Last Updated April 18th
Caspian Tern Colony Preparations The former tern colony site on Rice Island (roughly 7 acres) is completely vegetated and is unsuitable for tern nesting. Caspian Tern Colony Counts East Sand Island
Two surveys of the upper estuary dredge spoil islands were conducted this past week (4 and 7 April) looking for Caspian terns engaged in pre-nesting behaviors; no terns were observed roosting or attempting to nest in upland areas of Rice Island, Miller Sands Spit, or Pillar Rock Sands during these surveys. We will continue to monitor Rice Island and the other upper estuary dredged material disposal islands for early signs of nesting (e.g., nest scrape digging) and will promptly inform resource managers of any such activity.
Caspian terns were first observed in the vicinity of Crescent Island on 12 March, when 3 terns were seen flying past the island. Caspian terns were first observed roosting on the Crescent Island tern colony on 31 March, when a high count of 20 terns was recorded on-colony. The high and low on-colony counts for this past week on the Crescent Island tern colony were 125 terns (7 April) and 39 terns (3 April), respectively. Terns have not been observed at other historical nesting sites along the Mid-Columbia River (i.e., Rock Island, Miller Rocks, and Three Mile Canyon Island). For the week of 2-8 April, 38% of the identifiable fish delivered to the Crescent Island tern colony (N = 13 prey items) were salmonids. The majority of the prey items being delivered to the Crescent Island colony (54%) were centrachids (primarily smallmouth bass).
At East Sand Island, bald eagles have been numerous on the west end of the island, causing major disturbances to pre-nesting double-crested cormorants. The tern colony, located on the east end of the island, has been relatively undisturbed by bald eagles this past week (0.17 disturbances per hour of observation). We will continue to closely monitor the tern colony for disturbance and other factors that might limit tern colony size and productivity. Prior to 31 March, California gulls and Caspian terns were surprisingly absent from their respective nesting colonies on Crescent Island. Gulls, which generally occupy their nesting territories on Crescent Island before the terns, were seen repeatedly on the water just offshore of Crescent Island. This is unusual behavior for this time of year and suggests that the birds attempting to nest on Crescent Island were disturbed, perhaps by a mammalian or avian predator. Our surveys of Crescent Island for signs of predators, however, turned up no evidence of predator activity on Crescent Island. No mammal tracks have been seen and baited live traps (with the doors wired open) that were set on the island on 30 March have not been entered. We suspect that either a mammalian predator made its way onto the island and has since left or that the disturbance was caused by an avian predator (e.g., bald eagle). Both gulls and terns have since returned to Crescent Island and seem to be behaving normally.
During March 21-23, USACE personnel (Geoff Dorsey and Jim Beal) were on East Sand Island to prepare suitable tern nesting habitat. On 30 March, John Gahr (USFWS) visited Crescent Island. We would like to thank our field crew and former crew members (Brendan Courtot and Don Lyons) for all their hard work in getting blinds built and repaired and other colony preparations completed on East Sand and Crescent islands this year.
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On 21-23 March, habitat restoration was accomplished at the Caspian tern colony site on East Sand Island by the U.S. Army Corps of Engineers. Similar to the last five years, approximately 6.5 acres of suitable bare sand nesting habitat was prepared at the eastern end of East Sand Island by disking and harrowing the site in order to remove encroaching European beach grass and other invasive plants. Tern decoys (50) were deployed on the colony and the entire colony site was marked off with wooden stakes to assist efforts to census and monitor the colony. PIT tags (200) were sown on the tern colony in order to measure the detection efficiency of NOAA Fisheries’ smolt tag recovery efforts after the breeding season. On 5 April, a camp was set up on East Sand Island and will be continuously occupied by two colony monitors throughout the tern breeding season. 
This year the first Caspian terns were observed on East Sand Island on 6 March, when 3 terns were seen roosting on a sand bar to the north of the colony site. Caspian terns were first seen roosting on the colony site on 25 March, when 3 terns were on the colony. Nesting behaviors (i.e., scrape digging, courtship feeding, and copulations) were first observed at the colony on 2 April. Daily counts of all terns on the colony site commenced on 5 April, when colony monitors moved out to the island. The high and low on-colony counts for the past week on East Sand Island were 4,695 terns (8 April) and 428 terns (2 April), respectively. For the first week in April, the average number of terns counted on-colony this year was almost twice what it was last year.
For the week of 2–8 April, 54% of the identifiable fish delivered to the East Sand Island colony (N = 82 prey items) were salmonids. The majority of the non-salmonid prey items being delivered to the East Sand Island colony were surfperch (18%) and sandlance 12%).