Last Updated May 24th
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. 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.
Nesting Caspian terns have not been observed at other potential colony sites along the Mid-Columbia River, including the former colony sites at Three Mile Canyon Island and Miller Rocks. Inland Washington Sites off the Columbia River ( Sprague Lake and Banks Lake) This past week, 15 adult terns were observed on Harper Island in Sprague Lake ( approximately 50 miles east of Moses Lake on I-90). During a survey of Banks Lake (just above Dry Falls Dam near Coulee City) this past week, 11 and 19 adult terns were counted on Dry Falls Island and Goose Island, respectively. Caspian terns have nested on Sprague Lake and Banks Lake in previous years and appear to be nesting there again this year as evidenced by terns sitting tightly on nest scrapes at each site.
For the week, 68% of the identifiable fish delivered to the Crescent Island tern colony (N = 163) were salmonids. Year to date, 79% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,104) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 78% salmonids in the diet by 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. Since fish were stocked in the net pens, Caspian terns have removed five fish from the Burbank Slough net pen; terns have yet to forage on fish held within the Ice Harbor net pen, although terns have been observed foraging in the vicinity of the pen. The number of fish removed by Caspian terns from the Burbank Slough net pen this year is considerably down from last year at this time (N = 45), perhaps due to greater turbidity in the slough or higher food availability this year as compared to last year. Terns are commonly observed trying to forage in the vicinity of the Burbank Slough net pen but are not plunge diving, presumably because they are having difficult spotting the fish both inside and outside the pen. In the coming weeks, we will try to increase the density of fish within the net pen as a way to increase the number of fish removed by terns from the net pen.
On 18-19 May, 31 breeding adult terns were captured on the East Sand Island colony late in the incubation period using noose-mat traps placed over active nests. Each captured adult was weighed, measured, banded, and force-fed one fish (5-9 cm in length) containing one or two PIT tags. All fish were certified, disease-free triploid trout obtained from the Trout Lodge Hatchery, WA. Following sampling and force-feeding terns were released back onto the colony. Individually marked terns were observed following release to determine if and when normal on-colony behavior was resumed. Of the 31 terns that were force-fed fish, 100% successfully ingested the fish, and most (29 or 95%) returned to the colony to resume normal breeding behaviors within 6 hours following release. A total of 46 tern eggs were lost as a result of this research activity, the majority (40 eggs) due to depredation by gulls. Adult terns crushing eggs while captured by the noose mats (N = 3 eggs) and researchers inadvertently damaging eggs when trying to quickly free adult terns from the traps (N = 2 eggs) were other known causes of egg loss. No adult terns were injured during this experiment. The capture of adult terns for force-feeding experiments at Crescent and East Sand islands is now completed for the 2005 breeding season. Following the breeding season and after all the terns have left their respective colonies, East Sand and Crescent islands will be scanned for PIT tags by NOAA Fisheries and the proportion of force-fed tags that are detected on-colony will be determined. Predator Activity At East Sand Island, a total of 16 colony disturbances were observed at a rate of 0.9 disturbances/hr of observation. These disturbance data for the East Sand Island tern colony do not include disturbances associated with efforts to catch adult terns for the force feeding experiment. Generally, disturbances at the tern colony are short, causing terns to flush for only 10-30 seconds before returning to the colony. At Crescent Island, no colony disturbances were observed this past week. This past week, gull kleptoparasitism rates at East Sand Island were 2% of all known fates of fish delivered by terns. 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 17-18 May, David Craig from Willamette University visited East Sand Island. |
Site developed and maintained by Real Time Research, Inc. |
Comments about the site? Contact clientservices@realtimeresearch.org |
The high and low on-colony counts for the week on East Sand Island were 13,810 terns (16 May) and 8,750 terns (22 May), 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. Evening on-colony counts of terns on East Sand Island have declined this past week as compared to the previous week and are likely due to an increase in the number of colony disturbances caused by bald eagles, heavy rains that led to standing water on the colony, and the researcher-caused disturbance associated with the force feeding experiment (see below), all occurring this past week. 
For the week of 16 May – 22 May, 53% of the identifiable fish delivered to the East Sand Island colony (N = 339) were salmonids. The majority of the non-salmonid prey items being delivered to the East Sand Island colony were anchovies (17%) and clupeids (e.g., herring; 10%). Year to date, 39% of the identifiable fish delivered to the East Sand Island tern colony (N = 2,144) 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; consequently, there has been a 70% increase in the proportion of salmonids in the diet so far in 2005 compared to 2004 . 
The recovery of PIT tags on piscivorous waterbird colonies has been used as a direct measure of predation rates on ESA-listed salmonid populations from the Columbia and Snake rivers. Predation rates based on PIT tag recoveries are, however, underestimates; some proportion of tags consumed by terns is deposited off-colony, weather and other environmental factors remove PIT tags that are deposited on-colony, and some PIT tags are damaged and rendered unreadable before or after egestion on the colony. Understanding the magnitude of the bias in estimates of tern predation on smolts based on PIT tag recoveries on-colony is critical for deriving ESU-specific tern predation rates. One method we are using to estimate deposition rates is to force-feed PIT-tagged fish to adult terns captured on the East Sand Island and Crescent Ihsland tern colonies and then determine the proportion of force-fed tags that are subsequently deposited at each colony.