Last Updated June 5
Note: The following data are preliminary and may change upon further review.
Colony Counts
Rice Island and Other Upper Estuary Islands
The high and low on-colony counts for the week on Rice Island were on May 31st (2,193 terns) and May 30th (1,586 terns), respectively. This represents a slight decrease (roughly 50 - 175 terns) in both the high and low on-colony counts from the previous week. Gull predation rates on tern chicks continues to be high. Kleptoparasitism and egg predation by American crows has increased significantly on the Rice Island tern colony over the past several weeks.
An aerial photo census of the Rice Island tern colony was carried out on May 31st by BPA and their contractor, Bergman Photographic Services. Direct counts of terns on these photos, along with ground counts of terns in plots, will be used to estimate the number of breeding pairs on the Rice Island tern colony in 2000. The direct count of terns in the aerial photos will not be available for several weeks.
No terns have been observed nesting at other off-colony areas on Rice Island (i.e., East Ridge) or on other upper estuary islands (i.e., Miller Sands Spit and Pillar Rock Sands).
East Sand Island
The high and low on-colony counts for the week on East Sand Island were on May 30th (17,390 terns) and June 2nd (13,740 terns), respectively. On-colony counts were similar this week as compared to last week. The latest on-colony counts indicate that roughly 90% of the total number of terns counted on both the Rice Island and East Sand Island colonies are on East Sand Island.
An aerial photo census of the East Sand Island tern colony was carried out on May 31st, in association with the aerial photo census of the Rice Island colony.
Coastal Sites
Three aerial surveys of other potential Caspian tern colony sites along the coast of Washington were conducted this week (see below). No large aggregations of terns were observed anywhere outside the Columbia River Estuary. It does not appear that terns are nesting anywhere within Willapa Bay or Grays Harbor at this time.
Upriver Sites (Three Mile Canyon and Crescent Islands)
The high and low on-colony counts for the week on Crescent Island were on May 29th (781 terns) and June 2nd (749 terns), respectively. The high and low on-colony counts for the week on Three Mile Canyon Island were on May 29th (295 terns) and June 1st (206 terns), respectively. The number of terns counted at the up-river colonies has declined from the previous week. The decline at the Three Mile Canyon Island tern colony can be partially explained by nest predation activity, primarily on chicks, by a mink. A mink was first spotted on the colony last night (June 4) during an all night watch. The mink has apparently been responsible for the loss of nearly all the tern chicks that have so far hatched on the Three Mile Canyon Island tern colony. About eight tern chicks were still alive this morning and about 50 pairs of terns are still incubating eggs on the colony.
The radio-tagged tern from Rice Island that had been detected on the Crescent Island tern colony is now back on Rice Island. The radio-tagged tern from Rice Island that had been detected on the Three Mile Island tern colony is no longer at that colony.
Diet Composition
For
the week (29 May - 4 June), 56% of the identifiable fish delivered to East Sand
Island were salmonids (N = 354), compared to 96% at Rice Island (N = 391). This
represents a 23% decline from last week in the proportion of salmonids in the
diet of East Sand Island terns, whereas the proportion of salmonids in the diet
of Rice Island terns increased slightly from last week (95%). Year to date,
69% of the identifiable fish delivered to the East Sand Island tern colony were
salmonids (N = 2,629), compared to 93% at Rice Island tern colony (N = 2,410).
The year-to-date total for percent salmonids in the diet of terns nesting on
East Sand Island is similar to the corresponding value from last year (68%).
The year-to-date total for percent salmonids in the diet of terns nesting on
Rice Island is lower than the corresponding value from last year (97%).
At Crescent and Three Mile Canyon islands, 84% (N = 116) and 97% (N = 99) of the identifiable fish delivered to each colony this week were salmonids, respectively. This represents increases of 75% and 70% in the proportion of juvenile salmonids in the diet of terns nesting at Crescent and Three Mile Canyon islands from last week to this week, respectively.
Off-Colony Distribution
Banding and Radio-Tagging
All banding and radio-tagging of adult terns at the Rice Island and East Sand Island colony sites has been completed for this year.
Radio-Tracking and Resightings of Banded Birds
Three
radio-tracking flights were conducted in the Columbia River estuary this past
week (5/29, 5/30, 6/4). A total of 41, 40, and 45 radio-tagged terns (out of
a total of 50 terns radio-tagged at Rice Island) were detected, respectively.
Similar to previous weeks, most observations of terns radio-tagged on the Rice
Island colony were either on the Rice Island (7%) or East Sand Island (92%)
colonies. The one off-colony detection of a tern radio-tagged at Rice Island
was outside the Columbia River Estuary. Year to date, 25 off-colony detections
(45%) of terns radio-tagged at Rice Island were in the upper estuary (above
the Astoria Bridge), 14 off-colony detections (25%) were in the lower estuary
(below the Astoria Bridge), and 17 off-colony detections (30%) were outside
the estuary along the coast.
A total of 27, 24, and 29 radio-tagged terns (out of a total of 30 terns radio-tagged at East Sand Island) were detected, respectively. Similar to detections of the Rice Island radio-tagged terns, most observations of terns radio-tagged at East Sand Island were either on the Rice Island (17%) or East Sand Island (76%) colonies. Of those 5 detections of terns radio-tagged on East Sand Island that were off-colony, 1 off-colony detection (20%) was in the upper estuary (above the Astoria Bridge) and 4 off-colony detections (80%) were outside the estuary along the coast.
Of the 22 radio-tagged terns nesting on East Sand Island that had their nest contents removed, 9 (41%) are primarily in attendance on East Sand Island, 6 (27%) are primarily in attendance on Rice Island, 6 (27%) are moving back and forth between Rice and East Sand islands, and 1 (5%) has gone undetected.
Gull and Predator Control
There have been no signs of mammalian predators on either Rice or East Sand islands. Limited gull control is being carried out at the East Sand Island tern colony to enhance prospects for tern colony restoration at that site. No gulls were shot this week at East Sand Island. So far this season, 37 gulls have been shot on the East Sand Island tern colony. Currently, there are no plans to restrict or eliminate gull control at the East Sand Island tern colony.
Media and Other Visitors
A film crew from 60 Minutes came out onto the Rice Island tern colony on June 2nd to get film footage of terns carrying juvenile salmonids in their bills. The footage was for a story they are doing on Snake River dam breaching. Their visit to the colony was unannounced and was not coordinated with the U.S. Army Corps of Engineers.
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