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 8th (2,571 terns) and May 11th (1,630 terns), respectively. This represents a reduction 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. The Rice Island tern colony may decline further if gull predation on tern eggs continues at current rates. The colony monitors on Rice Island estimate that at least 100 tern eggs are being removed by gulls each day. 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 gull move in to take eggs. The monitors have noticed large numbers of abandoned nest scrapes on the colony, and the density of nesting terns has declined noticeably. The monitors predict that few, if any, young will be raised at the Rice Island colony this year. Terns that are unsuccessful in their first nesting attempt at Rice Island may re-nest at East Sand Island, behavior that we documented last year. We have some evidence from radio-tagged terns that this is happening again this year.

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 8th (20,140 terns) and May 14th (14,770 terns), respectively. This represents an increase in both the high and low on-colony counts from the previous week. Gull kleptoparasitism and predation rates on tern eggs on the East Sand Island tern colony continue to be very low, due in part to our gull control activities (see below). The latest on-colony counts indicate that 90% of the total number of terns counted on both the Rice Island and East Sand Island colonies are on East Sand Island.

Coastal Sites

On May 9th, we surveyed Cate Island in Grays Harbor by boat. About 50-70 ring-billed gulls were roosting above the high tide line on the eastern end of Cate Island, and were behaving as though they were interested in nesting there. One ring-billed gull nest with a single egg was located. There were also about 10 Caspian terns roosting adjacent to the gulls. Caspian terns frequently nest in association with ring-billed gulls (a smaller gull species that rarely steals tern eggs), so this increases the chances that some Caspian terns may attempt to nest on Cate Island this year. Also observed during this visit, which occurred during an extremely low tide, was a land bridge to the mainland, allowing access by mammalian predators.

An aerial survey of terns roosting and/or nesting at coastal Washington sites (i.e., Willapa Bay and Grays Harbor) was carried out on Friday (5/12). 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 11th (863 terns) and May 13th (806 terns), respectively. The high and low on-colony counts for the week on Three Mile Canyon Island were on May 12th (326 terns) and May 8th (285 terns), respectively. Both of these colonies are roughly the same size as last year, based on the 1999 aerial photo census conducted near the peak of hatching.

Diet Composition

For the week (8 - 14 May), 81% of the identifiable fish delivered to East Sand Island (N = 359) were salmonids, compared to 96% at Rice Island (N = 409). Year to date, 68% of the identifiable fish delivered to East Sand Island (N = 1,534) were salmonids, compared to 92% at Rice Island (N = 1,217).

At Crescent and Three Mile Canyon islands, 89% (N = 106) and 100% (N = 32) of the identifiable fish delivered to each colony this week were salmonids, respectively.

Off-Colony Distribution

Banding and Radio-Tagging

Banding and radio-tagging of adult terns on Rice Island was completed on April 15th and no additional banding or tagging is planned for terns at that colony. We intend to band and radio-tag 30 - 40 breeding terns at the East Sand Island colony during late incubation, beginning as early as next week.

Radio-Tracking & Resightings of Banded Birds

During the radio-tracking flight on Friday (5/12), a total of 45 radio-tagged terns (out of a total of 50 terns radio-tagged at Rice Island) were detected. In addition, two radio-tagged terns were detected at up-river colonies at the time the flight was conducted. These two up-river terns were visually verified, one on Three Mile Canyon Island and one on Crescent Island on 5/12 and 5/13, respectively. Both of these radio-tagged terns were seen copulating and digging nest scrapes, and are apparently attempting to nest at these up-river colonies.

Similar to the last few weeks, most observations of radio-tagged terns during the flight were either on the Rice Island or East Sand Island colonies (96%). Of the two off-colony detections of radio-tagged terns in the estuary and nearshore, both were in Willapa Bay. Year to date, 22 off-colony detections (43%) were in the upper estuary (above the Astoria Bridge), 13 off-colony detections (25%) were in the lower estuary (below the Astoria Bridge), and 16 off-colony detections (31%) were outside the estuary along the coast.

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. Five gulls were shot this week at East Sand Island. So far this season, 24 gulls have been shot on the East Sand Island tern colony.

The Caspian Tern Management Plan for 2000 includes a strategy for in-season management of tern nesting at East Sand Island. One component of in-season management was the elimination or reduction of selective gull control on the East Sand Island tern colony as a way to encourage more terns to nest at sites outside the Columbia River Estuary. Earlier in the week (5/9), researchers distributed an e-mail to the participating agencies in the Avian Predation Working Group asking if a consensus had been reached on whether to continue or cease gull control at the East Sand Island tern colony. Six participating agencies responded to the e-mail, with all but one agency suggesting that limited gull control continue on East Sand Island. Most agencies that supported continued gull control were concerned that failed breeders at East Sand Island might attempt to re-nest at Rice Island, as opposed to sites outside the Columbia River Estuary. Currently, there are no established tern colonies in either Willapa Bay or Grays Harbor, while an established tern colony exists on Rice Island (see above).

Tern Hazing

There will be no tern hazing at the Rice Island tern colony in 2000.

Media and Other Visitors

There were no visitors in the field this week.