Last Updated May 14

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 roosting or 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 13th (14,870 terns) and May 11th (10,800 terns), respectively. This represents a 40% increase in the median count of terns on the East Sand Island colony from last week to this week. Terns continue to become more settled on the colony (i.e., less willing to leave their nests during disturbances) and are distributing themselves more evenly across the entire colony area.

Due to dry weather in the estuary this past week, the wet area in the center of the East Sand Island tern colony has continued to dry out. The number of terns roosting and attempting to nest in this wet area has increased nearly three fold from last week to this week (0.17 terns/m2 and 0.47 terns/m2, respectively). If heavy rains return, we expect that tern nests in this area of the colony will fail.

Prior to the arrival of terns on the East Sand Island colony site this year, 20-meter-wide buffer strips were added to the east and west ends of the colony site. These buffer strips were scarified to remove existing herbaceous vegetation, but no sand was spread on the surface. The plaintiffs in the on-going lawsuit had requested the addition of these buffer strips to discourage predatory gulls from nesting right up to the edge of the tern colony. To date the buffer strip at the east end of the colony seems to be serving its intended purpose; terns are nesting right up to the edge of the buffer strip and gulls are avoiding the strip for nesting. The buffer strip at the west end of the colony, however, has been mostly occupied by nesting terns, and thus represents an expansion of the colony area occupied by terns in 2000.

Experimental Barge in Commencement Bay, WA

Tern activity at the experimental barge site has been low and highly variable over the past week. During roughly eight hours of observation/day at the barge this past week, terns were observed on the barge from 3.5 minutes (1% of the observation period) to 43 minutes (9% of the observation period). Terns at the site have frequently been observed carrying fish in their bills, an important part of their courtship display. Over the past week the maximum number of terns observed on the barge at one time was four (May 12th). 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 decline; with counts of terns at the site ranging from 0 to 50. No tern eggs have been observed at the Asarco Industrial Site, nor have we observed much nesting behavior (i.e., 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 10th, researchers observed 650 Caspian terns roosting on the rooftop of an abandoned warehouse on the south side of Blair Waterway in the Port of Tacoma. Terns at this site are not nesting, presumably due to the lack of suitable nesting substrate, and the number of birds roosting at the site has declined over the last few days (less than 100 terns counted at the site on May 13th).

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 13th (948 terns) and May 7th (800 terns), respectively. These high and low counts on Crescent Island were nearly identical to those same counts last week. This past week the high count of terns on the Three Mile Canyon Island colony was on May 8th (3 terns). Due to the presence of a mink on Three Mile Canyon Island, the terns have apparently abandoned the Three Mile Canyon Island colony site.

Inland Washington Sites (Potholes Reservoir)

The Solstice Island tern colony was not visited this past week.

Diet Composition

For the week of 7 May - 13 May, 63% of the identifiable fish delivered to East Sand Island (N = 375) were salmonids, a slight increase over the previous week (59%). Year to date, 47% of the identifiable fish delivered to East Sand Island (N = 2,179) were salmonids. This compares to 68% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2000.

For the week, 80% of the identifiable fish delivered to terns roosting in Commencement Bay near Tacoma (N = 60) were salmonids.

For the week, 72% of the identifiable fish delivered to Crescent Island (N = 160) were salmonids, a 20% decline 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

On May 7th, Gary Shugart (University of Puget Sound) successfully cannon-netted 6 adult terns at the Asarco Industrial Site near Tacoma, Washington. These birds were color-banded and released unharmed. In total, 54 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. To date, one of these 54 adult terns that were banded this spring at the Asarco site has been re-sighted on the East Sand Island tern colony. The WDFW continues to be committed to preventing all tern nesting at the Asarco Industrial Site in 2001.

Radio-Tracking

Two radio-tracking flights (5/8 and 5/9) were conducted in the Columbia River estuary this past week. Forty of the 55 relocations of radio-tagged terns (72%) were on the East Sand Island colony; 14 of the 30 terns radio-tagged on Rice Island in 2001 (47%) are known to have active nests with eggs on East Sand Island. Of all the off-colony detections of radio-tagged terns (N = 15), all but one were in the Columbia River Estuary. Of the 14 terns detected off-colony and in the estuary, an equal number were relocated above and below the Astoria Bridge (see Seasonal Trends). This represents a major shift in the distribution of foraging terns away from the upper estuary (i.e., above the Astoria Bridge) and toward the lower estuary (i.e., below the Astoria Bridge) as compared to previous weeks.

This shift was readily apparent to the observers flying the surveys; virtually no terns were observed further upriver than Rice Island. The number of roosting and foraging terns observed in the upper estuary (i.e., above the Astoria Bridge) during telemetry flights has decrease significantly, from well over 1,000 terns in previous weeks to less than 100 terns this week. This corresponds with an increase in the number of terns counted in the lower estuary, both on and off the East Sand Island colony. 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 declined this past week, as compared to the previous week (6% and 11% of all fish delivered to the colony, respectively), while egg predation rates by gulls remained low. This could be due to a decline in the frequency of eagle-induced disturbances 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 predation rates on eggs continue to be relatively high on the nearby double-crested cormorant colony on East Sand Island.

Media & Other Visitors

There were no visitors in the field this past week.