Last Updated June 26
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 22th (832 terns) and June 21st (391 terns), respectively. This represents a 28% decline in the average number of terns counted on the Rice Island tern colony this week, as compared to last week. Gull activity on the tern colony has subsided dramatically, 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. We estimate that 90 tern chicks remain on the Rice Island tern colony.
Click here to see an 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
20th (9,890 terns) and June 21st (5,310 terns), respectively. This represents
a 32% decline in the average number of terns counted on the East Sand Island
tern colony this week, as compared to last week. This large decline in colony
attendance is attributable to three factors: (1) terns that lost their eggs
or young during the severe storm on June 11 have dispersed from the East Sand
Island colony, (2) most terns nesting on East Sand Island are currently feeding
half grown chicks whose large appetites require more foraging time away from
the colony, and (3) most tern chicks are old enough that their parents leave
them unattended on the colony. Estimates of the number of tern chicks on the
East Sand Island colony are 7 – 9,000 chicks. This represents about 1.1
chicks per active tern nest.
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 an 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 19th (593 terns) and June 24th (438 terns), respectively. The Three Mile Canyon Island tern colony was visited on 6/23 and no adult terns or chicks were observed on the colony. As mentioned in the previous weekly update, a mink has apparently caused complete nesting failure at the Three Mile Canyon Island tern colony.
Diet Composition
For the week (19 June – 25 June), 19% of the identifiable fish delivered to East Sand Island were salmonids (n = 385), compared to 86% at Rice Island (n = 368). This represents 24% and 6% declines from the previous week in the proportion of salmonids in the diet of East Sand Island and Rice Island terns, respectively. 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. This week represents the first notable decline in the proportion of salmonids in the diet of Rice Island terns. Of the non-salmonid fish observed at the Rice Island tern colony this week, most were surf perch and herring, suggesting that Rice Island terns are beginning to forage more on marine fish, as compared to previous weeks.
Year to date, 58% of the identifiable fish delivered to the East Sand Island tern colony were salmonids (n = 3,735), compared to 93% at Rice Island tern colony (n = 3,505). The year-to-date totals for percent salmonids in the diet of terns nesting on East Sand Island are very similar to the corresponding values from last year (57%), whereas the year-to-date total for Rice Island terns is higher this year as compared to last year (86%).
At Crescent Island, 61% (n = 204) of the identifiable fish delivered to the colony this week were salmonids, representing a 19% decline in the proportion of salmonids in the diet from last week to this week.
Radio Telemetry
Nesting Distribution
One complete radio-tracking flight was conducted in the Columbia River estuary this past week (6/19). Of the 49 terns that were radio-tagged on Rice Island prior to egg laying, 3 terns are currently nesting on Rice Island (6%), 18 terns are currently nesting on East Sand Island (37%), 26 terns are either not nesting or their nesting status is unknown (53%), and 2 terns were not detected in the survey area (4%). Of those terns radio-tagged on Rice Island whose nesting status is known, the majority (86%) are nesting on East Sand Island.
Of the 23 terns radio-tagged on East Sand Island that had their nest contents removed (i.e., eggs), 1 tern has re-nested on Rice Island (4%), 4 terns have re-nested on East Sand Island (17%), 17 terns have not re-nested or their nesting status is unknown (74%), and 1 tern was not detected in the survey area (4%). Of those terns radio-tagged on East Sand Island that had their nest contents removed and whose nesting status is known, the majority (80%) re-nested on East Sand Island.
Off-Colony Distribution
Of the 2 off-colony detections of radio-tagged terns currently nesting on Rice Island (n = 4), both were above the Astoria Bridge. Of the 9 off-colony detections of radio-tagged terns currently nesting on East Sand Island (n = 24), 3 detections were above the Astoria Bridge (33%), 2 detections were below the Astoria Bridge (22%), and 4 detections were outside the estuary along the Washington Coast (44%).
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. No gulls were 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 (6/23), Adrienne Wolf-Lockett (Portland Audubon), Eve Gilbert, Eric Apalateui (Longview Daily News), Bill Wagner (Longview Daily News), and John Fialka (Wall Street Journal) visited the East Sand Island tern colony. On Saturday (6/24) and Sunday (6/25), Mike Wilhelm (freelance photographer) visited the East Sand Island tern colony.
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