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

Colony Counts

Rice Island & Other Upper Estuary Islands

The high and low on-colony counts for the week on Rice Island were on May 16th (2,225 terns) and May 15th (1,425 terns), respectively. This represents a slight reduction (roughly 200 terns) in both the high and low on-colony counts from the previous week. Recent declines in the number of terns counted on the Rice Island colony are likely due to the high incidence of egg predation and kleptoparasitism (i.e., stealing of fish from terns) by gulls. Egg losses are exacerbated by frequent bald eagle disturbance on the colony; every time an eagle flies by most or all of the terns flush and the gulls move in to take eggs. An aerial photo census of the Rice Island tern colony is scheduled for May 27th. This photo census will be used along with ground counts of terns in plots to estimate the number of breeding pairs on the Rice Island tern colony in 2000.

No terns have been observed nesting (or roosting) at other off-colony areas on Rice Island (i.e., East Ridge) or on other upper estuary islands (i.e., Miller Sands Spit and Pillar Rock Sands).

East Sand Island

The high and low on-colony counts for the week on East Sand Island were on May 19th (19,150 terns) and May 17th (13,400 terns), respectively. The first chick was spotted on the East Sand Island tern colony on May 21st. The latest on-colony counts indicate that 91% of the total number of terns counted on both the Rice Island and East Sand Island colonies are on East Sand Island. An aerial photo census of the East Sand Island tern colony is scheduled for May 27th (see above).

Coastal Sites

On May 18th, we visited Cate Island in Grays Harbor to determine the status of ring-billed gulls attempting to nest there and assess whether Caspian terns were also attempting to nest. Only 15 ring-billed gulls and three Caspian terns were counted on the island, and there was no evidence of nesting by either species. Apparently, the gull nests that were observed on Cate Island on May 9th were washed away by a high tide. No recent evidence of coyotes on Cate Island was found.

An aerial survey of terns roosting and/or nesting at coastal Washington sites (i.e., Willapa Bay and Grays Harbor) was carried out on Saturday (5/20). No aggregations of roosting terns were observed, either in Willapa Bay or Grays Harbor. At this time it does not appear that terns are nesting anywhere in Willapa Bay or Grays Harbor.

Upriver Sites (Three Mile Canyon and Crescent Islands)

The high and low on-colony counts for the week on Crescent Island were on May 18th (895 terns) and May 15th (866 terns), respectively. The high and low on-colony counts for the week on Three Mile Canyon Island were on May 19th (330 terns) and May 16th (286 terns), respectively. The number of terns counted at the up-river colonies remains relatively constant from week to week as compared to the tern colonies in the estuary. The Crescent Island and Three Mile Canyon Island tern colonies are roughly the same size as last year, based on the 1999 aerial photo census conducted near the peak of hatching. An aerial photo census is scheduled for today (May 22) at Crescent and Three Mile Canyon islands in order to get an accurate count the number of terns on each colony. Researchers will be stationed in blinds at both colonies from one hour before to one hour after the photos census. During that time they will be counting the number of brooding and non-brooding birds in plots so that counts from aerial photos can be corrected to estimate the number of active breeding pairs on each colony in 2000.

The first chick was observed at the Three Mile Canyon Island tern colony on May 19th. As was reported last week, the first chick on Crescent Island was observed on May 13th. The available evidence suggests that the delayed breeding at Three Mile Canyon Island is due to raptor predation at the colony.

Diet Composition

For the week (15 - 21 May), 81% of the identifiable fish delivered to East Sand Island (N = 364) were salmonids, compared to 97% at Rice Island (N = 408). Year to date, 71% of the identifiable fish delivered to East Sand Island (N = 1,898) were salmonids, compared to 93% at Rice Island (N = 1,625). The year to date totals for percent salmonids in the diet of terns nesting on East Sand Island and Rice Island are similar or lower this year, as compared to last year (70 % and 98% at East Sand and Rice islands through 21 May, 1999, respectively).

At Crescent and Three Mile Canyon islands, 64% (N = 122) and 92% (N = 49) of the identifiable fish delivered to each colony this week were salmonids, respectively.

Off-Colony Distribution

Banding and Radio-Tagging

We will attempt to radio tag 30 breeding terns at the East Sand Island colony beginning today. This work will be completed over the next few days. Roughly half of these 30 radio-tagged terns will have their nest contents removed to determine the subsequent success and location of re-nesting attempts.

Radio-Tracking & Resightings of Banded Birds

Three radio-tracking flights were conducted in the Columbia River estuary this past week (5/15, 5/18, 5/20). A total of 44, 45, and 44 radio-tagged terns (out of a total of 50 terns radio-tagged at Rice Island) were detected, respectively. Only one of the two radio-tagged terns that were detected at up-river tern colonies last week was detected this week (at Three Mile Canyon Island). This radio-tagged tern was observed bringing fish to the Three Mile Canyon Island colony site on several occasions.

Similar to the last few weeks, most observations of radio-tagged terns during the flights were either on the Rice Island or East Sand Island colonies (98%). Of the off-colony detections of radio-tagged terns, all were in the Columbia River Estuary (3 were detected above the Astoria Bridge and 1 was detected below the bridge). Year to date, 25 off-colony detections (45%) were in the upper estuary (above the Astoria Bridge), 14 off-colony detections (25%) were in the lower estuary (below the Astoria Bridge), and 16 off-colony detections (29%) were outside the estuary along the coast.

Warren McKalles of the Washington Department of Fish and Wildlife flew on May 16th and located 46 of our radio-tagged terns. This valuable assistance by WDFW is greatly appreciated by the research team.

Gull and Predator Control

There have been no signs of mammalian predators on either Rice or East Sand islands. Limited gull control is being carried out at the East Sand Island tern colony to enhance prospects for tern colony restoration at that site. Eight gulls were shot this week at East Sand Island. So far this season, 32 gulls have been shot on the East Sand Island tern colony. Currently, there are no plans to restrict or eliminate gull control at the East Sand Island tern colony.

Media and Other Visitors

There were no visitors in the field this week.