Last Updated April 30

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 left open for rocket netting 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. During a survey on April 29th, no terns were observed in any other upland areas on Rice Island (e.g., East Ridge) and roughly 750 terns were observed roosting on beaches adjacent to the colony, where nesting is unlikely to occur.

On April 25th, 190 terns were observed on an upland area on Miller Sands Spit, an upper estuary island just up-river and across the shipping channel from Rice Island. Fifty-five nest scrapes were counted at the site. To discourage tern nesting at Miller Sands Spit in 2001, the ODFW flagged the entire upland site that was used by the terns. Since flagging the area, no terns have been observed at the site. In 1998, terns attempted to nest at this same site after tern decoys and sound systems were deployed as part of a feasibility study. Although some terns were successful in laying eggs at the site in 1998 (perhaps as many as 30 nesting pairs), all tern-nesting attempts failed due to heavy nest predation by gulls and crows.

No terns have been observed attempting to nest at other off-colony areas on Rice Island or on other upper estuary islands (e.g., Pillar Rock Sands).

East Sand Island

The high and low on-colony counts for the week on East Sand Island were on April 27th (10,720 terns) and April 25th (3,421 terns), respectively. The first tern egg was spotted on the East Sand Island colony on April 19th, nearly a week earlier than the date eggs were first discovered at the East Sand Island tern colony in 2000. Gull activity at the colony has increased dramatically from last week to this week. On April 27th, we observed 4 tern eggs taken by gulls following two separate disturbance events caused by bald eagles flying over the tern colony. The number of gulls counted at the periphery of the colony has approximately doubled over the last week, from an average of about 10 gulls last week to roughly 20 gulls this week. Gull nest predation activity seems to be concentrated near the edges of the colony, especially near the edge of a central portion of the colony not used by terns for nesting because of poor drainage in that area (damp soil or standing water depending on the amount of rainfall). During periods of heavy rain this wet area increases in size, inundating nearby nests. Abandoned nest scrapes and broken eggs (presumably cause by nest predators) have been observed in this area.

Experimental Barge in Commencement Bay, WA

The first two terns were observed perched on the experimental barge on April 27th. The terns were perched on the barge for approximately 5 minutes, while two other terns flew close overhead, after which all four departed the area. No terns have been observed on the experimental barge colony site since April 27th.

Asarco Industrial Site, WA

The number of terns using the Asarco Industrial Site has been highly variable; the maximum count for the week was less than 300 terns. 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.

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 April 26th (660 terns) and April 23rd (606 terns), respectively. The high and low on-colony counts for the week on Three Mile Canyon Island were on April 24th (65 terns) and April 27th (25 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. Predators, primarily California gulls, have taken all eggs laid so far at the Three Mile Canyon Island tern colony.

Inland Washington Sites (Potholes Reservoir)

Solstice Island, located in Potholes Reservoir, was visited on April 28-29, when as many as 300 adult terns were counted on the colony. Terns were observed on the same site used for nesting last year. At least 40 scrapes were counted on the colony, but due to bad weather it was not determined if egg-laying has commenced 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 April 23 - 29, 45% of the identifiable fish delivered to East Sand Island (N = 415) were salmonids. Because there are currently no terns nesting on Rice Island, fish watch data are unavailable for that site. Year to date, 40% of the identifiable fish delivered to East Sand Island (N = 1,409) 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 week, 63% of the identifiable fish delivered to Crescent Island (N = 117) were salmonids. 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 April 27th, Chris Thompson of WDFW, with help from Gary Shugart (University of Puget Sound) and the research team, successfully cannon-netted 10 adult terns at the Asarco Industrial Site near Tacoma, Washington. These birds were color-banded and released unharmed. In total, 39 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 prevent all tern nesting at the Asarco Industrial Site in 2001.

Radio-Tracking

Two radio-tracking flights (4/25 and 4/26) were conducted in the Columbia River estuary this past week. Thirty-nine percent of radio-tagged terns detected during the flights (n = 28) were on the East Sand Island colony. Of all the off-colony detections of radio-tagged terns (n = 17), most were in the Columbia River Estuary (88%), while two terns were detected along the Washington Coast (one each in Willapa Bay and Grays Harbor). Of the terns detected off-colony and in the estuary, all were in the upper estuary (i.e., above the Astoria Bridge; see Seasonal Trends).

Large numbers (>1,000) of perching and foraging terns have been observed during telemetry flights in the upper estuary this week. 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

Bald eagle activity continues to be relatively high at East Sand Island this year. Bald eagles, known predators of adult Caspian terns, often cause terns to flush and leave their nests unattended (i.e., colony disturbance). Gull predation on tern eggs has increased over the past week and is often associated with eagle-induced disturbance events.

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

On April 26th, work crews from ODFW flagged roughly 0.75 acres on Miller Sands Spit to prevent terns from nesting (see above).