Blackish Oystercatcher Haematopus ater


Justification of Red List Category
This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds under the population trend criterion (>30% decline over ten years or three generations). The population size may be moderately small to large, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Population justification
The population of H. a. ater is estimated to number 22,000-120,000 individuals, while that of H. a. bachmani is estimated to number 8,900-11,000 individuals, giving a total population of 30,900-131,000 individuals, roughly equating to 20,900-87,300 mature individuals.

Trend justification
The population trend is difficult to determine because of uncertainty over the extent of threats to the species (del Hoyo et al. 1996). The overall population trend of H. a. bachmani is stable (Wetlands International 2006). H. a. bachmani has undergone a large and statistically significant increase over the last 40 years in North America (213% increase over 40 years, equating to a 33% increase per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).


Text account compilers
Butchart, S., Ekstrom, J., Symes, A. & Taylor, J.

Recommended citation
BirdLife International (2021) Species factsheet: Haematopus ater. Downloaded from on 20/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from on 20/10/2021.