Note: This will be the last weekly update for the 2003 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 4,214 terns (July 21) and 3,255 terns (July 23), respectively. This represents a 38% 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).

The aerial photo census to estimate the number of breeding pairs at the East Sand Island tern colony was conducted on May 23. A second aerial photo census of the colony was conducted on July 9 in order to estimate the number of young terns fledged from the East Sand Island colony this year. Once the aerial photos are counted (Fall 2003) we will be able to accurately estimate colony size and productivity to determine whether there has been a significant change since 2002.

Rice Island and Other Upper Estuary Islands

Our weekly surveys for nesting terns on Pillar Rock Sands, Miller Sands Spit, Rice Island, and other upper estuary dredged material disposal islands have concluded for the season; we do not anticipate the formation of new colonies at this late date.

Washington Coast (Willapa Bay, Grays Harbor)

Our aerial surveys for nesting terns along the southern Washington coast have concluded for the season; we do not anticipate the formation of new colonies at this late date.

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 124 terns (July 21) and 22 terns (July 21), respectively. This represents a 16% decrease in the median count of terns on the Crescent Island colony from last week to this week. The aerial photo census of the Crescent Island tern colony was conducted on May 21. Once the aerial photos are counted (Fall 2003) we will be able to accurately estimate colony size and determine whether there has been a significant change in colony size since 2002. 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 of July 21 – July 27, 10% of the identifiable fish delivered to the East Sand Island tern colony (N = 362) were salmonids, an increase in the percentage as compared to the previous week (8%). Other major prey items being delivered to the East Sand Island colony included anchovy (59%) and clupeids (e.g., herring; 14%). Year to date, 25% of the identifiable fish delivered to the East Sand Island tern colony (N = 5,476) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 32% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2002.

For the week, 57% of the identifiable fish delivered to the Crescent Island tern colony (N = 150) were salmonids, a decrease in the percentage as compared to the previous week (63%). Most of the non-salmonids observed being delivered to the Crescent Island colony were cyprinids (e.g., northern pikeminnow, peamouth; 25% of total diet) and bass (16% of total diet). Year to date, 68% of the identifiable fish delivered to the Crescent Island tern colony (N = 2,129) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 67% juvenile salmonids in the diet of terns on Crescent Island by the same date in 2002.

Net Pen Feasibility Study

The net pen feasibility study was concluded on June 6. This study demonstrated conclusively that Caspian terns can learn to forage for fish confined to a net pen that is equipped with deterrents that prevent other avian predators from using the net pen. The success of the feasibility study indicates that Caspian tern diet preferences can be assessed in controlled field experiments.

Off-Colony Distribution

Radio-Tagging

On May 13 and 14, a total of 12 adult Caspian terns were captured and radio-tagged at the Crescent Island tern colony. These radio-tagged terns will help determine the foraging patterns of terns nesting on Crescent Island (see the weekly report for May 12-18 for further details on the radio-tagging operation).

Resightings of Radio-Tagged Terns

Our weekly aerial surveys for radio-tagged terns have concluded for the season.

Predator Activity

Disturbance rates at the East Sand Island tern colony were higher this week (0.4 disturbances/hr of observation) compared to the previous week (0.0 disturbances/hr of observation). The disturbances to the East Sand Island tern colony this past week were caused by a bald eagle and peregrine falcon. There were no disturbances observed at the Crescent Island tern colony this past week.

We observed predation on 1 tern chick by gulls at the East Sand Island colony this past week or 0.2 eggs/chicks depredated/hr of observation, a decrease in the predation rate compared to the previous week (0.4 eggs/chicks depredated/hr of observation). We observed no predation on tern eggs or chicks by gulls at the Crescent Island tern colony this past week.

At East Sand Island, gull kleptoparasitism was not observed this past week, a decrease in the kleptoparasitism rate compared to the previous week (3% of all known fish fates). At Crescent Island, gull kleptoparasitism rates this past week were 35% of all known fates of fish delivered by terns, a decrease in the kleptoparasitism rate compared to the previous week (39% of all known fish fates).

Media & Other Visitors

There were no visitors to the East Sand Island tern colony 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 2003. We thank Bret Bastain, Bobby Begay, Garrett Dorsey, Su Elliott, Allen Evans, Karen Fischer, Tanya Harrison, Amanda Hover, Brooke Krolick, Don Lyons, Anne Mary Myers, Kim Nelson, Chris Neufeld, Rob Suryan, Kim Weersing, and Adam Wells.

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