Last Updated June 28th
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 10,110 terns (21 June) and 4,010 terns (24 June), respectively. 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. The first fledgling (i.e., young-of-the-year capable of flight) was observed at the East Sand Island colony on 23 June. Nesting success at the East Sand Island tern colony appears somewhat lower than has been observed in recent years. A second aerial photo census of the colony will be conducted in early July in order to estimate the number of young terns fledged from the East Sand Island colony this year.
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) During an aerial survey of Willapa Bay this past week (23 June), we observed 57, 108, and 72 Caspian terns roosting on Gunpowder Sands, Snag Island, and on the northeast end of Long Beach Peninsula, respectively. In Grays Harbor, we observed 28, 100, and 15 Caspian terns roosting on Sand Island, Cate Island, and an unnamed island near the Hoquium Airport, respectively. The terns observed in Willapa Bay and Grays Harbor were likely post-breeding terns that had dispersed from their nesting colony. During similar surveys in previous years, we have usually seen terns in these areas at this time of year.
The first fledgling (i.e., young-of-the-year capable of flight) was observed at the Crescent Island tern colony on 22 June. Nesting success at the Crescent Island tern colony appears fair so far this year. 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 of 20 June – 26 June, 5% 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 anchovies (49%) and surfperch (36%). Year to date, 30% of the identifiable fish delivered to the East Sand Island tern colony (N = 3,938) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 21% salmonids in the diet at this time last year. In the last four 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.
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 11 trout were removed from the Burbank Slough net pen by Caspian terns. In total, Caspian terns have removed 88 trout from the Burbank Slough net pen. On 22 June, the Ice Harbor net pen was removed from the river; we did not witness a Caspian tern remove a fish from the Ice Harbor net pen this year. We will continue our daily monitoring of the Burbank Slough net pen until 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 roosting on the colony and 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. This past week, no gull kleptoparasitism was observed during fish watch 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. To date, there have been no signs of mammalian predators on any of the tern colonies monitored as part of this study.
On 22 June, Lawrence Laslett visited East Sand Island. |
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The high and low on-colony counts for the week on Crescent Island were 399 terns (22 June) and 240 terns (26 June), respectively. 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. 
For the week, 72% of the identifiable fish delivered to the Crescent Island tern colony (N = 214) were salmonids. Year to date, 74% of the identifiable fish delivered to the Crescent Island tern colony (N = 2,280) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 73% salmonids in the diet at this time last year.