Bolivian Spinetail (Cranioleuca henricae): revise global status?

BirdLife species factsheet for Bolivian Spinetail

Bolivian Spinetail (Cranioleuca henricae) is endemic to western Bolivia, where it occurs in dry valleys of the eastern slopes of the Andes between 1,800 and 3,300 m. The species is known from very few localities in the basins of Río Cotacajes, Río Consata and Río La Paz in La Paz and Cochabamba departments (Maijer and Fjeldså 1997, Herzog et al. 1999, Lowen and Kennedy 1999, B. Hennessey per S. K. Herzog in litt. 1999, S. K. Herzog in litt. 1999, 2007). Field surveys revealed a population density of 168 individuals/km2 (S. K. Herzog in litt. 2013). Distribution modelling has yielded an estimated range area (not equivalent to the Extent of Occurrence) of 1,889 km2 (Herzog et al. 2012). Assuming that only 1% of this area contains suitable habitat for the species, extrapolating the population size results in an estimate of c.3,000 individuals. The total population is here placed in the band 2,500-9,999 individuals, roughly equating to 1,600-6,700 mature individuals (BirdLife International 2018).

The species occupies the understory of montane woodland and forest, as well as scrub and low brush in cleared areas adjacent to forest (Remsen and Sharpe 2018). Rarely, it ventures into plantations or even orchards. It has been hypothesised that Bolivian Spinetail depends on the epiphytic ‘grey beard’ bromeliad for nesting (A. Hennessey in litt. 2006).

Much suitable habitat has long been destroyed or severely degraded due to anthropogenic impact. For centuries, woodland within the range has been cut for firewood and charcoal production, which greatly reduced the abundance of the ‘grey beard’ bromeliad (Maijer and Fjeldså 1997, S. K. Herzog in litt. 1999, 2007). Habitat regeneration is impeded by heavy overgrazing and clearance for agriculture (Maijer and Fjeldså 1997, S. K. Herzog in litt. 1999, 2007). The conversion of native vegetation into Eucalyptus plantations has caused hydrological changes, leading to massive soil erosion (S. K. Herzog in litt. 1999, 2007). The species’s stronghold near Inquisivi in La Paz department might be extirpated by landslides by 2050 (S. K. Herzog in litt. 1999, 2007). The expansion of the road network threatens the remaining habitat by facilitating access to the area and exploitation of the forest for charcoal production (S. K. Herzog in litt. 1999, 2007). Climate change is likely to significantly reduce this species’s range (del Rosario Avalos and Hernández 2015). The species does not occur in any protected area (Remsen and Sharpe 2018). In view of these threats, Bolivian Spinetail is suspected to be in decline.

Currently, Bolivian Spinetail is listed as Endangered under Criterion B1ab(i,ii,iii,v), indicating a very small Extent of Occurrence (EOO) and declines in population size and habitat availability. Following IUCN guidelines, the EOO for this species has been re-calculated using a Minimum Convex Polygon, which is “the smallest polygon in which no internal angle exceeds 180 degrees and which contains all the sites of occurrence” (IUCN 2001, 2012, Joppa et al. 2016). After re-calculating the EOO for Bolivian Spinetail, this species appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

Criterion A – As a consequence of the destruction and degradation of its habitat, Bolivian Spinetail is suspected to be undergoing a decline, the rate of which has not been directly estimated. A remote sensing study found that no forest was lost within the range over the last three generations (Tracewski et al. 2016). Apart from woodland, the species also occupies shrub and brushland (Remsen and Sharpe 2018), but there is no information about the rate of conversion of this habitat. Therefore, we are not able to infer the rate of population decline from the rate of habitat loss within the range. Hence, as the rate of population decline is unknown, Bolivian Spinetail cannot be assessed accurately against this criterion.

Criterion B – Using a Minimum Convex Polygon, the Extent of Occurrence (EOO) has been calculated as 5,800 km2. While this value is too large for retaining the species as Endangered under Criterion B1 (EOO < 5,000 km2), it still meets the threshold for Vulnerable (EOO < 20,000 km2). In order to warrant listing as threatened under this criterion, at least two further conditions must be met. Bolivian Spinetail is considered to be severely fragmented sensu IUCN (most individuals are found in small and isolated subpopulations; IUCN 2012) and occurs in only 6 locations*. Consequently, Bolivian Spinetail qualifies for condition (a). Furthermore, species distribution modelling under different climate change scenarios predict a range contraction for the species (del Rosario Avalos and Hernández 2015). Precautionarily, this equates to a projected decline in EOO, AOO, as well as in the area, extent and/or quality of habitat, and the species thus meets the requirements for condition (b) under subconditions (i,ii,iii). As it is not known whether the number of locations or subpopulations are in decline and as the population decline is only suspected, Bolivian Spinetail does not qualify for subconditions (iv,v). Moreover, the species is not known to undergo extreme fluctuations and therefore does not meet condition (c). As the Area of Occupancy of the species has not been quantified, it cannot be assessed against Criterion B2. Consequently, Bolivian Spinetail may be listed as Vulnerable under Criterion B1ab(i,ii,iii).

Criterion C – The population size of Bolivian Spinetail is estimated at 1,600-6,700 mature individuals in total, split into multiple subpopulations and assumed to be declining (BirdLife International 2018). However, in order to qualify for listing as threatened under Criterion C, the population decline needs to be either observed, estimated, projected or inferred. In the case of Bolivian Spinetail, the population is suspected to be in decline, which is a lower level of confidence. Therefore, unless further information on the population decline becomes available, Bolivian Spinetail may be listed at worst as Near Threatened under Criterion C2a(i).

Criterion D – The species’s population size is too large to warrant listing as threatened, and thus Bolivian Spinetail may be considered Least Concern under Criterion D.

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 proposed that Bolivian Spinetail (Cranioleuca henricae) be listed as Vulnerable under Criterion B1ab(i,ii,iii). We welcome any comments on this 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.

*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

BirdLife International. 2018. Species factsheet: Cranioleuca henricae. http://www.birdlife.org (Accessed 20/12/2018).

Del Rosario Avalos, V.; Hernández, J. 2015. Projected distribution shifts and protected area coverage of range-restricted Andean birds under climate change. Global Ecology and Conservation 4: 459-469.

Herzog, S. K.; Fjeldså, J.; Kessler, M.; Balderrama, J. A. 1999. Ornithological surveys in the Cordillera Cocapata, depto Cochabamba, Bolivia, a transition zone between humid and dry intermontane Andean habitats. Bulletin of the British Ornithologists’ Club 119: 162-177.

Herzog, S. K.; Maillard Z., O.; Embert, D.; Caballero, P.; Quiroga, D. 2012. Range size estimates of Bolivian endemic bird species revisited: the importance of environmental data and national expert knowledge. Journal of Ornithology 153: 1189-1202.

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.

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.

Lowen, J. C.; Kennedy, C. P. 1999. Notes on scarce species in La Paz department, Bolivia. Cotinga 12: 82.

Maijer, S.; Fjeldså, J. 1997. Description of a new Cranioleuca spinetail from Bolivia and a ‘leapfrog pattern’ of geographic variation in the genus. Ibis 139: 606-616.

Remsen, J.V., Jr; Sharpe, C. J. 2018. Bolivian Spinetail (Cranioleuca henricae). 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/56469 (Accessed 20/12/2018).

Tracewski, Ł.; Butchart, S. H. M.; Di Marco, M.; Ficetola, G. F.; Rondinini, C.; Symes, A.; Wheatley, H.; Beresford, A. E.; Buchanan, G. M. 2016. Toward quantification of the impact of 21st-century deforestation on the extinction risk of terrestrial vertebrates. Conservation Biology 30: 1070-1079.

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4 Responses to Bolivian Spinetail (Cranioleuca henricae): revise global status?

  1. Dan Lane says:

    I’m surprised that Seeholzer et al. 2015. Ornithological inventory along an elevational gradient in the río Cotacajes Valley, dptos. La Paz and Cochabamba, Bolivia. Cotinga 37: 87-101. is not cited here. They gave some enlightening comments on the abundance of the species in the Cotacajes valley that would be important to consider.

  2. Red List Team (BirdLife International) says:

    Since posting this topic, we received new information regarding the distribution range of the species from Sebastian Herzog (Asociación Armonía).
    The species’ stronghold is considered to be in the Cotocajes basin. It is no longer thought to occur in the La Paz valley, as the observations there most likely refer to erroneous records. The species’ status in the Sorata valley is much less clear, though. While it used to be observed there in the past, there are no recent records from the area, and habitat is lost at a rapid rate. However, while the species is most likely declining there, the lack of recent records may be due to low survey effort. As long as there is no clear evidence that the species has disappeared from the Sorata valley, the area is included in the distribution range map.
    Based on this information, we recalculated the species’s Extent of Occurrence using a Minimum Convex Polygon as 12,800 km². While this value is larger than the previously calculated EOO, it still meets the threshold for Vulnerable, and consequently the species may be listed as Vulnerable under Criterion B1ab(i,ii,iii).

  3. Red List Team (BirdLife International) says:

    Preliminary proposal
    Based on available information, our preliminary proposal for the 2019 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 2019 Red List categories will be published on the BirdLife and IUCN websites in December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  4. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN
    Following further review, the recommended categorisation for this species has been changed.
    Bolivian Spinetail is now recommended to be listed as Vulnerable under Criteria B1ab(i,ii,iii,v); D1.
    The final 2019 Red List categories will be published on the BirdLife and IUCN websites in December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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