Last Updated April 11th
Caspian Tern Colony Preparations
The former tern colony site on Rice Island (roughly 7 acres) is completely vegetated and is unsuitable for tern nesting. Caspian Tern Colony Counts East Sand Island This year the first Caspian tern was observed near the colony at East Sand Island on March 16, when a lone tern was seen roosting on a sand bar at the east end of East Sand Island. Caspian terns were first seen roosting on the colony site on March 26, when 94 terns were on the colony. Daily counts of all terns on the colony site commenced on April 7, when colony monitors moved out to the island. The high and low on-colony counts for the period 7-9 April on East Sand Island were 2,952 terns (April 9) and 582 terns (April 7), respectively. Early breeding behaviors (i.e., nest scrape digging, courtship feeding, copulation) increased in frequency at the colony site throughout the week.
On 8 April, Caspian terns (10) were observed loafing in upland areas on Pillar Rock Sands (a dredged material disposal island in the upper estuary). No breeding behaviors (i.e., courtship displays, exchange of courtship meals, copulations, or digging of nest scrapes) or nest scrapes were observed at this site. During this past week, no terns were observed roosting or attempting to nest in upland areas of Rice Island or Miller Sands Spit (two other dredge material disposal sites in the upper estuary). 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 2006. 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.
Caspian terns were first observed in the vicinity of Crescent Island on March 23, when two terns were seen flying past the island. Caspian terns were first observed roosting on the Crescent Island tern colony on April 5, when a high count of 51 terns was recorded on-colony. Terns have not been observed at other historical nesting sites along the Mid-Columbia River (i.e., Miller Rocks and Three Mile Canyon Island).
Because terns transport whole fish in their bills to their mates (courtship meals) and young (chick meals), taxonomic composition of the diet can be determined by direct observation of adults as they return to the colony with fish (i.e., bill load observations). This past week crew members began fish watch training and beginning next week we will report the diet composition of terns nesting on East Sand Island and Crescent Island.
A total of 2 colony disturbances were observed (unknown causes) at a rate of 0.5 disturbances/hr of observation at the Crescent Island tern colony this past week. To date, there have been no signs of mammalian predators on any of the tern colonies monitored as part of this study.
During March 21-22, USACE personnel (Geoff Dorsey and Jim Beal) were on East Sand Island to prepare suitable tern nesting habitat. Patrick McKann visited East Sand Island on April 1 to erect two observations blinds that he had constructed for us. We would like to thank our field crew and past crew members (Karen Fischer, Brendan Courtot, Anne Mary Myers, Don Lyons, and Garrett Dorsey) for all their hard work in getting blinds built and repaired and other colony preparations completed on East Sand Island this year. |
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In September 2005, the tern colony area on East Sand Island was treated with herbicide, which helped suppress encroaching European beach grass and other invasive vegetation on the colony site over winter. On March 21-22, habitat restoration on the Caspian tern colony site was accomplished by the U.S. Army Corps of Engineers. Similar to the last four years, approximately 6.5 acres of suitable bare sand nesting habitat was prepared at the eastern end of East Sand Island by disking and harrowing the site, and mechanical removal of encroaching grass and other invasive plants. Tern decoys (50) were deployed on the colony site and the entire colony site was marked off with wooden stakes to assist efforts to census and monitor the colony. Severe winter storms destroyed all three of our observations blinds used to collect data at the tern colony. These blinds were rebuilt and were in place at the north, southeast, and southwest ends of the colony by April 1. On April 7, a camp was set up on East Sand Island and will be continuously occupied by two colony monitors throughout the tern breeding season. 
At East Sand Island, bald eagles have been observed at the colony throughout the week, frequently causing terns to take flight. Generally, these disturbances are short, causing terns to flush for only 10-30 seconds before returning to the colony.