Last Updated July 29th

Note: This will be the last weekly update for the 2002 field season. We plan to provide additional updates on a less frequent basis, including a season summary that will be posted in the coming months.

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 3,185 terns (July 24) and 3,010 terns (July 22), respectively. This represents a 24% decrease in the median count of terns on the East Sand Island colony from last week to this week. Most young terns have fledged from the colony and have joined the post-breeding season dispersal with their parents (Caspian terns provide their young with post-fledging care). Seasonal trends in tern attendance at the East Sand Island colony were generally similar to the previous two years (see figures of Colony Counts under "Seasonal trends" at this web site).

Up-river Sites (Crescent Island, Three Mile Canyon Island, Miller Rocks)

The high and low on-colony counts for the week on Crescent Island were 101 terns (July 22) and 1 tern (July 23), respectively. This represents a 41% decrease in the median count of terns on the Crescent Island colony from last week to this week. Nearly all young terns have fledged from this colony and have joined the post-breeding season dispersal. Seasonal trends in tern attendance at the Crescent Island colony were generally similar to the previous two years (see figures of Colony Counts under "Seasonal trends" at this web site). The Crescent Island colony was the only site on the Columbia River between the estuary and the Tri-Cities area where Caspian terns successfully nested this year.

Diet Composition

For the week, 7% of the identifiable fish delivered to the East Sand Island tern colony (N = 361) were salmonids. This represents a 13% decrease in the percentage of the diet that was salmonids for terns on the East Sand Island colony from last week to this week. As was the case last week, the majority of non-salmonid prey items delivered to the East Sand Island colony were surfperch. Year to date, 32% of the identifiable fish delivered to the East Sand Island tern colony (N = 5,665) were salmonids (this cumulative percent is an average of the previous weeks' percentages). This compares to 34% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2001. This year, the proportion of salmonids in the diet of the East Sand Island tern colony peaked on about 1 June, 2-4 weeks later than the peak salmonid consumption in previous years (see figures of Diet Composition under "Seasonal trends" at this web site).

For the week, 20% of the identifiable fish delivered to the Crescent Island tern colony (N = 152) were salmonids. This represents a 47% decrease in the percentage of the diet that was salmonids for terns on the Crescent Island colony from last week to this week. Year to date, 67% of the identifiable fish delivered to the Crescent Island tern colony (N = 2,222) were salmonids (this cumulative percent is an average of the previous weeks'
percentages). This compares to 68% juvenile salmonids in the diet of terns on Crescent Island by the same date in 2001. As in previous years, the proportion of salmonids in the diet of the Crescent Island tern colony declined sharply at the end of the breeding season (see figures of Diet Composition under "Seasonal trends" at this web site).

Observations at McNary Dam

Observations of bird activity at McNary Dam were not conducted this past week

Predator Activity

Bald eagle disturbance rates to the East Sand Island tern colony were higher this last week (0.15 disturbances/hr of observation), as compared to the previous week (0.06 disturbances/hr of observation). These disturbances were generally short, causing terns to leave the colony for only 10-15 seconds before returning.

No gull predation on tern eggs and chicks was observed during eagle disturbances to the tern colony this past week.

Media & Other Visitors

There were no visitors in the field this past week.

Thanks to the Field Crew

We would like to take this opportunity to thank our field crew whose hard work and dedication contributed greatly to the success of our research and monitoring efforts in 2002. We thank Bobby Begay, Cari Cardoni, Garrett Dorsey, Karen Fischer, P.J. Klavon, Anne Mary Myers, Ian Rose, Penny Spiering, Rob Suryan, Melissa Thompson, Rob Westra, and Sadie Wright.