Last Updated May 07

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

Caspian Tern Colony Counts

Rice Island and Other Upper Estuary Islands

No terns have been observed on the former colony site at Rice Island since the area was flagged on April 20th. We suspect that the flagging, fencing, and encroaching vegetation have rendered the former colony site at Rice Island unsuitable for tern nesting in 2001.

On Tuesday (May 1st), terns were beginning to nest on the East Ridge on Rice Island (just east of the former tern colony). A total of 96 terns and 6 nest scrapes were counted. On Wednesday (May 2nd), no terns were observed roosting or nesting on the East Ridge, but 87 terns and 8 nest scrapes were counted on the North Shore (above the high high-tide line). But during a subsequent visit to these sites on May 6th, no terns were observed roosting or attempting to nest at either site. No tern eggs have been observed on Rice Island so far this year.

No terns have been observed roosting on Miller Sand Spit in the area where terns and nest scrapes were discovered since it was flagged on April 25th by ODFW. No evidence of attempted nesting by Caspian terns has been observed at other sites in the upper estuary in 2001.

East Sand Island

The high and low on-colony counts for the week on East Sand Island were on May 4th (12,550 terns) and April 30th (5,735 terns), respectively. Terns appear to be more settled at the East Sand Island colony site (i.e., less willing to leave their nests during disturbances) and are more uniformly distributed across the entire colony area.

Following heavy rains late in April, as much as 1,000 square meters (1/4 acre) of the central portion of the colony had standing water and some nests containing eggs were lost. This past week this area has dried out considerable and terns are nesting in all but 150 - 200 square meters of this poorly drained area. Gulls previously used this central portion of the colony as a staging area for forays into the tern colony to steal fish and tern eggs. Currently, terns are roosting in this area, precluding use of the area by gulls. If heavy rains return, we expect more tern nest failures in this area of the colony.

Experimental Barge in Commencement Bay, WA

Tern activity at the experimental barge site has increased over this past week. On Saturday (May 5th), a maximum of 8 terns was observed on the barge at one time. Terns at the site have frequently been observed carrying fish in their bills, an important part of their courtship display. Despite this apparent interest in the barge as a potential nesting site, no nest scrapes have been observed on the barge to date.

Asarco Industrial Site, WA and the Port of Tacoma, WA

The number of terns using the Asarco Industrial Site continues to be highly variable; with counts of terns at the site ranging from 0 to 400. This total is down from the maximum count of terns using the site last year (1,800 terns). No tern eggs have been observed at the Asarco Industrial Site, nor have we observed much nesting behavior (e.g., nest scrape digging, courtship feeding, copulation). We do not expect nesting to occur at the Asarco Industrial Site in 2001 because (1) the areas used by terns for nesting in 1999 and 2000 have been covered with plastic tarps and (2) the WDFW is conducting intermittent hazing of terns roosting at the site, including cannon-netting activities.

On May 3rd, researchers observed 200-300 Caspian terns on the rooftop of an abandoned warehouse on the south side of Blair Waterway in the Port of Tacoma. We are currently seeking access to the site to determine if terns might be attempting to nest there.

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 3rd (938 terns) and April 30th (783 terns), respectively. The high and low on-colony counts for the week on Three Mile Canyon Island were on April 30th (23 terns) and May 3rd (0 terns), respectively. The number of terns counted at the Three Mile Canyon Island tern colony is continuing to decline, presumably due to visits to the colony by a mink. We expect that if the colony continues to be visited by the mink, the terns will eventually abandon the site altogether.

Inland Washington Sites (Potholes Reservoir)

Solstice Island, located in Potholes Reservoir, was visited on May 6th, when 290 adult terns were counted on the colony. As many as 110 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 30 April - 6 May, 59% of the identifiable fish delivered to East Sand Island (N = 395) were salmonids, a 31% increase from the previous week. Year to date, 44% of the identifiable fish delivered to East Sand Island (N = 1,804) were salmonids. This compares to 65% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2000.

For the week, 90% of the identifiable fish delivered to Crescent Island (N = 160) were salmonids, a 43% increase from the previous week. Fish watch data have not been collected at the Three Mile Canyon Island tern colony site due to the low and inconsistent numbers of terns observed at the site to date.

Off-Colony Distribution

Banding and Radio-Tagging

Banding and radio-tagging of adult terns at Rice Island was completed on April 20th. There are no plans to band or radio-tag additional terns at the Rice Island colony site in 2001.

On May 6th, Gary Shugart (University of Puget Sound) successfully cannon-netted 9 adult terns at the Asarco Industrial Site near Tacoma, Washington. These birds were color-banded and released unharmed. In total, 48 adult terns have been color-banded at the Asarco Industrial Site in 2001. These marked terns will help determine the dispersal pattern of terns to other nesting areas. The WDFW continues to be committed to preventing all tern nesting at the Asarco Industrial Site in 2001.

Radio-Tracking

Two radio-tracking flights (4/30 and 5/1) were conducted in the Columbia River estuary this past week. Forty percent of radio-tagged terns detected during the flights (n = 42) were on the East Sand Island colony, three of which are known to be nesting there. Of all the off-colony detections of radio-tagged terns (n = 25), all were in the Columbia River Estuary. Of the terns detected off colony and in the estuary, most (68%) were in the upper estuary (i.e., above the Astoria Bridge; see Seasonal Trends).

For the second consecutive week, large numbers (>1,000) of perching and foraging terns have been observed during telemetry flights in the upper estuary. Most tern activity in the upper estuary is concentrated on the shoals of Fitzpatrick Island at river mile 32 near Skamokawa, Washington. To date, these birds have been roosting below the high tide line and are not apparently attempting to nest; however, we will continue to closely monitor these and other areas (e.g., Willapa Bay and Grays Harbor) for evidence of future nesting activity.

Gull Control & Predator Activity

Gull kleptoparasitism rates at the East Sand Island tern colony have increased from last week to this week (6% and 10% of all fish delivered to the colony, respectively), while egg predation rates by gulls have declined. This could be due to an observed decrease in frequency of eagle-related disturbances this week, as compared to previous weeks. Bald eagles, known predators of adult Caspian terns, often cause terns to flush and leave their nests unattended, which is often associated with gull predation on tern eggs. Bald eagle disturbances and gull nest predation rates continue to be relatively high on the nearby double-crested cormorant colony on East Sand Island.

Gull control activities have not been initiated at the East Sand Island tern colony because the Caspian Tern Working Group has not decided that gull control is necessary.

Media & Other Visitors

There were no visitors in the field this week.