Caspian Tern Colony Counts

East Sand Island

The high and low on-colony counts for the week on East Sand Island were 12,225 terns (April 27) and 5,485 terns (April 23), respectively. The first tern egg was seen at the East Sand Island colony on April 23rd, 5 days later than the first egg date on the East Sand Island tern colony in 2002.

Rice Island and Other Upper Estuary Islands

On Wednesday (April 23), about 1,000 terns were observed loafing in an upland area on the eastern end of Pillar Rock Sands, a dredged material disposal site in the upper estuary (River Mile 27), above Rice Island. The site was investigated and no nest scrapes were observed; however, terns attending the site were copulating and bringing in fish as part of courtship. Resource managers were informed of the situation and on Wednesday afternoon the U.S. Army Corps of Engineers (USACE) had their personnel brought to the island to discourage terns from nesting at the site. To date, these activities (i.e., continuous day and night time monitoring of the site and hazing of any terns that settle in upland areas) have succeeded in keeping terns from nesting on Pillar Rock Sands.

On Friday (April 25), about 450 terns were observed loafing in an upland area on Miller Sands Spit, a dredged material disposal site in the upper estuary just above Rice Island. The site was investigated and no nest scrapes were observed; however, terns attending the site were copulating and bringing in fish as part of courtship. Resource managers were informed of the situation and on Friday afternoon the USACE had their personnel brought to the island to discourage terns from nesting at the site. To date, these activities (i.e., continuous day and night time monitoring of the site and hazing of any terns that settle in upland areas) have succeeded in keeping terns from nesting on Miller Sands Spit.

During an aerial survey conducted on Friday (April 25), 120 terns were observed roosting in an upland area on Brown Island, a dredge material disposal island in the upper estuary. The USACE was informed of this situation and currently they have no plans to haze terns off this site due to the presence of mammalian predators on the island. No aggregations of terns were observed in upland areas of other upper estuary dredged material disposal islands (Rice Island and Crimms Island).

Washington Coast (Willapa Bay, Grays Harbor)

During aerial surveys conducted along the southern Washington coast this past week (April 25), no terns were observed roosting or attempting to nest in upland areas on any of the islands in Willapa Bay or Grays Harbor. Sixty 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 634 terns (April 27) and 374 terns (April 21), 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), Richland Island, and Island 18 (both in the Richland area) 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 April 21 - 27, 28% of the identifiable fish delivered to the East Sand Island tern colony (N = 348) were salmonids. The most prominent prey item being delivered to the East Sand Island colony were smelt (29%). Year to date, 20% of the identifiable fish delivered to the East Sand Island tern colony (N = 899) were salmonids (this cumulative percent is an average of the previous weeks’ percentages).

For the week, 54% of the identifiable fish delivered to the Crescent Island tern colony (N = 155) were salmonids. Most of the non-salmonids observed being delivered to the Crescent Island colony were cyprinids (e.g., northern pikeminnow, peamouth; 29% of total diet) and bass (7% of total diet). Year to date, 62% of the identifiable fish delivered to the Crescent Island tern colony (N = 276) were salmonids (this cumulative percent is an average of the previous weeks’ percentages).

Predator Activity

Disturbances to the East Sand Island tern colony increased (0.8 disturbances/hr of observation) as compared to the previous week (0.6 disturbances/hr of observation). The majority (75%) of these disturbances this past week were caused by bald eagles. Terns appear to be much more settled on the colony and are less likely to take flight when an eagle is flying high over the colony, as compared to earlier in the breeding season. These disturbances are short, causing terns to leave the colony for only 10-15 seconds before returning. There were no disturbances observed at the Crescent Island tern colony this past week.

At total of 10 eggs were preyed upon by gulls at the East Sand island tern colony this past week, or 0.5 eggs predations/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 13% of all known fates of fish delivered by terns, roughly the same rate as was observed the previous week. At Crescent Island, gull kleptoparasitism rates were 20% of all known fates of fish delivered by terns this past week. 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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