Last Updated August 1st
Note: This will be the last weekly update for the 2006 field season. We plan to provide additional updates on a less frequent basis, including a season summary that will be posted in the coming months. The following data are preliminary and may change upon further review. Caspian Tern Colony Counts East Sand Island
The first fledgling (i.e., young-of-the-year capable of flight) was observed at the East Sand Island colony on 28 June. As a result of a large number of failed nesting attempts early in the season and the subsequent renesting of failed breeders, nesting at the East Sand Island tern colony is more asynchronous than in most previous years. It appears that many of these renesting attempts have failed, especially during the past several weeks. A second aerial photo census of the colony was conducted on 7 July. Once these aerial photos are counted (Fall 2006) we will be able to accurately estimate the number of young terns fledged from the East Sand Island colony this year.
No active Caspian tern nests (nest scrapes containing eggs) were detected at any of the upper estuary dredge disposal sites (i.e., Rice Island, Miller Sands Spit, or Pillar Rock Sands) this year, and we do not anticipate the formation of any new colonies this late in the breeding season.
No evidence of nesting Caspian terns along the southwest coast of Washington (i.e., Willapa Bay, Grays Harbor) was detected this year, and we do not anticipate the formation of any new colonies this late in the breeding season. The Caspian tern nesting colony at Dungeness National Wildlife Refuge on the Strait of Juan de Fuca increased in size again in 2006. Once aerial photos have been analyzed later this year a more precise estimate of colony size and nesting success will be available. We are monitoring this colony under a separate contract with the U.S. Fish and Wildlife Service. A roof-top Caspian tern colony in Bremerton Naval Shipyard was confirmed again this nesting season. The Caspian tern colony was again spread over the roofs of three adjacent warehouses on the waterfront in the shipyard, and had grown since the 2005 nesting season to several hundred nesting pairs. A more precise estimate of the size of this colony will be available later this year once aerial photos have been counted. Glaucous-winged/western gulls were also nesting on these and other roof-tops in the shipyard. The Caspian tern colonies at Dungeness National Wildlife Refuge and at Bremerton Naval Shipyard are the only known active Caspian tern breeding colonies along the inner coast of Washington. Former Caspian tern colony sites at the Port of Tacoma, Port of Seattle, Everett Naval Base, Port of Bellingham, and Padilla Bay were checked, but no active Caspian tern colonies were found.
The high and low on-colony counts for the week on Crescent Island were 14 terns (24 July) and 1 tern (24 July), respectively. Most terns have now dispersed from the island. Earlier counts of incubating or brooding adult terns on the Crescent Island colony indicate that about 450 pairs of Caspian terns attempted to nest at the colony this year. This represents about a 5% decline in the size of the colony compared to 2005, when about 475 pairs nested on Crescent Island. The first fledgling was observed on Crescent Island on 14 June, eight days earlier than was observed last year. The number of fledgling terns raised on the Crescent Island tern colony this year was only about 191, or about 0.4 young raised per breeding pair, the lowest nesting success we have ever observed at Crescent Island. On 30 May an aerial survey of Rock Island, one of the Blalock Islands in John Day Pool, revealed that about 110 pairs of Caspian terns were nesting on the island, along with about 200 pairs of ring-billed gulls. At that time the nesting Caspian terns were attending either eggs or chicks. This was a major increase in the size of this Caspian tern colony compared to last year, when only about 6 pairs of Caspian terns attempted to nest on Rock Island. On 18 June, however, when Rock Island was revisited, the Caspian tern colony had experienced complete nesting failure. There were no adult terns attending either eggs or chicks. Dead tern and gull chicks that had died at least 10 days earlier were scattered over the colony. Although 35 dead adult ring-billed gulls were counted on the colony, no dead adult Caspian terns were found. One ring-billed gull carcass and 56 Caspian tern eggs were found cached in a hollow log located near the colony. All the evidence indicated that the colony failure was caused by an American mink. The mink nearly caused complete nesting failure for the ring-billed gull colony as well; only one chick survived and 5-10 pairs of ring-billed gulls had renested on the island and were sitting on eggs on 18 June. With the exception of Rock Island, nesting Caspian terns have not been observed at other potential colony sites along the Mid-Columbia River this year. Caspian terns nested on Harper Island in Sprague Lake (approximately 50 miles east of Moses Lake on I-90) in 2006. In late June, 12 adult terns and 7 one-egg nests were counted on colony. Based on surveys conducted at Harper Island earlier in the season, we suspect these were renesting attempts by failed breeders. In 2005, terns attempted to nest on Harper Island but failed. During a survey of Banks Lake (just above Dry Falls Dam near Coulee City) in late June, 38 adult terns were counted on Dry Falls Island. A total of 21 tern chicks and some nests with eggs were counted on Dry Fall Island during this survey. In 2005, terns were successful in hatching young on islands in Banks Lake. In 2006, we do not know whether any of the Caspian tern nesting attempts on Sprague Lake or Banks Lake were successful (i.e., resulting in fledged young).
For the week, 11% of the identifiable fish delivered to the Crescent Island tern colony (N = 28) were salmonids. Year to date, 62% of the identifiable fish delivered to the Crescent Island tern colony (N = 2,250) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 66% salmonids in the diet by this time last year.
On 24 July, great horned owl tracks were spotted next to a decapitated tern on the northeast beach. Earlier this year (3 May), a great horned owl was captured on East Sand Island using a padded leg hold trap and was removed from the island. The owl that was captured and removed from the island was first spotted on East Sand Islands on 24 April. During the ensuing 10-day period, this great horned owl repeatedly visited the Caspian tern colony at night and regularly killed adult terns. Great horned owls are known predators of adult Caspian terns and have preyed on terns nesting on the East Sand Island colony in previous years. Great horned owls can cause large disturbances to colonial nesting birds, sometimes leading to colony abandonment. In 1999 and 2003, great horned owls caused serious disruption to the East Sand Island tern colony and in 1999 two owls had to be removed from East Sand Island to prevent the colony from abandoning (in 2003 the owl left the island on its own). Since removal of the owl on 3 May, there has been no further evidence of owl depredation of Caspian terns on East Sand Island until our sighting of owl tracks near the colony on 24 July. For the week ending 7 May we reported that the raccoon on East Sand Island had depredated tern nests, as evidenced by raccoon tracks and broken tern eggs on the East Sand Island tern colony. Since then we have detected no evidence of depredation of tern eggs by the raccoon, although fresh raccoon tracks are regularly seen on the north beach below the high tide line. Live traps have been set in an effort to capture and remove the raccoon before it causes significant nest failure or colony abandonment. It seems likely that this animal was intentionally released on the island, as the raccoon is trap-shy of live traps and has so far refused to enter one to take the bait. On 20 July, an opossum was captured and removed from East Sand Island. Crew members were unaware that an opossum, another mammalian predator on ground nesting birds, was on the island, suggesting that it might have been intentionally released on the island recently. All live traps were removed from East Sand Island on 21 July. At East Sand Island, two colony disturbances were observed at a rate of 0.3 disturbances/hr of observation. One colony disturbance was observed at the Crescent Island tern colony this past week at a rate of 0.3 disturbances/hr of observation. Generally, disturbances at the tern colonies are short, causing terns to flush for only 10-30 seconds before returning to the colony. This past week, gull kleptoparasitism rates at East Sand Island were 4% of all known fates of fish delivered by terns. One kleptoparasitism was observed during fish watch at the Crescent Island tern colony this past week. At the East Sand Island tern colony, kleptoparasitism is by glaucous-winged/western gulls, while at Crescent Island kleptoparasitism is by the smaller California gull. This year predation on Caspian tern chicks by California gulls at the Crescent Island tern colony was a significant source of mortality for tern chicks. In previous years predation by California gulls was limited to take of a few young chicks. This year a few California gulls have apparently developed the skills and the habit of killing even older Caspian tern chicks, and have done so regularly. One California gull nest was observed with the carcasses of at least 8 Caspian tern chicks scattered around it. In 2006, the raccoon and opossum on East Sand Island and the mink on Rock Island were the only indications of mammalian predators on tern colonies monitored as part of this study. However, it should be noted that in the effort to trap and remove the raccoon from East Sand Island, several Norway rats have been captured. Rats have apparently inhabited East Sand Island at least since the 1970s. Although they may cause some nest failure to Caspian terns and other breeding colonial waterbirds on East Sand Island, their impact is evidently small.
Gary Miller assisted with research activities in the Columbia River estuary this past week (thank you, Gary!).
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The high and low on-colony counts for the week on East Sand Island were 6,430 terns (24 July) and 5,470 terns (26 July), respectively. The annual photo census of the Caspian tern colony on East Sand Island was conducted on 26 May. Visual estimates of colony size from the ground suggest that the East Sand Island colony has increased somewhat since the 2005 nesting season. Once these aerial photos are counted (Fall 2006) we will be able to accurately estimate colony size and determine if, in fact, the colony is larger in 2006 relative to 2005. 
For the week of 24 July - 30 July, 10% of the identifiable fish delivered to the East Sand Island colony (N = 350) were salmonids. The majority of the identified non-salmonid prey items being delivered to the East Sand Island colony were anchovies (61%) and surfperch (18%). Year to date, 32% of the identifiable fish delivered to the East Sand Island tern colony (N = 5,452) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 23% salmonids in the diet by this time last year. In the last half of the breeding season the percent salmonids in the diet of East Sand Island Caspian terns has declined to the levels seen in recent years at this time, suggesting that there has been an influx of anchovies and other marine forage fishes into the estuary concurrent with the decline in out-migrating salmonid smolts.
The Principal Investigators for this project, Dan Roby and Ken Collis, would like to take this opportunity to thank the crew members whose hard work and dedication were essential to the success of our research and monitoring efforts along the Columbia River in 2006. We are very grateful to Jessica Adkins, Sasha Auer, Evan Buechley, Danielle Castle, Esther Cole, Beth Decelles, Allen Evans, Erin Feinblatt, Christy Hand, Mike Hawbecker, Nathan Hostetter, Nathan Kluthe, Jeff Lewis, Don Lyons, Coy Miller, Anne Mary Myers, Lauren Reinalda, Dan Quinn, and Yasuko Suzuki.