Podiceps Nigricollis Research Articles

Behavioural and population responses to changing availability of Artemia prey by moulting black-necked grebes, Podiceps nigricollis

We examined how availability of brine shrimps, Artemia parthenogenetica, influenced temporal aspects of foraging behaviour and population dynamics of moulting black-necked grebes, Podiceps nigricollis, from late August to early December in four salt ponds in the Odiel marshes, southern Spain, in 2008 and 2009. The moulting grebe population was higher in 2009, coinciding with an increase in shrimp biomass, with a peak of 2,500 birds in October. Grebes increased their time spent foraging as the season progressed, coinciding with decreases in shrimp biomass and water temperature. Foraging activity was lower in 2009, when shrimp biomass was greater. Diving was the most frequent feeding method, especially as the season progressed. Brine shrimps at the bottom of the water column were larger than those near the surface. Differences between years in grebe body mass suggest that changing shrimp availability and water temperature had an influence on body condition. The grebe population consumed an estimated 0.2–2.0% of the standing crop of Artemia per day, with this fraction increasing as the season progresses, thus contributing to the decline in the Artemia population. Our results suggest that moulting grebes are probably only able to adjust foraging effort within certain limits, especially at the end of moulting period when thermal stress is greatest and food supply is lowest. They may leave the study area when they can no longer meet their energy requirements.

The Postbreeding Migration of Eared Grebes

Eared Grebes (Podiceps nigricollis) in autumn make a postbreeding/molt migration from breeding areas in western North America to hypersaline lakes in the Great Basin. We studied their biology in 2001–2006 during this phase of the annual migration near Green River, Wyoming, USA where migrants en route to Great Salt Lake, Utah land on industrial ponds. Most evidently originate in the Prairie Pothole Region of North Dakota. The main movement extends from late July to mid-October. Migrants arrive almost daily with the cumulative percentage of transiting birds increasing by about 1% per day. Adult males and females migrate on the same schedule and precede juveniles by 2–3 weeks. Annual differences in phenology, abundance, age ratio, and wing molt vary with availability of wetland habitats in the main source area. Data on mass, body composition, energetics, and stomach contents indicate a typical flight involves a direct 2–3 day non-feeding migration, which is accomplished at night. Grebes are quiescent during the day and do not resume their migration until 45 min after sunset. We documented two undescribed vocalizations, a short-range contact note and one associated with departure. The possibility that Eared Grebe productivity, as inferred from studies of migrants through Wyoming, can provide insight into the status of waterbirds in the source area is worth further investigation.

Drive-by Netting: a Technique for Capturing Grebes and Other Diving Waterfowl

We describe a new method (drive-by netting) for capturing grebes (Podiceps spp.) and other birds that dive under water to escape capture. We used a fl oating gill net to capture 203 eared grebes (Podiceps nigricollis) in 20 days in 1999 on the Great Salt Lake (GSL), 652 eared grebes in 41 days on the GSL in 2000, and 409 grebes in 20 days in 2001. Other species captured during the 2000 and 2001 fi eld seasons included 1 western grebe (Aechmophorus occidentalis), 9 ruddy ducks (Oxyura jamaicensis), and 1 Canada goose (Branta canadensis). Two people, a motorboat, and a gill net are required for drive-by netting. Our method was effi cient, having a high capture rate per unit effort and a low mortality rate. Drive-by netting can be used to capture both individual grebes and large numbers of grebes on open water.

Two new nematode species of the genus Cosmocephalus Molin, 1858 (Spirurida: Acuariidae), with an amended generic diagnosis and an identification key to Cosmocephalus spp.

Cosmocephalus podicipis n. sp. is described from Podiceps cristatus from the vicinity of Ramsar, Iran (type host and type locality) and from Podiceps nigricollis from the Bulgarian Black Sea coast. Cosmocephalus pelecani n. sp. is described from Pelecanus conspicillatus from Mansfield, Victoria, Australia. Comparative materials of three other species of Cosmocephalus were examined and described. These are C. obvelatus (based on specimens from Larus argentatus from Bulgaria), C. jaenschi (based on a paratype from Phalacrocorax carbo from Australia) and C. capellae (based on a male nematode from Tringa totanus from Bulgaria, a new geographical record). Cosmocephalus faridi from Pelecanus onocrotalus from Egypt, which has been considered by previous authors as a synonym of C. obvelatus, is validated. Results of SEM observations are presented for C. podicipis and C. obvelatus. In all the species examined, the presence of a single ventral ridge was recorded in males anterior to the caudal bursa. The generic diagnosis is amended to include more comprehensive information on the morphology of the studied species. Currently, the genus Cosmocephalus includes 7 species. Cosmocephalus imperialis is recognised as a species inquirenda. Cosmocephalus argentinensis is proposed as a junior synonym of C. obvelatus. An identification key to the species of Cosmocephalus is presented.

Do eared grebes engage in flight during courtship?

Do eared grebes engage in flight during courtship?

Energy Budgets for Eared Grebes on the Great Salt Lake and Implications for Harvest of Brine Shrimp

ABSTRACT About 1.5‐million eared grebes (Podiceps nigricollis), representing half of the North American population, stage on Utah's Great Salt Lake, USA (GSL) during autumn migration to forage on brine shrimp (Artemia franciscana). Indirectly competing with birds for brine shrimp are commercial harvesters who annually collect >1 million kg (dry wt) of shrimp cysts (i.e., hardened eggs), an amount that during some years equals up to half of all brine shrimp cysts produced annually on the GSL. No information was available regarding what impact this commercial harvest was having on eared grebes. We determined daily energy requirements of eared grebes so that regulations governing brine shrimp cyst harvest would better reflect foraging needs of grebes. We measured basal metabolic rate (BMR) of eared grebes from June 2000 to October 2000. Mean BMR of 106 adult and subadult eared grebes was 0.023 kJ/g/hour (SD = 0.004), and mean BMR of 37 juveniles was 0.024 kJ/g/hour (SD = 0.003). Resting and preening metabolic rates were 1.2 times higher than BMR, whereas diving‐bout metabolic rate was 1.7 times higher than BMR. Daily energy needs of an average‐sized grebe (550 g) during November were 391 kJ. Meeting this energy need requires daily consumption of 24,400 adult brine shrimp. In addition, grebes must consume 2,100–5,200 adult shrimp daily to obtain enough energy reserves to continue their migration to California, USA, and Mexico. Hence, grebes need to consume 26,500–29,600 adult brine shrimp daily while staging on GSL. To achieve this high harvest rate, grebes need adult brine shrimp densities at >380 shrimp/m3during autumn. Commercial harvest of brine shrimp cysts from GSL should be curtailed when cyst densities fall below 20,000 cysts/m3to ensure enough adult brine shrimp for grebes during the subsequent year.

Concentrations of selenium and mercury in eared grebes (Podiceps nigricollis) from Utah's great Salt Lake, USA

We examined selenium and mercury concentrations in eared grebes (Podiceps nigricollis) that spent the fall of 2006 on the Great Salt Lake (UT, U.S.A.), where their diet consisted mainly of brine shrimp (Artemia franciscana). Selenium concentrations in livers varied based on when the grebes were collected (lower in September [mean +/- standard error, 9.4 +/- 0.7 microg/g dry wt] than in November [14.5 +/- 1.4 microg/g]), on where the birds were collected on the Great Salt Lake (Antelope Island, 8.6 +/- 0.5 +/- microg/g; Stansbury Island, 15.2 +/- 1.4 microg/g), and on the grebe's age (juveniles, 8.5 +/- 1.5 mcirog/g; adults, 15.8 +/- 1.3 microg/g), but not by sex. Selenium concentrations in blood differed only by collection site (Antelope Island, 16.8 +/- 2.3 microg/g; Stansbury Island, 25.4 +/- 3.0 microg/g). Mercury concentration in the blood of grebes varied by when the grebes were collected (September, 5.6 +/- 0.5 microg/g; November, 8.4 +/- 1.2 microg/g), where the birds were collected (Antelope Island, 4.3 +/- 0.5 microg/g; Stansbury Island, 10.1 +/- 2.6 microg/g), and the grebe's age (juveniles, 5.5 +/- 0.8 microg/g; adults, 8.4 +/- 1.0 microg/g), but not by sex. Selenium concentrations in blood were correlated with selenium concentrations in the liver and with mercury concentrations in both blood and liver. Body mass of grebes increased dramatically from September (381 +/- 14 g wet wt) to November (591 +/- 11 g). Body, liver, and spleen mass either were not correlated with selenium or mercury concentrations or the relationship was positive. These results suggest that high mercury and selenium levels were not preventing grebes from increasing or maintaining mass.

Anthropogenic influences on the input and biogeochemical cycling of nutrients and mercury in Great Salt Lake, Utah, USA

Despite the ecological and economic importance of Great Salt Lake (GSL), little is known about the input and biogeochemical cycling of nutrients and trace elements in the lake. In response to increasing public concern regarding anthropogenic inputs to the GSL ecosystem, the US Geological Survey (USGS) and US Fish and Wildlife Service (USFWS) initiated coordinated studies to quantify and evaluate the significance of nutrient and Hg inputs into GSL. A 6‰ decrease in δ15N observed in brine shrimp (Artemia franciscana) samples collected from GSL during summer time periods is likely due to the consumption of cyanobacteria produced in freshwater bays entering the lake. Supporting data collected from the outflow of Farmington Bay indicates decreasing trends in δ15N in particulate organic matter (POM) during the mid-summer time period, reflective of increasing proportions of cyanobacteria in algae exported to GSL on a seasonal basis. The C:N molar ratio of POM in outflow from Farmington Bay decreases during the summer period, supportive of the increased activity of N fixation indicated by decreasing δ15N in brine shrimp and POM. Although N fixation is only taking place in the relatively freshwater inflows to GSL, data indicate that influx of fresh water influences large areas of the lake. Separation of GSL into two distinct hydrologic and geochemical systems from the construction of a railroad causeway in the late 1950s has created a persistent and widespread anoxic layer in the southern part of GSL. This anoxic layer, referred to as the deep brine layer (DBL), has high rates of SO42- reduction, likely increasing the Hg methylation capacity. High concentrations of methyl mercury (CH3Hg) (median concentration = 24 ng/L) were observed in the DBL with a significant proportion (31–60%) of total Hg in the CH3Hg form. Hydroacoustic and sediment-trap evidence indicate that turbulence introduced by internal waves generated during sustained wind events can temporarily mix the elevated CH3Hg concentrations in the DBL with the more biologically active upper brine layer (UBL). Brine shrimp collected during the summer/fall time periods contained elevated Hg concentrations (median concentration = 0.34 mg/kg, dry weight (dw)) relative to samples collected during the spring (median concentration < 0.2 mg/kg, dw). Higher Hg in brine shrimp during the summer and fall may reflect the higher proportion of adult brine shrimp during this time period, resulting in an increased time for bioaccumulation of Hg. Eared grebes (Podiceps nigricollis) consume brine shrimp from GSL during the fall molting period. Median Hg concentrations in eared grebe livers increased by almost three times during the 3–5 month fall molting period. Selected duck species utilizing GSL have consistently exceeded the US Environmental Protection Agency (USEPA) screening level for Hg (0.3 mg/kg Hg wet weight), resulting in the issuance of warnings against unlimited human consumption of breast muscle tissue.

Waterbirds and nutrient enrichment in Mar Menor Lagoon, a shallow coastal lake in southeast Spain

The Mar Menor, a 135-km2 saline lake, is the largest water surface on the western Mediterranean coast, and an internationally important bird area. It is surrounded by a large irrigated agricultural plain, with dense tourism developments. Although the impacts of these activities on water quality are locally evident, their effects on waterbird populations are poorly known. In the winter 2004–2005, we studied the distribution of four waterbird species (Podiceps cristatus, Podiceps nigricollis, Phalacrocorax carbo and Fulica atra) around the main drainage channel that discharges into the lake, where it was feasible to infer spatial patterns of eutrophication (alongshore and shore centre) from previous environmental surveys. Waterbirds were counted along a stretch of undeveloped shoreline extending southwards from the channel outlet, in contiguous sections, and in bands parallel to the shoreline. Linear mixed models (LMM) indicated the population density increased only markedly for grebes (Podiceps cristatus, Podiceps nigricollis) and coot (Fulica atra) in littoral bands qualifying as eutrophic, but not an alongshore response, with their finescale alongshore distribution being apparently unrelated to nutrient sources. Considering the whole lake, however, the temporal trends and distribution of the wintering populations indicated that waterbirds respond numerically, in a guild-specific way, to nutrient inputs. Grebes and coot could be a useful ‘two-stage’ warning signal for potential problem areas affected by similar influences.

Stratification, sulfide, worms, and decline of the Eared Grebe (Podiceps nigricollis) at the Salton Sea, California

Over the last half century the Salton Sea has been an important migratory stopover site for the Eared Grebe (Podiceps nigricollis). However, in recent years there have been sporadic mass mortalities (i.e., 150,000 in 1992) and a great reduction in the number of grebes visiting during the winter. We propose that a worsening food supply is causing the decline and that starvation may be a major cause of the unexplained mortalities. While at the Sea, grebes forage almost exclusively on a benthic polychaete, the pileworm (Neanthes succinea). This resident pileworm population has increasingly been subject to periodic crashes driven by exposure to anoxic, sulfide rich, hypolimnetic water following lake mixing events. A set of interlocking mechanisms seem to be operating. These involve, in particular, increasing lake salinity, weather events favoring lake stratification, and booms and busts in tilapia (Oreochromis mossambicus × O. urolepis hornorum) and plankton populations, including those of toxic cyanobacteria. In spring, Eared Grebes arrive from the Gulf of California and many arrive in need of food to fuel the remainder of their migration. When pileworms are scarce, many grebes are able to continue on toward their northern breeding grounds, but those that lack sufficient energy stores are forced to stay and may eventually perish. This analysis is surely incomplete, and definitive explanations of the excessive drinking and waterlogged plumage often exhibited by Eared Grebes during mass dieoffs have yet to be found.

Decline of springtime abundance of the pileworm Neanthes succinea in relation to hydrographic conditions at the Salton Sea, California

The Salton Sea is the largest lake in California, and its most abundant macroinvertebrate is the pileworm (Neanthes succinea: Polychaeta). This is a major dietary item for three of the four most abundant fish species in the lake, and for at least one waterbird, the eared grebe (Podiceps nigricollis). Pileworm abundance in April 2004 was monitored at depths of 2, 6 and 10 m on seven transects distributed around the perimeter of the lake. Temperature and oxygen showed marked stratification with depth. Densities were compared to those observed in April 1999. Abundances at 2 m stations were similar to those in 1999; however, densities were greatly reduced at 6 and 10 m stations compared to 1999. The development of hypoxic or anoxic bottom conditions apparently occurred earlier in the spring in 2004 than in 1999. This was the most likely cause for the low densities at 6 and 10 m. Worm densities were higher at sites with coarser sediments (sand and/or barnacle shell debris), and lowest at 2 m sites near or downstream of freshwater inflows and at 10 m where near anoxic conditions prevailed. In March 2005, a sampling of 74 stations at depths ranging from 1 m to 10 m all around the perimeter of the lake found only a single pileworm. It was evident that the lake had just turned over and that sulfide levels were very high and had probably killed off most pileworms and many other organisms as well.

Heavy Metals and Selenium in Grebe Feathers from Agassiz National Wildlife Refuge in Northern Minnesota

Metal levels in feathers can often be used as an indicator of exposure and of potential effects in birds. In previous work at Agassiz National Wildlife Refuge, northwestern Minnesota, pied-billed grebe (Podilymbus podiceps) eggs had significantly higher levels of manganese and mercury and significantly lower levels of selenium than eared (Podiceps nigricollis) or red-necked grebes (Podiceps grisegena), but in 1999, pied-billed grebes had significantly higher levels of mercury, but lower levels of selenium and tin than the other grebes. This led us to examine whether these patterns held up in feathers of grebes as a function of age. The feathers of young birds represent local exposure. We collected feathers of flightless young and adult grebes from 1997 to 1999 in the marshes at Agassiz National Wildlife Refuge. Regression models indicated that year, age, or species were significant factors accounting for variations in the levels of arsenic, cadmium, chromium, lead, manganese, mercury, and selenium, depending on the metal. Overall, there were significant intraspecific differences for all metals. Pied-billed grebes had the highest levels of arsenic, chromium, and selenium, and eared grebes had the highest levels of cadmium, manganese, and mercury. Pied-billed and western grebes (Aechmophorus occidentalis) had the highest levels of lead. There were significant age-related differences in cadmium, chromium, and mercury for both eared and red-necked grebes, for arsenic in eared grebes, and for lead and manganese in red-necked grebes. Adults had higher levels of all metals, except young had higher levels of chromium. Mercury in the feathers of eared grebes were higher than found from other studies with a wide range of aquatic and marine birds and were above those known to cause adverse effects in laboratory studies, suggesting some cause for concern.

Selenium and Metal Concentrations in Waterbird Eggs and Chicks at Agassiz National Wildlife Refuge, Minnesota

Exceptionally high cadmium (Cd) and chromium (Cr) concentrations were reported in eggs, feathers, or livers of selected waterbird species nesting at Agassiz National Wildlife Refuge (Agassiz) in 1994. Ten- to 15-day-old Franklin's gull (Larus pipixcan), black-crowned night-heron (Nycticorax nycticorax), and eared grebe (Podiceps nigricollis) chicks were collected in 1998, 1999, and 2001 at Agassiz and analyzed for selenium (Se) and metals including Cd and Cr. Freshly laid eggs were collected in 2001 from Franklin's gull, black-crowned night-heron, eared grebe, and pied-billed grebe (Podilymbus podiceps) nests at Agassiz. Based on a multivariate analysis, the pattern of Se and metal concentrations differed among species for eggs, chick feathers, and chick livers. Low Cd and Cr concentrations were measured in eggs, chick livers, and chick feathers of all four species. Mercury concentrations in black-crowned night-heron and eared grebe eggs collected from Agassiz in 2001 were lower than concentrations reported in 1994. Se and metal concentrations, including Cd and Cr, in waterbird eggs and chicks collected at Agassiz in 1998, 1999, and 2001 were not at toxic levels.

Short communication. Can highly pathogenic avian influenza (HPAI) reach the Iberian Peninsula from Asia by means of migratory birds?

This work discusses the possibilities of direct and indirect contact across Central Asia, between migratory bird populations from the Iberian Peninsula, Southwestern Eurasian and Eastern Asian countries. This fact should be considered when preparing surveillance studies for highly pathogenic avian influenza viruses. Records were checked from birds ringed or recovered between 1980 and 2002 in the Iberian Peninsula, an important wintering area for waterfowl in the European Union. This study only addresses migrations covering more than 5000 km and exclusively to or from Asia. A total of seven species have developed migratory routes between Europe and the Caspian Sea/Central Asia in the following proportions to the total of birds recovered: Podiceps nigricollis (17%), Anas penelope (11.1%), A. clypeata (2.17%), A. platyrhynchos (1.86%), Pluvialis squatarola (33.33%), Calidris ferruginea (1.36%) and Sterna sandvicensis (0.67%). These recovery rates suggest the possibility of interchange - at the Central Asia and Caspian breeding groundsbetween the populations originating in Europe and those from Southeast Asia. Over the following seasons, through direct migration, misorientation or, as frequently observed in certain duck species, through a phenomenon of abmigration, some birds with a priori Asian wintering quarters could conceivably escort their "European" brethren to this continent and thus contribute to the propagation of avian flu to so far virus-free areas.

Predation of Eared Grebe by Great Blue Heron

Great Blue Herons (Ardea herodias) typically prey upon fish and other aquatic organisms, and they occasionally take small mammals and birds. We observed a Great Blue Heron attack, kill, and attempt to consume an Eared Grebe (Podiceps nigricollis). The heron was unable to swallow the grebe, and it abandoned the carcass after approximately 30 min. An examination of the carcass showed that the grebe lacked obvious physical deformities. Our observation, coupled with a similar one nearby, indicates that Great Blue Herons attack and kill birds larger than reported previously.

Energy content and digestibility of brine shrimp ( Artemia franciscana) and other prey items of eared grebes ( Podiceps nigricollis) on the Great Salt Lake, Utah

We measured the gross energy of brine shrimp ( Artemia franciscana), brine shrimp cysts, brine flies ( Ephydra spp.), brine fly larva, and corixids ( Trichocorixa verticalis) from the Great Salt Lake (GSL). We estimated the apparent and true digestible energy in eared grebes ( Podiceps nigricollis) for these prey items through feeding trials. We found no difference in energy concentration (kJ/g) between any of the invertebrates except for brine fly larva. Invertebrates from the GSL have a relatively high mean energy concentration ranging from 18.8 kJ/g to 23.9 kJ/g. Eared grebes are able to use 82.2–94.9% of the dry mass and 87.4–89.7% of the gross energy (true digestibility) content of their prey items. The high energy content and digestibility partially explain how an eared grebe can successfully forage on such small prey items on the GSL. In contrast, brine shrimp cysts had a high-energy concentration (23.5 kJ/g), but had the lowest amount of true digestible energy (34% of dry mass and 51% of energy), which helps explain why grebes are rarely observed foraging on them.

HABITAT PREFERENCES OF SURFACE-DIVING WATERBIRDS AND AMERICAN WHITE PELICANS WINTERING IN REDFISH BAY, TEXAS

Habitat preferences were determined for a guild of surface-diving waterbirds wintering in Redfish Bay, Texas: common loon (Gavia immer), eared grebe (Podiceps nigricollis), pied-billed grebe (Podilymbus podiceps), double-crested cormorant (Phalacrocorax auritus), red-breasted merganser (Mergus serrator), and American coot (Fulica americana). American white pelican (Pelecanus erythrorhynchos) also was included because it occupies habitats similar to those of the surface divers. Between November 2001 and April 2002, the locations of 4,232 surface divers and American white pelicans using aquatic habitats in Redfish Bay were recorded and entered into a GIS that included a National Wetlands Inventory layer. Bird habitat preferences-avoidances were determined using a test based on Bonferroni's inequality. American coots, American white pelicans, and pied-billed grebes preferred shallower estuarine subtidal seagrass beds, whereas common loons, double-crested cormorants, and eared grebes preferred deeper estuarine subtidal unconsolidated bay bottom. Red-breasted mergansers showed no habitat preferences.

BEHAVIORAL AND PHYSIOLOGICAL RESPONSES OF EARED GREBES (PODICEPS NIGRICOLLIS) TO VARIATIONS IN BRINE SHRIMP (ARTEMIA FRANCISCANA) DENSITIES

Abstract Eared Grebes (Podiceps nigricollis) use the Great Salt Lake (GSL) primarily as a fall staging area. They feed on brine shrimp (Artemia franciscana) to build up energy reserves to complete their southward migration. Whereas it has been speculated that timing of grebe departure from the GSL is due to declining shrimp density, this hypothesis has not been tested. We monitored grebe weight, behavior, and departure dates to test this hypothesis and to determine the effects of declining shrimp densities on Eared Grebes during 1999, 2000, and 2001 when there were different shrimp densities. Despite differences in shrimp densities, grebes left the GSL about the same time each year. Juvenile and subadult mass was significantly lighter (P 0.05) in dive or surface duration between 1999 and 2000, there were differences in the perc...

Cyanobacteria toxins in the Salton Sea

BackgroundThe Salton Sea (SS) is the largest inland body of water in California: surface area 980 km2, volume 7.3 million acre-feet, 58 km long, 14–22 km wide, maximum depth 15 m. Located in the southeastern Sonoran desert of California, it is 85 m below sea level at its lowest point. It was formed between 1905 and 1907 from heavy river flows of the Colorado River. Since its formation, it has attracted both people and wildlife, including flocks of migratory birds that have made the Salton Sea a critical stopover on the Pacific flyway. Over the past 15 years wintering populations of eared grebe (Podiceps nigricollis) at the Salton Sea, have experienced over 200,000 mortalities. The cause of these large die-offs remains unknown. The unique environmental conditions of the Salton Sea, including salinities from brackish freshwater at river inlets to hypersaline conditions, extreme daily summer temperatures (>38°C), and high nutrient loading from rivers and agricultural drainage favor eutrophic conditions that encourage algal blooms throughout the year. A significant component of these algal blooms are the prokaryotic group – the Cyanophyta or blue-green algae (also called Cyanobacteria). Since many Cyanobacteria produce toxins (the cyanotoxins) it became important to evaluate their presence and to determine if they are a contributing factor in eared-grebe mortalities at the Salton Sea.ResultsFrom November 1999 to April 2001, 247 water and sediment samples were received for phytoplankton identification and cyanotoxin analyses. Immunoassay (ELISA) screening of these samples found that eighty five percent of all water samples contained low but detectable levels of the potent cyclic peptide liver toxin called microcystins. Isolation and identification of cyanobacteria isolates showed that the picoplanktonic Synechococcus and the benthic filamentous Oscillatoria were dominant. Both organisms were found to produce microcystins dominated by microcystin-LR and YR. A laboratory strain of Synechococcus was identified by PCR as being closest to known marine forms of this genus. Analyses of affected grebe livers found microcystins at levels that may account for some of the acute mortalities.ConclusionThe production of microcystins by a marine Synechococcus indicates that microcystins may be a more common occurrence in marine environments – a finding not recognized before this work. Further research should be done to define the distribution of microcystin producing marine cyanobacteria and to determine exposure/response effects of microcystins and possibly other cyanotoxins in the Salton Sea. Future efforts to reduce avian mortalities and remediate the Salton Sea should evaluate vectors by which microcystins enter avian species and ways to control and mitigate toxic cyanobacteria waterblooms at the Salton Sea.

HEAVY METALS AND SELENIUM IN GREBE EGGS FROM AGASSIZ NATIONAL WILDLIFE REFUGE IN NORTHERN MINNESOTA

Metal levels in eggs can often be used as an indicator of exposure and of potential effects. In previous work at Agassiz National Wildlife Refuge, northwestern Minnesota, the levels of several heavy metals were shown to be significantly higher in the eggs of eared grebes (Podiceps nigricollis) compared to those in the eggs of Franklin's gulls (Larus pipixcan), black-crowned night-herons (Nycticorax nycticorax) and double-crested cormorants (Phalacrocorax auritus, except for mercury). In the present study we test the hypothesis that there are no differences in the levels of heavy metals in eggs of three species of grebes nesting at Agassiz National Wildlife Refuge (1997, 1999). There were significant differences in levels of selenium, manganese and mercury in the eggs of the grebes collected in 1997, with pied-billed grebe (Podilymbus podiceps) having significantly higher levels of manganese and mercury, and significantly lower levels of selenium, than eared or red-necked grebes (Podiceps grisegena). In 1999, pied-billed grebes had significantly higher levels of mercury, but lower levels of selenium and tin than the other species. The only pattern that was significant and consistent among years was selenium; in both years pied-billed grebes had lower levels than the other species. For eared grebes, there was a decline from 1997 to 1998, and again to 1999 for arsenic, cadmium, and selenium. Levels of mercury in the eggs of grebes were not as high, however, as those found in cormorants or night-herons sampled in 1994 at Agassiz National Wildlife Refuge. There were few consistent patterns in the relationships among metals in eared grebe eggs (with the largest sample sizes). The possible reasons for the high levels of some metals in eggs of grebes are unknown, but presumably egg levels represent exposure on the wintering grounds or migratory routes. In comparison to eggs of other birds: 1) the mean levels for manganese were at the high end of the range, and the mean was an order of magnitude higher than the median for the studies examined, 2) mean levels were above the median in the eggs of other birds for lead (red-necked grebe), mercury (pied-billed grebe) and selenium (eared and red-necked grebe).