Last Updated April 29th

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 12,539 terns (April 26) and 3,173 terns (April 22), respectively. Quite a few terns appeared to be incubating eggs by the end of last week. The first tern egg was observed on the East Sand Island colony last week (April 18th), a day earlier than the first egg date on the East Sand Island tern colony in 2001.

Beach grass is quickly emerging at the periphery of the area cleared for tern nesting on East Sand Island and nesting terns are avoiding some of these areas. To date, the central portions of the colony area on East Sand Island are mostly clear of beach grass.

Rice Island and Other Upper Estuary Islands

On Tuesday (April 23), roughly 300 terns were observed loafing in an upland area on the eastern end of Pillar Rock Sands, a dredged material disposal site in the upper estuary (River Mile 27), above Rice Island. The site was investigated and no nest scrapes were observed; however, terns attending the site were copulating and bringing in fish as part of courtship. Resource managers were informed of the situation and on Tuesday afternoon the USACE had their personnel brought to the island to discourage terns from nesting at the site. To date, these activities (i.e., continuous day and night time monitoring of the site and hazing of any terns that settle in upland areas) have succeeded in keeping terns from nesting on Pillar Rock Sands. No aggregations of terns have been observed at other upland areas in the upper estuary (Rice Island, Miller Sands Spit, Puget Island) this week.

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 832 terns (April 27) and 590 terns (April 23), respectively. The first tern egg was observed on the Crescent Island colony last week (April 15th), a day earlier than the first egg date on Crescent Island tern colony in 2001. No terns have been observed on the former colony on Three Mile Canyon Island so far this season; mink predation caused complete failure of the tern colony on Three Mile Canyon Island in the previous two years. Thus far in 2002, terns have not been observed at Miller Rocks either, the site of a new tern colony (roughly 10-15 pairs) in 2001.

Diet Composition

For the week of April 22 - 28, 41% of the identifiable fish delivered to the East Sand Island tern colony (N = 367) were salmonids. The majority of the prey items being delivered to the East Sand Island colony were anchovies, smelt, and clupeids (i.e., herring, sardines). Year to date, 36% of the identifiable fish delivered to the East Sand Island tern colony (N = 942) were salmonids (this cumulative percent is an average of the previous weeks' percentages).

For the week, 88% of the identifiable fish delivered to the Crescent Island tern colony (N = 153) were salmonids. Most of the non-salmonids observed being delivered to the Crescent Island colony were bluegill. Year to date, 61% of the identifiable fish delivered to the Crescent Island tern colony (N = 287) were salmonids (this cumulative percent is an average of the previous weeks' percentages).

Off-Colony Distribution

In 2002, researchers will be investigating the distribution and foraging behavior of piscivorous waterbirds (primarily gulls, terns, cormorants, and pelicans) at McNary Dam. Surveys during the past week revealed a notable increase in the number of piscivorous waterbirds observed in the immediate vicinity of McNary Dam. During two days of observation at McNary Dam this week, as many as 60 western grebes, 15 gulls, and 4 white pelicans were observed near the dam. Foraging activity near the dam has also increased, particularly by gulls in the dam tailrace. The number of successful foraging attempts by gulls ranged between 1-4 captured fish per hour of observation this week.

Predator Activity

Bald eagle disturbances to the East Sand Island tern colony continued to decline (0.06 disturbances/hr of observation) as compared to previous weeks (0.25 disturbances/hr of observation). Terns are much more settled on the colony and are less likely to take flight when an eagle is flying high over the colony, as compared to earlier in the breeding season. These disturbances are short, causing terns to leave the colony for only 10-15 seconds before returning.

Gull predation on tern eggs at the East Sand Island colony also is waning, as more terns settle into incubation and there are fewer flushes of nesting terns in response to bald eagle disturbance.

There were no disturbances observed at the Crescent Island tern colony tern colony this past week.

Media & Other Visitors

On Tuesday (April 23), Assistant Secretary Dominic Izzo (USACE), Witt Anderson (USACE), Bob Willis (USACE), and Matt Van Ess (Columbia River Estuary Study Taskforce) visited the East Sand Island tern colony.