Last Updated June 21st
Note: The following data are preliminary and may change upon further review.
Caspian Tern Colony Counts East Sand Island The high and low on-colony counts for the week on East Sand Island were 11,040 terns (16 June) and 4,810 terns (16 June), respectively. Black-capped chicks are present on the colony and are beginning to exercise their wings. The annual photo census of the Caspian tern colony on East Sand Island was conducted on 17 May. Visual estimates of colony size from the ground suggest that the East Sand Island colony has declined somewhat since the 2004 nesting season. Once the aerial photos are counted (Fall 2005) we will be able to accurately estimate colony size and determine whether there has been a significant decline in colony size since 2004.
Our weekly boat-based surveys to monitor Pillar Rock Sands, Miller Sands Spit, Rice Island, and other upper estuary dredged material disposal islands looking for early signs of nesting (e.g., scrape digging) have been discontinued; we may check these dredged material disposal islands occasionally, but we do not anticipate the formation of any new colonies this late in the season. Washington Coast (Willapa Bay, Grays Harbor) Aerial surveys for active Caspian tern colonies were conducted along the inner coast of Washington this past week (13 June). Former Caspian tern colony sites at the Port of Tacoma, Port of Seattle, Port of Bellingham, Padilla Bay, and the Fraser River Delta ( British Columbia) were checked, but no active Caspian tern colonies were found. A possible new colony of Caspian terns was located in Skagit Bay near Goat Island, but this observation requires confirmation from the ground. A roof-top Caspian tern colony reported by USDA-Wildlife Services in the Bremerton Naval Shipyard was confirmed. The Caspian tern colony consists of about 130 breeding pairs spread over the roofs of three adjacent warehouses on the waterfront in the shipyard. Glaucous-winged/western gulls are also nesting on these and other roof-tops in the shipyard. The Caspian tern colony at Bremerton Naval Shipyard is the only known active Caspian tern breeding colony along the coast of Washington other than the larger colony at Dungeness National Wildlife Refuge, which we are monitoring under a separate contract with the U.S. Fish and Wildlife Service.
The annual photo census of the Caspian tern colony on Crescent Island was conducted on 17 May. Preliminary visual counts on the ground suggest that the Crescent Island tern colony has declined by about 10% since the 2004 nesting season. Once the aerial photos are counted (Fall 2005) we will be able to accurately estimate colony size and determine whether there has been a significant decline in colony size since 2004. Nesting Caspian terns have not been observed at former colony sites along the Mid-Columbia River at Three Mile Canyon Island (John Day Pool), Miller Rocks (The Dalles Pool), and Cabin Island (Priest Rapids Pool). A small, new Caspian tern breeding colony has been discovered on Rock Island in the Blalock Islands, John Day pool (between the towns of Boardman and Irrigon, Oregon). It only consists of six breeding pairs, and shares the island with nesting California gulls and Forster’s terns (ca. 60 pairs). This small Caspian tern colony has both eggs and small chicks.
For the week, 71% of the identifiable fish delivered to the Crescent Island tern colony (N = 201) were salmonids. Year to date, 75% of the identifiable fish delivered to the Crescent Island tern colony (N = 2,066) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 74% salmonids in the diet at this time last year.
On 19 April and 20 April, net pens were deployed in the forebay of Ice Harbor Dam and in Burbank Slough, respectively. Roughly 650 and 850 PIT-tagged trout were stocked in the Ice Harbor and Burbank Slough net pens, respectively. PIT-tagged fish removed from the net pens by Caspian terns will be used to determine (1) PIT tag deposition rates at the Crescent Island tern colony and (2) vulnerability of fish in different size classes to tern predation. This past week, a total of 13 trout were removed from the Burbank Slough net pen by Caspian terns. In total, Caspian terns have removed 77 trout from the Burbank Slough net pen. On 18 June, we observed Caspian tern foraging activity art the Ice Harbor net pen; two dives were recorded, both unsuccessful. To date, we have not witnessed a Caspian tern remove a fish from the Ice Harbor net pen. We will continue our daily monitoring of the Burbank Slough net pen until late June or early July.
At East Sand Island, four colony disturbances were observed at a rate of 0.4 disturbances/hr of observation. Generally, disturbances of the East Sand Island tern colony by bald eagles have been more frequent and more intense than last year, including observations of eagles preying on adult Caspian terns on or near the colony. During these eagle disturbances, a large proportion of the adult terns on the colony may flush, leaving tern eggs and chicks vulnerable to predation by gulls nesting near the tern colony. At Crescent Island, no colony disturbances were observed this past week.
On 13-16 June, Dave Craig, Paul Swenson, and Jacquelyn Grace from Willamette University visited East Sand Island. Rollin Swenson visited East Sand Island on 16 June. |
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For the week of 13 June – 19 June, 12% of the identifiable fish delivered to the East Sand Island colony (N = 356) were salmonids. The majority of the prey items being delivered to the East Sand Island colony were surfperch (37%) and anchovies (32%). Year to date, 32% of the identifiable fish delivered to the East Sand Island tern colony (N = 3,582) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 22% salmonids in the diet at this time last year. In the last three weeks the percent salmonids in the diet of East Sand Island Caspian terns has declined to the levels seen last year at this time, suggesting that there has been an influx of anchovies and other marine forage fishes into the estuary. 
This past week, gull kleptoparasitism rates were 1% of all known fates of fish delivered by terns at the East Sand Island Caspian tern colony. At Crescent Island, gull kleptoparasitism rates were 2% 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.