Last Updated June 7th
Note: The following data are preliminary and may change upon further review.
Caspian Tern Colony Counts East Sand Island 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 may have 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 change in colony size since 2004.
During this past week, no terns were observed roosting or attempting to nest in upland areas of Pillar Rock Sands, Miller Sands Spit, or Rice Island. Given that the entire former colony site on Rice Island is now vegetated, we do not expect that terns will attempt to nest there in 2005. 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. Washington Coast (Willapa Bay, Grays Harbor) During aerial surveys conducted along the southern Washington coast this past week (30 May), no terns were observed roosting or attempting to nest in upland areas of any of the islands in Willapa Bay or Grays Harbor.
For the week of 30 May – 5 June, 17% of the identifiable fish delivered to the East Sand Island colony (N = 360) were salmonids. The majority of the non-salmonid prey items being delivered to the East Sand Island colony were anchovies (44%) and surfperch (17%). Year to date, 36% of the identifiable fish delivered to the East Sand Island tern colony (N = 2,872) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 23% 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. During the previous week, we supplemented the Burbank Slough net pen with approximately 100 PIT-tagged trout removed from the Ice Harbor net pen. The cover was removed from the Ice Harbor net pen and observations of the pen were reduced to just two hours every other day due to the lack of tern foraging activity at the site.
At East Sand Island and Crescent Island, no colony disturbances were observed during fish-watch, although disturbances were observed at East Sand Island at other times. Colony disturbances, mostly by bald eagles, have been common this year, more so than in previous years. This past week, we observed bald eagles take two adult Caspian terns on the wing, a rarely observed event. 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 1% 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 3-4 June, Michael Wilhelm (freelance photographer) visited the Burbank Slough net pen and Crescent Island. Michael provided us with some wonderful photographs to use in our updates: Thank you Michael! On 30 May – 1 June, Dave Craig, Paul Swenson, and Jacquelyn Grace from Willamette University visited East Sand Island. |
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The high and low on-colony counts for the week on East Sand Island were 14,710 terns (31 May) and 7,900 terns (5 June), respectively. The first tern chick was observed on East Sand Island on 16 May, 3 days later than the first chick was seen on the East Sand Island tern colony in 2004. 
For the week, 69% of the identifiable fish delivered to the Crescent Island tern colony (N = 299) were salmonids. Year to date, 76% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,648) were salmonids (this cumulative percent is an average of the previous weeks’ percentages), the same cumulative percentage as was recorded last year at this time.
This past week, a total of 30 trout were removed from the Burbank Slough net pen by Caspian terns. In total, Caspian terns have removed 50 trout from the Burbank Slough net pen. We recorded no tern activity at the Ice Harbor net pen this past week and have yet to observe a tern remove a fish from that net pen. We will continue our daily monitoring of the Burbank Slough net pen until mid- to late June.