Last Updated June 19
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 12th (1,359 terns) and June 18th (344 terns), respectively. This represents a substantial decrease in both the high and low on-colony counts from the previous week (roughly 750 and 900 terns, respectively). Gull activity on the tern colony has somewhat subsided, apparently because gull predation has nearly eliminated the supply of tern eggs and small chicks. Most of the terns that remain on the colony are caring for larger chicks, which are less susceptible to gull predation than small chicks. As of yesterday (6/18), a total of 92 tern chicks were counted on the Rice Island tern colony. It is possible that some of these chicks may survive to fledging (i.e., capable of flight). Regardless, productivity on the Rice Island tern colony in 2000 will be very low, less than the poor productivity measured in 1997, when only 5% of initiated nests at the Rice Island colony successfully fledged young.
Click here to see the aerial photo of the Rice Island tern colony taken on May 31st. These photos are in the process of being analyzed by the Photogrammetry Department at the Bonneville Power Administration (BPA). These results will not be available for several weeks.
East Sand Island
The
high and low on-colony counts for the week on East Sand Island were on June
12th (15,330 terns) and June 18th (7,070 terns), respectively. This represents a 29% decline in the average number of terns counted
on the colony this week, as compared to last week. This decline in colony attendance at East
Sand Island is at least partly a consequence of the severe storm that occurred
over the previous weekend (June 10 – 11). As we reported last week, this storm caused
extensive chick mortality on the colony. Chick mortality was especially high in
the area between the north and south blinds, where some standing water was observed
late on June 11th after heavy rains. Up to 600 dead chicks were counted on
the colony following the storm, but total losses could have been as high as
1,000 tern chicks. Despite these
losses, productivity of terns nesting on East Sand Island this year will likely
be considerably better than the productivity of terns nesting on Rice Island
in previous years.
The latest on-colony counts indicate that roughly 93% of the total number of terns counted on both the Rice Island and East Sand Island colonies are on East Sand Island.
Click here to see the aerial photo of the East Sand Island tern colony taken on May 31st (see above).
Coastal Sites
One complete aerial survey of other potential Caspian tern colony sites along the coast of Washington was 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 in 2000.
Upriver Sites (Three Mile Canyon and Crescent Islands)
The high and low on-colony counts for the week on Crescent Island were on June 14th (721 terns) and June 16th (639 terns), respectively. The Three Mile Canyon Island tern colony was visited on 6/16 and only 10 adult terns and 5 chicks were counted. As mentioned in the last weekly update, a mink has apparently caused nearly complete nesting failure at the Three Mile Canyon Island tern colony. The few chicks that remain on the Three Mile Canyon Island tern colony are large enough so that they may escape mink predation and fledge.
Diet Composition
For the week (12 June – 18 June), 25% of the identifiable fish delivered to East Sand Island were salmonids (n = 357), compared to 92% at Rice Island (n = 354). This represents a 32% 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 nearly the same. Over the past several weeks the proportion of salmonids in the diet of East Sand Island terns has been steadily declining, while the proportion of salmonids in the diet of Rice Island terns has remained high and constant. We continue to see a much greater diversity of marine fishes at the East Sand Island colony than at the Rice Island colony.
Year to date, 61% of the identifiable fish delivered to the East Sand Island tern colony were salmonids (n = 3,350), compared to 93% at Rice Island tern colony (n = 3,137). The year-to-date totals for percent salmonids in the diet of terns nesting on East Sand and Rice islands are very similar to the corresponding values from last year (61% and 90%, respectively).
At Crescent Island, 75% (n = 187) of the identifiable fish delivered to the colony this week were salmonids, unchanged from the previous week. As we reported last week, diet data can no longer be collected at the Three Mile Canyon Island tern colony due to the nearly complete nesting failure (see above).
Off-Colony Distribution
Radio-Tracking and Resightings of Banded Birds
One complete radio-tracking flight was conducted in the Columbia River estuary this past week. Thirty-two of the 50 terns that were radio-tagged on Rice Island were detected. Of these detections, 3 detections were on the Rice Island colony (9%) and 22 detections were on the East Sand Island colony (69%). Of the 7 off-colony detections of terns radio-tagged at Rice Island, 4 detections were above the Astoria Bridge (57%), 1 detection was below the Astoria Bridge (14%), and 2 detections were outside the estuary along the Washington Coast (29%).
A total of 21 terns radio-tagged on East Sand Island (out of a total of 30 terns) were detected during the aerial survey this past week. Of the these detections, 3 detections were on the Rice Island colony (14%) and 13 detections were on the East Sand Island colony (62%). Of all the off-colony detections of terns radio-tagged at East Sand Island (n = 5), 3 detections were above the Astoria Bridge (60%), 1 detection was below the Astoria Bridge (20%), and 1 detection was outside the estuary along the Washington Coast (20%).
Of the 23 radio-tagged terns nesting on East Sand Island that had their nest contents removed, 12 (52%) are primarily in attendance on East Sand Island, 5 (22%) are primarily in attendance on Rice Island, 5 (22%) are moving back and forth between Rice and East Sand islands, and 1 (4%) is not in attendance at either island. To date, the majority of 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 so far this season. Limited gull control is still being carried out at the East Sand Island tern colony to enhance prospects for tern colony restoration at that site. One gull was shot this past week at East Sand Island, for a total of 40 gulls shot on the East Sand Island tern colony to date this season. The low level of gull control activities over the last few weeks is a reflection of the low level of gull activity on the East Sand Island tern colony, not a reduction in gull control efforts.
Media and Other Visitors
On Friday (6/16), Robert Warren (Sea Resources), Garth Gale (Sea Resources), Vera Gedze (Sea Resources), Joan Jewett (USFWS), Jenny Valdivia (USFWS), and Lee Garnett (Reporter for KPAM) visited the East Sand Island tern colony.
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