Viridian Dacnis (Dacnis viguieri): revise global status?

BirdLife species factsheet for Viridian Dacnis

Viridian Dacnis (Dacnis viguieri) occurs in north-west Colombia (north Chocó, north-west Antioquia, south-west Córdoba) and east Panama (east Darién) (Hilty and Brown 1986, Ridgely and Gywnne 1989, Ridgely and Tudor 1989). Within this range it is generally rare. Although primarily a humid forest species, it uses edge habitat and has been recorded in scrub (Hilty and Brown 1986, Isler and Isler 1987). It has been recorded most often in foothills up to 700 m, where it may be more numerous than in the flat coastal lowlands (Hilty and Brown 1986, Ridgely and Tudor 1989).

The species is currently listed as Near Threatened under Criterion B1. However, following the revision of the species’s range map in 2018, we are now undertaking a review of the species’s Red List Category.

Our current information on the species’s conservation status will now be compared to all Red List Criteria.

Criterion A – We have no data on population trends. An analysis of forest loss from 2000 to 2012 found that forest within the species’s range was lost at a rate equivalent to 2% over three generation lengths (Tracewski et al. 2016). Assuming the population has declined at the same rate as the forest cover, the species is suspected to have undergone a reduction of 2% over the past three generation lengths, and assuming that forest loss continues at a similar rate, the population may be assumed to continue to decline at this rate in future. This magnitudes of reduction do not approach the thresholds for listing the species as threatened under Criterion A. The species is therefore assessed as Least Concern under this criterion.

Criterion B – The species’s Extent of Occurrence (EOO) is estimated to be 24,400km2. This does not meet the thresholds for listing the species as threatened under Criterion B1. However it could qualify the species as Near Threatened under this criterion.The species’s Area of Occupancy (AOO) has not been quantified, so the species cannot be assessed under Criterion B2. To list the species as threatened or Near Threatened on the Red List under Criterion B, two of conditions a-c must also be met or nearly met.

The species is not severely fragmented. The main threat to the species is considered to be deforestation, which is estimated to be occurring at a rate of 2% across three generations (11.1 years; Tracewski et al. 2016). The number of locations is therefore likely to be significantly greater than 10. Therefore, condition a is not met. Based on tree cover data (Tracewski et al. 2016), there is an estimated continuing decline in the extent of habitat and the species’s population size and area of occupancy can also be inferred to be undergoing a continuing decline. Condition b is met. There is no evidence that the species’s population or range size are undergoing extreme fluctuations. Condition c is not met.

Although the species’s EOO approaches the threshold for listing the species as Vulnerable under Criterion B, only one of the three conditions is met or nearly met. Therefore, the species is assessed as Least Concern under this criterion.

Criterion C – The species’s population size has not previously been estimated and no survey data are available, but it has been described as ‘rare’.

Based on the estimated area of forest with at least 30% canopy cover in the species’s mapped range in 2018 (14,000 km2), the recorded population densities of a closely-related species with a similar ecology (Dacnis cayana: 0.7 individuals/km2 in lowland rainforest in southern Guyana [Thiollay 1986], 12 individuals/km2 in rainforest in Peru [Munn 1995]), and assuming that 22-45% of suitable habitat is occupied, the species’s population size is estimated to fall within the range 4,412 – 75,636 individuals, roughly equivalent to 2,941-50,424 mature individuals. This could qualify the species for listing as Vulnerable, Near Threatened or Least Concern under Criterion C, depending on where the true population size is most likely to fall. Whilst the species is described as rare, the species has been recorded over a wide area and it could be fairly cryptic and overlooked. Additionally, the lower bound of habitat occupancy (22% of forest within its range) could be unduly conservative, given that large parts of the species’s range contain reasonably intact forest. It is therefore considered unlikely that the true population size falls below or approaches the threshold of 10,000 mature individuals.  The species is therefore assessed as Least Concern under Criterion C.

Criterion D – Based on the population estimates described above, the species’s population size does not meet or approach the threshold for Vulnerable under Criterion D. The species is therefore assessed as Least Concern under this criterion.

Criterion E – To the best of our knowledge no quantitative assessment of the probability of extinction has been conducted for this species, and so it cannot be assessed against this criterion.

Based on the above assessment, it is proposed to list Viridian Dacnis (Dacnis viguieri) as Least Concern. However, should evidence arise that indicates that the population size is likely to be fewer than 15,000 mature individuals, the species may be retained as Near Threatened or listed under a higher category of threat. Therefore, to allow us to achieve a clearer assessment of the species’s status, information is requested on the species population size and population densities across its range.

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’s Red List status. Therefore, please make sure your comments are about the proposed listing.

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

Hilty, S.L. and Brown, W.L. (1986) A guide to the birds of Colombia. Princeton University Press, Princeton.

Isler, M.L. and Isler, P.R. (1987) The tanagers: natural history, distribution, and identification. Smithsonian Institution Press, Washington, DC.

Munn, C. (1995) Permanent canopy and understory flocks in Amazonia: species composition and population density. Ecological Monographs 36: 683-712.

Ridgely, R.S. and Gwynne, J.A. (1989) A guide to the birds of Panama with Costa Rica, Nicaragua, and Honduras. Princeton University Press, Princeton.

Ridgely, R.S. and Tudor, G. (1989) The birds of South America. University of Texas Press, Austin, Texas.

Thiollay, J.M. (1986) Structure comparee du peuplement avien dans trois sites de foret primaire en Guyane. Revue d’Ecologie (Terre et la Vie) 41: 59-105.

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2 Responses to Viridian Dacnis (Dacnis viguieri): revise global status?

  1. Trevor Ellery says:

    No mention seem to be made of its elevation range. Based on my limited experience in Colombia and from what I have heard of its occurrence in Panama – this species only occurs in foothill and subtropical forest. If it does occur in a narrow altitudinal belt then that would greatly reduce the potential amount of forest cover in which it could persist. I suspect due to long term security problems vast swathes of suitable habitat currently exist in the Colombian/Panam Darien border area. Increased political stability may lead to increasing future rates of deforestation (at least in the Colombian Darien). A survey of forest cover within it’s range should perhaps also be combined with a detailed assessment of the elevation limits of this species to produce a clearer picture. Certainly the main current site at which it currently occurs in Colombia is highly fragmented and deforested. It may well occur commonly in more extensive habitat that is less accessible and/or less secure. Publishing the above request in Spanish may well produce some useful and informative response from Colombian and Panamanian birders/ornithologists/biologists who are non English speakers.

  2. 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.

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