This discussion was first published as part of the 2013 Red List update, but remains open for comment to enable reassessment in 2014.
Wood Thrush Hylocichla mustelina (BirdLife species factsheet) is a widespread breeding visitor to the eastern half of the USA and south-eastern Canada, wintering in southern Mexico and Central America. It is currently listed as being of Least Concern, on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN Red List criteria.
Survey data obtained in the species’s breeding range indicate that its population is in decline. Breeding Bird Survey (BBS) data yield an average survey-wide yearly trend of -2.71% between 1999 and 2011, decreasing from an abundance index of 4.08 birds/route in 1999 to 2.86 birds/route in 2011 (Sauer et al. 2012). These results imply that the species underwent a c.30% decline over those 12 years (BirdLife estimate of three generations for this species), suggesting that it qualifies as Vulnerable or Near Threatened. The trend between 1999 and 2011 appears to be part of a longer term negative trend overall, stretching back to 1966 at least, when the annual index was 8.03 birds/route (Sauer et al. 2012). The average survey-wide yearly trend from 1966 to 2011 is -2.22%.
As with any broad-scale analysis of population trends, there are inherent uncertainties in the BBS trend data and analyses (Sauer et al. 2012), and given that the results imply a rate of decline that may just meet the threshold of a 30% decline over a three-generation period that does not equate to the past three generations (which would be 2001-2013), it may be appropriate to estimate the overall rate of decline at 25-29% over the past 12 years until further evidence is obtained.
It is therefore proposed that the species be uplisted to Near Threatened under criterion A2a, on the basis that it is estimated to have undergone a moderately rapid population decline (approaching 30%) over the past three generations (12 years), based on survey results.
Comments are invited on this proposed category change and further information would be welcomed.
Sauer, J. R., Hines, J. E., Fallon, J. E., Pardieck, K. L., Ziolkowski, D. J., Jr., and Link, W. A. (2012) The North American Breeding Bird Survey, Results and Analysis 1966 – 2011. Version 12.13.2011. USGS Patuxent Wildlife Research Center, Laurel, MD.