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Investigations of a large scale eared grebe (Podiceps nigricollis) die-off at the Salton Sea, California in 1992

Studies in Avian Biology

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Abstract

An estimated 150,000 Eared Grebes (Podiceps nigricollis) died at the Salton Sea between 16 December 1991 and 21 April 1992. This represented the largest documented mortality event of Eared Grebes at the time and approximately 6% of the North American population. During the die-off, grebes exhibited several uncharacteristic behaviors, such as congregating at freshwater tributaries, repeatedly gulping freshwater, preening excessively, moving onto land, and allowing close approach and/or capture. Avian cholera was diagnosed in Eared Grebes collected along the north and west shoreline of the Sea late in the die-off but not from the majority of the Eared Grebes dying along the south shore. Gross and histological examinations and diagnostic testing for viruses, bacteria, and parasites did not identify the cause of mortality in the majority of Eared Grebes examined from the south shore of the Sea. Liver concentrations of arsenic, chromium, DDE, mercury, selenium, and zinc were elevated in some Eared Grebes, but none of those contaminants exceeded known thresholds for independent lethality. Poisoning by heavy metals, organochlorine, organophosphorus, or carbamate pesticides, avian botulism, and salt were ruled out as the cause of mortality. Hypotheses for the die-off are interactive effects of contaminants, immunosuppression, a yet unidentified biotoxin or pathogen present in the Salton Sea, impairment of feather waterproofing leading to hypothermia, or a unique manifestation of avian cholera that evades laboratory detection.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Investigations of a large scale eared grebe (Podiceps nigricollis) die-off at the Salton Sea, California in 1992
Series title:
Studies in Avian Biology
Volume
27
Year Published:
2004
Language:
English
Contributing office(s):
National Wildlife Health Center
Description:
p. 141-151
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Studies in Avian Biology
First page:
141
Last page:
151
Number of Pages:
11