Black-capped Vireo (Vireo atricapilla): revise global status?

Black-capped Vireo (Vireo atricapilla) once bred from south Kansas through Oklahoma and Texas (U.S.A.) into Coahuila, Nuevo Leon and Tamaulipas (Mexico). Its breeding range has contracted though, and it is now thought to be absent from Kansas, and is only found in isolated patches in Oklahoma. In the non-breeding season it migrates to the west of Mexico along the Pacific coast. The species generally occurs in dry scrubland, and is often found in areas of successional vegetation after fires (see Brewer 2018).

The species is threatened by several processes, including intense nest predation (as high as 50%) (Stake and Cimprich 2003, Campomizzi et al. 2009) and cowbird brood parasitism (up to 100% at some sites) (Grzybowski 1995, Farrell et al. 2011). However, it is habitat loss and degradation that are thought to be the key threats to the species, through fire suppression, urbanisation, grazing and agricultural conversion (Grzybowski 1995, J. Lyons in litt. 1999). As a result, the species has been considered to be undergoing a rapid decline, and is currently listed as Vulnerable (see BirdLife International 2018), although it is not clear whether declines are continuing any more (T. McFarland in litt. 2016).

Following the publication of Partners in Flight (PiF) Landbird Conservation Plan (Rosenberg et al. 2016) and The State of North America’s Birds 2016 (North American Bird Conservation Initiative 2016) we have reviewed the new information held in these publications, particularly regarding population trends. This has allowed us to reassess the species outlined in these publications against IUCN Red List Categories and Criteria. As the PiF data are long-term trends (1970-2014), where possible we have also used data from the North American Breeding Bird Survey (Sauer et al. 2017) to assess more recent trends over the period relevant to the Red List. Having completed this review, Black-capped Vireo appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

 

Criterion A – There are no data available for this species from the North American Breeding Bird Survey. As such, Partners in Flight also do not have a clear population trend estimate. Instead Rosenberg et al. (2016) give a range within which the population reduction between 1970 and 2014 is suspected to fall. They propose that the reduction has been between 15-50% over this time period, which would roughly equate to a reduction of 4.5-18.0% over three generations (12.6 years) assuming a constant rate of decline. However, even though the species was previously thought to be declining rapidly, it is not clear whether it continues to decline (T. McFarland in litt. 2016), and so any population decrease over the past three generations could be even lower. Therefore, even using the suspected greatest population reduction figure, the species would not approach the threshold for listed as Vulnerable under this criterion, although we request any information about when population declines may have started to slow down or stop.

 

Criterion B – The species’s range is too large to warrant listing under this criterion (Extent of Occurrence [breeding] = 601,000km2; Extent of Occurrence [non-breeding] = 323,000km2).

 

Criterion C – Rosenberg et al. (2016) estimate the global population size to be 24,000 mature individuals, as Wilkins et al. (2006) estimated c.12,000 mature individuals in U.S.A., and recent discoveries of high-density breeding populations in Mexico could mean that a doubling of the U.S.A. estimate may be appropriate (Rosenberg et al. 2016). It should be noted, though, that while Benson and Benson (1990) did estimate 6,301 ± 3,162 pairs in northern Coahuila, other estimates for Mexican populations have been very low. Wilkins et al. (2006) estimated only 259 males in Mexico and Morrison and Gonzalez-Rojas (2014) found only 341 vireos in three states of Mexico. Therefore, we tentatively place the global population size in the range 10,000-19,999 mature individuals.

It is unclear whether the population is still undergoing a decline (T. McFarland in litt. 2016), but in the absence of further evidence to show a stable population, the species is conservatively retained as declining. As the species is migratory, this means that all individuals may be able to come into contact with one another and it is proposed that the species be treated as one subpopulation. Thus, the species would not meet the threshold for Vulnerable, but it may be assessed as approaching the threshold for Vulnerable under this criterion, and as such would warrant listing as Near Threatened under criterion C2a(ii).

 

Criterion D – The species’s population size and range are too large to warrant listing under this criterion.

 

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, Black-capped Vireo potentially warrants downlisting. Given the information from Partners in Flight, it could warrant listing as Least Concern, but here we tentatively place the population size in the range 10,000-19,999 mature individuals and instead propose listing the species as Near Threatened under criterion C2a(ii). We welcome any comments or further information, but 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 about the proposed listing.

 

 

References

Benson, R. H.; Benson, K. L. P. 1990. Estimated size of Black-capped Vireo population in northern Coahuila, Mexico. Condor 92: 777-779.

BirdLife International. 2018. Species factsheet: Vireo atricapilla. Downloaded from http://www.birdlife.org on 11/05/2018.

Brewer, D. 2018. Black-capped Vireo (Vireo atricapilla). 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. (retrieved from https://www.hbw.com/node/61251 on 8 March 2018).

Campomizzi, A. J.; Morrison, M. L.; Farrell, S. L.; Wilkins, R. N.; Drees, B. M.; Packard J. M. 2009. Red imported fire ants can decrease songbird nest survival. Condor 111:534–537. 111: 534–537.

Farrell, S. L.; Morrison, M. L.; Wilkins, R. N.; Slack, R. D.; Campomizzi, A. J. 2011. Brown-headed cowbird parasitism on endangered species: relationships with neighboring avian species. Western North American Naturalist 70: 474–482.

Grzybowski, J. A. 1995. Black-capped Vireo (Vireo atricapillus). In: Poole, A.; Gill, F. (ed.), The birds of North America, No. 181, pp. 1-24. The Academy of Natural Sciences, and The American Ornithologists’ Union, Philadelphia, and Washington, DC.

Morrison, M. L.; Gonzalez-Rojas, J. 2014. Breeding ecology and population status of the black-capped vireo in Mexico: Filling critical information gaps. Section 6 Report.

North American Bird Conservation Initiative. 2016. The State of North America’s Birds 2016. Environment and Climate Change Canada, Ottawa, Ontario.

Rosenberg, K. V., Kennedy, J. A., Dettmers, R., Ford, R. P., Reynolds, D., Alexander, J. D., Beardmore, C. J., Blancher, P. J., Bogart, R. E., Butcher, G. S., Camfield, A. F., Couturier, A., Demarest, D. W., Easton, W. E., Giocomo, J. J., Keller, R. H., Mini, A. E., Panjabi, A. O., Pashley, D. N., Rich, T. D., Ruth, J. M., Stabins, H., Stanton, J. and Will., T. 2016. Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee.

Sauer, J. R.; Niven, D. K. ; Hines, J. E.; Ziolkowski, Jr, D. J.; Pardieck, K. L.; Fallon, J. E.; Link, W. A. 2017. The North American Breeding Bird Survey, Results and Analysis 1966 – 2015. Version 2.07.2017 USGS Patuxent Wildlife Research Center, Laurel, MD.

Stake, M. M.; Cimprich, D. A. 2003. Using video to monitor predation at Black-capped Vireo nests. Condor 105: 348-357.

Wilkins, N.; Powell, R. A.; Conkey, A. A. T.; Snelgrove, A. G. 2006. Population status and threat analysis for the black-capped vireo. Department of Wildlife and Fisheries Science, Texas A&M University. College Station, Texas, USA.

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