Last Updated June 4

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

Caspian Tern Colony Counts

Rice Island and Other Upper Estuary Islands

During the past week, no terns have been observed attempting to nest in upland areas on Rice Island (i.e., former colony site, East Ridge, North Shore) or elsewhere in the upper estuary (i.e., Miller Sands Spit, Pillar Rock Sands).

East Sand Island

The high and low on-colony counts for the week on East Sand Island were on May 31st (17,295 terns) and May 28th (14,305 terns), respectively. This represents a 1% decrease in the median count of terns on the East Sand Island colony from last week to this week.

On Monday (5/28), 20 recently hatched tern chicks were collected from the East Sand Island colony for captive rearing experiments designed to determine energy and food requirements of young terns throughout the development period prior to fledging (leaving the nesting colony). These data will be used to further refine estimates of salmon consumption by the terns in the Columbia River estuary in 2001. At fledging, terns used in the experiment will either be donated to the Oregon Coast Aquarium (or similar licensed educational facility) for public display in their seabird aviary or sacrificed for determination of body composition and whole body energy content.

Experimental Barge in Commencement Bay, WA

Washington Department of Fish and Wildlife (WDFW) in consultation with its research partners cut short the experimental tern barge project. The barge was dismantled and removed from Commencement Bay on May 31st. This was done at the request of the Puyallup Tribe because of concerns for a release of out-migrating salmon smolts and for endangered salmon stocks in the area. (Note: This was the explanation given by WDFW for the barge removal at that time. Subsequently, the WDFW revised that explanation (see 2001 Draft Season Summary)). Any questions regarding the removal of the experimental tern barge should be directed to WDFW, Wildlife Program at wildthing@dfw.wa.gov.

On Thursday (5/31), tern eggs were collected from the experimental barge. To quantify the number of eggs and nests on the barge at the time the barge was removed, a grid (5 x 14 = 70 plots) was laid out across the entire nesting area on the barge and all nest scrapes and eggs were counted in each plot. Nest scrapes and eggs were counted from photos taken direct over each plot (i.e., from a step ladder). In total, there were 969 tern eggs counted on the barge. Of those, 236 eggs were apparently abandoned (outside nest scrapes) and 733 eggs were in nest scrapes. We estimate that 337 nests had been initiated on the barge, but not all of these nests were active at the time the barge was dismantled. All of the eggs were collected by WDFW and will be distributed to research institutions and museums.

See Seasonal Trends for daily counts of terns on the experimental barge prior to its removal from Commencement Bay, WA.

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

Other Sites in Commencement Bay, WA

This past week, terns continued to roost and nest on barges on the Foss barge boom located near the experimental tern barge. On Tuesday (5/29), 614 terns were counted on a barge named the "Isla Del Sol". Up to 51 incubating terns and 22 eggs (abandoned) were counted on the barge. On Wednesday (5/30) the "Isla Del Sol" was moved off the barge boom, causing the terns to relocate to adjacent barges (the "Malolo" and barge # 410). On Wednesday afternoon (5/30), 620 terns were counted on these two barges. Following the removal of the experimental tern barge (5/31), most of terns using the experimental tern barge and the nearby barges on the Foss barge boom, apparently left Commencement Bay. On Sunday (6/3), only 175 terns were observed in Commencement Bay (all near the Port of Tacoma), compared to bay-wide counts ranging between 675 - 900 terns prior to the removal of the experimental tern barge. We will continue to conduct surveys in Commencement Bay and the surrounding area for roosting and nesting terns.

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 28th (982 terns) and June 1st (904 terns), respectively. These high and low counts on Crescent Island are higher than those same counts last week (946 terns and 762 terns, respectively). Due to the presence of a mink on Three Mile Canyon Island, the terns have abandoned that colony site.

Inland Washington Sites (Potholes Reservoir)

Solstice Island, located in Potholes Reservoir, was visited this past week, when 298 adult terns were counted on the colony. As many as 165 adult terns were sitting in nest scrapes at the time, which represents our most current and best estimate of the number of nesting pairs at the site. We will continue to monitor this site and other potential Caspian tern nesting sites at inland locations in the coming months.

Diet Composition

For the week of 28 May - 3 June, 46% of the identifiable fish delivered to the East Sand Island tern colony (N = 352) were salmonids, the same percentage as the previous week (see Seasonal Trends for the weekly salmonid proportion of the diet for terns on East Sand Island). Year to date, 47% of the identifiable fish delivered to the East Sand Island tern colony (N = 3,178) were salmonids. This compares to 69% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2000.

For the week (prior to barge removal on May 31st), 68% of the identifiable fish delivered to terns on the experimental tern barge in Commencement Bay, WA (N = 288) were salmonids, a 19% decrease from the previous week (see Seasonal Trends for the weekly salmonid proportion of the diet for terns in Commencement Bay, WA). Year to date, 77% of the identifiable fish delivered to terns in Commencement Bay (N = 1,061) were salmonids.

For the week, 93% of the identifiable fish delivered to Crescent Island (N = 175) were salmonids, a 52% increase from the previous week. This increase was apparently associated with an increase in the availability of hatchery-reared steelhead in the area. Year to date, 72% of the identifiable fish delivered to terns on Crescent Island (N = 1,067) were salmonids.

For the week, 42% of the identifiable fish delivered to Solstice Island in Potholes Reservoir were juvenile salmonids (N = 52).

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 (5/29 and 5/30) were conducted in the Columbia River estuary this past week. Sixty-one of the 66 relocations of radio-tagged terns (92%) were on the East Sand Island colony; 15 of the 30 terns radio-tagged on Rice Island in 2001 (50%) and 20 of the 24 terns radio-tagged on East Sand Island in 2001 (83%) are known to have active nests on East Sand Island. Of all the off-colony detections of radio-tagged terns (N = 4), one was in Willapa Bay and three were in the 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 50 - 100 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 (<1% and 4% of all fish delivered to the colony, respectively), while egg and chick predation rates by gulls remained low.

Media & Other Visitors

Susan Gordon from the Tacoma News Tribune visited the experimental tern barge in Commencement Bay, WA on May 31st.