San Cristobal Mockingbird (Mimus melanotis): revise global status?

BirdLife species factsheet for San Cristobal Mockingbird

San Cristobal Mockingbird (Mimus melanotis) is endemic to the Galápagos Islands (Ecuador), where it occurs only on the island of San Cristóbal. It inhabits a wide range of habitats, including farmland, woodland with scattered trees of native Miconia or introduced guava, as well as scrub woodland and cactus scrub (Dvorak et al. 2019). The species is widely distributed throughout its range. Until recently, the population was believed to be small; however, following a thorough survey the population size is now estimated at 10,000-19,999 territories (Dvorak et al. 2019), which equates to 20,000-39,999 mature individuals. Moreover, population densities were found to be similar to densities recorded in the 1980s, which led the authors to conclude that the species has remained stable over the last three decades (Dvorak et al. 2019).

The original vegetation on San Cristóbal is highly degraded and disturbed, mainly through overgrazing by goats, human settlements and the introduction of non-native plants and animals (Curry 1989, Vargas 1996, Dvorak et al. 2019). Moreover, the nestling parasite Philornis downsi is present on the island (Wiedenfeld et al. 2007, Bulgarella et al. 2019). Nevertheless, the high density and stable population of San Cristobal Mockingbird suggest that the species is able to adapt to and tolerate these conditions.

San Cristobal Mockingbird is currently listed as Endangered under Criterion B1ab(ii,iii,v) (BirdLife International 2020). However, new information regarding the population size and trend suggests that the species may warrant a change in Red List status. Therefore, it will be re-assessed against all criteria:

Criterion A – The species is thought to have been stable over the past ten years (one generation length being 3.3 years; Bird et al. 2020*). It therefore qualifies as Least Concern under Criterion A.

Criterion B – Both the Extent of Occurrence (EOO) and the maximum Area of Occupancy (AOO), as calculated by a 4 km2 grid over the area of mapped range, are 630 km2. Hence, the EOO meets the threshold for Endangered under Criterion B1 (EOO < 20,000 km2) and the AOO meets the threshold for Vulnerable under Criterion B2 (AOO < 2,000 km2). However, in order to be listed as threatened under Criterion B, at least two further conditions have to be met.

The species is restricted to one island, on which it is widespread, and therefore it cannot be considered severely fragmented sensu IUCN (see IUCN Standards and Petitions Committee 2019). Given that the species has been stable for several decades, there is no evidence of any threats whose impacts could potentially extirpate large parts of the population within the next ten years. Hence, the number of locations** cannot be determined, and the species cannot be assessed against condition a. Throughout the range, habitat is severely degraded and converted for agricultural use, and the parasitic Philornis fly has been introduced to the island (Bulgarella et al. 2019, Dvorak et al. 2019). Despite these threats not having an impact on the population, we can precautionarily assume a decline in habitat quality, and so condition b(iii) is met. The species is not known to undergo extreme fluctuations, and thus subcriterion c is not met.

Overall, even though EOO and AOO are small, the species does not meet sufficient conditions to qualify as threatened. It may nevertheless precautionarily be considered Near Threatened, approaching the threshold for listing as threatened under Criterion B1b(iii)+2b(iii).

Criterion C – The population size of San Cristobal Mockingbird has been placed in the band 20,000-39,999 mature individuals. This is too large to meet the threshold for listing as threatened under Criterion C, and so the species is considered Least Concern under this criterion.

Criterion D – The population size and range are too large to warrant listing as threatened under Criterion D, and therefore San Cristobal Mockingbird is considered 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 San Cristobal Mockingbird (Mimus melanotis) be listed as Near Threatened, approaching the threshold for listing as threatened under Criterion B1b(iii)+2b(iii). 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).

**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: Mimus melanotis. http://www.birdlife.org (Accessed 08 April 2020).

Bulgarella, M.; Quiroga, M. A.; Heimpel, G. E. 2019. Additive negative effects of Philornis nest parasitism on small and declining Neotropical bird populations. Bird Conservation International 29: 339-360.

Curry, R. L. 1989. Geographic variation in social organization of Galapagos mockingbirds: ecological correlates of group territoriality and co-operative breeding. Behavioral Ecology and Sociobiology 25: 147-160.

Dvorak, M.; Fessl, B.; Nemeth, E.; Anchundia, D.; Cotín, J.; Schulze, C. H.; Tapia, W.; Wendelin, B. 2019. Survival and extinction of breeding landbirds on San Cristóbal, a highly degraded island in the Galápagos. Bird Conservation International, online first view.

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

Vargas, H. 1996. What is happening with the avifauna of San Cristobal? Notícias de Galápagos: 23-24.

Wiedenfeld, D. A.; Jiménez, G. A.; Fessl, B.; Kleindorfer, S.; Valerezo, J. C. 2007. Distribution of the introduced parasitic fly Philornis downsi (Diptera, Muscidae) in the Galapagos Islands. Pacific Conservation Biology 13: 14-19.

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2 Responses to San Cristobal Mockingbird (Mimus melanotis): revise global status?

  1. Red List Team (BirdLife International) says:

    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,
    BirdLife Red List Team

  2. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2020 Red List would be to adopt the proposed classification 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.

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