Mono Lake gull research update
By Nataniel H. Taylor, Justin Hite, and David W. Winkler
In
1999, a team of researchers from Cornell University augmented the team
from the Point Reyes Bird Observatory to carry out annual monitoring as
well as to investigate the effects of meromixis on the feeding and
productivity of California Gulls at Mono Lake. (Meromixis is a state in
which the lake does not completely mix on an annual basis, resulting in a
less saline water layer floating on top of a more saline layer—for more
information on meromixis see www.monobasinresearch.org/timelines/meromixis.htm.)
Researchers assisted in the censusing of the gulls and began studies directed toward understanding the poor productivity of gull nesting in recent years. Much of the Cornell team’s work was involved in developing methods for research and establishing a new plot and observation site on Little Tahiti islet. Relatively small sample sizes obtained last summer are sufficient to suggest the following tentative conclusions:
• the growth rates of chicks in 1999 appear to have been slightly lower than those that Winkler observed at Mono in 1980-1982
• the rate of gull predation on other gulls in 1999 appears to have been higher than “normal”
• gulls fed their chicks a large amount of alkali fly larvae and pupae, though there are still a lot of shrimp being taken
• they also added long-legged fly larvae to their diet, a relatively fresh-water species that has not been common at the lake since the meromictic event of the early 1980s.
Last summer’s research makes it clear that the gulls are taking substantial numbers of alkali flies, but future research needs to explore just how good alkali flies are as food items. If, as seems likely, the flies are better prey than shrimp, where are the limits to greater use of the flies by the gulls? Click here to read the annual gull research reports online.
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