Last Updated July 1st

Note: The following data are preliminary and may change upon further review. The next weekly report will be posted on the web page on Monday, July 15.

Caspian Tern Colony Counts

East Sand Island

The high and low on-colony counts for the week on East Sand Island were 11,004 terns (June 24) and 5,786 terns (June 28), respectively. This represents a 7% decrease in the median count of terns on the East Sand Island colony from last week to this week.

Heavy rains and high winds on Friday (June 28) caused considerable chick mortality on the East Sand Island tern colony. Over 500 dead chicks were counted on the colony following the storm, but total losses could be twice that high. Associated with the storm, chick mortality on monitoring plots was about 10%, but this may be somewhat higher than the average mortality rate for the entire colony. Despite these losses, productivity of terns nesting on East Sand Island this year will likely be good (i.e., above average productivity for terns nesting in the estuary from 1997-2001). A second aerial photo census of the colony will be conducted early this week in order to estimate the number of young terns fledged from the East Sand Island colony this year.

Rice Island and Other Upper Estuary Islands

Because of boat trouble, no surveys for roosting and foraging terns were conducted in the upper estuary this past week.

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

During an aerial survey conducted along the Washington coast this past week (June 24), 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, 400-450 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 420 terns (June 24) and 287 terns (June 29), respectively. This represents a 5% decrease in the median count of terns on the Crescent Island colony from last week to this week.

The first fledgling (i.e., young-of-the-year capable of flight) was observed at the Crescent Island on Monday, June 24; nesting success so far this year appears to be similar to the last two years.

Diet Composition

For the week, 15% of the identifiable fish delivered to the East Sand Island tern colony (N = 354) were salmonids. This represents a 17% decrease in the percent of the diet that was 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 anchovies and clupeids (i.e., sardines, herring). Year to date, 40% of the identifiable fish delivered to the East Sand Island tern colony (N = 4,199) were salmonids (this cumulative percent is an average of the previous weeks' percentages). This compares to 41% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2001.

For the week, 83% of the identifiable fish delivered to the Crescent Island tern colony (N = 157) were salmonids. This represents a 1% decrease in the percent of the diet that was salmonids for terns on the Crescent Island colony from last week to this week. Year to date, 74% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,665) were salmonids (this cumulative percent is an average of the previous weeks' percentages), the same percentage as was recorded by this date in 2001.

Observations at McNary Dam

We conducted surveys for fish-eating birds at McNary Dam on Tuesday, June 25 and Friday, June 28. This past week, the average numbers of foraging Caspian terns, gulls, and white pelicans counted in the tailrace of McNary Dam were 15, 16, and 12, respectively. This represents an increase in the average number of terns, gulls, and pelicans observed foraging near McNary Dam this week, as compared to the previous week. This past week, the number of tern, gull, and pelican foraging attempts below McNary Dam was roughly 19, 16, and 1 attempt(s) per hour, respectively. Roughly half of the tern, gull, and pelican foraging attempts were successful.

Predator Activity

Bald eagle disturbance rates to the East Sand Island tern colony were lower this last week (0.08 disturbances/hr of observation), as compared to the previous week (0.10 disturbances/hr of observation). These disturbances were generally short, causing terns to leave the colony for only 10-15 seconds before returning.

No gull predation on tern eggs and chicks was observed during eagle disturbances to the tern colony this past week. Gull kleptoparasitism rates increased this past week (1.4% of all known fates of fish delivered by terns), as compared to the previous week (0.6% of all known fates).

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.