Last Updated June 3rd

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 13,177 terns (May 30) and 11,061 terns (May 27), respectively. This represents an 8% decline 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 a decline in the number of terns observed roosting on the beaches at Rice Island, Miller Sands Spit, and Pillar Rock Sands. In total, only 16 terns were observed roosting on the beaches of these three upper estuary dredge spoil islands on May 31. 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)

As was the case the previous week, we were unable to conduct an aerial survey along the southern Washington coast this past week due to poor weather. 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 975 terns (June 2) and 862 terns (May 28), respectively. This represents no change 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, 65% of the identifiable fish delivered to the East Sand Island tern colony (N = 360) were salmonids. This represents a 23% 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, 46% of the identifiable fish delivered to the East Sand Island tern colony (N = 2,755) 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, 81% of the identifiable fish delivered to the Crescent Island tern colony (N = 150) were salmonids. This represents a 21% 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, 72% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,044) 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 (May 27) and Thursday (May 30). This past week, the average numbers of gulls and white pelicans counted in the tailrace of McNary Dam were 18 and 8, respectively. The average number of gulls and pelicans counted near McNary Dam was once again higher when hazing activities were not taking place (May 27; active hazing on that day was completed before our observations), as compared to when hazing activities were taking place (May 30). The number of gull foraging attempts below McNary Dam was roughly 6 attempts per hour this past week, with roughly half of those attempts resulting in the bird catching a fish. This past week, as many as 5 Caspian terns were observed foraging below McNary Dam, which was the first time we observed terns in appreciable numbers at the dam since beginning our observations on April 2.

Predator Activity

Bald eagle disturbance rates to the East Sand Island tern colony were lower this last week (0.23 disturbances/hr of observation), as compared to the previous week (0.27 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 nearly doubled this week (1.34 predation events/disturbance), as compared to the previous week (0.69 predation events/disturbance). Concurrently, gull kleptoparasitism rates have been declining over the past several weeks (i.e., 7.1%, 3.7%, and 0.8% of all known fates of fish delivered by terns in each of the last three 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

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