Archived 2018 topic: Le Conte’s Thrasher (Toxostoma lecontei): request for information.

Currently listed as Least Concern (BirdLife International 2018), Le Conte’s Thrasher (Toxostoma lecontei) is found only in dry scrubland of south-west U.S.A. and north-west Mexico (north-west Sonora and Baja California) (see Cody 2018). Although currently listed as stable, declines are thought to have occurred in at least some parts of its range due to agricultural and urban development, grazing and All Terrain Vehicle use (see Sheppard 1996, Cody 2018). Pesticides, pollution hunting and collisions with vehicles are also other potential minor threats (see Sheppard 1996).

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, Le Conte’s Thrasher may warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

 

Criterion A – Rosenberg et al. (2016) suggest a global population reduction of 67% between 1970 and 2014, which would equate to a decline of 27.2% over three generations (12.6 years) assuming declines continued throughout at a similar rate. However, short term data (2005-2015) from Sauer et al. (2017) suggest a non-significant annual increase of 0.55% (10.12% increase to 5.97% decrease), although it is acknowledged that this is slightly data deficient, and it is from U.S.A. populations only. From this though, we would not be able to say that significant declines have taken place within the past three generations.

Partners in Flight does provide the species with a half-life of 27 years though (Rosenberg et al. 2016), suggesting future declines of 27.6% over three generations. Thus the species could warrant listing as Near Threatened under criterion A3, based on suspected future declines. We therefore, request any further information about the potential for moderately rapid declines in this species’s population in the future, and for further information regarding population trends in the Mexican populations.

 

Criterion B – The species’s range is too large to warrant listing under this criterion (Extent of Occurrence = 666,000km2).

 

Criterion C – Rosenberg et al. (2016) estimate the global population size to be 79,000 mature individuals. This is too large to warrant listing under this criterion.

 

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, Le Conte’s Thrasher potentially warrants uplisting to Near Threatened, although further information is sought. Please note though 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

BirdLife International. 2018. Species factsheet: Toxostoma lecontei. Downloaded from http://www.birdlife.org on 08/03/2018.

Cody, M. 2018. Le Conte’s Thrasher (Toxostoma lecontei). 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/58208 on 8 March 2018).

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.

Sheppard, J. M. 1996. LeConte’s Thrasher (Toxostoma lecontei), version 2.0. In: Rodewald, P. G. (ed.). The Birds of North America. Cornell Lab of Ornithology, Ithaca, New York, U.S.A. https://doi.org/10.2173/bna.230.

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2 Responses to Archived 2018 topic: Le Conte’s Thrasher (Toxostoma lecontei): request for information.

  1. James Westrip (BirdLife) says:

    Tim Meehan has kindly provided analyses of Christmas Bird Count data. Taken from long-term trends (1966-2017), these data suggest an annual decline of 0.11% (2.42% annual decline to 2.89% annual increase) in this species. This would equate to a reduction of 1.32% (26.54% reduction to 43.12% increase) over three generations.

  2. James Westrip (BirdLife) says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2018 Red List would be to retain the species as Least Concern.

    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 2018 Red List categories will be published on the BirdLife and IUCN websites in November, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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