Great Salt Lake Biology by Unknown

Great Salt Lake Biology by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030403522
Publisher: Springer International Publishing


Grebes in pelagic bays of GSL during the fall-staging period feed almost exclusively on adult brine shrimp (Paul 1996; Conover and Vest 2009a). This is not true in less saline parts of GSL. Paul (1996) collected grebes in Farmington Bay during fall staging and found half of their diet to be brine fly larva, with brine shrimp making up the rest.

Grebes are not randomly located across the pelagic bays of GSL during fall staging but are concentrated over microbialites where brine shrimp adults and brine fly larva are most abundant (Roberts and Conover 2014b). Microbialites, which include subcategories of layered stromatolites or disorganized thrombolites, are organo-sedimentary carbonate structures that contain cyanobacteria and rich microbial mats that contribute to primary production. In Mono Lake, there are no stromatolites, but there are rocky shoals made of tufa, which may also be biologically precipitated (Scholl and Taft 1964). These are similar in geochemistry to the microbialites in GSL, and grebes are concentrated around these structures as are brine fly larva and adults.

Grebes leave GSL over a 30-day period in November and December to migrate to their wintering areas in the Gulf of California and Pacific Ocean. Grebes depart earlier during years when brine shrimp densities are high and water temperatures are above average. Frank and Conover (2017) concluded that grebes depart from GSL when they have gained sufficient mass to migrate successfully rather than lingering at GSL for as long as possible. Eared grebes departed from GSL over a period of 31 days each year, with departures occurring on 17 of those days.

Migration between GSL and the Gulf of California is dangerous for grebes because it must be made without stopping, and most of the trip occurs over the desert where lakes and reservoirs are uncommon. To increase the odds of a successful migration, grebes depart on nights when the barometric pressure is high and the local weather fair. High barometric pressure is related to low wind speeds and little precipitation (Frank and Conover 2017). Still, some grebes are unsuccessful in their migration attempt. Sometimes, large flocks of grebes crash-land (called a downing) in deserts of Utah and Arizona. Grebes cannot become airborne from land so most grebes involved in a downing die where they land. One downing in Cedar City occurred during a snowstorm and involved 7000 grebes. Grebes involved in a downing were similar in body condition and age as grebes that successfully migrate, leading Roberts et al. (2014) to conclude that most grebes involved in a downing were simply at the wrong place and the wrong time (i.e., caught in bad weather). But Roberts et al. (2014) also noted that the grebes that crash-landed in Cedar City had higher blood levels of mercury and selenium than most grebes.

As winter turns to spring, grebes start flying back to their nesting areas. Aerial surveys of GSL during the spring have found hundreds of thousands of grebes in the pelagic bays of GSL. We assume that these birds are migrating north to their



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