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 7,200 terns (July 8) and 4,673 terns (July 14), respectively. This represents a 17% 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

Surveys of foraging and roosting terns were not conducted in the upper estuary this past week.

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 350 terns (July 9) and 25 terns (July 11), respectively. This represents a 37% 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, 6% of the identifiable fish delivered to the East Sand Island tern colony (N = 379) were salmonids. This represents a 25% decrease in the percentage of the diet that was salmonids for terns on the East Sand Island colony from last week to this week. As was the case the previous week, the majority of non-salmonid prey items delivered to the East Sand Island colony were clupeids (i.e., sardines, herring). Year to date, 36% of the identifiable fish delivered to the East Sand Island tern colony (N = 4,947) were salmonids (this cumulative percent is an average of the previous weeks' percentages). This compares to 37% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2001.

For the week, 41% of the identifiable fish delivered to the Crescent Island tern colony (N = 98) were salmonids. This represents a 49% 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, 72% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,918) were salmonids (this cumulative percent is an average of the previous weeks'
percentages), the same percentage as was recorded by this date in 2001.

Chick Banding

On July 9, a total of 72 tern chicks that were near fledging were banded at the Crescent Island tern colony. Each chick was banded with a numbered U.S. Fish and Wildlife Service metal leg band. Of the 72 chicks that were banded at Crescent Island, 60 chicks were also banded with unique color band combinations placed on both legs.

Also on July 9, we attempted to band fledglings at the Solstice Island tern colony, located in the Potholes Reservoir in Central Washington. Despite there being 30-50 tern chicks on the colony the previous week, there were only 3 chicks present on July 9 and all three were capable of flight. Consequently, no terns were banded at Solstice Island in 2002.

On July 11-12, a total of 375 tern chicks that were near fledging were banded at the East Sand Island tern colony. Each chick was banded with a numbered U.S. Fish and Wildlife Service metal leg band. Of the 375 chicks that were banded at East Sand Island, 369 chicks were also banded with unique color band combinations placed on both legs.

No mortality or injuries occurred to the banded tern chicks during the above-mentioned banding operations. These banded fledglings will provide important data on survivorship, dispersal patterns, and recruitment of young terns to breeding colonies in future years.

Observations at McNary Dam

We conducted surveys for fish-eating birds at McNary Dam on Wednesday, July 10 and Friday, July 12. This past week, the average numbers of foraging Caspian terns, gulls, and white pelicans counted in the tailrace of McNary Dam were 6, 5, and 7, respectively. This represents little change 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, gull, and pelican foraging attempts below McNary Dam was roughly 22, 11, and 1 attempt(s) per hour, respectively. Roughly half of the tern, gull, and pelican foraging attempts were successful.

Predator Activity

Bald eagle disturbance rates to the East Sand Island tern colony were higher this last week (0.13 disturbances/hr of observation), as compared to the previous two weeks (0.08 disturbances/hr of observation). These disturbances were generally short, causing terns to leave the colony for only 10-15 seconds before returning.

No gull predation on tern eggs and chicks was observed during eagle disturbances to the tern colony this past week. Gull kleptoparasitism rates decreased this past week (0.6% of all known fates of fish delivered by terns), as compared to the previous week (1.1% of all known fates).

There were no predator-caused disturbances at the Crescent Island tern colony this past week.

Media & Other Visitors

Herb Curl, Alex Morgan, Don Norman, Chuck Lennox, and Liz Young from the Seattle Audubon Society visited the East Sand Island tern colony on July 11.

Dave Craig (Willamette University [WU]), Danica Praza (WU), Evan Larson (WU), Zach Holmboe (WU), Daniel Rameriz (WU), David Leal (USFWS), Timmie Mandish (USFWS), Dan Rizzolo (OSU) Megan Heinrich (University of Idaho), and Chris Thompson (WDFW) assisted project staff with the chick banding operation this past week, for which we are grateful.