Podiceps Nigricollis Research Articles

Cyclical Changes in Body Composition in the Annual Cycle and Migration of the Eared Grebe Podiceps nigricollis

In changes that are among the most dramatic known for birds, Eared Grebes undergo 3-6 atrophy/hypertrophy cycles in major body constituents annually. The most pronounced takes place at staging areas in fall, when grebes become flightless for up to several months. At this season they accumulate huge fat stores (to 46% of lean body mass) and more than double the mass of body, liver, stomach, and intestine; leg and heart mass also increase. Concurrrently, pectoral muscles atrophy and can shrink below the size needed for flight (11% of total body mass). Before grebes depart for wintering areas these changes are reversed. In a 2-3 week predeparture period body mass drops by one-third as birds catabolize fat and reduce viscera mass by ?50%; leg mass also declines, while pectoral muscle increases. Similar cycles, which do not involve fattening to obesity, are repeated at wintering and breeding locations and, in some birds, on additional spring staging and fall molting areas. Heavy fat deposits in fall may insure that grebes can postpone their migration to wintering areas into the months of maximum darkness, thereby minimizing the risk of predation. The extreme predeparture reductions in leg and visceral mass, which occur in all seasons, reduce flight costs by minimizing wing loading and enhancing flight speed. Why grebes allow pectoral muscles to atrophy if they must rebuild them presently remains a puzzle. Several lines of evidence suggest that grebes attain a specific (optimal?) body composition prior to migrating. Further research into changes that may take place in other species prior to migration or at different times of the annual cycle is warranted.

Nest Distance Mediates the Costs of Coloniality in Eared Grebes

-We examined the behaviors and reproductive characteristics of 4 Eared Grebe (Podiceps nigricollis) colonies located at the Malheur National Wildlife Refuge in eastern Oregon that varied in nesting density. In 1993, we studied 2 colonies found on 2 different lakes, whereas in 1994 we conducted a within-lake comparison of 2 subcolonies. During both years, nearest neighbor distances differed significantly between the colonies investigated. Breeding pairs were significantly more aggressive at those colonies with smaller distances among nests. Within each year, there was a greater rate of intraspecific brood parasitism and egg loss at the higher density colony. Infanticide occurred at high rates when nests were very densely packed, whereas a relatively high rate of predation by American Coots (Fulica americana) resulted when nests were quite dispersed. Thus, in spite of the distinct breeding characteristics of Eared Grebes, many disadvantages associated with nesting density in seabirds also have an impact on these colonially breeding waterbirds. Received 30 May 1997, accepted 19 August 1997, final version received 11 September 1997.

Heavy metal and selenium levels in birds at Agassiz National Wildlife Refuge, Minnesota: Food chain differences

The levels of heavy metals and selenium in the eggs and in breast feathers of adult doublecrested cormorant (Phalacrocorax auritus), black-crowned night heron (Nycticorax nycticorax), and franklin's gull (Larus pipixcan) nesting at Agassiz National Wildlife Refuge in Marshall County, northwestern Minnesota were examined. Also examined were metal levels in the feathers of fledgling night herons and gulls, in the feathers of adult and fledgling American bittern (Botaurus lentiginosus), in eggs of American coot (Fulica americana) and eared grebe (Podiceps caspicus), and in feathers of adult Canada geese (Branta canadensis). These species represent different levels on the food chain from primarily vegetation-eating species (geese, coot) to species that eat primarily fish (cormorant). A clear, positive relationship between level on the food chain and levels of heavy metals occurred only for mercury in feathers and eggs. Otherwise, eared grebes had the highest levels of all other metals in their eggs compared to the other species. No clear food chain pattern existed for feathers for the other metals. For eggs at Agassiz: 1) lead, selenium, and manganese levels were similar to those reported in the literature, 2) mercury levels were slightly higher for cormorants and night herons, 3) all species had higher chromium and cadmium levels than generally reported, and 4) eared grebes had significantly higher levels of cadmium than reported for any species from elsewhere. For adult feathers: 1) gulls had higher levels of lead than the other species, 2) cadmium levels were elevated in gulls and adult herons and cormorants, 3) mercury levels showed an increase with position on the food chain, 4) selenium and chromium levels of all birds at Agassiz were generally low and 5) manganese levels in adults were generally higher than in the literature for other species. Adults had significantly higher mercury levels than fledgling gulls, night herons, and bitterns.

High Frequency of Conspecific Brood Parasitism in a Colonial Waterbird, the Eared Grebe Podiceps nigricollis

We made daily visits to 47 Eared Grebe Podiceps nigricollis nests in two colonies to determine the frequency of conspecific brood parasitism. Three criteria were used to detect parasitism: the appearance of two or more new eggs in a 24 hour period, new eggs after the host had ceased laying, and the disappearance of a marked egg with the simultaneous appearance of a new unmarked egg. We detected parasitism at 68% of nests in one colony, 14% of nests in the second colony, and 38% of nests in both colonies combined. The spatial dispersion of parasitic eggs among host nests within one colony did not differ from random expectation but, with respect to temporal dispersion, parasites were more likely to lay in host nests in the laying stage than expected by chance. Egg loss was more common at parasitized nests than unparasitized nests, but further studies are needed to confirm whether this is due to egg rejection by hosts. A comparison of clutch sizes in parasitized and unparasitized nests indicated that unparasitized nests never contained more that four eggs - supernormal clutches of five or more eggs thus indicate that parasitism has taken place and, if used as an assay for parasitism, would have identified two thirds of the cases of parasitism in our study. Applying this assay to clutch size information collected 40 years ago at a site close to our study area indicates that parasitism may be a regular feature of Eared Grebe reproduction.

Vocal Response of Eared Grebe Embryos to Egg Cooling and Egg Turning

In a laboratory study, the vocal responses of Eared Grebe (Podiceps nigricollis) embryos to egg cooling and egg turning were examined. Nineteen late-stage, prepipping embryos were twice subjected to 10 min of egg cooling and 10 min of normal incubation temperatures. Experimentally cooled embryos vocalized more than embryos exposed to normal incubation temperatures. Cooled embryos produced more bouts of calls and fewer calls per bout than when exposed to normal incubation temperatures. Intercall intervals within bouts did not differ between warm and cold periods. Results of the egg-cooling experiment support the "care-soliciting signal" hypothesis. In a separate paired experiment, embryos vocalized more when turned than when at rest. Because grebe nests are composed of sodden materials, embryos that are about to hatch may signal their parents to turn the eggs, because positioning a pipped egg upside down may suffocate the embryo. Also, prepipped embryos may vocalize more frequently when turned as a signal to their parents that they are viable and will soon hatch. Eared Grebe embryonic vocalizations probably are multifunctional, with care-soliciting being one of their functions.

Impact of Embryonic Vocalizations On the Incubation Behaviour of Eared Grebes

AbstractTwo experiments were performed during the summers of 1991 and 1992 to determine whether embryonic vocalizations cause changes in the behaviour of adult eared grebes (Podiceps nigricollis) during late incubation. In Experiment 1, a vocalizing egg was substituted in 14 nests, two days before the first egg in that nest was to begin vocalizing. Parents reduced the amount of rising and resettling and the time spent off the nest while incubating and increased the frequency of egg turning, nest building, and percent of time the 'off-duty' parent spent near the nest. Only nest builds per h in the pre-peep period differed between the sexes in Experiment 1. For Experiment 2, the incubation period was extended by two days. At that time a vocalizing egg was substituted in 15 nests. Males reduced the amount of rising and resettling, whereas there was no difference between periods for females. Males and females reduced the amount of time spent off the nest while incubating. Egg turns per h, nest builds per h, and the percent time the off-duty parent spent near the nest increased for both sexes. No differences between males and females were detected except for egg turns per h during the peeping egg stage of Experiment 2. Parents also brought food to the nest in response to embryonic vocalizations. The behavioural changes by eared grebes during late incubation appear to be due to embryonic vocalizations. Several changes in behaviour are consistent with the care-soliciting hypothesis, such as reduction in exposure time of the embryo and possibly shortening of the incubation time of the embryo by an increased egg turning rate. Presenting food at the nest and possible acceptance of the young are further adaptive features of embryonic vocalizations.

Threats to Burdur Lake ecosystem, Turkey and its waterbirds, particularly the white-headed duck Oxyura leucocephala

Burdur Lake, a closed-basin saline lake in south-west Anatolia, Turkey, is internationally important for its wintering waterbirds. It is the most important wintering site in the world for the white-headed duck Oxyura leucocephala, a globally threatened species. It has also held internationally important numbers of 10 other waterbird species. The lake is threatened by the construction of an industrial complex and airport on the northern shore. Falling water levels (from construction of upstream dams), sedimentation (from catchment erosion), organic pollution (from food processing and sewage) and inorganic effluent (from a sulphur mine) represent long-term threats to the lake system. Illegal hunting from the shore has a serious impact upon white-headed ducks, which concentrate close inshore and show little escape response in the presence of hunters. White-headed duck numbers have fluctuated considerably since 1967 with a peak (incomplete) count of 10,927 in February 1991. By January 1995, numbers had declined to 2805. Numbers of black-necked grebe Podiceps nigricollis, white-fronted goose Anser albifrons and tufted duck Aythya fuligula have declined. Numbers of large gulls of the Larus argentatus group which prey upon white-headed duck have increased, possibly due to pollution. For 10 of 16 waterbird species regularly observed at the site, highest numbers were recorded before 1974. Recommendations for the conservation of the lake are presented.

Pararetinometra lateralacantha Stock and Holmes, 1981 (Cestoda: Hymenolepididae): the first record in the Palaearctic region and comments on its morphology and taxonomy

Pararetinometra lateralacantha Stock and Holmes, 1981, known until now only from Alberta, Canada, as a parasite of three species of grebes (Aves: Podicipediformes: Podicipedidae), was found in a wintering Podiceps nigricollis (Brehm) on the Bulgarian coast of the Black Sea. The species is redescribed and illustrated on the basis of both the Bulgarian specimens and specimens from Canada (paratypes). Some corrections or additions to the original description in relation to the characteristics of the rostellum, rostellar sheath, vitellarium, ovary, testes, cirrus sac, cirrus, and vagina are presented. In contrast to a recent opinion, Pararetinometra Stock and Holmes, 1981 is regarded as a valid genus and not as a synonym of Cladogynia Baer, 1937. The geographical distribution of P. lateralacantha is supposed to be circumboreal.

Landscape pattern and population conservation : S. Harrison & L. Fahrig, in: Mosaic landscapes and ecological processes, ed L. Hanson & others, (Chapman & Hall; IALE Studies in Landscape Ecology, 2), 1995, pp 293–308

Burdur Lake, a closed-basin saline lake in south-west Anatolia, Turkey, is internationally important for its wintering waterbirds. It is the most important wintering site in the world for the white-headed duck Oxyura leucocephala, a globally threatened species. It has also held internationally important numbers of 10 other waterbird species. The lake is threatened by the construction of an industrial complex and airport on the northern shore. Falling water levels (from construction of upstream dams), sedimentation (from catchment erosion), organic pollution (from food processing and sewage) and inorganic effluent (from a sulphur mine) represent long-term threats to the lake system. Illegal hunting from the shore has a serious impact upon white-headed ducks, which concentrate close inshore and show little escape response in the presence of hunters. White-headed duck numbers have fluctuated considerably since 1967 with a peak (incomplete) count of 10,927 in February 1991. By January 1995, numbers had declined to 2805. Numbers of black-necked grebe Podiceps nigricollis, white-fronted goose Anser albifrons and tufted duck Aythya fuligula have declined. Numbers of large gulls of the Larus argentatus group which prey upon white-headed duck have increased, possibly due to pollution. For 10 of 16 waterbird species regularly observed at the site, highest numbers were recorded before 1974. Recommendations for the conservation of the lake are presented.

Field Estimates of Energetics in Migrating and Downed Blacknecked Grebes

Field Estimates of Energetics in Migrating and Downed Blacknecked Grebes

Nest Site Selection by Eared Grebes in Minnesota

This study examined nest site selection within Eared Grebe (Podiceps nigricollis) colonies in terms of nesting synchrony, nearest-neighbor distances, vegetation, exposure, and nest success. Nests in 11 Eared Grebe colonies in Minnesota were initiated over a span of 11-45 days, with most nests in each colony initiated in < 11 days. In each of six colonies studied, mean nearest-neighbor distance of the earliest nests was greater than that of the complete colony. Nearest-neighbor distance tended to decrease with an increase in emergent vegetation density. Early nests seemed to form the skeleton of a neighborhood, with later nests filling in or establishing other neighborhoods. In five of six colonies, clutch sizes were larger in earlier nests. No significant difference in egg volume between early and late nests was apparent in the two colonies studied. Early nests were more successful than were late nests in two of four colonies; center nests were more successful than were edge nests at only one of four colonies. Most nest destruction in this study was caused by waves generated by high winds; < 2% of nests showed evidence of predation.

Predation of Nesting Larids by Peregrine Falcons at Rasa Island, Gulf of California, Mexico

Peregrine Falcon (Falco peregrinus) diets vary widely. On the Pacific Coast of North America, they feed on petrels and alcids (Oceanodroma, Synthliboramphus, Ptychoramphus) (Green 1916, Brooks 1926, Bent 1938, Beebe 1960), while in the Gulf of California they take Eared Grebe (Podiceps nigricollis), Black Storm-Petrel (Oceanodroma melania), Least Storm-Petrel (O. microsoma), Red-necked Phalarope (Phalaropus lobatus), Bonaparte's Gull (Larus philadelphia), Heermann's Gull (L. heermanni) and Craveri's Murrelet (Synthliboramphus craveri) (Porter and Jenkins 1988). Due to seabird coloniality, close to exclusive dependence of individual Peregrine Falcons on particular prey species may put their survival in an inverse relation to the degree of pollution of marine areas where their prey feed. In the case of Rasa Island, 95% of the population of the two main prey species nest synchronously, providing close to 300,000 prey available for three months.

Observations on the Fall Migration of Eared Grebes, Based on Evidence from a Mass Downing in Utah

After the breeding season in North America, most Eared Grebes (Podiceps nigricollis) migrate to highly saline lakes in the Great Basin to molt and stage for several months. During this period they molt, undergo a cycle of breast muscle atrophy and hypertropy, and accumulate huge fat deposits before flying to wintering areas (Jehl 1988, unpubl. manuscript; Gaunt et al. 1990). On 10 December 1991 thousands of grebes departed Great Salt Lake en route to the Salton Sea, California, or Gulf of California, Mexico. Their route was southwesterly, and for the first 500 km-roughly between Salt Lake City and the Arizona border-paralleled Interstate Highway 15 and the Wasatch Mountains, which are slightly to the east. Several hours into the flight, over southern and central Utah, large numbers were forced down by a snowstorm along a 180 km stretch between Holden and Cedar City; a few were also reported in the Provo/Springfield area (Fig. 1). The birds did not fall uniformly, but apparently were attracted to lights from towns and highway intersections. Many died when they crashed to earth; others were hit by cars on the highway, which they evidently mistook for open water. Thousands more were captured alive and released on whatever local water bodies remained open. Most of our current understanding about the biology of Eared Grebes in fall migration is based on studies of birds staging at Mono Lake, California (Jehl 1988). The data from this downing provided an opportunity to test and extend some earlier findings or inferences about the differential migration of age classes, duration of the flight to wintering areas, physical condition of departing and arriving migrants, the size of pectoral muscles needed for flight, and the risks of mortality along the migratory routes (Jehl 1988, Gaunt et al. 1990).

Parent-Young Vocal Communication in Eared Grebes

In a series of experiments, we played eared grebe (Podiceps nigricollis) and western grebe (Aechmophorus occidentalis) food calls in random order to eared grebe chicks brooded under the back-feathers of their parents. We examined the responses of chicks that were 12-23 h, I day, and 2-3 days old. Over the first 3 days, there was a significant increase in responsiveness (poking out the head and begging) to the parental food call. In similar experiments using the alarm call, eared grebe chicks with their heads out responded strongly to their own species' calls by ducking their heads beneath the back-feathers. Cross-fostered eared and western grebe chicks rarely responded to food calls of their own species, but responded vigorously to their foster species' calls. On the other hand, a cross-fostered eared grebe chick showed strong responses to the alarm calls of its own species, even though its foster parents were not using that type of call. This chick had not learned to respond to its foster species' alarms. Cross-fostered western grebe chicks responded to the alarms of both species, even though they were unlikely to have heard their own species' calls. Whether their alarm responses to both species was a manifestation of incomplete learning or of an absence of species specificity unaffected by early experiences remains to be determined. If learning was involved, it appeared to occur at a slower rate than did responses to the food calls of foster parents. The importance of learning appeared to vary considerably between the two types of calls, and the advantages of this are discussed. Although young chicks respond to the food and alarm calls from any adult of their species, playback experiments using the advertising calls of adults suggest that older grebe chicks can learn to individually identify their parents by the time they begin swimming on their own.

Vocal Advertising and Sex Recognition in Eared Grebes

As a preliminary display of the Discovery Ceremony, male and female Eared Grebes (Podiceps nigricollis) advertise in bouts of 1-12 calls. Although superficially similar, female Advertising calls were significantly higher in frequency than male calls for all three frequency measures taken. Playback experiments demonstrated that courting males readily distinguished advertising calls of unpaired females from those of unpaired males. When the playback speed of the male calls was increased by 10%, courting males responded to them as though they were female calls, demonstrating that call frequency or duration cues play an important role in sex recognition. Since courting grebes already know the species and sex of their display partner upon hearing its initial, spontaneous advertising, the many elaborate and vigorous pair-formation displays of the Discovery Ceremony of grebes may be functioning in mate choice decisions at more subtle levels.

Wetland selection by Eared Grebes, Podiceps nigricollis, in Minnesota

Wetland selection by Eared Grebes, Podiceps nigricollis, in Minnesota

Rapid Atrophy and Hypertrophy of an Avian Flight Muscle

Eared Grebes (Podiceps nigricollis) use Mono Lake in eastern California as a rest stop during spring migration. Some nonbreeders remain for the summer, and in the autumn the lake becomes a staging area that may accommodate 750,000 returning breeders and young of the year. There the birds become obese by feeding on invertebrates and, if they have not already done so, molt. Most grebes remain several months until a decline in prey populations stimulates further migration. During this period the birds become flightless, and the flight muscles may lose up to 50% of their mass. Myofibers from atrophic birds show evidence of mitochondrial division (or fusion). Even severely atrophic fibers retain a high mitochondrial density (27% vs. 33% in migratory condition), so that relative volume remains stable although absolute volume is reduced. In contrast, intracellular triglyceride droplets are extremely sparse in atrophic fibers, even though most of the birds are carrying >200 g of subcutaneous fat. Mean myofiber diameter increases and decreases with atrophy and hypertrophy. In late autumn, as food availability declines, the birds engage in conspicuous flapping exercises. In the same period, intracellular lipid reappears in the muscles. Within several weeks the muscles are rebuilt to full size and the grebes emigrate. The benefits, if any, of this cycle of muscle atrophy and concomitant obesity, followed by muscle hypertrophy and weight loss, remain obscure.

Microsomal preparation from an animal tissue catalyzes release of carbon monoxide from a fatty aldehyde to generate an alkane.

Alkanes are widely distributed in nature and impaired alkane synthesis was implicated in certain neurological disorders. However, the mechanism of synthesis of alkanes in animals is unknown. Our search to find a convenient animal tissue to study alkane biosynthesis resulted in the finding that the uropygial gland (a modified sebaceous gland) of the eared grebe (Podiceps nigricollis) produces large amounts of alkanes. These alkanes, which constitute 35-41% of the total lipid produced, are mainly C21, C23, C25, and C27 n-alkanes. Cell free homogenates of this tissue synthesized alkanes from both fatty acid and aldehyde in the absence of O2. Differential centrifugation of the homogenates indicated that this activity was located in the microsomal fraction. With isolated microsomes conversion of fatty acid to alkane required CoA, ATP, and NADH whereas conversion of an aldehyde to alkane did not require the addition of cofactors. That the final step in alkane synthesis is a decarbonylation was shown by the stoichiometric production of heptadecane and CO from octadecanal. CO was identified by adsorption to RhCl [(C6H6)3P]3 and oxidation of the trapped CO to CO2 by watergas shift reaction. The enzyme preparation also catalyzed incorporation of 14C from 14CO into octadecanal showing the reversible nature of the decarbonylase. This decarbonylase had a sharp pH optimum at 7.0, a Kapp of 180 microM and a V1/2 of 90 rho mol/min/mg protein for octadecanal. The enzyme was inhibited by the metal chelators EDTA, O-phenanthroline, and 8-hydroxyquinoline, but not by KCN. It was stimulated nearly 3-fold by 5 microM 2-mercaptoethanol and inhibited by the presence of O2. During the conversion of [1-3H]octadecanal to heptadecane, 3H was lost to water and 3H from 3H2O was incorporated into the alkane generated from unlabeled octadecanal. The mechanism of the decarbonylation and the nature of the enzyme remain to be elucidated.

The Beached-bird Assemblage of a Highly Saline Lake and Its Relevance for Reconstructing Paleoenvironments

Abstract The beached-bird deposits of saline (80-90%) Mono Lake, California, are dominated by Eared Grebes (Podiceps nigricollis) and California Gulls (Larus californicus), which together comprise 95% of the specimens. Nevertheless, the diversity of waterbirds in these deposits is high (31 species), because mortality is high among migratory species that are poorly adapted to saline environments. The composition of the Mono Lake assemblage differs markedly from local Pleistocene faunas that accumulated in fresh or slightly saline habitats.

Surplus killing of Eared Grebes, Podiceps nigricollis, by Mink, Mustela vison, in central British Columbia

Surplus killing of Eared Grebes, Podiceps nigricollis, by Mink, Mustela vison, in central British Columbia