Gull research 1999

Point Reyes Bird Observatory (PRBO) and Dr. David Winkler of Cornell University collaborated in designing the expanded 1999 field research. PRBO’s gull nesting monitoring continued as it has in the past, with paying volunteers helping count nests and band surviving chicks. New this year was field work carried out by two Cornell University students. The new research was aimed at answering focused questions about gull foraging behavior and the relationship between fly-dominated and shrimp-dominated diet for chick growth and survival.

While the final stage of the field work—the mortality count—remained to be done at the time this Newsletter went to press, it is clear that gull productivity was down again in 1999 as it had been in 1998. A number of factors could be involved, such as the El Niño/La Niña fluctuations in the weather patterns. The gull study will help answer if and how this is connected with the current meromictic state of the lake (in which the lake does not completely mix on an annual basis) and the resulting modification of brine shrimp life cycles and alkali fly distribution.

Information derived from Cornell-directed feeding studies can also help develop a more accurate picture of how Mono Lake’s chemical mechanisms interact with the lake ecology in the large scale. Cornell undergraduates Nat Taylor and Justin Hite spent two months on the islands making detailed observations of a specific nesting plot, in which all gulls were individually identified, noting:

• frequency of feedings and by which parent

• general type of food brought back

• amount of time parents spent away

• growth measurements on chicks

In the process, they collected regurgitated food samples with pertinent data about the specific chick these came from. These samples will be analyzed this fall.

Off the islands, Nat and Justin conducted foraging observations at specific sites around the shores of Mono Lake, loosely coordinated with baseline alkali fly monitoring by Dr. David Herbst of the Sierra Nevada Aquatic Research Laboratory. The foraging observations included such detailed information as numbers of "pecks" per minute and data on the arrival and departure of birds. The researchers also collected samples of the general food composition in the lake at the time of the foraging observations. These samples also will be analyzed this fall.