Last Updated May 8th
Caspian Tern Colony Counts East Sand Island The high and low on-colony counts for the past week on East Sand Island were 14,300 terns (6 May) and 3,440 terns (2 May), respectively. The average number of terns counted on-colony this week (8,916 terns) was similar to counts conducted at the colony during this time last year (8,682 terns). For the past three weeks, the weather in the Columbia River estuary has been more typical for this time of year (i.e., some moderate to strong winds and light rain); whereas in early April the weather was mostly dry with calm winds.
Two surveys were conducted this past week (2 and 5 April) looking for nesting terns at dredged material disposal sites in the upper estuary. Although we have observed an increase in the number of terns roosting and foraging in the upper estuary in recent weeks, no terns were observed in upland areas (where terns might nest) on Rice Island, Pillar Rock Sands, or Miller Sands Spit during these surveys. We will continue to monitor Rice Island and the other upper estuary dredge disposal islands for early signs of nesting (e.g., nest scrape digging) and will promptly inform resource managers of any such activity.
This past week (1 May) we conducted an aerial survey of the mid-Columbia River from The Dalles Dam to just above Priest Rapids Dam, the lower Snake River from the confluence with the Clearwater River to its mouth, and Potholes Reservoir searching for incipient Caspian tern colonies. Caspian terns were once again observed on Rock Island within the Blalock Islands, which is located on the mid-Columbia River between the towns of Boardman and Irrigon, Oregon. Thirty-nine Caspian terns were counted on or near Rock Island during this aerial survey, although they did not appear to be nesting. A subsequent boat survey of Rock Island on 5 May revealed 63 Caspian terns on the island, with 9 terns apparently sitting on nests. Caspian terns were first observed nesting on Rock Island in 2005, when 6 pairs attempted to nest there with at least one young successfully fledged from the colony during that year. The Rock Island Caspian tern colony increased dramatically in 2006 (110 nesting pairs), but subsequently failed due to mink predation on all tern eggs and chicks produced at the colony. Nesting terns were not observed at any other sites on the mid-Columbia River (e.g., Miller Rocks, Three Mile Canyon Island, Sand Island, Nelson Island, Fencepost Island, Richland Island, Island 18, Johnson Island, Cabin Island) during this survey. Caspian terns were seen nesting on Goose Island in Potholes Reservoir, where terns have nested for the last few years. We will continue to fly periodic surveys in these areas looking for nesting terns. For the week, 92% of the identifiable fish delivered to the Crescent Island tern colony (n = 166) were salmonids. The majority of the non-salmonid prey items being delivered to the Crescent Island colony were centrarchids (i.e., bass and sunfish; 3%). Year to date, 75% of the identifiable fish delivered to the Crescent Island tern colony (n = 574) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 79% salmonids in the diet by this time last year.
Avian predation rates often vary by salmonid species, run-type, stock, and rearing type (hatchery vs. wild). Furthermore, predation rates for specific groups of fish can vary greatly from one year to the next. Despite this well-documented variation, limited data are available to determine which biotic and abiotic factors account for differences in smolt vulnerability to avian predators. One method to evaluate the potential intrinsic and extrinsic factors affecting relative vulnerability of smolts to avian predation is to PIT-tag smolts and subsequently recover their tags on bird colonies following the breeding season. This year, we initiated a pilot study whereby run-of-the-river steelhead smolts encountered at the juvenile fish facility at Lower Monumental and Ice Harbor dams on the lower Snake River are PIT-tagged, weighed, measured, photographed (for condition scoring), and released back into the river to resume their out-migration. Following the breeding season, PIT tags will be recovered from various bird colonies in order to test hypotheses concerning how differences in smolt morphology, condition, abundance, origin, river conditions, and dam operations are associated with differences in smolt vulnerability to avian predation. PIT-tagging commenced on 5 April at Lower Monumental Dam and on 10 April at Ice Harbor Dam. This past week, 799 and 82 steelhead smolts were PIT-tagged at Lower Monumental Dam and Ice Harbor Dam, respectively. The majority of fish were in either good (59%) or fair (25%) physical condition, with some fish classified as being in poor (10%) or bad (5%) condition. To date, 1,722 steelhead have been PIT-tagged at either Lower Monumental or Ice Harbor dams as part of this study.
At the East Sand Island tern colony, disturbances by peregrine falcons and bald eagles have decreased significantly as compared to previous weeks. This past week at East Sand Island, a total of 13 colony disturbances were observed (all causes) at a rate of 0.7 disturbances/hr of observation. At Crescent Island this past week, one colony disturbance was observed at the tern colony at a rate of 0.1 disturbances/hr of observation. Generally, disturbances at the tern colony are short, causing terns to flush for only 10-30 seconds before returning to the colony. This past week, gull kleptoparasitism rates at East Sand Island were 5% of all known fates of fish delivered by terns. At Crescent Island, gull kleptoparasitism rates were 4% 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.
On 1 May, Brendan Courtot and Ram Papish visited East Sand Island.
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The first Caspian tern egg of the season on East Sand Island was seen on 19 April. This is 7 days earlier than the first egg was observed on the East Sand Island colony last year, but later than the first-egg dates in 2005 (14 April) and 2004 (16 April).
The high and low on-colony counts for the week on Crescent Island were 568 terns and 500 terns, respectively. The average number of terns counted on-colony this week (543 terns) was lower than counts conducted at the colony during this time last year (701 terns). The first Caspian tern egg of the season on Crescent Island was seen on 19 April, 3 days later than the first egg was observed on the Crescent Island colony last year. 
For the week of 30 April – 6 May, 60% of the identifiable fish delivered to the East Sand Island colony (n = 359 prey items) were salmonids. The majority of the non-salmonid prey items being delivered to the East Sand Island colony were clupeids (i.e., herring or sardines; 14%) and smelt (9%). Year to date, 46% of the identifiable fish delivered to the East Sand Island tern colony (n = 1,117) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 48% salmonids in the diet by this time last year.