Caspian Tern Colony Counts

East Sand Island

The high and low on-colony counts for the week on East Sand Island were 16,700 terns (June 1) and 12,455 terns (May 28), respectively. This represents a 2% 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. We will continue to monitor Pillar Rock Sands, Miller Sands Spit, Rice Island, and other upper estuary dredged material disposal islands 3 times each week looking for early signs of nesting (e.g., scrape digging) and will promptly inform resource managers of any such activity.

Washington Coast (Willapa Bay, Grays Harbor)

During aerial surveys conducted along the southern Washington coast this past week (May 27), no terns were observed roosting or attempting to nest in upland areas on any of the islands in Willapa Bay or Grays Harbor. Twenty-two terns were observed in Willapa Bay and 34 terns were seen in Grays Harbor; both groups were roosting on sand bars below the high tide line. We will continue to fly periodic surveys in these areas looking for nesting terns.

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 849 terns (May 26) and 843 terns (May 27), respectively. 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) revealed no nesting Caspian terns. Little Memaloose Island (just above The Dalles Dam), which formerly was home to a small California gull colony, had no nesting gulls or terns.

Diet Composition

For the week of May 26 – June 1, 36% of the identifiable fish delivered to the East Sand Island tern colony (N = 352) were salmonids, a decrease in the percentage as compared to the previous week (47%). Other major prey items being delivered to the East Sand Island colony included clupeids (e.g., herring; 21%) and smelt (18%). Year to date, 37% of the identifiable fish delivered to the East Sand Island tern colony (N = 2,676) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 46% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2002.

For the week, 66% of the identifiable fish delivered to the Crescent Island tern colony (N = 110) were salmonids, an increase 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; 18% of total diet) and bass (8% of total diet). Year to date, 71% of the identifiable fish delivered to the Crescent Island tern colony (N = 966) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 72% juvenile salmonids in the diet of terns on Crescent Island by the same date in 2002.

Net Pen Feasibility Study

On May 7, a feasibility study was initiated to determine if Caspian terns will feed on fish held in a net pen. If so, this approach can potentially be used to assess the relative vulnerability of various stocks of juvenile salmonids and other fish to Caspian tern predation in a controlled environment.

A 6-meter circular net pen was anchored in a backwater slough off the Columbia River near Crescent Island. A total of 2,000 juvenile rainbow trout (approximately 10-15 cm in length) were placed in the net pen. All fish were certified, disease-free triploids (sterile as adults) obtained from the Trout Lodge Hatchery, WA. The net pen and the surrounding slough were monitored both before and after the fish were placed in the net pen (approximately 4 hrs/day and 8 hrs/day, respectively).

This past week, Caspian terns were observed foraging on fish within the net pen during 6 of 7 (86%) 4-hour observation periods. A total of 34 plunge dives were observed, 11 of which were successful (i.e., resulting in a fish being captured). As many as 7 Caspian terns have been observed foraging in the vicinity of the net pen at one time and many more commute past the site each day to other foraging areas. As was reported last week, Forster’s terns continue to use the net pen frame as a roost and as many as four individuals have been observed repeatedly feeding on fish within the net pen. To dissuade Forster’s terns from roosting on the net pen frame, we reinstalled wire spike strips on the net pen frame on June 2. These spike strips were initially installed on May 7 and removed nine days later because we suspected they might be deterring feeding by Caspian terns at the net pen. We will continue to monitor bird activity at the net pen for the remainder of this week and will remove the net pen from Burbank Slough on Friday, June 6.

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 (May 29) 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. Ten of the 12 radio-tagged terns (83%) were detected during the morning flight and of these, 7 were on the Crescent Island tern colony (70%), two were on the lower Columbia River downstream of Crescent Island (20%), and one was at the mouth of the Walla Walla River (10%). All ten 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 one tern was 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

Disturbance rates at the East Sand Island tern colony were lower this week (0.3 disturbances/hr of observation) compared to the previous week (0.6 disturbances/hr of observation). Most disturbances to the East Sand Island tern colony this past week were caused by bald eagles (67%). There were no disturbances observed at the Crescent Island tern colony this past week.

We observed predation on 2 tern eggs and 2 tern chicks by gulls at the East Sand Island colony this past week or 0.4 eggs/chicks depredated/hr of observation, a decrease in the predation rate compared to the previous week (0.7 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.

This past week, gull kleptoparasitism rates at East Sand Island were 2% of all known fates of fish delivered by terns, a decrease in the kleptoparasitism rate compared to the previous week (7% of all known fish fates). At Crescent Island, gull kleptoparasitism rates this past week were 9% of all known fates of fish delivered by terns, a decrease in the kleptoparasitism rate compared to the previous week (26% of all known fish fates).

Media & Other Visitors

David Allen (Regional Director, USFWS), Lindsay Ball (Director, ODFW), Brad Bortner (Division Chief, Migratory Birds and Habitat Programs, USFWS), Dave Brittell (Assistant Director, Wildlife Program, WDFW), Mike Crouse (Assistant Regional Administrator, Habitat Division, NOAA Fisheries), Geoff Dorsey (Wildlife Biologist, USACE), Roy Elicker (Deputy Director, ODFW), Colonel Richard Hobernicht (Commander, Portland District, USACE), Jeff Koenings (Director, WDFW), Holly Michael (Wildlife Diversity Biologist, ODFW), Nanette Seto (Wildlife Biologist, USFWS), Cathy Tortorici (Columbia River Estuary Coordinator, NOAA Fisheries), David Wesley (Deputy Regional Director, USFWS), Bob Willis (Chief, Environmental Resources Branch, Portland District, USACE), Tara Zimmerman (Branch Chief, Bird Conservation, USFWS) visited the East Sand Island tern colony site on Friday, May 30.

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