Last Updated July 15th

Note: The following data are preliminary and may change upon further review.

Caspian Tern Colony Counts

East Sand Island

The high and low on-colony counts for the week on East Sand Island were 7,554 terns (July 1) and 6,685 terns (July 2), respectively. This represents a 15% decrease in the median count of terns on the East Sand Island colony from last week to this week.

Rice Island and Other Upper Estuary Islands

During this past week, no terns were observed roosting or attempting to nest in upland areas on Rice Island, Miller Sands Spit, or Pillar Rock Sands. In total, 37 terns were observed roosting on the beaches of these three upper estuary dredge spoil islands on July 1. Because of the stage of the Caspian tern nesting season (late chick-rearing) and the absence of any nesting behavior at the upper estuary dredge spoil islands for over a month, we are confident that nesting by terns will not occur on these islands this season.

Up-river Sites (Crescent Island, Three Mile Canyon Island, Miller Rocks)

The high and low on-colony counts for the week on Crescent Island were 362 terns (July 1) and 236 terns (July 3), respectively. This represents a 16% decrease in the median count of terns on the Crescent Island colony from last week to this week.

Because of the stage of the Caspian tern nesting season (late chick-rearing) and the absence of any nesting behavior at Three Mile Canyon Island and Miller Rocks so far this breeding season, we are confident that nesting by terns will not occur on these islands in 2002.

Diet Composition

For the week, 8% of the identifiable fish delivered to the East Sand Island tern colony (N = 369) were salmonids. This represents a 47% decrease in the percentage of the diet that was salmonids for terns on the East Sand Island colony from last week to this week. The majority of non-salmonid prey items delivered to the East Sand Island colony were clupeids (i.e., sardines, herring). Year to date, 38% of the identifiable fish delivered to the East Sand Island tern colony (N = 4,568) were salmonids (this cumulative percent is an average of the previous weeks' percentages). This compares to 39% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2001.

For the week, 81% of the identifiable fish delivered to the Crescent Island tern colony (N = 155) were salmonids. This represents a 2% decrease in the percentage of the diet that was salmonids for terns on the Crescent Island colony from last week to this week. Year to date, 75% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,820) were salmonids (this cumulative percent is an average of the previous weeks'
percentages). This compares to 74% juvenile salmonids in the diet of terns on Crescent Island by the same date in 2001.

Observations at McNary Dam

We conducted surveys for fish-eating birds at McNary Dam on Tuesday, July 2 and Saturday, July 6. This past week, the average numbers of foraging Caspian terns, gulls, and white pelicans counted in the tailrace of McNary Dam were 4, 3, and 6, respectively. This represents a decrease in the average number of terns, gulls, and pelicans observed foraging near McNary Dam this week, as compared to the previous week. This past week, the rate of tern and pelican foraging attempts below McNary Dam was roughly 5 and 1 attempt(s) per hour, respectively. Roughly 20% of the tern and pelican foraging attempts were successful.

Predator Activity

The bald eagle disturbance rate to the East Sand Island tern colony was 0.08 disturbances/hr of observation this past week, the same rate as the previous week. These disturbances were generally short, causing terns to leave the colony for only 10-15 seconds before returning.

One gull predation on a tern chick was observed during eagle disturbances to the tern colony this past week. Gull kleptoparasitism rates decreased this past week (1.1% of all known fates of fish delivered by terns), as compared to the previous week (1.4% of all known fates).

Two disturbances were observed at the Crescent Island tern colony this past week; the cause of these disturbances was undetermined.

Media & Other Visitors

Howard Browers (USFWS), Nanette Seto (USFWS), and Jeff Dillon (USFWS) visited Crescent, Foundation, and Badger islands on July 3.