Last Updated July 24
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 21st (334 terns) and July 23rd (83 terns), respectively. This represents a 58% decrease in the average number of terns counted on the Rice Island tern colony this week, as compared to last week. All but 3 tern chicks have fledged from the Rice Island tern colony as of Sunday, July 23rd.
This past week we have seen an increase in the number of terns roosting on islands in the upper estuary. During an aerial survey conducted on July 17th, 200 and 75 terns were observed roosting on Wallace Island and Miller Sands Spit, respectively.
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
18th (3,840 terns) and July 22nd (2,415 terns), respectively. This represents
a 38% decrease in the average number of terns counted on the East Sand Island
tern colony this week, as compared to last week. Adult and fledgling terns continue
to disperse from the East Sand Island colony and are roosting at various off-colony
locations (both on and off East Sand Island). Yesterday, roughly 520 tern fledglings
were counted on the beaches (north and south) adjacent the East Sand Island
tern colony.
The latest on-colony counts indicate that roughly 94% 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
Two complete aerial surveys of sites along the coast of Washington were conducted this week (see below). The number and size of tern post-nesting aggregations along the Washington coast increased in comparison to last week. In Willapa Bay, we observed aggregations of terns on Snag Island (roughly 400 terns) and Gunpowder Island (roughly 100 terns). In Grays Harbor, we observed a total of about 1,500 terns on various islands (i.e., Cate Island, Sand Island, and No-name Island).
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 20th (24 terns) and July 17th (15 terns), respectively. This represents a 43% 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 attributable to chicks continuing to fledge from the Crescent Island colony. Three Mile Canyon Island was not visited this week. No young were produced from the Three Mile Canyon Island tern colony this season 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)
Our up-river crew (Michelle Antolos and Naomi Bargmann) visited the Solstice Island tern colony in Potholes Reservoir on 7/19 and reported that the colony had been abandoned. There was evidence of considerable human disturbance on the colony site (footprints, dog tracks, fire pits, spent fireworks) since our crew last visited the colony on 7/7.
On 7/19, only one tern was observed on the Goose Island tern colony in Banks Lake. Just three weeks prior, 30 terns had been observed on the Goose Island colony, 10 of which were incubating eggs. It appears that no young will be produced from the Goose Island tern colony this season. One tern fledgling that was banded on Crescent Island on 7/7 was observed foraging near the Goose Island colony site.
No new Caspian tern colony sites were discovered in Eastern Washington this week. Our surveys of inland Washington suggest that Solstice Island in Potholes Reservoir, Goose Island in Banks Lake, and Harper Island in Sprague Lake are the only sites where Caspian terns attempted to breed in Eastern Washington off the Columbia River.
Click here to see a map of the inland Washington tern colonies.
Diet Composition
For the week (17 July - 23 July), 14% of the identifiable fish delivered by adult terns to the East Sand Island colony were salmonids (n = 352), compared to 84% at the Rice Island tern colony (n = 350). Compared to last week, there was no change in the proportion of salmonids in the diet of terns at the East Sand Island and Rice Islands colonies. Year to date, 46% of the identifiable fish delivered by terns to the East Sand Island colony were salmonids (n = 5,187), compared to 91% at the Rice Island tern colony (n = 4,945). 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 (46%), whereas the year-to-date total for Rice Island terns is higher this year as compared to last year (76%).
So far this year, terns nesting on East Sand Island have consumed 49% fewer juvenile salmonids than terns nesting on Rice Island.
At Crescent Island, 19% of the identifiable fish delivered by adult terns to the colony this week (n = 57) were juvenile salmonids, less than half the proportion of salmonids in the diet from last week.
Last week we reported collecting 55 PIT tags from the Solstice Island tern colony in Potholes Reservoir (see map ).
Radio Telemetry
Nesting Distribution
Two complete radio-tracking flights were 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%), 12 terns are currently nesting on East Sand Island (24%), 20 terns are either not nesting or their nesting status is unknown (41%), and 14 terns were not detected in the survey area (29%). Of those terns radio-tagged on Rice Island whose nesting status is known (n = 15), the majority (80%) are 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%), 5 terns have not re-nested or their nesting status is unknown (22%), and 7 terns were not detected in the survey area (30%). 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
Of the 12 off-colony detections of radio-tagged terns currently nesting on Rice Island (n = 7), 7 detections were above the Astoria Bridge (58%), 2 detections were below the Astoria Bridge (17%), and 3 detections were outside the estuary along the Washington Coast (25%). Of the 13 off-colony detections of radio-tagged terns currently nesting on East Sand Island (n = 19), 2 detections were above the Astoria Bridge (15%), 6 detections were below the Astoria Bridge (46%), and 5 detections were outside the estuary along the Washington Coast (38%).
Fledgling Tern Banding
On
July 17, 120 fledglings were banded at the East Sand Island tern colony. Each
fledgling was banded with a numbered U.S. Fish and Wildlife Service metal leg
band. Of the 120 chicks that were banded, 111 were also banded with unique color
combinations of plastic leg bands. No mortality occurred to tern fledglings
during the banding operation, but one fledgling was injured (i.e., abrasions
on upper legs) while in the pheasant boxes. Three fledglings that were banded
last week (July 12-13) were found dead on the colony this week. In total, 340
chicks were banded on the East Sand Island tern colony. These marked fledglings
will provide important data on juvenile survivorship, recruitment, and dispersal
patterns of young terns to breeding colonies.
Gull and Predator Control
There have been no signs of mammalian predators on either Rice or East Sand islands so far this season. 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.
Media and Other Visitors
On Saturday (7/22), Jeff Fryer (Columbia River Inter-Tribal Fish Commission) visited the East Sand Island tern colony.
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