Last Updated June 5th
Caspian Tern Colony Counts East Sand Island The high and low on-colony counts for the past week on East Sand Island were 16,495 terns and 10,450 terns, respectively. The annual photo census of the Caspian tern colony on East Sand Island was conducted on 23 May. Once the aerial photos are counted (Fall 2007) we will be able to accurately estimate colony size and determine whether there has been a significant change in colony size since 2006. The first Caspian tern chick of the season on East Sand Island was seen on 27 May. This is 4 days later than the first chick was observed on the East Sand Island colony last year, which previous to this year, was the latest first-chick date we have observed at the East Sand Island tern colony. The late first-chick date this year was apparently due to early nests failing because of gull predation on tern eggs.
Two boat-based surveys were conducted this past week (31 May and 2 June) looking for nesting terns at dredged material disposal sites in the upper estuary. During these surveys, no terns were observed roosting or attempting to nest in upland areas of Pillar Rock Sands, Miller Sands Spit, or Rice Island. The total number of terns roosting at sites in the upper estuary has declined considerably from what was observed earlier in the season. We will continue to monitor Rice Island and the other upper estuary dredge disposal islands for early signs of nesting (e.g., nest scrape digging) and will promptly inform resource managers of any such activity.
The first Caspian tern chick hatched at the Crescent Island colony on 16 May, 8 days later than the first chick hatched on the Crescent Island colony last year. This past week (31 May and 1 June) we conducted aerial surveys of the mid-Columbia River from The Dalles Dam to just above Priest Rapids Dam, the lower Snake River from the confluence with the Clearwater River to its mouth, and areas off the mid-Columbia at Sprague Lake, Banks Lake, and Potholes Reservoir searching for incipient Caspian tern colonies. During this survey Caspian terns were observed on Rock Island (located on the mid-Columbia River in the John Day Pool), Harper Island (located in Sprague Lake, which is roughly 50 miles east of Moses Lake), Dry Falls Island (located in Banks Lake near Coulee City), and on Goose Island (in Potholes Reservoir). Although counts of terns in aerial photos taken during this survey were not available at the time of this report, nesting by Caspian terns has been confirmed at all of these sites, with the exception of Harper Island, where 50 terns were observed loafing on cliffs at the north side of the island. Recent boat surveys at Rock Island and Dry Falls Island suggest that as many as 24 and 18 terns were nesting at the two islands, respectively. In previous years terns have attempted to nest at all of the sites mentioned above.
Adult Banding
One adult tern was injured and 44 tern eggs were lost (most due to gull predation) as a result of the above-mentioned banding operations. The injured adult tern was taken to the North Coast Wildlife Rehabilitation Center in Astoria. We expect this bird to be rehabilitated for release back into the wild. The capture of adult terns for banding at East Sand Island is now completed for the 2007 breeding season. Adult terns will not be banded at the Crescent Island colony in 2007.
Avian predation rates often vary by salmonid species, run-type, stock, and rearing type (hatchery vs. wild). Furthermore, predation rates for specific groups of fish can vary greatly from one year to the next. Despite this well-documented variation, few data are available to determine which biotic and abiotic factors account for differences in smolt vulnerability to avian predators. One method to evaluate the potential intrinsic and extrinsic factors affecting relative vulnerability of smolts to avian predation is to PIT-tag smolts and subsequently recover their tags on bird colonies following the breeding season. This year, we initiated a pilot study whereby run-of-the-river steelhead smolts encountered at the juvenile fish facilities at Lower Monumental and Ice Harbor dams on the lower Snake River are PIT-tagged, weighed, measured, photographed (for condition scoring), and released back into the river to resume their out-migration. Following the breeding season, PIT tags will be recovered from various bird colonies in order to test hypotheses concerning how differences in smolt morphology, condition, abundance, origin, river conditions, and dam operations are associated with differences in smolt vulnerability to avian predation. This past week, 607 and 131 steelhead smolts were PIT-tagged at Lower Monumental Dam and Ice Harbor Dam, respectively. The majority of fish were in either excellent (44%) or good (42%) physical condition, with some fish classified as being in fair (12%) or poor (2%) condition. To date, 5,748 steelhead have been PIT-tagged at either Lower Monumental or Ice Harbor dams as part of this study.
This past week at East Sand Island, a total of 7 colony disturbances were observed (all causes) at a rate of 0.4 disturbances/hr of observation. Generally, disturbances at the tern colony are short, causing terns to flush for only 10-30 seconds before returning to the colony. There were no disturbances observed at the Crescent Island tern colony this past week. This past week, gull kleptoparasitism rates at East Sand Island were 3% of all known fates of fish delivered by terns. At Crescent Island, gull kleptoparasitism rates rose dramatically this past week to 11% of all known fates of fish delivered by terns (only 3% the previous week), presumably associated with the increase in the number of larger fish, primarily steelhead smolts, being brought to the colony to feed larger chicks. 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 28 May, Matt Tennis (ODFW) visited East Sand Island. On 29 May, Laura Cooke, a manager from the Columbia Basin Wildlife Area, accompanied us on our survey of Sprague Lake. |
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The high and low on-colony counts for the week on Crescent Island were 485 terns and 407 terns, respectively. Counts of incubating or brooding adult terns on the Crescent Island colony indicate that about 355 pairs of Caspian terns attempted to nest at the colony this year. This represents about a 21% decline in the size of the colony compared to 2006, when about 450 pairs nested on Crescent Island. 
