Caspian Tern Colony Counts

East Sand Island

The high and low on-colony counts for the week on East Sand Island were 15,990 terns (June 10) and 12,250 terns (June 12), respectively. This represents a 10% increase in the median count of terns on the East Sand Island colony from last week to this week. The aerial photo census of the East Sand Island tern colony was conducted on Friday, May 23. 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.

Rice Island and Other Upper Estuary Islands

During this past week, no terns were observed roosting or attempting to nest in upland areas on Rice Island, Miller Sands Spit, Pillar Rock Sands, Fitzpatrick Island, Grassy Island, Crimms Island, and Browns Island (referred to as the upstream end of Puget Island in previous reports). No tern eggs have been found at any of these sites so far this season. This concludes our weekly monitoring of Pillar Rock Sands, Miller Sands Spit, Rice Island, and other upper estuary dredged material disposal islands looking for early signs of nesting (e.g., scrape digging); subsequently, these dredge material disposal islands may be checked occasionally, as we do not anticipate the formation of new colonies after mid-June.

Washington Coast (Willapa Bay, Grays Harbor)

During aerial surveys conducted along the southern Washington coast this past week (June 9), no terns were observed roosting or attempting to nest in upland areas on any of the islands in Willapa Bay or Grays Harbor. Five terns were observed in Willapa Bay and 18 terns were seen in Grays Harbor; both groups were roosting on sand bars below the high tide line.

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 653 terns (June 9) and 425 terns (June 12), respectively. This represents a 25% 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 Wednesday, 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.

No terns have been observed at the former colony on Three Mile Canyon Island so far this season; mink predation caused complete colony failure in 2000 and 2001 (no terns attempted to nest there in 2002).

This past week, surveys of gull colonies located on the lower Columbia River at Miller Rocks (just above the Deschutes River confluence) and Little Memaloose Island (just above The Dalles Dam) revealed no nesting Caspian terns.

Diet Composition

For the week of June 9 – June 15, 25% of the identifiable fish delivered to the East Sand Island tern colony (N = 350) were salmonids, a decrease in the percentage as compared to the previous week (34%). Other major prey items being delivered to the East Sand Island colony included anchovy (29%) and clupeids (e.g., herring; 23%). Year to date, 35% of the identifiable fish delivered to the East Sand Island tern colony (N = 3,351) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 45% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2002.

For the week, 72% of the identifiable fish delivered to the Crescent Island tern colony (N = 151) were salmonids, a decrease in the percentage as compared to the previous week (80%). Most of the non-salmonids observed being delivered to the Crescent Island colony were cyprinids (e.g., northern pikeminnow, peamouth; 15% of total diet) and bass (11% of total diet). Year to date, 72% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,219) were salmonids (this cumulative percent is an average of the previous weeks’ percentages), the same percentage as was recorded by this date in 2002.

Net Pen Feasibility Study

The net pen feasibility study was concluded on Friday, 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.

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 previous weekly report for further details on the radio-tagging operation).

Resightings of Radio-Tagged Terns

One radio-tracking flight (June 13) was conducted this past week. The area surveyed included: the lower Columbia River from one mile below McNary Dam to Richland, Washington; the lower Snake River from the Columbia River confluence to 10 miles above Ice Harbor Dam; the Walla Walla River from the Columbia River confluence to Touchet, Washington; and the Yakima River from the Columbia River confluence to river mile 7. Eight of the 12 radio-tagged terns (67%) were detected during the early morning flight and of these, 2 were on the Crescent Island tern colony (25%), 3 were on the mainstem Columbia River downstream of Crescent Island (38%), one was on the mainstem Columbia River at McNary Dam (13%), one was on the mainstem Snake River above Ice Harbor Dam (13%), and one was on the Walla Walla River (13%), roughly 5 miles from the Columbia River confluence. All eight of these terns are confirmed breeders on Crescent Island based on our colony observations from the blind. This past week, one tern that was radio-tagged on Crescent Island on May 13th was observed at the East Sand Island tern colony and three terns were not detected at any of the areas surveyed. We plan to conduct one radio-tracking flight per week for the remainder of the breeding season.

Predator Activity

There were no disturbances observed at the East Sand Island tern colony this past week. Disturbance rates at the Crescent Island tern colony were higher this week (0.2 disturbances/hr of observation) compared to the previous week (0.0 disturbances/hr of observation). The cause of the disturbance to the Crescent Island tern colony this past week was unknown.

We observed no predation on tern eggs or chicks at the East Sand or Crescent island tern colonies this past week.

This past week, gull kleptoparasitism rates at East Sand Island were 2% of all known fates of fish delivered by terns, an increase in the kleptoparasitism rate compared to the previous week (1% of all known fish fates). At Crescent Island, gull kleptoparasitism rates this past week were 13% of all known fates of fish delivered by terns, a decrease in the kleptoparasitism rate compared to the previous week (15% of all known fish fates).

Media & Other Visitors

There were no visitors to the East Sand Island tern colony site this past week.

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