Caspian Tern Colony Counts

East Sand Island

The high and low on-colony counts for the week on East Sand Island were 15,825 terns (May 3) and 7,720 terns (May 1), respectively. The number of terns counted on colony continues to increase and will likely reach a peak in 2-3 weeks. Many of the terns on the East Sand Island colony are incubating eggs.

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. The continuous hazing of terns prospecting at Pillar Rock Sands and Miller Sands Spit (conducted by the USACE) is ongoing and will be discontinued when tern nesting at those sites is no longer expected. We will continue to monitor Rice Island and other upper estuary dredged material disposal islands (3 times a 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 1), no terns were observed roosting or attempting to nest in upland areas on any of the islands in Willapa Bay or Grays Harbor. Three terns were observed in Willapa Bay and only 28 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 645 terns (May 2) and 588 terns (April 28), respectively. 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 April 28 – May 4, 36% of the identifiable fish delivered to the East Sand Island tern colony (N = 357) were salmonids. The majority of the prey items being delivered to the East Sand Island colony were smelt (27%), clupeids (e.g., herring; 15%), and anchovies (8%). Year to date, 24% of the identifiable fish delivered to the East Sand Island tern colony (N = 1,256) were salmonids (this cumulative percent is an average of the previous weeks’ percentages).

For the week, 86% of the identifiable fish delivered to the Crescent Island tern colony (N = 160) were salmonids. Most of the non-salmonids observed being delivered to the Crescent Island colony were cyprinids (e.g., northern pikeminnow, peamouth; 10% of total diet). Year to date, 68% of the identifiable fish delivered to the Crescent Island tern colony (N = 436) were salmonids (this cumulative percent is an average of the previous weeks’ percentages).

Predator Activity

Disturbances to the East Sand Island tern colony were similar this week (0.7 disturbances/hr of observation) as compared to the previous week (0.8 disturbances/hr of observation). All of the colony disturbances on East Sand Island this past week were caused by bald eagles. There were no disturbances observed at the Crescent Island tern colony this past week.

At total of 4 eggs were preyed upon by gulls at the East Sand Island tern colony this past week, or 0.4 eggs depredated/hr of observation. Egg predation was not observed at the Crescent Island tern colony this past week.

This past week, gull kleptoparasitism rates at East Sand Island were 7% of all known fates of fish delivered by terns, a little greater than half the rate that was observed the previous week (13% of all known fish fates). At Crescent Island, gull kleptoparasitism rates were 15% of all known fates of fish delivered by terns this past week, also a reduction from the rate observed the previous week (20% of all known fish fates). At the East Sand Island tern colony, kleptoparasitism is by glaucous-winged/western gulls, while at Crescent Island kleptoparasitism is by the smaller California gull.

To date, there have been no signs of mammalian predators on any of the tern colonies monitored as part of this study.

Media & Other Visitors

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

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