Last Updated July 16

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 8,720 terns (July 9th) and 5,355 terns (July 15th), respectively. This represents a 25% 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 250 adult terns were counted in this area, of which half were 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 1,600 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 Island and Miller Rocks)

The high and low on-colony counts for the week on Crescent Island were 209 terns (July 13th) and 40 terns (July 12th), respectively. This represents a 49% 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. During our visit, we banded chicks near fledging age at the Crescent Island tern colony (see below for more details).

Miller Rocks, an island located on the lower Columbia River just upstream of the mouth of the Deschutes River, was visited on July 15th. Ten adult terns were counted on the island, of which 5 were sitting in nest scrapes. One large tern chick (probably about 30 days old) was also seen at the colony site. This is the first documentation of terns attempting to nest on Miller Rocks, or any other up-river location on the lower Columbia River (other than Crescent and Three Mile Canyon islands).

Inland Washington Sites (Potholes Reservoir)

Solstice Island, located in Potholes Reservoir, was visited on July 11th. Approximately, 190 adult terns and 170 chicks were counted on the colony. During our visit, we banded chicks near fledging age at the Solstice island tern colony (see below for more details).

Diet Composition

For the week of 9 July - 15 July, 9% of the identifiable fish delivered to the East Sand Island tern colony (N = 364) were salmonids, a 18% decrease from the previous week (see Seasonal Trends for the weekly salmonid proportion of the diet for terns on East Sand Island). Anchovies made up the majority of the tern diet (60-70%) this past week. Year to date, 37% of the identifiable fish delivered to the East Sand Island tern colony (N = 5,286) were salmonids. This compares to 48% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2000.

For the week, 51% of the identifiable fish delivered to Crescent Island (N = 150) were salmonids, a 22% decrease from the previous week. Year to date, 72% of the identifiable fish delivered to terns on Crescent Island (N = 1,964) were salmonids.

Off-Colony Distribution

Radio-Tracking

Two radio-tracking flights (7/12 and 7/13) were conducted in the Columbia River estuary this past week. Twenty-four of the 48 relocations of radio-tagged terns (50%) were on the East Sand Island colony, a 37% decline in on-colony re-sightings from the previous week. Of all the off-colony detections of radio-tagged terns that are known to be nesting on East Sand Island (N = 12), one (8%) was in Willapa Bay, five (42%) were in the lower Columbia River estuary below the Astoria Bridge, one (8%) was in the estuary between Rice Island and the Astoria Bridge, and five (42%) were above Rice Island.

Chick Banding

On July 11th, a total of 199 chicks that were near fledging were banded at the Crescent Island and Solstice Island tern colonies. Each chick was banded with a numbered U.S. Fish and Wildlife Service metal leg band. Of the 199 chicks that were banded at both colonies, 175 chicks were also banded with unique color band combinations placed on both legs (88 and 87 chicks at Solstice Island and Crescent Island, respectively). No mortality or injuries occurred to tern chicks during this banding operation. These banded fledglings will provide important data on survivorship and dispersal patterns of young terns to breeding colonies in future years.

Predator Activity

Gull kleptoparasitism and predation rates at the East Sand Island tern colony has increase somewhat now that the number of terns on colony has declined.

Media & Other Visitors

There were no visitors in the field this past week.