Size of the California Brown Pelican Metapopulation During a Non-El Nino Year

Abstract

Overall, we estimated a total metapopulation within the geographical range of the California brown pelican subspecies (Pelecanus occidentalis californicus) as about 70,680 ± 2,640 breeding pairs (mean ± SD). Little change in at least three decades is indicated in the total metapopulation south of the Southern California Bight (SCB) subpopulation, but significant improve ments in the breeding subpopulation size in the SCB reported elsewhere, support the present high numbers observed in this northernmost subpopulation. The largest breeding aggregation within the entire range (consisting of three immediately adjacent sub-colonies), at the San Lorenzo Archipelago, consisted of about 17,225 breeding pairs, or about 24.4% of the metapopula tion in 2006. Other, smaller colonies are no less important, however, although each subpopulation defined by us seemed to have a single or small number of large "core" breeding colonies, plus many smaller colonies (for example, in 2006, one colony consisted of only 2 breeding pairs). Small colonies (< about 70 nests) comprised about 35.6% of the total occupied colonies, but only about 0.87% of the total estimated numbers (values corrected for detectability). The modal colony-size throughout the range was much smaller (about 230 to 1,300 breeding pairs, depending on subpopulation), indicating that small, scattered colonies and sub-colonies, especially on the range peripheries, function in brown pelican population dynamics and are no less important from a conservation viewpoint. These smaller breeding colonies probably represent some colonies of antiquity, but also range expansions and contractions that occur within the typically-defined metapopulation, and local manifestations of source-sink phenomena. Given such dynamics, even unoccupied islands within the range in 2006 have conservation importance from the viewpoint of such dynamics as potential alternate nesting sites. Natural variations in the estimated population levels seem to be related to the natural cycles of El Niño/Southern Oscillation (ENSO) phenomena where very low breeding popula tions (as low as no nesting in many areas) might be expected to occur in these same areas censused in 2006 at least 40% of the time. From the 2006 aerial survey, extensive commercial and sport-fishing activity, resort/tourist developments and associated human activities along the coastal areas and at offshore islands, and extensive aquacultural (and to a lesser degree, agricultural) developments seen from the Río Colorado Delta region, Sonora, south at least through San Blas, Nayarit (the southern terminus of our 2006 aerial survey) may result in substantial loss of breeding habitat. Juvenile (young of the 2005 breeding season) plus subadult brown pelicans comprised 28.1% ± 0.33% (mean ± 95% CI) of the total numbers in age-ratio samples. Thus, our over all metapopulation estimate for P. o. californicus in 2006 was 195,900 ± 7,225 individuals.

East versus West: Organic contaminant differences in brown pelican (Pelecanus occidentalis) eggs from South Carolina, USA and the Gulf of California, Mexico

“…Overall, there are clearly differences in contaminants between the east and the west populations of brown pelicans. While contaminant levels should be below those causing an effect on the population levels, the different trajectories of the population sizes was a driver in undertaking this study (Anderson et al, 2007;Jodice et al, 2007;Watts and Byrd, 2006), so the observed differences between the populations is still intriguing and worthy of further study. Explanations for these differences cannot be readily obtained, but one may suspect that proximity to industrial sources or areas of use would be the main reason.…”

“…carolinensis has experienced several important shifts in its population including an expansion in breeding range to the north, establishment of new colonies in Georgia, and a decline in nesting effort in South Carolina (Jodice et al, 2007;Watts and Byrd, 2006). Meanwhile, recent assessment of nesting effort in the Gulf of California population revealed a steady to increasing trend (Anderson et al, 2007). In both populations, it is unclear what mechanism may be underlying these trends, and it is likely that multiple factors are interacting in each population.…”

Age Determination in California Brown Pelican (Pelecanus occidentalis californicus) Chicks in the Gulf of California

“…The California Brown Pelican nesting colony where this study was conducted is located on Isla Piojo in Bahía de Los Angeles, Baja California, Mexico (29° 01ʹ 12ʺ N, 113° 28ʹ 02ʺ W), where on average about 500 pairs of California Brown Pelicans typically nest in smaller subcolonies of different sizes (Anderson et al 2013), usually from February through July. Subcolonies are defined here as clusters of birds within a colony that are separated from adjacent clusters by a habitat discontinuity (Gochfeld 1980).…”

Presencia y abundancia de aves que se reproducen en islas de la bahía de Mazatlán, Sinaloa, México

“…La reproducción de esta especie comenzó en enero y finalizó en mayo, anidó únicamente en isla Pájaros con un máximo de 596 nidos activos registrados en el mes de marzo. Anderson et al (2007Anderson et al ( , 2013 calcularon 850 nidos en 2006 (año no Niño) en esta colonia y la consideran como la más importante para su segmento poblacional (subpoblación "Mexican Mainland Island").…”