Justification of Red List Category
This species has an extremely 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 appears to be increasing, and hence the species does not 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.
Delany and Scott (2006) estimate the population to be 300,000 individuals.
The overall population trend is increasing, although some populations have unknown trends (Delany and Scott 2006). This species has undergone a large and statistically significant increase over the last 40 years in North America (712% increase over 40 years, equating to a 68.8% increase per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007) Note, however, that these surveys cover less than 50% of the species's range in North America.
This species is found in the Americas, breeding along the Pacific coast from California (USA) to Chile and along the Atlantic coast from South Carolina (USA) through the West Indies to Venezuela, ranging as far as Canada and Tierra del Fuego (Chile) in the non-breeding season (del Hoyo et al. 1992).
This species inhabits shallow inshore waters, estuaries and bays, avoiding the open sea. Its diet is comprised mostly of fish, causing great congregations in areas with abundant prey. Prey species include sardines and anchovies, but has been seem to take shrimps and carrion, and even nestling egrets. It regularly feeds by plunge-diving and is often the victim of kleptoparasites. The timing of breeding varies depending on latitude, breeding in spring in the extreme north of its range compared to all year round in the tropics. Brown Pelicans are colonial, with some colonies being maintained over several years. It mostly nests on the ground, sometimes on cliffs and less often in small trees or bushes. Movements and migrations depend on local conditions (e.g. northern populations migrate south) (del Hoyo et al. 1992).
This species is highly sensitive to organochlorine pesticides (Blus 1982). In the past, bioaccumulation of DDT in the marine environment severely impaired the species’ reproductive success through eggshell thinning and breakage (Blus 1982, 1984) and increased adult mortality (Keith et al. 1971). Following the ban on general use of DDT in the US (Environmental Protection Agency 1972), eggshell thickness, productivity and population sizes increased (Mendenhall and Prouty 1978, Blus 1982).
Ongoing threats include injuries caused by entanglement in fishing hooks and lines (Hanson et al. 2014), the collapse of sardine populations along the west coast of America, unintentional disturbance from tourists of birds in breeding colonies, as well as intentional disturbance from fishermen (Elliott et al. 2018). There is evidence for human disturbance causing reduced breeding success in colonies nesting in the Gulf of California (Anderson and Keith 1980), Mexico (Anderson 1988) and Costa Rica (Stiles 1984). At present, the populations appear to be sufficiently large for these threats not to cause population declines.
Text account compilers
Ekstrom, J., Calvert, R., Fjagesund, T., Butchart, S., Martin, R., Temple, H.
BirdLife International (2021) Species factsheet: Pelecanus occidentalis. Downloaded from http://www.birdlife.org on 22/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/10/2021.