is suggested that Gunnison Grouse (Centrocercus minimus) be listed as Vulnerable under Criterion C2a(ii). We welcome any comments on 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 its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic. 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: Centrocercus minimus. http://www.birdlife.org (Accessed 11 March 2020).

Braun, C. E.; Oyler-McCance, S. J.; Nehring, J. A.; Commons, M. L.; Young, J. R.; Potter, K. M. 2014. The historical distribution of Gunnison Sage-grouse in Colorado. The Wilson Journal of Ornithology 126: 207-217.

Davis, A. J.; Phillips, M. L.; Doherty Jr, P. F. 2015. Survival of Gunnison sage-grouse Centrocercus minimus in Colorado, USA. Journal of Avian Biology 45: 186-192.

Fjeldså, J.; Kirwan, G. M. 2020. Gunnison Grouse (Centrocercus minimus). 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, Spain. https://www.hbw.com/node/204311 (Accessed 11 March 2020).

Panjabi, A. O.; Easton, W. E.; Blancher, P. J.; Shaw, A. E.; Andres, B. A.; Beardmore, C. J.; Camfield, A. F.; Demarest, D. W.; Dettmers, R.; Keller, R. H.; Rosenberg, K. V.; Will, T. 2019. Avian Conservation Assessment Database Handbook, version 2019. Partners in Flight Technical Series No. 8. http://pif.birdconservancy.org/acad_handbook.pdf.

Partners in Flight. 2019. Avian Conservation Assessment Database, version 2019. http://pif.birdconservancy.org/ACAD.

Schroeder, M. A.; Aldridge, C. L.; Apa, A. D.; Bohne, J. R.; Braun, C. E.; Bunnell, S. D.; Connelly, J. W.; Deibert, P. A.; Gardner, M. A.; Hilliard, M. A.; Kobriger, G. D.; McAdam, S. M.; McCarthy, C. M.; McCarthy, J. J.; Mitchell, D. L.; Rickerson, E. V.; Stiver, S. J. 2004. Distribution of Sage-grouse in North America. The Condor 106: 363-376.

USFWS. 2019. Species status assessment report for Gunnison sage-grouse (Centrocercus minimus). Version April 20, 2019. Lakewood, Colorado, USA.

Young, J. R.; Braun, C. E.; Oyler-McCance, S. J.; Aldridge, C. L.; Magee, P. A.; Schroeder, M. A. 2020. Gunnison Sage-Grouse (Centrocercus minimus), version 1.0. In: Rodewald, P. G. (ed.). Birds of the World. Cornell Lab of Ornithology, Ithaca, New York, USA. https://doi.org/10.2173/bow.gusgro.01 (Accessed 11 March 2020).

Zimmerman, S. J.; Aldridge, C. L.; Apa, A. D.; Oyler-McCance, S. J. 2019. Evaluation of genetic change from translocation among Gunnison Sage-Grouse (Centrocercus minimus) populations. The Condor Ornithological Applications 121: 1-14.

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5 Responses to Archived 2020 topic: Gunnison Grouse (Centrocercus minimus): revise global status?

  1. Clait E. Braun says:

    Populations of this species markedly decreased in 2019. Only one of the 7 small populations is possibly viable. The total estimated population size is about 2,000 individuals with most of those in the Gunnison Basin (Gunnison and Saguache counties, Colorado). Only 3 birds were counted in Spring 2020 in Utah. The long-term outlook for this species is very bleak. It should be listed as highly endangered. A draft Recovery Plan is too flawed to be helpful.

  2. Russell Norvell says:

    I would suggest a re-evaluation of this review. It seems cursory. The apparent reliance on 1) the PIF population estimate, which is a generated via a separate process distinct from most annual sub-population monitoring data sources, 2) an apparent general mis-reading of the 2019 SSA, and 3) the easily checked Criterion E misstatement, all point to this conclusion. While I am unfamiliar with the specific Criteria B-D thresholds, if they are not scaled to the ecology of the species and the threats they face, they would seem to be uninformative.

  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
    New information submitted during the Forum process indicates that the population size may be considerably smaller than given by Partners in Flight (8,400 mature individuals) and Birds of the World (5,000 individuals, equating to roughly 3,300 mature individuals. This has implications for the listing under Criterion C.
    High counts (3-year average; FWS 2019) give numbers of 885 males on leks. Assuming an equal sex ratio, this would equate to 1,770 mature individuals. We have no information on detectability, but it is likely that the true population size is larger than this number. Precautionarily though we can assume that the population size is below 2,500 mature individuals (though this will require confirmation). In view of the low level of gene flow between sites, we assume here that the species forms only one population; the species is projected to undergo a slow decline.
    Based on this information, our preliminary proposal for the 2020 Red List would be to list Gunnison Grouse 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.

  5. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    The final categorisation for this species has not changed. Gunnison Grouse 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.

Comments are closed.