Last Updated June 10th

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 13,743 terns (June 8) and 11,323 terns (June 7), respectively. This represents a 3% increase in the median count of terns on the East Sand Island colony from last week to this week. The aerial photo census of the East Sand Island tern colony was conducted on Tuesday, May 21. Once the aerial photos are counted we will be able to accurately estimate colony size and determine whether there has been a significant change in colony size since 2001.

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. This week as compared to the previous week, there was an increase in the number of terns observed roosting on the beaches at Rice Island, Miller Sands Spit, and Pillar Rock Sands. In total, 147 terns were observed roosting on the beaches of these three upper estuary dredge spoil islands on June 6. We will continue to monitor Rice Island and other upper estuary dredged material disposal islands looking for early signs of nesting (e.g., scrape digging) and will promptly inform resource managers of any such activity.

Washington Coast (Willapa Bay, Grays Harbor, Commencement Bay)

During aerial surveys conducted along the Washington coast this past week (June 6), no terns were observed roosting or attempting to nest in upland areas on any of the islands in Willapa Bay or Grays Harbor. During that same survey, 200-300 nesting terns were observed on the rooftop of a building near the mouth of the Hylebos Waterway in the Port of Tacoma (Commencement Bay). No other nesting or roosting terns were observed in Commencement Bay, including at the old colony location at the ASARCO Industrial Site. We will continue to fly periodic surveys in these areas looking for nesting terns.

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 875 terns (June 4) and 782 terns (June 6), respectively. This represents a 10% decrease in the median count of terns on the Crescent Island colony from last week to this week. The aerial photo census of the Crescent Island tern colony was conducted on Thursday (May 23). Once the aerial photos are counted we will be able to estimate colony size with greater accuracy and determine whether there has been a significant change in colony size since 2001.

Diet Composition

For the week, 49% of the identifiable fish delivered to the East Sand Island tern colony (N = 356) were salmonids. This represents a 25% decrease in the percent of the diet that were 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 anchovy and clupeids (i.e., herring). Year to date, 46% of the identifiable fish delivered to the East Sand Island tern colony (N = 3,111) were salmonids (this cumulative percent is an average of the previous weeks' percentages). This compares to 47% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2001.

For the week, 79% of the identifiable fish delivered to the Crescent Island tern colony (N = 156) were salmonids. This represents a 2% increase in the percent of the diet that were salmonids for terns on the Crescent Island colony from last week to this week. Year to date, 73% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,200) were salmonids (this cumulative percent is an average of the previous weeks' percentages), the same percentage as was recorded by the same date in 2001.

Observations at McNary Dam

We conducted surveys for fish-eating birds at McNary Dam on Monday (June 3), Wednesday (June 5), and Thursday (June 6). This past week, the average numbers of foraging gulls and white pelicans counted in the tailrace of McNary Dam were 41 and 8, respectively. The number of gull foraging attempts below McNary Dam was roughly 14 attempts per hour this past week, with roughly a third of those attempts resulting in the bird catching a fish. Only one Caspian tern was observed foraging below McNary Dam this week, compared to as many as 5 foraging terns observed at McNary Dam the previous week.

Predator Activity

Bald eagle disturbance rates to the East Sand Island tern colony were lower this last week (0.10 disturbances/hr of observation), as compared to the previous week (0.23 disturbances/hr of observation). These disturbances were generally short, causing terns to leave the colony for only 10-15 seconds before returning.

Gull predation rates on tern eggs and chicks increased this week (1.80 predation events/disturbance), as compared to the previous week (1.34 predation events/disturbance). Concurrently, gull kleptoparasitism rates have been declining over the past several weeks (i.e., 7.1%, 3.7%, 0.8%, and 0.0% of all known fates of fish delivered by terns in each of the last four weeks, respectively). We will continue to monitor the level of nest predation by gulls at the East Sand Island tern colony and present those results in subsequent weekly reports.

There were no disturbances observed at the Crescent Island tern colony this past week.

Media & Other Visitors

Nanette Seto (USFWS) and Marie Morin (USFWS) visited the East Sand Island tern and cormorant colonies this past week.