Last Updated July 31

Note:  This will be the last weekly update for the 2000 field season.  We plan to provide additional updates on a less frequent basis, including a season summary that we will post in a few weeks. The following data are preliminary and may change upon further review.

Colony Counts

Rice Island & Other Upper Estuary Islands

The high and low on-colony counts for the week on Rice Island were on July 25th (116 terns) and July 24th (64 terns), respectively. This represents a 57% decrease in the average number of terns counted on the Rice Island tern colony this week, as compared to last week. Seven tern chicks were counted on the Rice Island tern colony on July 24th.

This past week we have seen a decrease in the number of terns roosting on islands in the upper estuary.  The largest roosting aggregation of terns in the estuary was down river from Rice Island at Desdemona Sands, near the Astoria Bridge (see map). 

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 24th (2,715 terns) and July 25th (2,025 terns), respectively.  This represents a 24% 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). On average, about 200 tern fledglings were counted on the beaches adjacent to the East Sand Island tern colony this week. 

The latest on-colony counts indicate that roughly 96% 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)

Results from an aerial photo census conducted to estimate of the number of breeding pairs on Rice and East Sand islands in 2000 are now available.  Our best estimates of the number of breeding pairs that attempted to nest on East Sand and Rice islands are 9,456 and 580 pairs, respectively.  This represents a 14% increase in the estimated number of terns nesting in the Columbia River Estuary this year, as compared to last year.  We believe that this increase is due to a combination of recruitment of new breeding adults into the population that were hatched and raised at the Rice Island colony prior to 1998 and adult terns that formerly nested at colonies in California or Nevada that have recently experienced declines.

Coastal Sites

One complete aerial survey of sites along the coast of Washington was conducted this week (see below).  In Willapa Bay, we observed aggregations of terns on Snag Island (roughly 350 terns) and Gunpowder Island (roughly 200 terns).  In Grays Harbor, we observed roughly 400 terns on Sand and No-name islands.  No terns were observed on Cate Island during the aerial survey this week.

Mid-Columbia River Sites (Three Mile Canyon Island and Crescent Island)

Crescent Island was visited on July 27th when 4 adult terns were counted on colony.  This represents a 79% decrease in the average number of terns counted on the Crescent Island tern colony this week, as compared to last week.  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)

We visited the Solstice Island tern colony in Potholes Reservoir (7/26) with biologists from the Douglas County Public Utility District (Shane Bickford, Rick Klinge, and Jim McGee) to recover PIT tags from the colony (see below). As with our previous visit (7/19), no terns were observed on the colony site. 

The tern colonies in Banks and Sprague lakes were not visited this week.

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 map of the inland Washington tern colonies.

Inland Oregon Sites (Crump Lake and Malheur Lake)

Over the past several weeks Ken Collis has investigated various inland Oregon locations (off the Columbia River) looking for active Caspian tern nesting sites. Caspian tern breeding colonies were discovered in the Warner Valley in Southern Oregon near Lakeview, Oregon and in the Malheur National Wildlife Refuge in Eastern Oregon near Burns, Oregon. The Warner Valley tern colony is located on Piper Island in the northern end of Crump Lake.  This site was visited on July 21st, when roughly 250 adult terns and 50 chicks were counted on the colony.  Chicks were on average 1-2 weeks old, while some terns were still incubating eggs.  In previous years, tern breeding was reported on Pelican Lake, which is just south (<10 miles) of Crump Lake. On July 21st, terns were not nesting on Pelican Lake.  To our knowledge, this represents the first documented breeding of terns on Crump Lake. 

On July 27th, Ken accompanied Meg Laws (biologist working at the Malheur National Wildlife Refuge) on a survey of nesting terns in Malheur Lake.  Caspian tern colonies were discovered on two unnamed islands on the north end of the lake.  These colonies were roughly the same size (100-150 breeding pairs) but differed in their nesting chronology.  The first colony had chicks that were on average 3 weeks old, while the other colony had terns on eggs and chicks that were only a few days old.  It's possible that the terns on the colony having the earlier chronology are re-nesting after having failed at another colony location, perhaps due to receding water levels providing a land bridge for mammalian predators on the mainland.  Unlike all the other tern colonies we have reported on thus far (i.e., terns nesting on bare substrate), the terns in Malheur Lake are nesting on low-lying vegetation (salt grass) and, in some cases, have situated their nests amidst dense vegetation.

All colonies discovered in inland Oregon are on shallow lakes (1-6 feet deep) and in each case the nesting chronologies are behind those tern colonies located on the Columbia River and in inland Washington, off the Columbia River. 

Diet Composition

For the week (24 July - 30 July), 17% of the identifiable fish delivered to East Sand Island were salmonids (n = 352), compared to 82% at Rice Island (n = 296).   The proportion of salmonids in the diet of terns on East Sand and Rice islands was similar this week, as compared to last week.  Year to date, 44% of the identifiable fish delivered to the East Sand Island tern colony were salmonids (n = 5,539), compared to 91% at the Rice Island tern colony (n = 5,241).  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 (44%), whereas the year-to-date total for Rice Island terns is higher this year as compared to last year (75%).

So far this year, terns nesting on East Sand Island have consumed 52% fewer juvenile salmonids than terns nesting on Rice Island.  On this date last year, the terns nesting on East Sand Island had consumed 41% fewer juvenile salmonids that terns nesting on Rice Island.

On July 26th, we (see above) recovered 716 PIT tags, 48 radio tags, and 7 acoustic tags from the Solstice Island tern colony in Potholes Reservoir.  In total (i.e., including tag recoveries on July 7th), 771 PIT tags, 52 radio tags, and 9 acoustic tags were recovered at the Solstice Island tern colony. We are in the process of getting the release and interrogation records associated with each of the tags and will report these results in a subsequent update.

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%), 9 terns are currently nesting on East Sand Island (18%), 18 terns are either not nesting or their nesting status is unknown (37%), and 19 terns were not detected in the survey area (39%).  Of those terns radio-tagged on Rice Island whose nesting status is known (n = 12), the majority (75%) is nesting on East Sand Island.

Of the 23 terns radio-tagged on East Sand Island that had the eggs removed from their nests, 3 terns have re-nested on Rice Island (13%), 4 terns have re-nested on East Sand Island (17%), 8 terns have not re-nested or their nesting status is unknown (35%), and 8 terns were not detected in the survey area (35%).  Of those terns radio-tagged on East Sand Island that had their nest contents removed and whose nesting status is known (n = 7), the majority (57%) re-nested on East Sand Island.

Off-Colony Distribution

Of the 3 off-colony detections of radio-tagged terns currently nesting on Rice Island (n = 6), 1 detection was above the Astoria Bridge, 1 detection was below the Astoria Bridge, and 1 detection was outside the estuary along the Washington Coast.  Of the 2 off-colony detections of radio-tagged terns currently nesting on East Sand Island (n = 13), 1 detection was above the Astoria Bridge and 1 detection was below the Astoria Bridge. 

Gull & 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 & Other Visitors

On Monday (7/24), Reid Carscadden, Allison Reak, Michael Shaw, and Brad Theil of Landau Associates, along with Tom Poe and Stan Smith visited the East Sand and Rice island tern colonies. On Tuesday (7/25), Dean Schwickerath, President of the Audubon Society of Grays Harbor, and two members of the board visited Cate Island in Grays Harbor.  On Wednesday (7/26), Deborah Jaques, Charlie Stenvall, and Dave Pitkin from the U.S. Fish and Wildlife Service visited East Sand Island.  Also on Wednesday, Shane Bickford, Rick Klinge, and Jim McGee from Douglas County PUD visited the Solstice Island tern colony in Potholes Reservoir. 

Thanks to the Field Crew

As mentioned earlier in this report, this will be our last weekly update for the 2000 field season.  We would like to take this opportunity to thank all of the field biologists we had working with us this season.  Their passion, dedication, and hard work contributed greatly to the success of our research and monitoring efforts.