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). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size has not been quantified, 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.
There is no global population estimate. However, national population estimates include: <100 breeding pairs and c.50-1,000 wintering individuals in China; c.100-10,000 breeding pairs, c.50-1,000 individuals on migration and c.50-1,000 wintering individuals in Korea; c.10,000-100,000 breeding pairs, c.1,000-10,000 individuals on migration and c.1,000-10,000 wintering individuals in Japan and c.10,000-100,000 breeding pairs and c.1,000-10,000 individuals on migration in Russia (Brazil 2009).
The overall population trend is decreasing, although some populations may be stable and others have unknown trends (Delany and Scott 2006). In North America, this species has had stable population trends over the last 40 years (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).
This seabird is found on the northern coasts of the Pacific, from California (U.S.A.), Canada, Alaska, the Aleutian Islands, Russia and South Kuril Islands (Japan) to the southern tip of Japan. It can also be found north of the Berings Sea (del Hoyo et al. 1992).
This marine species feeds in sheltered coastal waters, including inlets and bays, on a diet of non-schooling fish captured over rocky substrate or kelp beds. The specific species caught is variable depending on locality. Laying occurs from May to July, with individuals normally forming small colonies, although the species is sometimes solitary. Nests are formed on narrow cliff edges and sometimes in caves (del Hoyo et al. 1992).
Climatic fluctuations can have devastating impacts on the species's breeding success. Breeding efforts were essentially zero in 1978, 1983, 1990 and 1992, likely caused by reduced prey availability associated with El Niño-events. Pelagic Cormorants are one of the first species to leave young exposed and/or abandon nesting attempts entirely. Therefore, climate-induced changes in food resources may increase adult mortality and result in behavioural changes which increase the risk of nest predation (Sydeman et al. 2001).
Camera monitoring of a sub-colony in California (Año Nuevo Island) revealed high frequency of raven Corvus corax visits, interaction with all nests and removal of (at least) 3.3 eggs per nest over a period of 101 days. Carle et al. (2017) attributed the low breeding success to egg depredation by ravens. A single pair of breeding ravens was deemed responsible, and there were large mismatches in hatching success between adjacent colonies. Depredation by ravens resulting in near-total reproductive failure has only been observed as a local phenomenon, and as noted above may be in part mediated through poor adult condition.
Text account compilers
Fjagesund, T., Butchart, S., Calvert, R., Ekstrom, J., Martin, R., Westrip, J.
BirdLife International (2019) Species factsheet: Urile pelagicus. Downloaded from http://www.birdlife.org on 17/10/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 17/10/2019.