Last Updated May 28th

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 14,450 terns (May 25) and 11,949 terns (May 20), respectively. This represents a 10% 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 have been 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 has been an increase in the number of terns observed roosting (several hundred in total) on the beaches at Rice Island, Miller Sands Spit, and 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)

Due to bad weather, we were unable to conduct an aerial survey along the southern Washington coast this past week. We plan to conduct an aerial survey of this area this coming week, weather permitting.

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 966 terns (May 23) and 879 terns (May 23), respectively. This represents an 8% decrease 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 70 (8%) 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 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, 53% of the identifiable fish delivered to the East Sand Island tern colony (N = 359) 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 the last few weeks, the majority of non-salmonid prey items delivered to the East Sand Island colony were surfperch and anchovy. Year to date, 43% of the identifiable fish delivered to the East Sand Island tern colony (N = 2,395) 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, 67% of the identifiable fish delivered to the Crescent Island tern colony (N = 165) were salmonids. This represents an 8% 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, 70% of the identifiable fish delivered to the Crescent Island tern colony (N = 894) were salmonids (this cumulative percent is an average of the previous weeks' percentages). This compares to 69% 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 (May 21) and Wednesday (May 22). This past week, the average number of gulls and white pelicans counted in the tailrace of McNary Dam were 42 and 3, respectively. The average number of gulls counted near McNary Dam was 3 times higher when hazing activities were not taking place (May 21; active hazing on that day was completed before our observations), as compared to when hazing activities were taking place (May 22). The number of gull foraging attempts below McNary Dam was roughly 12 attempts per hour on May 21, and roughly 4 attempts per hour on May 22, with roughly a third 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 disturbance rates to the East Sand Island tern colony were lower this last week (0.27 disturbances/hr of observation), as compared to the previous week (0.35 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 of the East Sand Island tern colony by bald eagles was lower this past week compared to the previous week, gull predation rates on tern eggs per disturbance remained unchanged. We observed 0.7 egg predation events per disturbance during the past 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 were no disturbances observed at the Crescent Island tern colony this past week.

Media & Other Visitors

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