Last Updated May 30

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

Caspian Tern Colony Counts

Rice Island and Other Upper Estuary Islands

On Thursday, May 24th, one abandoned tern egg (e.g., egg was cold and not in a nest scrape) and 230 terns were observed on the ridge just east of the former Caspian tern colony on Rice Island. Forty-one nest scrapes were counted in the area. When researchers returned to the site on Friday (May 25), the tern egg had been depredated (presumably by a gull) and there were only 32 nest scrapes and 12 terns counted on the site. Tern use of upland areas in the upper estuary (e.g., Rice Island and Miller Sands Spit) has been very sporadic in 2001. On several occasions, terns have attended a site only to abandon the site within a few days. We suspect that these terns are either failed breeders that previously attempted to nest at the East Sand Island colony or are inexperienced breeders that are late in initiating nesting.

No terns have been observed attempting to nest elsewhere on Rice Island or on other upper estuary islands (e.g., Miller Sands Spit, Pillar Rock Sands) during the past week.

East Sand Island

The high and low on-colony counts for the week on East Sand Island were on May 27th (18,020 terns) and May 21st (13,990 terns), respectively. This represents a 8% increase in the median count of terns on the East Sand Island colony from last week to this week. Roughly half of the nests in productivity plots that were not flooded during the storm two weeks ago now have chicks.

All the wet areas on the colony are now completely dried out. Although the number of nest scrapes in those areas is slightly lower than in areas that were not flooded, the number of terns counted in flooded and unflooded plots is similar.

Experimental Barge in Commencement Bay, WA

Tern nesting activity on the experimental barge has increased dramatically over the past week (see Seasonal Trends). At last count (May 27th) there were 200 eggs on the experimental barge in roughly 170 nests. The maximum count of terns on the barge this past week was 387 on Sunday (5/27). This represents a 105% increase in the maximum count of terns on the experimental barge from last week to this week. Terns are spread out over the entire nesting area on the barge, and the barge appears to be near maximum capacity for nesting terns.

The high levels of gull predation on eggs observed at the barge the previous week (see weekly report for May 14 - May 20) have declined significantly this past week. We suspect that terns may be better able to protect their nests from gulls now that the barge is completely covered with nesting and roosting terns. Based on our most current observations, we expect that terns can successfully fledge young from the barge without gull control. As was reported last week, no gull control is currently planned because of the location of the barge within the Tacoma City limits and concern over the negative reaction of various publics over lethally removing problem gulls.

Click here to see additional photos of the experimental tern barge.

Other Sites in Commencement Bay, WA

On Friday (May 25th), terns began to abandon other roosts sites in Commencement Bay (i.e., the Asarco Industrial Site, an abandoned warehouse building at the Port of Tacoma, the mouth of the Puyallup River) for a roost on a non-commissioned barge (the "Malolo") located on the Foss barge boom near the experimental tern barge. On Friday, 400-500 terns were counted on the barge and 14 eggs were discovered. Some of these eggs were laid in debris scraped into piles (rust flakes) on the deck of the barge, others were found lying directly on the metal deck. Some of these eggs were being incubated and others had been abandoned. This nest/roost site was abandoned by late in the day on Friday (5/25) and the terns began roosting/nesting on an adjacent barge (the "Isla Del Sol"). As of Sunday (5/27), there were 690 terns counted on the barge with up to 50 terns apparently incubating eggs. Neither one of these large barges (both are over 10 times the size of the experimental tern barge) are scheduled to be commissioned prior to when the terns might successfully fledge young from those sites. We expect, however, that given the sub-optimal nesting conditions on these two barges (i.e., lack of nesting substrate and high levels of human activity and disturbance on or near the barge boom), terns will not be successful in rearing young at these sites.

Mid-Columbia River Sites (Three Mile Canyon and Crescent Islands)

The high and low on-colony counts for the week on Crescent Island were on May 25th (946 terns) and May 23rd (762 terns), respectively. These high and low counts on Crescent Island are lower than those same counts last week (988 terns and 893 terns, respectively). Due to the presence of a mink on Three Mile Canyon Island, the terns have abandoned that colony site.

Diet Composition

For the week of 21 May - 27 May, 46% of the identifiable fish delivered to the East Sand Island tern colony (N = 358) were salmonids, a 15% decrease from the previous week. Year to date, 48% of the identifiable fish delivered to the East Sand Island tern colony (N = 2,826) were salmonids. This compares to 71% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2000.

For the week, 84% of the identifiable fish delivered to terns on the experimental barge in Commencement Bay, WA (N = 603) were salmonids, an 8% increase from the previous week (see Seasonal Trends for the weekly salmonid proportion of the diet for terns in Commencement Bay, WA). Year to date, 82% of the identifiable fish delivered to terns in Commencement Bay (N = 773) were salmonids.

For the week, 61% of the identifiable fish delivered to Crescent Island (N = 148) were salmonids, a 25% decrease from the previous week. Year to date, 69% of the identifiable fish delivered to terns on Crescent Island (N = 888) were salmonids.

Off-Colony Distribution

Banding and Radio-Tagging

Banding and radio-tagging of adult terns has been completed in the Columbia River Estuary and the Asarco Industrial Site in 2001.

Radio-Tracking

Two radio-tracking flights (5/21 and 5/27) were conducted in the Columbia River estuary this past week. Fifty-five of the 59 relocations of radio-tagged terns (93%) were on the East Sand Island colony; 14 of the 30 terns radio-tagged on Rice Island in 2001 (47%) and 18 of the 24 terns radio-tagged on East Sand Island in 2001 (75%) are known to have active nests with eggs on East Sand Island. Of all the off-colony detections of radio-tagged terns (N = 4), two were in Willapa Bay and two were in the lower estuary (below Rice Island).

The number of roosting and foraging terns observed in the upper estuary (i.e., above the Astoria Bridge) during telemetry flights has decreased dramatically, from well over 1,000 terns in previous weeks to about 20 terns this week. We continue to observe relatively few terns roosting at sites along the Washington Coast (i.e., Willapa Bay and Grays Harbor) this year, as compared to last year.

Predator Activity

Gull kleptoparasitism rates at the East Sand Island tern colony decreased this past week, as compared to the previous week (4% and 15% of all fish delivered to the colony, respectively), while egg and chick predation rates by gulls remained low.

Media & Other Visitors

There were no visitors in the field this past week.