Franklin Gress

Climate change, reproductive performance and diet composition of marine birds in the southern California Current system, 1969-1997

We studied the effects of low-frequency climate change on the reproductive performance of 11 species of marine bird in the southern California Current system, 1969–1997. Reproductive performance of Brown Pelican (Pelecanus occidentalis) and Double-crested Cormorant (Phalacrocrax auritus) in southern California demonstrated an increase in the 1970s and early 1980s, attributable to recovery from organochlorine contamination (primarily DDE). Brandt’s Cormorant (Phalacrocorax penicillatus) in central California was the only species to demonstrate a secular increase in performance through time, a pattern that remains unexplained. Ashy Storm-petrel (Oceanodroma homochroa ) and Pelagic Cormorant (Phalacrocorax pelagicus) demonstrated curvilinear patterns of change, with decreasing reproductive performance in the past decade. All other species including Western Gull (Larus occidentalis), Pigeon Guillemot (Cepphus columba), Xantus’s Murrelet (Synthiloboramphus hypoleucus ), Common Murre (Uria aalge), Cassin’s Auklet (Ptychoramphus aleuticus) and Rhinoceros Auklet (Cerorhinca monocerata ) showed diminishing reproductive performance through time. Patterns of change for the murre and auklets were not significant, presumably because of a lack of reproductive variation for these species, which display a conservative breeding effort (i.e. single-egg clutches). Changes in the birds’ abilities to provision young and maintain chick survival during May–July each year appeared most closely related to overall changes in reproductive performance. Dietary change indicated a decline in use of juvenile rockfish ( Sebastes spp.) by marine birds in central California. There was also significant interannual variability in consumption of juvenile rockfish and the euphausiid Thysanoessa spinifera. Patterns of change in marine bird reproductive performance were generally concordant between southern and central California after considering the period of recovery for Brown Pelican and Double-crested Cormorant. The decline in reproductive performance and changes in diet composition do not appear directly related to the polarity reversal of the Pacific Decadal Oscillation

Brown pelicans: influence of food supply on reproduction

From 1970 through 1979, availability of northern anchovies Engraulis mordax, the major food source for breeding brown pelicans Pelecanus occidentalis californicus, was the most important determinant of fledging success. Once the birds are constrained to a breeding area, a weak relationship exists between large scale indices of anchovy abundance in the Southern California Bight (about 105 kM2) and mean pelican fledging rates. This relationship becomes much stronger if pelican feeding behavior and more localized areas associated with their breeding colonies (about 8 x 103 kM2) are considered separately. Anchovy abundance over small areas (about 2 x 103 km2) showed no relationship to pelican reproduction. This suggests that events which influence large geographic areas (such as weather-patterns) affect reproduction through prey levels. Yet, pelican reproductive output is more precisely related to local aspects of prey availability and abundance. Fledging rates are a suitable indicator of local food conditions because pelicans are constrained to more local feeding areas during breeding. High levels of annual variation in food supply result in high annual variations in pelican reproductive performance. Anchovy densities are greater near the two island areas where pelicans most commonly breed than mean density over the entire Southern California Bight. Other regions of high density in prey also exist during the pelican breeding season but they are probably not available to breeders. The locations of traditional breeding colonies most likely represent environmental situations where the combination of nesting substrate and attainable food supplies occur together with consistency.

Survival and dispersal of oiled brown pelicans after rehabilitation and release

Abstract California brown pelicans (Pelecanus occidentalis californicus) were exposed to oil spills just prior to the 1990 breeding season and during the 1991 breeding season in the Southern California Bight (SCB); some were captured, rehabilitated (cleaned and given veterinary care) and released (total = 31 colour- and radio-marked + 81 colour-marked only; = RHB). Nineteen unoiled controls (= CON) from the SCB population, but from an unaffected area, were captured, radio-marked (11) and/or colour-marked (8) in 1990. Despite extensive surveys in the Gulf of California and western Baja California (latitude 23° to 30°N), all radio signals, recoveries and sightings were on the Pacific Coast between 30° and 47°N from 1990–1992. After release and until radio-telemetry data ceased to provide a complete sampling of RHB and CON (after about 6 months), RHB pelicans disappeared at a higher rate than CON; a continuing lower survival of RHB was also indicated from independent sightings of colour-marked pelicans by late 1992. RHB pelicans showed no breeding activity (or even presence or association with breeding colonies) in both years. In contrast, expected proportions of radio-marked CON pelicans were active at breeding colonies in 1990, and the general brown pelican population (which acted as controls in 1991) was active at breeding colonies in 1991. Post-breeding dispersal occurred as expected (mostly to the north) in 1990 and 1991 with CON. RHB pelicans remained sedentary in the SCB for at least 5–6 months in 1990 but dispersed north ahead of CON (as expected for non-breeders) in 1991, apparently in response to building ENSO (El Nino/Southern Oscillation) conditions in the SCB 1991–1992. RHB pelicans (1990) tended to remain farther away from the breeding colonies than CON (1990) in their second post-rehabilitation breeding season. At that time, their dispersal behaviour was similar to that expected for non-breeding adults and juveniles. We conclude that oil and/or rescue and treatment result in long-term injury to brown pelicans, and that current efforts do not restore them to breeding condition or normal survivability.