Caspian Tern Colony Counts
East Sand Island
 The high and low on-colony counts for the past week on East Sand Island were 14,185 terns and 10,150 terns, respectively. The average number of terns counted on-colony this week (12,419 terns) continues to increase (39% increase as compared to the previous week) and is 20% greater than the number of terns counted on the colony at this time last year (10,368 terns).
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).
Rice Island and Other Upper Estuary Islands
Two surveys were conducted this past week (8 and 12 May) 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 on islands (where terns might nest) in the upper estuary during these surveys. An aerial survey (i.e., on the Columbia River from the mouth to Crimms Island just west of Longview, WA) conducted on 8 May revealed no terns in upland areas on Rice Island, Miller Sands Spit, Pillar Rock Sands, Grassy Island, Fitzpatrick Island, Welch Island, Tenasillahe Island, Puget Island, Wallace Island, and Crimms Island. Terns were observed, however, roosting on the rooftop of a building located near the water just east of the Astoria-Megler Bridge in Astoria, OR. These birds were first observed on 5 May, when terns were seen engaged in courtship feeding at the site and 50-60 Caspian terns were counted on the rooftop along with some roosting gulls. Although Caspian terns have been observed regularly at this site since 5 May (including during the above mentioned aerial survey), terns do not appear to be nesting at the site (i.e., no incubating terns).
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.
Up-river Sites (Crescent Island, Rock Island, and Other Up-river Islands)
The high and low on-colony counts for the week on Crescent Island were 615 terns and 468 terns, respectively. The average number of terns counted on-colony this week (551 terns) was lower than counts conducted at the colony during this time last year (691 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.
During the previous week, 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.
During the above mentioned aerial survey, Caspian terns were also seen nesting on Goose Island in Potholes Reservoir, where terns have nested for the last few years.
Nesting terns have not been 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) so far this year. We will continue to fly periodic surveys in these areas looking for nesting terns.
Diet Composition
 For the week of 7 May – 13 May, 66% of the identifiable fish delivered to the East Sand Island colony (n = 408 prey items) were salmonids. The majority of the non-salmonid prey items being delivered to the East Sand Island colony were anchovies (10%) and clupeids (i.e., herring or sardines; 9%). Year to date, 50% of the identifiable fish delivered to the East Sand Island tern colony (n = 1,525) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 54% salmonids in the diet by this time last year.
For the week, 84% 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; 7%) and perch (6%). Year to date, 76% of the identifiable fish delivered to the Crescent Island tern colony (n = 740) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 80% salmonids in the diet by this time last year.
Relative Vulnerability - Steelhead Tagging Study
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, 804 and 156 steelhead smolts were PIT-tagged at Lower Monumental Dam and Ice Harbor Dam, respectively. The majority of fish were in either good (45%) or fair (41%) physical condition, with some fish classified as being in poor (10%) or bad (4%) condition. To date, 2,682 steelhead have been PIT-tagged at either Lower Monumental or Ice Harbor dams as part of this study.
Predator Activity and Colony Disturbance
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. Generally, disturbances at the tern colony are short, causing terns to flush for only 10-30 seconds before returning to the colony.
There were no disturbances observed at the Crescent Island tern colony this past week.
This past week, gull kleptoparasitism rates at East Sand Island were 3% 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.
Media & Other Visitors
On 10 May, Dick Ledgerwood and Scott Sebring from NOAA Fisheries visited East Sand Island.
On 12 May, Michael Wilhelm and Eric Baker visited East Sand Island. We would like to thank Michael for providing us with many wonderful photos of the birds over the years, including some of those posted in this report.
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