This discussion was first published as part of the 2013 Red List update, but remains open for comment to enable reassessment in 2015.
Cassin’s Auklet Ptychoramphus aleuticus ranges from Baja California (Mexico) up the Pacific coast of the USA and Canada, through Alaska to the Aleutian Islands. It is listed as Least Concern on the basis that it was not thought to approach the thresholds for vulnerable under any of the IUCN criteria.
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence of less than 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 size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (fewer than 10,000 mature individuals with a continuing decline estimated to be at least 10% over ten years or three generations, or with a specified population structure).
Until recently, the population trend appeared to be decreasing but the decline was not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (at least a 30% decline over ten years or three generations). This species has undergone a large and statistically significant decrease over the last 40 years in North America (-96.8% decline over 40 years, equating to a -57.9% decline per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007). However, these surveys cover less than 50% of the species’ range in North America. A recent study by Rodway and Lemon (2011) found declines in monitored burrows at several colonies in British Columbia, and estimated a 40% decline in monitored Cassin’s Auklet burrows over 20 years between 1989 and 2009 in the largest known breeding population on Staple Island. Declines appear to have begun in c.1990, and could equate to a total loss of approximately 800,000 birds in the region, or >20% of the world breeding population. If such declines are similar or higher elsewhere within the range, it could qualify for uplisting to Near Threatened or Vulnerable under criterion A2b of the IUCN Red List, based on a global population decline approaching or exceeding 30% in three generations (estimated at 23 years for this species).
Further information is requested on population trends from other parts of this species’s range.
Butcher, G. S. and Niven, D. K. (2007) Combining data from the Christmas Bird Count and the Breeding Bird Survey to determine the continental status and trends of North American birds. National Audobon Society: New York, USA.
Rodway, M. S. and Lemon, M. J. F. (2011) Use of permanent plots to monitor trends in burrow-nesting seabird population in British Columbia. Marine Ornithology 39: 243–253.