Note: The following data are preliminary and may change upon further review.

Colony Counts

Rice Island & Other Upper Estuary Islands

The high and low on-colony counts for the week on Rice Island were both on May 22nd (2,379 and 1,630 terns, respectively). This represents a slight increase (150- 200 terns) in both the high and low on-colony counts from the previous week. The first chick was observed on the Rice Island tern colony on May 26th, and it was approximately 3 days old. Coincident with the initiation of hatching on Rice Island, there was a noticeable decline in gull predation rates on tern eggs at the Rice Island colony. Adult terns were not flushing as readily from their nests in response to eagle activities near the colony. Recently (May 27-28), however, the frequency of tern flushes in response to bald eagle disturbances has increased, resulting in a resumption of heavy gull predation on unattended tern eggs.

An aerial photo census of the Rice Island tern colony is scheduled for May 31st. This photo census will be used along with ground counts of terns in plots to estimate the number of breeding pairs on the Rice Island tern colony in 2000. The direct count of terns in the aerial photos will not be available for several weeks.

No terns have been observed nesting at other off-colony areas on Rice Island (i.e., East Ridge) or on other upper estuary islands (i.e., Miller Sands Spit and Pillar Rock Sands).

East Sand Island

The high and low on-colony counts for the week on East Sand Island were on May 23rd (18,470 terns) and May 26th (11,730 terns), respectively. This represents a decline in both the high and low on-colony counts from the previous week (roughly 700 and 1,700 terns, respectively). This decline may have been associated with trapping activities on the East Sand Island tern colony this week. We used noose mats to trap 30 adult terns on the colony for radio-tagging (see below). Once we completed our activities on the tern colony (May 25th), the number of terns counted on colony has been increasing. The latest on-colony counts indicate that 90% of the total number of terns counted on both the Rice Island and East Sand Island colonies are on East Sand Island.

An aerial photo census of the East Sand Island tern colony is scheduled for May 31st, in association with the aerial photo census of the Rice Island colony.

Coastal Sites

No surveys of other potential Caspian tern colony sites along the coast of Washington were conducted this week, due to other research activities.

Upriver Sites (Three Mile Canyon and Crescent Islands)

The high and low on-colony counts for the week on Crescent Island were on May 22nd (875 terns) and May 25th (842 terns), respectively. The high and low on-colony counts for the week on Three Mile Canyon Island were on May 22nd (339 terns) and May 26th (286 terns), respectively. The number of terns counted at the up-river colonies remains relatively constant from week to week as compared to the tern colonies in the estuary. The Crescent Island and Three Mile Canyon Island tern colonies are roughly the same size as last year, based on the 1999 aerial photo census conducted near the peak of hatching.

An aerial photo census was carried out on May 22nd at Crescent and Three Mile Canyon islands in order to get an accurate count the number of terns on each colony. Researchers were stationed in blinds at both colonies from one hour before to one hour after the photos census. During that time they counted the number of brooding and non-brooding birds in plots so that counts from aerial photos can be corrected to estimate the number of active breeding pairs on each colony.

Diet Composition

For the week (22 - 28 May), 73% of the identifiable fish delivered to East Sand Island were salmonids (N = 377), compared to 95% at Rice Island (N = 394). This represents 10% and 2% declines from last week in the proportion of salmonids in the diet of East Sand Island and Rice Island terns, respectively (NOTE: The percent salmonids in the diet of Rice Island terns that was reported last week (93%) was incorrect. The correct proportion was 97%. This correction has been made to the previous weekly report). Year to date, 71% of the identifiable fish delivered to the East Sand Island tern colony were salmonids (N = 2,275), compared to 93% at Rice Island tern colony (N = 2,019). The year-to-date total for percentsalmonids in the diet of terns nesting on East Sand Island is similar to the corresponding value from last year (70%). The year-to-date total for percent salmonids in the diet of terns nesting on Rice Island is lower than the corresponding value from last year 98%).

At Crescent and Three Mile Canyon islands, 48% (N = 151) and 57% (N = 117) of the identifiable fish delivered to each colony this week were salmonids, respectively. This represents declines of 25% and 38% in the proportion of juvenile salmonids in the diet of terns nesting at Crescent and Three Mile Canyon islands from last week to this week, respectively.

Off-Colony Distribution

Banding and Radio-Tagging

A total of 30 terns were captured this week using noose mats placed over nests with eggs on the East Sand Island tern colony. Each captured tern was weighed and measured, color-banded, and radio-tagged before release. The nest contents of 23 of these radio-tagged terns were removed in order to monitor subsequent re-nesting attempts and to determine where failed breeders would attempt to re-nest. Nearly half (11) of these radio-tagged terns have already been re-sighted on Rice Island, but re-nesting behavior has not been observed yet. Eggs collected from the colony will be provided to academic institutions (University of Washington and University of Puget Sound) for scientific purposes.

Radio-Tracking & Resightings of Banded Birds

No telemetry flights were conducted this week because of the trapping and tagging efforts on the East Sand Island tern colony this week. These flights will resume next week.

Gull and Predator Control

There have been no signs of mammalian predators on either Rice or East Sand islands. Limited gull control is being carried out at the East Sand Island tern colony to enhance prospects for tern colony restoration at that site. Five gulls were shot this week at East Sand Island. So far this season, 37 gulls have been shot on the East Sand Island tern colony. Currently, there are no plans to restrict or eliminate gull control at the East Sand Island tern colony.

Media and Other Visitors

Surveyors from BPA came out to the estuary this week (5/23 - 5/25) to set out markers on Rice and East Sand islands that will be used in the analysis of aerial photos of nesting colonies.