Last Updated May 20th

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 13,450 terns (May 19) and 10,638 terns (May 13), respectively. This represents a 4% increase in the median count of terns on the East Sand Island colony from last week to this week. Compared to last year at this time, there are an estimated 2,800 (19%) fewer terns on the East Sand tern colony this year (based on median ground counts). The aerial photo census of the East Sand Island tern colony is scheduled for this week. 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.

The first Caspian tern chicks were observed on the East Sand Island colony on Wednesday, May 15, a day earlier than the date the first chick was sighted at East Sand Island last year.

Rice Island and Other Upper Estuary Islands

During this past week, no terns have been observed roosting or attempting to nest in upland areas on Rice Island, Miller Sands Spit, or Pillar Rock Sands. 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)

During aerial surveys conducted along the southern Washington coast this past week (May 15), no terns were observed roosting or attempting to nest in upland areas on any of the islands in Willapa Bay or Grays Harbor. No terns were observed in Willapa Bay and only 13 terns were seen in Grays Harbor, roosting on a sand bar below the high tide line. 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 1,027 terns (May 18) and 973 terns (May 13), respectively. This represents a 15% increase in the median count of terns on the Crescent Island colony from last week to this week. Compared to last year at this time, there are an estimated 60 (6%) more terns on the Crescent Island tern colony this year (based on median ground counts). The aerial photo census of the Crescent Island tern colony is scheduled for this week. 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.

The first Caspian tern chicks were observed on the Crescent Island colony on Monday, May 13, the same date as the first chick sighting at Crescent Island last year.

Diet Composition

For the week of May 13 - May 19, 50% of the identifiable fish delivered to the East Sand Island tern colony (N = 365) were salmonids. This represents a 6% increase in the percent of the diet that were salmonids for terns on the East Sand Island colony from last week to this week. Similar to last week, the majority of the non-salmonid prey items delivered to the East Sand Island colony were surfperch and anchovy. Year to date, 41% of the identifiable fish delivered to the East Sand Island tern colony (N = 2,036) were salmonids (this cumulative percent is an average of the previous weeks' percentages). This compares to 48% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2001.

For the week, 62% of the identifiable fish delivered to the Crescent Island tern colony (N = 121) were salmonids. This represents a 35% decrease 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, 71% of the identifiable fish delivered to the Crescent Island tern colony (N = 729) were salmonids (this cumulative percent is an average of the previous weeks' percentages), the same cumulative percentage (71%) as was recorded for terns on Crescent Island by the same date in 2001.

Off-Colony Distribution

We conducted our surveys at McNary Dam on Thursday (May 16) and Sunday (May 19). This past week, the average number of gulls and white pelicans counted in the tailrace of McNary Dam were 40 and 8, respectively. The numbers of gulls and pelicans counted below McNary Dam was generally lower when active hazing activities were taking place throughout the tailrace (May 16; primarily pyrotechnics), as compared to when those activities were restricted to the juvenile fish bypass (May 19; propane cannon). The number of foraging attempts, primarily by gulls in the tailrace, was roughly 13 attempts per hour, with roughly half of those attempts resulting in the bird catching a fish. Thus far, double-crested cormorants and Caspian terns have not been observed at McNary Dam in appreciable numbers.

Predator Activity

Bald eagle disturbances to the East Sand Island tern colony were higher this last week (0.35 disturbances/hr of observation), as compared to the previous week (0.24 disturbances/hr of observation). These disturbances are generally short, causing terns to leave the colony for only 10-15 seconds before returning.

Although the disturbance rate to the East Sand Island tern colony was higher this past week as compared to the previous week, gull predation on tern eggs decreased. We observed 0.7 egg predation events per disturbance this last week, compared to 1.5 egg predation events per disturbance the previous week. 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 was one accidental observer-caused disturbance at the Crescent Island tern colony this past week. The disturbance caused roughly 10% of the nesting terns to momentarily leave their nests; during which time no nest predations were observed.

Media & Other Visitors

There were no visitors to the East Sand Island tern colony this past week.