Last Updated May 21

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

Caspian Tern Colony Counts

Rice Island and Other Upper Estuary Islands

On Friday, May 18th, 198 terns were observed on an upland area on Miller Sands Spit, an upper estuary island just across the shipping channel from Rice Island. The terns were occupying a 1/4-acre area just southwest of the area previously flagged on April 19th by ODFW in order to deter nesting. Ninety-nine fresh nest scrapes were counted at the site. Researchers visited the site on Saturday (5/19) and Sunday (5/20) and counted 6 and 0 terns roosting at the site, respectively. No tern eggs have been found on Miller Sands Spit so far this season. ODFW has chosen not to set up more passive exclusion (i.e., flagging) on Miller Sands Spit in 2001.

In 1998, terns attempted to nest on Miller Sands Spit 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 nesting attempts by terns failed due to intense nest predation by gulls and crows.

No terns have been observed attempting to nest on Rice Island or on other upper estuary islands (e.g., Pillar Rock Sands) during the past week.

East Sand Island

The high and low on-colony counts for the week on East Sand Island were on May 19th (17,890 terns) and May 14th (11,830 terns), respectively. This represents a 14% increase in the median count of terns on the East Sand Island colony from last week to this week. The first tern chick was observed on the East Sand Island colony on Wednesday (5/16).

Following heavy rains on Monday (5/14) and Tuesday (5/15), there was standing water on as much as 2,000 square meters (1/2 acre) of the central portion of the colony, and some nests containing eggs were lost. This flooding event covered roughly twice the acreage of the previous flooding event in late April (see weekly report for April 30 - May 6). Wet areas on the colony dried out quickly once the rain stopped and terns have once again moved into these areas to roost and dig nest scrapes, although tern nesting density in this area (0.4 terns/m2) is about half that of the rest of the colony (0.8/m2).

Experimental Barge in Commencement Bay, WA

The first tern egg was laid on the experimental barge on Tuesday (5/15). Since then, tern nesting activity on the barge has increased dramatically. The maximum count of terns on the barge this past week was 189 on Saturday (5/19). Over the weekend, gull activity at the barge began to intensify. On Saturday and Sunday, gulls preyed on eggs from 12 different nests. We suspect that without limited gull control at the barge it is unlikely that nesting terns will successfully fledge young from the barge colony site. No gull control is currently planned, however, because of the location of the barge within the Tacoma City limits and concern over the negative reaction of various publics over lethally removing problem gulls. As of Sunday evening (5/20), the average number of terns sitting in scrapes was 18, and represents our best and most recent estimate of the number of tern nests with eggs on the barge.

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

The number of terns using the Asarco Industrial Site continues to be sporadic; with counts of terns at the site ranging from 0 to 100. No tern eggs have been observed at the Asarco Industrial Site so far this season, 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.

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 15th (988 terns) and May 14th (893 terns), respectively. These high and low counts on Crescent Island are slightly higher than those same counts last week (948 terns and 893 terns, respectively). Due to the presence of a mink on Three Mile Canyon Island, the terns have apparently abandoned that colony site.

Inland Washington Sites (Potholes Reservoir)

Solstice Island, located in Potholes Reservoir, was visited on May 19-20, when 349 adult terns were counted on the colony. As many as 131 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 14 May - 20 May, 54% of the identifiable fish delivered to East Sand Island (N = 289) were salmonids, a 14% decrease from the previous week. Year to date, 48% of the identifiable fish delivered to East Sand Island (N = 2,468) were salmonids. This compares to 71% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2000.

For the week, 78% of the identifiable fish delivered to terns on the experimental barge in Commencement Bay, WA (N = 117) were salmonids. The previous week, diet composition of terns roosting at the mouth of the Puyallup River (roughly 1.5 miles from the barge and adjacent to the Port of Tacoma) was 80% juvenile salmonids (N = 60).

For the week, 81% of the identifiable fish delivered to Crescent Island (N = 150) were salmonids, a 12% 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.

For the week, 26% of the identifiable fish delivered to Solstice Island in Potholes Reservoir were juvenile salmonids (N = 49).

Off-Colony Distribution

Banding and Radio-Tagging

A total of 24 terns were captured this past week using noose mats placed over nests with eggs on the East Sand Island tern colony. Each captured tern was weighed and measured, color-banded, and radio-tagged. These marked terns will help determine the foraging patterns of terns nesting on East Sand Island. On 5/18, we observed two tern eggs taken from nests by ring-billed gulls during our trapping on the colony. No other predation events were witnessed during our trapping activities on East Sand Island and all captured terns were released unharmed.

No terns were banded at the Asarco Industrial Site this past week.

One of the terns that was banded previously at the Asarco Industrial site was re-sighted near Delta, B.C. Canada on May 19th (thanks to alert birder Richard Swanston for this record).

Radio-Tracking

Due to poor weather and the tern trapping activities on East Sand Island, no telemetry flights were flown this past week. The telemetry flights will resume this week.

Predator Activity

Gull kleptoparasitism rates at the East Sand Island tern colony increased this past week, as compared to the previous week (15% and 6% of all fish delivered to the colony, respectively), while egg predation rates by gulls remained low. The increase in gull kleptoparasitism rates occurred despite the absence of eagle-induced disturbances (often associated with gull predation on tern nests) this past week.

Media & Other Visitors

There were no visitors in the field this past week.