| 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 8,310 terns (April 18) and 3,614 terns (April 14), respectively. Early breeding behaviors (i.e., scrape digging, courtship feeding, copulation) increased in frequency at the colony site throughout the week.
The first Caspian tern egg of the season on East Sand Island was seen on 16 April. This is 7 days earlier than the first egg was laid on the East Sand Island colony last year, and the earliest lay date so far recorded for Caspian terns in the Columbia River estuary. The egg was seen being carried off the tern colony by a glaucous-winged/western gull during a disturbance caused by a bald eagle flying over the tern colony.
Despite heavy rains last week, there has been no standing water observed so far on the tern colony site, unlike some previous years.
Rice Island and Other Upper
Estuary Islands
On April 13, Caspian terns were observed loafing on Pillar Rock Sands (a dredged material disposal island in the upper estuary) in upland areas (13 terns). On April 16, as many as 297 terns were seen on the upland area of Pillar Rocks Sands during low tide. This is significant because if the terns were just loafing near a foraging site they would likely use the beach during low tide. Other indications of their intention to nest on Pillar Rock Sands were courtship displays, exchange of courtship meals, copulations, and the digging of nest scrapes. Resource managers were informed of the situation and the USACE began continuous monitoring and hazing of terns in upland areas on Pillar Rock Sands on April 17.
No aggregations of terns have been observed at upland areas on Rice Island this week, but a group of about 30 Caspian terns was observed on recent dredged material on Miller Sands Spit on 18 April. Given that the entire former colony area on Rice Island is now vegetated, we do not expect that terns will attempt to nest at the former colony site on Rice Island in 2004. We will continue to monitor Rice Island, Pillar Rock Sands, and Miller Sands Spit for early signs of nesting (e.g., nest scrape digging) and will promptly inform resource managers of any such activity.
Up-river Sites (Crescent Island,
Three Mile Canyon Island, Miller Rocks)
 The high and low on-colony counts for the week on Crescent Island were 183 terns (April 16) and 160 terns (April 14), respectively. The first tern egg was observed at the Crescent Island colony on April 12th, 8 days earlier than the first egg date on the Crescent Island tern colony in 2003, and earlier than the first egg date in any previous year of this study.
No terns have been observed at other past or potential Caspian tern colony sites along the mid-Columbia River so far this season.
Diet Composition For the week of April 12 – 18, 8% of the identifiable fish delivered to the East Sand Island tern colony (N = 362) were salmonids. The majority of the prey items being delivered to the East Sand Island colony were clupeids (e.g., herring; 48%) and smelt (24%). Year to date, 8% of the identifiable fish delivered to the East Sand Island tern colony (N = 402) were salmonids (this cumulative percent is an average of the previous weeks' percentages).
For the week, 80% of the identifiable fish delivered to the Crescent Island tern colony (N = 88) were salmonids. Most of the non-salmonids observed being delivered to the Crescent Island colony were centrachids (e.g., bass, sunfish; 18% of total diet).
Predator Activity
At East Sand Island, bald eagles have been observed at the colony throughout the week, frequently causing terns to take flight. A total of 11 colony disturbances were observed (all causes) at a rate of 0.4 disturbances/hr of observation. Generally, these disturbances are short, causing terns to flush for only 10-30 seconds before returning to the colony.
A peregrine falcon caused a disturbance at the Crescent Island tern colony (0.10 disturbances/hr of observation) this past week. The falcon flew high over the colony causing the non-incubating terns to leave the colony while those terns that were on eggs did not take flight. We expect the number of peregrine and eagle disturbances to terns on Crescent Island will decline once migratory waterfowl in the vicinity of Crescent Island leave the area.
One egg was preyed upon by gulls at the Crescent Island tern colony this past week, or 0.1 eggs depredated/hr of observation. Egg predation rate data was not collected at East Sand Island this past week, but a number of tern eggs were removed from the colony by gulls.
This past week, gull kleptoparasitism rates at East Sand Island were 1% of all known fates of fish delivered by terns. At Crescent Island, gull kleptoparasitism rates were 14% 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.
Media & Other Visitors
There were no visitors to the East Sand Island tern colony site this past week.
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