02/11/2002 Council Packet - Laserfiche WebLink

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• • Figure 1. Location of great blue heron and great egret rookeries where feeding habitat data were collected in 1998. 2 clockwise direction, approximately 300 meters above the ground, and a bird selected as it left the rookery. That bird was then followed to its feeding location (Custer and Osborn 1978, Custer and Bunck 1992). The time of day that the bird left the rookery and the time it arrived at its feeding location were recorded. The location where the bird landed was mapped using a combination of global position system equipment and/or landmarks. The general habitat characteristics (small pond, lake, river, main channel of UMR, open water, emergent vegetation, submergent vegetation, forest, urban, agricultural, etc.), surface water characteristics (glass -like, rippled, or rough), and the presence of other herons and egrets was quantified. After those data were recorded, the observer returned to the nesting rookery and repeated the flight following with a different bird. The next bird to follow was chosen by beginning the search for a new bird at the location in the rookery where the previous bird had departed from and then continuing to fly around the rookery in a counter- clockwise direction. The next bird to leave the rookery was then followed. This eliminated any bias in choosing which bird to follow and ensured that all directions from the rookery had an equal chance of being selected. As many birds as possible were followed from each rookery during a 2- to 3 -hr period in the morning and a 2- to 3 -hr period in the afternoon. Only one species was followed during a specific time period (i.e. either morning or afternoon) and the species followed during a specific time period was alternated so that each species was followed both in the morning and afternoon. The time -of -day that a flight was made, however, was probably unimportant because great blue herons feed steadily throughout the day (McNeil et al. 1993). Results and Discussion One hundred eighty -nine great blue herons and 86 great egrets were followed from 4 rookeries, Pigs Eye, Vermillion River, Peltier Lake, and Smith Slough, between April and July 1998. The Vermillion River and Pigs Eye rookeries were only flown twice. Excessive air traffic in the vicinity of Pigs Eye rookery made those flights dangerous and reduced the quality of the data to the point that it would have been virtually useless. The Vermillion River rookery was discontinued because it lacked great egrets. Peltier Lake and Smith Slough rookeries were substituted at that time. The numbers of birds followed and the distribution of flights covered the breeding season (Custer et al. 1996, Table 1). Observations were terminated at the Pigs Eye rookery before the great egrets arrived there in numbers, and no great egrets were present in the Vermillion River rookery.