Last Updated April 26th
Caspian Tern Colony Counts East Sand Island In general, terns are delayed in their nesting chronology at East Sand Island this year compared to previous years. High winds, frequent disturbance by bald eagles, and an apparent shortage of available forage fish have resulted in low colony attendance by terns during the day, and even colony abandonment for short periods. When on the colony, the terns are not sitting tight on nest scrapes as they usually are at this time of year. Furthermore, we have yet to observe the first tern egg at East Sand Island in 2006. The first egg dates at East Sand Island over the past 6 years have ranged from 14 April (2005) to 24 April (2000), making this year the latest first egg date yet recorded at this Caspian tern colony. In summary, although the numbers of terns roosting overnight on the colony site are similar to these dates in previous years, nesting behavior and onset of egg-laying are not apace with previous years.
Three surveys were conducted this week (18, 21, and 23 April) looking for nesting terns at dredge disposal sites in the upper estuary; no terns were observed roosting or attempting to nest in upland areas of Rice Island, Miller Sands Spit, Pillar Rock Sands, or Puget Island during these surveys. 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.
On 19 April, Caspian terns were observed on three small islands within the Blalock Islands, which are located in John Day pool between the towns of Boardman and Irrigon, Oregon. Thirty-seven Caspian terns were counted on Rock Island in two separate areas, eight of which appeared to be sitting in nest scrapes. During this same survey another four terns were observed loafing on an unnamed island within the Blalock Islands. Finally, 35 Caspian terns were counted on Sand Island, also within the Blalock Islands, but these birds may have been the same birds counted at Rock Island earlier in the day. As many as six breeding pairs were observed at Rock Island last year and at least one Caspian tern chick was raised to fledging, the first Caspian tern breeding ever recorded on these islands during our study (1997-2006). It appears that terns may attempt to nest on islands within the Blalock Islands again this year. Nesting terns have not been observed at other sites along the Mid-Columbia River (Miller Rocks, Three Mile Canyon Island, Nelson Island, Fencepost Island, Richland Island, Island 18, and Johnson Island).
For the week, 86% of the identifiable fish delivered to the Crescent Island tern colony (N = 159) were salmonids. Year to date, 69% of the identifiable fish delivered to the Crescent Island tern colony (N = 247) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 85% salmonids in the diet by this time last year.
At East Sand Island, bald eagle disturbances at the tern colony were frequent. A total of 6 colony disturbances were observed (all causes) at a rate of 0.3 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 1% 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.
This past week, Ian Rose, a past member of our field crew, volunteered to help with research activities in the Columbia River estuary (thank you, Ian!). |
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The high and low on-colony counts for the week on East Sand Island were 10,410 terns (20 April) and 2,030 terns (21 April), respectively. The high count for this week is 36% higher than during this week last year, although the weekly low counts were comparable between the two years. Strong winds were prevalent at the colony early in the week and filled in most of the existing nest scrapes that breeding terns had previously dug. 
The high and low on-colony counts for the week on Crescent Island were 564 terns (22 April) and 332 terns (17 April), respectively. These counts are similar to those recorded at this colony last year during the comparable week. The first tern egg was laid at the Crescent Island colony on 16 April, four days later than was observed the previous year. 
For the week of 17–23 April, 32% of the identifiable fish delivered to the East Sand Island colony (N = 346) were salmonids. The majority of the prey items being delivered to the East Sand Island colony were salmonids, followed by clupeids (herring and sardines, 27%) and smelt (15%). Year to date, 28% of the identifiable fish delivered to the East Sand Island tern colony (N = 708) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 27% salmonids in the diet by this time last year.