Last Updated June 18

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 June 17th (16,790 terns) and June 12th (12,045 terns), respectively. This represents nearly the same median count of terns on the East Sand Island colony from last week to this week. A satellite tern colony continues to be active on the beach southeast of the main colony above the high-high tide line. Approximately 200 terns were counted in this area, of which 118 terns were apparently incubating eggs. At least one chick has been sited in this area. In general, we are seeing many more two-chick broods on the East Sand Island tern colony at this time in the breeding season, as compared to this same time in previous years. Based on these observations, we suspect that tern productivity at the East Sand Island tern colony could be higher this year, as compared to last year.

Three out of 54 terns (6%) banded at the Asarco Industrial Site in Commencement Bay earlier this year have been resighted at the East Sand Island tern colony. These three banded terns are currently sitting in scrapes on the colony. These data suggest that at least some of the terns that left Commencement Bay have relocated to the Columbia River Estuary.

Commencement Bay and Surrounding Area, WA

Following the removal of the experimental tern barge (5/31; see weekly report for May 28 - June 3 for further information), most of the terns using the experimental tern barge and the nearby barges on the Foss barge boom, apparently left Commencement Bay. Roughly 150 - 200 terns remain in the Commencement Bay area (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. On June 15th, we observed adult terns feeding chicks on the roof of the Northcoast Yachts building in the Port of Tacoma. The total number of nesting terns and chicks on the rooftop is difficult to determine since we have been unable to gain access to the site to do a complete count.

We have been conducting surveys for terns throughout the Puget Sound area for the past two weeks and have discovered only a few small concentrations. Roughly, 180 terns were counted on the rooftop of Pier 90 and a nearby gravel pile at the Port of Seattle on June 15th. At least 7 adult terns are incubating eggs at the site. We suspect that the majority of these birds were at this site prior to the removal of the experimental tern barge in Commencement Bay. Martin Muller of Seattle first reported having seen terns at Pier 90 on May 16th (prior to the removal of the tern barge), when he counted 156 terns at the site. He further reported (on the Tweeters web site; http://www.scn.org/earth/tweeters/) seeing the terns engaged in nesting behavior (i.e., courtship feeding and copulation).

We also observed roughly 100 terns roosting at the Nisqually mudflats (roughly 20 miles south of Commencement Bay) on June 12th and 15th. This is an area where we have seen terns roosting throughout the field season (before and after the removal of the experimental tern barge).

Additional sites we would like to survey for terns are; Skagit Delta, Swinomish Channel, Old Everett Naval Station, and Nooksack Delta. Any information on tern use of these and other areas in the Puget Sound in 2001 can be reported to clientservices@realtimeresearch.org.

Mid-Columbia River Sites (Three Mile Canyon Is., Crescent Is., and Miller Rocks)

The high and low on-colony counts for the week on Crescent Island were on June 13th (840 terns) and June 16th (765 terns), respectively. These high and low counts on Crescent Island are lower than those same counts last week (886 terns and 831 terns, respectively). Due to the presence of a mink on Three Mile Canyon Island, the terns have abandoned that colony site.

On Thursday (6/7), Dave Craig (Willamette University) and Brad Ryan (NMFS) discovered Caspian terns nesting on Miller Rocks, an island located on the lower Columbia River just upstream of the mouth of the Deschutes River. Only 6 incubating terns were observed at the site on June 17th, down from a previous count of thirty-two terns on June 7th. Often times late nesting terns ultimately fail, which will likely be the case for the late nesting terns nesting at Miller Rocks. This is the first documentation of terns attempting to nest on Miller Rocks, or any other upriver location on the lower Columbia River (other than Three Mile Canyon and Crescent islands).

Inland Washington Sites (Potholes Reservoir)

Solstice Island, located in Potholes Reservoir, was not visited this past week.

Diet Composition

For the week of 11 June - 17 June, 28% of the identifiable fish delivered to the East Sand Island tern colony (N = 332) were salmonids, a 38% decrease from the previous week (see Seasonal Trends for the weekly salmonid proportion of the diet for terns on East Sand Island). This dramatic decrease in the proportion of the diet that was salmonids was associated with a sharp increase in the number of herring, anchovies, and smelt (all marine species) in the diet. We also noted a sharp decrease in the foraging trip duration this past week, presumably due to an increase in the local availability of marine fish. Year to date, 45% of the identifiable fish delivered to the East Sand Island tern colony (N = 3,869) were salmonids. This compares to 61% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2000.

For the month of May, 77% of the identifiable fish delivered to terns in Commencement Bay (N = 1,061) were salmonids.

For the week, 78% of the identifiable fish delivered to Crescent Island (N = 150) were salmonids, a 7% increase from the previous week. Year to date, 73% of the identifiable fish delivered to terns on Crescent Island (N = 1,363) 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 (6/15 and 6/16) were conducted in the Columbia River estuary this past week. Forty-four of the 66 relocations of radio-tagged terns (67%) were on the East Sand Island colony; 15 of the 30 terns radio-tagged on Rice Island in 2001 (50%) and 18 of the 24 terns radio-tagged on East Sand Island in 2001 (75%) are known to have active nests on East Sand Island. Of all the off-colony detections of radio-tagged terns that are known to be nesting on East Sand Island (N = 10), one (10%) was in Willapa Bay, one (10%) was above Rice Island, and 8 (80%) were below Rice Island.

We continue to observe relatively few terns roosting at sites in the upper estuary and along the Washington Coast (i.e., Willapa Bay and Grays Harbor) this year, as compared to last year.

Predator Activity

Gull kleptoparasitism and predation rates at the East Sand Island tern colony remained low this past week. As mentioned above, the relatively low gull predation rates on tern eggs and chicks at the East Sand Island tern colony will likely lead to higher nesting success of terns this year, as compared to last year.

Media & Other Visitors

This past week, Todd Dunkirk, Jen Gamber, and an intern from the Oregon Coast Aquarium visited East Sand Island and our field house in Chinook, WA to see the tern chicks that we are rearing in captivity. These experiments were 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, many of the terns used in the experiment will be donated to the Oregon Coast Aquarium for public display in their seabird aviary.