Last Updated June 17th

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 12,557 terns (June 10) and 10,360 terns (June 11), respectively. This represents a 9% decrease 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, 61 terns were observed roosting on the beaches of these three upper estuary dredge spoil islands on June 10. 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.

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 740 terns (June 12) and 679 terns (June 12), respectively. This represents a 14% 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, 37% of the identifiable fish delivered to the East Sand Island tern colony (N = 355) were salmonids. This represents a 24% 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 clupeids (i.e., herring) and smelt. Year to date, 45% of the identifiable fish delivered to the East Sand Island tern colony (N = 3,466) were salmonids (this cumulative percent is an average of the previous weeks' percentages), the same percentage as was recorded by this date in 2001.

For the week, 72% of the identifiable fish delivered to the Crescent Island tern colony (N = 155) were salmonids. This represents a 9% 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, 72% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,355) were salmonids (this cumulative percent is an average of the previous weeks' percentages). This compares to 73% 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 Monday (June 10) and Tuesday (June 11). This past week, the average numbers of foraging gulls and white pelicans counted in the tailrace of McNary Dam were 11 and 7, respectively. The number of gull foraging attempts below McNary Dam was roughly 11 attempts per hour this past week, with roughly a third of those attempts resulting in the bird catching a fish. As many as 5 Caspian terns were observed foraging below McNary Dam this week, compared to only one foraging tern observed at McNary Dam the previous week.

Predator Activity

Bald eagle disturbance rate to the East Sand Island tern colony was 0.10 disturbances/hr of observation, the same disturbance rate as was recorded last week. 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 decreased this week (1.00 predation events/disturbance), as compared to the previous week (1.80 predation events/disturbance). Concurrently, gull kleptoparasitism rates have been declining over the past several weeks (i.e., 3.7%, 0.8%, 0.0%, and 0.0% of all known fates of fish delivered by terns in each of the last four weeks, respectively).

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.