Last Updated July 10
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 July 7th (832 terns) and July 3rd (423 terns), respectively. This represents a 11% decrease in the average number of terns counted on the Rice Island tern colony this week, as compared to last week.
Gull activity on the Rice Island tern colony is still down from the levels observed earlier in the season; however, gulls continue to steal chick meals from adult terns (i.e., kleptoparasitism) and prey on tern eggs and chicks. Colony monitors observed 20 eggs and 1 chick taken by gulls this week. These late nesting attempts are presumably by terns that failed in earlier nesting attempts. We expect that terns re-nesting this late in the season will not be successful in rearing young. The chicks that remain on the colony (n = 81) are large enough now that they are relatively safe from predation by gulls. The first young tern was observed flying around the colony (i.e., fledged) on July 4th.
Click here to see an aerial photo of the Rice Island tern colony taken on May 31st.
East Sand Island
The
high and low on-colony counts for the week on East Sand Island were on July
3rd (7,920 terns) and July 5th (6,050 terns), respectively. The average number
of terns counted on the East Sand Island tern colony this week was the same
as the corresponding average from last week (6,980 terns). Young terns continue
to fledge from the East Sand Island colony and are roosting at various off-colony
locations (both on and off East Sand Island). Yesterday, roughly 600 tern fledglings
were counted on the south beach adjacent the East Sand Island tern colony. High
resolution aerial photographs were taken of the East Sand Island tern colony
and surrounding areas on July 6th by Bergman Photographic Services. These photos
will be analyzed in the coming weeks to estimate the number of young produced
at the East Sand Island tern colony in 2000.
The latest on-colony counts indicate that roughly 92% 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 sites along the coast of Washington was conducted this week (see below). In contrast to last week, no large aggregations of terns were observed in Willapa Bay this week. In Grays Harbor, we observed aggregations (somewhat smaller than last week) of terns on No-name Island (120 terns) and Sand Island (200 terns). In contrast to last week, no terns were observed on Cate Island in Grays Harbor this week. Prior to beginning their southern migration to over-wintering grounds, many terns that nested in the estuary will first disperse to coastal sites north and south of the estuary, presumably to feed. On July 6th, Richard Swanston reported seeing a color banded bird (banded this year at Rice Island prior to egg laying) in a group of 46 adult terns in Delta, British Columbia (just south of Vancouver, B.C.). This is the first reported sighting of a tern banded in the Columbia River Estuary in Canada. Dr. Wayne Weber, a biologist in Kamloops B.C., reports having seen 100's of post-breeding Caspian terns with fledged young at various locations in British Columbia from July through September (with peak numbers in August) in previous years. According to Dr. Weber, there are no confirmed breeding records for Caspian terns in British Columbia to date.
Mid-Columbia River Sites (Three Mile Canyon Island and Crescent Island)
The high and low on-colony counts for the week on Crescent Island were on July 7th (275 terns) and July 5th (200 terns), respectively. This represents a 31% decrease in the average number of terns counted on the Crescent Island tern colony this week, as compared to last week. This decline in colony attendance is at least partially attributable to chicks beginning to fledge from the Crescent Island colony. Three Mile Canyon Island was visited on July 5th and no adult terns or chicks were observed at the colony site. No young were produced from the Three Mile Canyon Island tern colony due to mink predation on young chicks and eggs.
Click here to see a map of the up-river tern colony locations.
Inland Washington Sites (Potholes Reservoir, Banks Lake, and Sprague Lake)
Over the past several weeks our up-river crew (Michelle Antolos, Naomi Bargmann, and Chris Couch) has investigated various inland Washington locations (off the Columbia River) looking for active Caspian tern nesting sites. Three nesting sites have been discovered (click here to see map of inland Washington Caspian tern nesting sites). All three of these sites are located east of the mid-Columbia River and north of the Snake River. Solstice Island, located in Potholes Reservoir, was last visited on July 7th, when 143 adult terns and 118 chicks were counted on the colony. On that same date, 44 chicks were color-banded by our crew at the Solstice Island tern colony (see below). Goose Island is located in Banks Lake just above Dry Falls Dam near Coulee City. That colony was last visited on June 29th when 30 adult terns were counted on the colony. No chicks were observed on the Goose Island colony; however, 10 adult terns were apparently incubating eggs (one egg predation event by a gull was observed at this site on June 29th). On July 8th, 35 adult terns and 18 chicks were observed on Harper Island in Sprague Lake. We will continue to investigate other potential Caspian tern nesting sites at inland locations over the next several weeks.
Diet Composition
For the week (3 July – 9 July), 12% of the identifiable fish delivered to East Sand Island were salmonids (n = 370), compared to 91% at Rice Island (n = 358). Compared to the previous week, there was a slight decrease in the proportion of salmonids in the diet of East Sand Island terns (19%) and no change in the proportion of salmonids in the diet of Rice Island terns (91%). Year to date, 51% of the identifiable fish delivered to the East Sand Island tern colony were salmonids (n = 4,473), compared to 93% at the Rice Island tern colony (n = 4,221). The year-to-date total for percent salmonids in the diet of terns nesting on East Sand Island is the same as the corresponding value from last year (51%), whereas the year-to-date total for Rice Island terns is higher this year as compared to last year (80%).
So far this year, terns nesting on East Sand Island have consumed 45% fewer juvenile salmonids than terns nesting on Rice Island.
At Crescent Island, 21% (n = 113) of the identifiable fish delivered to the colony this week were salmonids, representing a 62% decline in the proportion of salmonids in the diet from last week to this week.
During chick banding at Solstice Island on July 7th, 55 PIT tags and 6 radio tags were recovered from the colony. We are in the process of reading the PIT tags to determine where they came from and will report these results in a subsequent update. We expect that these tags came from juvenile salmonids PIT-tagged and released in the upper or mid-Columbia River, at least 30 miles from the colony location.
Radio Telemetry
Nesting Distribution
One complete radio-tracking flight was conducted in the Columbia River estuary this past week. Of the 49 terns that were radio-tagged on Rice Island prior to egg laying, 3 terns are currently nesting on Rice Island (6%), 23 terns are currently nesting on East Sand Island (47%), 12 terns are either not nesting or their nesting status is unknown (24%), and 11 terns were not detected in the survey area (22%). Of those terns radio-tagged on Rice Island whose nesting status is known (n = 26), the majority (88%) is nesting on East Sand Island.
Of the 23 terns radio-tagged on East Sand Island that had the eggs removed from their nests, 4 terns have re-nested on Rice Island (17%), 7 terns have re-nested on East Sand Island (30%), 11 terns have not re-nested or their nesting status is unknown (48%), 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 (n = 11), the majority (64%) re-nested on East Sand Island.
Off-Colony Distribution
The one off-colony detection of a radio-tagged tern currently nesting on Rice Island (n = 7) was outside the Columbia River Estuary along the Washington Coast. Of the 13 off-colony detections of radio-tagged terns currently nesting on East Sand Island (n = 30), 2 detections were above the Astoria Bridge (15%), 4 detections were below the Astoria Bridge (31%), and 7 detections were outside the estuary along the Washington Coast (54%).
Chick Banding
On July 7th, chicks that were near fledging were color-banded at the Crescent Island and Solstice Island tern colonies. Unique color band combinations were placed on the legs of 44 and 69 chicks at Solstice and Crescent islands, respectively. No mortality or injuries occurred to tern chicks during this banding operation. If permitted by the USFWS and ODFW, we plan to color-band up to 350 chicks at the East Sand Island tern colony beginning this week. These marked fledglings will provide important data on survivorship and dispersal patterns of young terns to breeding colonies in future years.
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 (7/7), Charlie Bruce, Holly Michael, Martin Nugent, and Ray Rainbolt
of the Oregon Department of Fish and Wildlife (ODFW), and Shelly McIntyre of
the Oregon State Attorney General's Office visited East Sand Island. Also on
Friday, John Kart, Bob Salinger, Lauren Esserman, and Elizabeth Neely from the
Audubon Society of Portland visited the East Sand Island tern colony. On Thursday
(7/8), Kelsey Collis visited the tern colony on East Sand Island (with great
enthusiasm, I might add).
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