Last Updated July 22th

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 4,278 terns (July 16) and 3,915 terns (July 17), respectively. This represents a 31% decrease in the median count of terns on the East Sand Island colony from last week to this week. Most young terns have fledged from the colony and have joined the post-breeding season dispersal with their parents (Caspian terns provide their young with post-fledging care).

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 162 terns (July 20) and 10 terns (July 21), respectively. This represents a 54% decrease in the median count of terns on the Crescent Island colony from last week to this week. Nearly all young terns have fledged from this colony and have joined the post-breeding season dispersal. The Crescent Island colony was the only site on the Columbia River between the estuary and the Tri-Cities area where Caspian terns successfully nested this year.

Commencement Bay, Washington

Caspian terns nesting on the rooftop of a building near the mouth of the Hylebos Waterway in the Port of Tacoma (Commencement Bay) were surveyed from the ground by Michelle Tirhi of the Washington Department of Fish and Wildlife on July 9. A total of 347 adult terns, 96 tern chicks, and 11 tern eggs were counted on the rooftop. The terns had apparently selected this rooftop because of some accumulation of dirt and debris on the roof, although nest scrapes were barely discernible due to a paucity of nesting substrate. This represents the only known Caspian tern breeding colony along the coast of Washington in 2002. The Port of Tacoma plans to remove the dirt and debris from the roof prior to tern nesting season next year.

Diet Composition

For the week, 8% of the identifiable fish delivered to the East Sand Island tern colony (N = 357) were salmonids. This represents a 33% increase 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 surfperch. Year to date, 34% of the identifiable fish delivered to the East Sand Island tern colony (N = 5,304) were salmonids (this cumulative percent is an average of the previous weeks' percentages). This compares to 35% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2001.

For the week, 38% of the identifiable fish delivered to the Crescent Island tern colony (N = 152) were salmonids. This represents a 7% 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, 70% of the identifiable fish delivered to the Crescent Island tern colony (N = 2,070) were salmonids (this cumulative percent is an average of the previous weeks'
percentages), the same percentage as was recorded by this date in 2001.

Observations at McNary Dam

We conducted surveys for fish-eating birds at McNary Dam on Monday (July 15), Tuesday (July 16), and Thursday (July 18). This past week, the average numbers of foraging Caspian terns, gulls, and white pelicans counted in the tailrace of McNary Dam were 12, 5, and 5, respectively. This represents little change in the average number of gulls and pelicans, and an increase in the average number of Caspian terns, 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 15 and 1 attempt(s) per hour, respectively. Successful foraging attempts ranged from 71% for gulls to 37% for pelicans. Roughly half of the tern foraging attempts were successful.

Predator Activity

Bald eagle disturbance rates to the East Sand Island tern colony were lower this last week (0.06 disturbances/hr of observation), as compared to the previous two weeks (0.13 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.

Media & Other Visitors

There were no visitors in the field this past week.