Showing papers by "Point Blue Conservation Science published in 2002"

Global Climate Change and Sea Level Rise: Potential Losses of Intertidal Habitat for Shorebirds

Abstract: Global warming is expected to result in an acceleration in current rates of sea level rise, inundating many low-lying coastal and intertidal areas. This could have important implications for organisms that depend on these sites, including shorebirds that rely on them for feeding habitat during their migrations and in winter. We modeled the potential changes in the extent of intertidal foraging habitat for shorebirds at five sites in the United States that currently support internationally important numbers of migrating and wintering birds. Even assuming a conservative global warming scenario of 2°C within the next century (the most recent projections range between 1.4°C and 5.8°C), we project major intertidal habitat loss at four of the sites (Willapa Bay, Humboldt Bay, San Francisco Bay, and Delaware Bay). Projected losses range between 20% and 70% of current intertidal habitat. Such losses might jeopardize the ability of these sites to continue to support their current shorebird numbers. The mo...

Expanded niche for white sharks

Abstract: Until the advent of electronic tagging technology1,2,3,4, the inherent difficulty of studying swift and powerful marine animals made ecological information about sharks of the family Lamnidae5,6 difficult to obtain. Here we report the tracking of movements of white sharks by using pop-up satellite archival tags, which reveal that their migratory movements, depth and ambient thermal ranges are wider than was previously thought.

Western sandpipers (calidris mauri) during the nonbreeding season: spatial segregation on a hemispheric scale

Abstract: The nonbreeding distribution of Western Sandpipers (Calidris mauri) was documented using 19 data sets from 13 sites along the Pacific and Atlantic coasts of the Americas. Western Sandpipers showed latitudinal segregation with regard to sex and age. Females wintered farther south than males. A “U” shaped pattern was found with respect to age, with juveniles occurring at higher proportions at both the northern and southern ends of the range. Distribution of sexes might be affected by differences in bill length and a latitudinal trend in depth distribution of prey. For age class distribution, two different life-history tactics of juveniles might exist that are related to the higher cost of feather wear for juveniles compared to adults. Most juveniles complete three long-distance migrations on one set of flight feathers whereas adults complete two. Juveniles may winter either far north, thereby reducing feather wear induced by ultraviolet light, migration, or both, or far south and spend the summer o...

Effects of weather on daily body mass regulation in wintering dunlin.

Abstract: We investigated the influence of changes in weather associated with winter storms on mass balance, activity and food consumption in captive dunlin (Calidris alpina) held in outdoor aviaries, and compared the aviary results with weather-related body mass differences in free-living dunlin collected at Bolinas Lagoon, California. Captive birds fed ad libitum increased their body mass at higher wind speeds and lower temperatures, suggesting regulation of energy stores, whereas free-living birds exhibited patterns suggesting thermoregulatory limits on body mass regulation. Daily energy expenditure in aviary dunlin was 2.85 kJ g d ‐1 , or 2.8〈 basal metabolic rate (BMR), with thermostatic costs averaging 59 % of daily expenditure. Slight but significant increases in body mass and energy expenditure in captive birds on rainy days, adjusted for possible external water mass, suggested rainfall as a proximate cue in regulating daily body mass. Body mass changes under artificial rainfall indicated similar results, and field masses suggested that free-living birds have greater body mass on days with measurable rainfall. Increased activity costs under artificial rainfall were associated with an increase in maintenance activities, relative to controls. Whether activity costs increased on days with natural rates of rainfall was unclear. Our results are consistent with current hypotheses regarding the role of body mass regulation in providing insurance against increased starvation risk during deteriorating thermal or foraging conditions, or in reducing the costs of extra mass as conditions improve. Summary

The Salton Sea as critical habitat to migratory and resident waterbirds

Abstract: Concern about the Salton Sea ecosystem, based on potential impacts of increasing salinity, contaminants, disease outbreaks, and large die-offs of birds, is heightened because of tremendous prior loss and degradation of wetland habitat in western North America. In 1999, we used a variety of survey methods to describe patterns of abundance of birds at the Salton Sea and in adjacent habitats. Our results further documented the great importance of the Salton Sea within the Pacific Flyway to wintering, migratory, and breeding waterbirds. Exclusive of Eared Grebes, we ‘stimated about 187 000 individual waterbirds at the Salton Sea in January, 88 000 in April, 170 000 in August, and 261 000 in November. Additional surveys of Eared Grebes in November and December suggested the total population of all waterbirds was about 434 000 to 583 000 in those months, respectively. We also documented breeding by about 14000 pairs of colonial waterbirds. Waterbirds were particularly concentrated along the northern, southwestern, southern, and southeastern shorelines and river deltas. By contrast, some species of wading birds (Cattle Egret, White-faced Ibis, Sandhill Crane) and shorebirds (Mountain Plover, Whimbrel, Long-billed Curlew) were much more numerous in agricultural fields of the Imperial Valley than in wetland habitats at the Sea, Various studies indicate the Salton Sea is of regional or national importance to pelicans and cormorants, wading birds, waterfowl, shorebirds, and gulls and terns. Important taxa are the Eared Grebe, American White Pelican, Double-crested Cormorant, Cattle Egret, White-faced Ibis, Ruddy Duck, Yuma Clapper Rail, Snowy Plover, Mountain Plover, Gull-billed, Caspian, and Black terns, and Black Skimmer. Proposed restoration projects should be carefully assessed to ensure they do not have unintended impacts and are not placed where large numbers of breeding, roosting, or foraging birds concentrate. Similarly, plans to enhance opportunities for recreation or commerce at the Sea should aim to avoid or minimize disturbance to birds. Future research should focus on filling gaps in knowledge needed to effectively conserve birds at the Salton Sea.

Altitudinal variation in parental energy expenditure by white-crowned sparrows

Abstract: SUMMARY We used the doubly labeled water technique to measure daily energy expenditure (DEE) during the incubation and feeding nestling stages in two populations of white-crowned sparrows (Zonotrichia leucophrys)— one montane and migratory, the other coastal and sedentary — that differ in thermal environment and clutch size. We assessed the birds9 thermal environment by continuously monitoring (among other variables) operative temperature and wind speed both in the open and within bushes and willow thickets occupied by sparrows. From these measurements, we derived several estimates of the birds9 thermal environment, including standard operative temperature (Tes). Shade air temperature and Tes averaged 6.6 and 10.3°C lower, respectively, at the montane study site during DEE measurements. The montane population9s DEE averaged 24% higher than that of the sea-level population (103.6±12.2 versus 83.7±9.6 kJ day-1; means ± S.D., N=31 and 22, respectively), reflecting both its larger brood size (3.7 versus 2.9) and the colder environment. The DEE:BMR ratio was lowest in the sea-level population (2.1 versus 2.6), but neither population worked to their physiological capacity to produce young. DEE was significantly correlated with temperature across populations, with Tes explaining 42% of the variation in DEE. Statistically removing the effect of temperature by adjusting DEE to a common temperature reduced the difference in DEE between populations by 34% to 87.7 and 100.8 kJ day-1, respectively, for sea-level and montane populations. Basal and resting metabolic rates were similar in both populations, implying that greater activity in the montane population accounted for its higher temperature-adjusted DEE. Our results indicate that the thermal context within which behavior occurs can significantly affect interindividual variation in DEE. Attempts to assess reproductive effort by measuring DEE should therefore account explicitly for the effect of temperature.