Last Updated June 12
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 June 5th (2,120 terns) and June 11th (1,255 terns), respectively. This represents a decrease (roughly 75 - 350 terns) in both the high and low on-colony counts from the previous week. The colony monitors estimate that no more than 400 active tern nests still remain on the Rice Island colony. Gull kleptoparasitism rates have increased dramatically, and gull predation rates on tern chicks continue to be high. The number of gulls in regular attendance around the Rice Island tern colony has more than doubled over the past few days (from approximately 20 to 45 gulls), apparently in association with the onset of hatching of gull eggs on Rice Island.
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). We do not anticipate any future nesting attempts by terns at these upper estuary sites in 2000.
East Sand Island
The
high and low on-colony counts for the week on East Sand Island were on June
11th (18,190 terns) and June 5th (13,500 terns), respectively. These counts
are similar to the on-colony counts from last week. Terns nesting on East Sand
Island currently occupy all of the available bare sand habitat and there is
very little disturbance by gulls and other nest predators at the colony site.
Heavy rains and high winds over the weekend have caused chick mortality on the
East Sand Island tern colony. At this time it is too early to tell the magnitude
of egg and chick losses on the colony, but these losses appear to be localized,
but significant. The latest on-colony counts indicate that roughly 91% of the
total number of terns counted on both the Rice Island and East Sand Island colonies
are on East Sand Island.
Coastal Sites
Two complete 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 June 7th (795 terns) and June 11th (633 terns), respectively. The high and low on-colony counts for the week on Three Mile Canyon Island were on June 5th (141 terns) and June 8th (28 terns), respectively. As was reported last week, a 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 five tern chicks and one egg were found on the colony on June 10th. We do not expect that there will any terns fledged from the Three Mile Island tern colony this year.
Diet Composition
For the week (5 June - 11 June), 37% of the identifiable fish delivered to East Sand Island were salmonids (n = 364), compared to 96% at Rice Island (n = 373). This represents a 34% 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 is unchanged. Over the past several weeks the proportion of salmonids in the diet of East Sand Island terns has been declining, while the proportion of salmonids in the diet of Rice Island terns remains high. Recently, we have observed a much greater diversity of fishes at the East Sand Island colony than at the Rice Island colony. Sand lance, surf perch, smelt, and sculpin were among the non-salmonid prey fish commonly observed on the East Sand Island colony this past week.
Year to date, 65% of the identifiable fish delivered to the East Sand Island tern colony were salmonids (n = 2,993), compared to 94% at Rice Island tern colony (n = 2,783). The year-to-date totals for percent salmonids in the diet of terns nesting on East Sand and Rice island are very similar to the corresponding values from last year (65% and 95%, respectively). This is especially noteworthy given the shift of the bulk of the tern population from Rice Island to East Sand Island this year, and supports the hypothesis that the prevalence of salmonids in the diet of Rice Island terns is a reflection of the local availability of alternative prey.
At Crescent and Three Mile Canyon islands, 76% (n = 144) and 77% (n = 13) of the identifiable fish delivered to each colony this week were salmonids, respectively. This represents decreases from last week of 10% and 21% in the proportion of juvenile salmonids in the diet of terns nesting at Crescent and Three Mile Canyon islands, respectively. This will probably be the last week that diet data can be collected at the Three Mile Canyon Island tern colony due to the nearly complete nesting failure apparently caused by a mink (see above).
Off-Colony Distribution
Radio-Tracking and Resightings of Banded Birds
Two
complete radio-tracking flights were conducted in the Columbia River estuary
this past week (6/8 and 6/11). A total of 35 and 40 radio-tagged terns (out
of a total of 50 terns radio-tagged at Rice Island) were detected, respectively.
Of the total number of detections of terns radio-tagged on Rice Island (n =
75), 8 detections (11%) were on the Rice Island colony and 52 detections (69%)
were on the East Sand Island colony. Of all the off-colony detections of terns
radio-tagged at Rice Island (n = 15), 2 detections (13%) were above the Astoria
Bridge, 8 detections (53%) were below the Astoria Bridge, and 5 detections (33%)
were outside the estuary along the Washington Coast. We are in the process of
re-analyzing the previously reported off-colony distribution data of radio-tagged
terns. We will present the revised year-to-date totals for off-colony detections
of radio-tagged terns in a subsequent report.
A total of 22 and 24 of the terns radio-tagged on East Sand Island (out of a total of 30 terns) were detected on 6/8 and 6/11, respectively. Of the total number of detections of terns radio-tagged on East Sand Island (n = 46), 4 detections (9%) were on the Rice Island colony and 30 detections (65%) were on the East Sand Island colony. Of all the off-colony detections of terns radio-tagged at East Sand Island (n = 12), 3 detections (25%) were above the Astoria Bridge, 6 detections (50%) were below the Astoria Bridge, and 3 detections (25%) were outside the estuary along the Washington Coast.
Of the 23 radio-tagged terns nesting on East Sand Island that had their nest contents removed, 14 (61%) are primarily in attendance on East Sand Island, 4 (17%) are primarily in attendance on Rice Island, 4 (17%) are moving back and forth between Rice and East Sand islands, and 1 (4%) is not in attendance at either island. To date most of the terns that lost their nest contents on East Sand Island have remained on East Sand Island.
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. Two gulls were shot this past week at East Sand Island, for a total of 39 gulls shot on the East Sand Island tern colony to date. Currently, there are no plans to restrict or eliminate gull control at the East Sand Island tern colony.
Media and Other Visitors
There were no visitors in the field this week.
|
Site developed and maintained by Real Time Research, Inc. |
|
Comments about the site? Contact clientservices@realtimeresearch.org |