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 is very large, and hence does not 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.
The population is estimated at 230,000 individuals.
The overall trend is decreasing (Delany and Scott 2006). In North America, this species has undergone a large and statistically significant increase over the last 40 years (168% increase over 40 years, equating to a 28% increase per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).
Brandt's Cormorant occupies the Pacific coast of North America, ranging from south-east Alaska (U.S.A.) to Baja California (Mexico) (del Hoyo et al. 1992).
This species is strictly marine and is restricted to rocky coasts and islands, foraging over rocky substrates, sometimes over sand or mud, but also in mid-water. It mainly feeds on fish, which it catches by pursuit-diving, and sometimes fishing co-operatively forming large aggregations. Laying occurs mainly from March to July, with individuals forming colonies sometimes alongside other seabirds. It nests on rocks, islands and sandy beaches, usually on slopes, headlands and cliff tops (del Hoyo et al. 1992).
Dramatic reductions in productivity following climatic extremes, suggest high vulnerability to climate change. The largest sub-colony on Alcatraz Island (Laundry Building) has been monitored since 1995, and the two worst years on record were 2009 (total breeding failure) and 2010 (0.5 chick fledged per pair). High air temperatures in 2008, poor ocean productivity in 2009 and the El Niño event in 2010 are proposed explanations. After these three unfavourable years, the 2010 count of 145 nesting pairs amounted to less than half of the peak population size in 2008 (Acosta et al. 2010).
Human disturbance from recreational activities in the species's range may have detrimental impacts on the population. Buxton et al. (2017) showed that visitor noise alters cormorant behaviour and decreases colony attendance, particularly in the presence of nest predating gulls.
Text account compilers
Ekstrom, J., Calvert, R., Fjagesund, T., Butchart, S., Martin, R., Westrip, J.
BirdLife International (2019) Species factsheet: Urile penicillatus. Downloaded from http://www.birdlife.org on 12/12/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 12/12/2019.