Last Updated July 09

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

Caspian Tern Colony Counts

East Sand Island

The high and low on-colony counts for the week on East Sand Island were 10,835 terns (July 6th) and 7,851 terns (July 7th), respectively. This represents a 7% decrease in the median count of terns on the East Sand Island colony from last week to this week. A satellite tern colony continues to be active on the beach southeast of the main colony, above the high-high tide line. This week, approximately 275 adult terns were counted in this area, of which 125 are sitting in nest scrapes. At least 30 young tern chicks have been sighted in this area.

Young terns continue to fledge from the East Sand Island tern colony. As many as 1,400 fledged tern chicks have moved from the East Sand Island tern colony to the adjacent beaches this past week, with thousands more young chicks remaining on the colony itself. We suspect that production of young terns at the East Sand Island tern colony this year could be considerably higher as compared to last year. An aerial photo census was conducted on July 2nd to determine the number of young terns that have been raised to fledging age this year. Those photos will be analyzed in the coming weeks and the results made available in an upcoming update.

Mid-Columbia River Sites (Crescent Is.)

The high and low on-colony counts for the week on Crescent Island were 364 terns (July 3rd) and 125 terns (July 8th), respectively. This represents a 48% decrease in the median count of terns on the Crescent Island tern colony from last week to this week. Many young terns have already fledged from the Crescent Island tern colony. We suspect that the productivity of terns nesting on Crescent Island this year will be somewhat higher than last year.

Inland Washington Sites (Potholes Reservoir)

Solstice Island, located in Potholes Reservoir, was visited on July 7th. A total of 173 adult terns and 265 chicks were counted on the colony. During our visit, we observed a great deal of boating and camping activity near the Solstice Island tern colony, presumably occurring throughout the July 4th holiday. This activity caused over 10 colony disturbances (e.g., terns taking flight) during our visit on Saturday. Despite these repeated disturbances, the terns quickly resettled at the colony location following each disturbance. Last year, the Solstice Island tern colony was abandoned late in the season (sometime between 7/7 and 7/19), apparently due to a high level of human disturbance at the colony site (see past weekly report for July17 - July 23, 2000 for further information).

Diet Composition

For the week of 2 July - 8 July, 11% of the identifiable fish delivered to the East Sand Island tern colony (N = 334) were salmonids, a 45% decrease from the previous week (see Seasonal Trends for the weekly salmonid proportion of the diet for terns on East Sand Island). Anchovies, smelt, surfperch, and cod were all prevalent in tern diets this past week. Year to date, 39% of the identifiable fish delivered to the East Sand Island tern colony (N = 4,922) were salmonids. This compares to 51% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2000.

For the week, 65% of the identifiable fish delivered to Crescent Island (N = 150) were salmonids, a 16% decrease from the previous week. Year to date, 74% of the identifiable fish delivered to terns on Crescent Island (N = 1,814) were salmonids.

On July 7th, 50 fish were identified on Solstice Island as they were fed to chicks on the colony. Of these fish, 14% were salmonids, while Centrarchids (e.g., sunfish, bass) were the most prevalent fish in the sample.

Off-Colony Distribution

Radio-Tracking

Two radio-tracking flights (7/2 and 7/3) were conducted in the Columbia River estuary this past week. Forty-one of the 52 relocations of radio-tagged terns (79%) were on the East Sand Island colony. Of all the off-colony detections of radio-tagged terns that are known to be nesting on East Sand Island (N = 6), one (17%) was in Willapa Bay and 5 (83%) were in the lower Columbia River estuary below the Astoria Bridge.

Predator Activity

Gull kleptoparasitism and predation rates at the East Sand Island tern colony remained low this past week.

Oil Spill (near East Sand Island)

On July 3rd, a dredge barge (named "Padre Island") struck Buoy 7 near the mouth of the Columbia River in heavy fog. The accident caused the buoy to sink, the port engine room of the barge to flood, and a small amount of diesel fuel to spill into the Columbia River. The incident (National Response Center Incident # 571659; Oregon Emergency Response Systems Incident # 01-1568) was determined to be relatively minor, with no apparent impact to birds nesting on East Sand Island.

Media & Other Visitors

There were no visitors in the field this past week.