Last Updated May 30th
Caspian Tern Colony Counts East Sand Island
The annual photo census of the Caspian tern colony on East Sand Island was conducted on 26 May. Once the aerial photos are counted (Fall 2006) we will be able to accurately estimate colony size and determine whether there has been a significant change in colony size since 2005.
Two surveys of the upper estuary were conducted this past week (23 and 26 May) looking for nesting terns at dredge disposal sites. During these surveys, no terns were observed roosting or attempting to nest in upland areas of Pillar Rock Sands, Miller Sands Spit, or Rice Island. The total number of terns roosting at sites in the upper estuary has declined considerably from what was observed earlier in the season. We will continue to monitor Rice Island and the other upper estuary dredged material disposal islands for early signs of nesting (e.g., nest scrape digging) and will promptly inform resource managers of any such activity.
The high and low on-colony counts for the week on Crescent Island were 579 terns (23 May) and 508 terns (27 May), respectively. 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 More than 70 Caspian terns were counted on Rock Island during a boat survey conducted on 26 May. During that survey, we observed 20-40 active Caspian tern nests with eggs and some (3) with chicks. As many as six breeding pairs were observed at Rock Island last year and at least one Caspian tern chick was raised to fledging, the first Caspian tern breeding ever recorded on these islands during our study (1997-2006). A severe wind and hail storm occurred on the upper Columbia River on 19 May, which caused considerable nest failure to double-crested cormorants and black-crowned night herons nesting in trees on Foundation Island. We did not observe significant nest failure associated with the storm at the Crescent Island tern colony. Two surveys of other upper Columbia River islands were conducted this past week (26 and 28 May) looking for nesting terns. During these surveys, no terns were observed roosting or attempting to nest in upland areas of Miller Rocks, Three-Mile Canyon Island, Nelson Island, Fencepost Island, Richland Island, and two unnamed islands near Pasco, Washington. With the exception of Rock Island, nesting Caspian terns have not been observed at other potential colony sites along the Mid-Columbia River so far this year.
For the week of 22-28 May, 65% 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 surfperch (11%) and anchovies (10%). Year to date, 58% of the identifiable fish delivered to the East Sand Island tern colony (N = 2,456) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 39% salmonids in the diet by this time last year. For the week, 65% of the identifiable fish delivered to the Crescent Island tern colony (N = 161) were salmonids. Year to date, 77% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,064) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This is the same year to date percentage as was observed by this time last year.
On 26-27 April, net pens were deployed in Burbank Slough and Peninsula Slough, just downstream of the confluence of the Snake and Columbia rivers. This will be the third year in which a net pen has been located in Burbank Slough (McNary National Wildlife Refuge, 8 km northeast of the Crescent Island tern colony) and the first year in Peninsula Slough (also McNary NWR, 6 km northeast of the Crescent Island tern colony). Roughly 800 PIT-tagged trout in two size class (large and small) were stocked in each net pen. PIT-tagged fish removed from the net pens by Caspian terns will be used to determine (1) PIT tag deposition rates at the Crescent Island tern colony and (2) vulnerability of fish in different size classes to tern predation. This past week, 3 trout were removed from the Burbank Slough net pen by Caspian terns; to date a total of 24 trout have been removed from the Burbank Slough net pen by Caspian terns. A total of 5 trout were removed by Caspian terns from the Peninsula Slough net pen this past week, or 11 trout total since the study began. We will continue to monitor bird activity at the net pens in the coming weeks.
Capturing and marking breeding adult Caspian terns with plastic leg bands that are engraved with easily readable alpha-numeric code is being used to measure annual adult survival and dispersal of breeding adults to other nesting colonies. These are important data for modeling the demography of the Caspian tern population in the Pacific Northwest. The recovery of PIT tags on piscivorous waterbird colonies has been used as a direct measure of predation rates on ESA-listed salmonid populations from the Columbia and Snake rivers. Predation rates based on PIT tag recoveries are, however, underestimates; some proportion of tags consumed by terns is deposited off-colony, weather and other environmental factors remove PIT tags that are deposited on-colony, and some PIT tags are damaged and rendered unreadable before or after egestion on the colony. Understanding the magnitude of the bias in estimates of tern predation on smolts based on PIT tag recoveries on-colony is critical for deriving ESU-specific tern predation rates. One method we are using to estimate PIT tag deposition rates on-colony is to force-feed PIT-tagged fish to adult terns captured on the East Sand and Crescent island tern colonies and then determine the proportion of force-fed tags that are subsequently deposited at each colony. On 28-29 May, 45 breeding adult terns were captured on the East Sand Island colony late in the egg incubation period using noose-mat traps placed over active nests. Each captured adult was weighed, measured, banded with an engraved plastic leg band plus a federal numbered metal leg band, and force-fed one fish (4-5 cm in length) containing one PIT tag. All fish were certified, disease-free triploid trout obtained from the Trout Lodge Hatchery, WA.
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. This past week no evidence of depredation of tern eggs by the raccoon was discovered. 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. If the raccoon and any other mammalian predators are not removed from East Sand Island, it will likely lead to greater numbers of terns from East Sand Island prospecting for nest sites in the upper estuary or further up-river, which would result in higher predation rates on juvenile salmonids from the Columbia River Basin. At East Sand Island, a total of 6 colony disturbances were observed at a rate of 0.6 disturbances/hr of observation. Generally, disturbances at the tern colony are short, causing terns to flush for only 10-30 seconds before returning to the colony. At Crescent Island, no colony disturbances were observed this past week. This past week, gull kleptoparasitism rates at East Sand Island were 5% of all known fates of fish delivered by terns. At Crescent Island, gull kleptoparasitism rates were 2% of all known fates of fish delivered by terns 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. Other than the raccoon on East Sand Island, there have been no signs to date 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.
On 25 May, Scott Dunmire, Greg Graham, Rebecca Kalamasz, and Ann Setter, from the U.S. Army Corps of Engineers, Walla Walla District visited Crescent Island. This past week, Karen Fischer and Dacey Mercer from Oregon State University assisted with the adult banding and force feeding on East Sand Island (thanks Karen and Dacey!). |
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The high and low on-colony counts for the week on East Sand Island were 15,500 terns (24 May) and 10,255 terns (27 May), respectively. The weather in the estuary this past week was mostly overcast and raining. The first tern chick hatched on East Sand Island on 23 May, 7 days later than the first chick was seen on the East Sand Island tern colony in 2005. Nesting chronology at East Sand Island is delayed compared to previous years (2000-2005), when the first chick dates ranged from 13 May (2004) to 21 May (2000). 
Caspian terns have once again occupied a breeding colony on Dungeness Spit, which is on the Olympic Peninsula in Washington. Occasional surveys of this colony by Kirsten Bixler revealed that on May 21 over 750 were present on the colony, and at least 220 of these terns were sitting on eggs. These observation indicate that the Dungeness Spit colony was growing to a larger size than it was last year (ca. 680 nesting pairs). On May 27, however, only 389 terns were present on the colony, and only 128 terns were sitting on eggs. During observations from a blind on May 27, two coyotes arrived at the tern colony, flushed all the adults, and began eating tern eggs. It seems likely that the Dungeness Spit Caspian tern colony will fail this year because of nest depredation by coyotes. 
Of the 45 terns that were force-fed fish, 44 terns (98%) successfully ingested the fish, and most (43 or 96%) returned to the colony to resume normal breeding behaviors within roughly 4 hours post-release. One adult tern was injured during this activity and was taken to the North Coast Wildlife Rehabilitation Center in Astoria. We expect this bird to be rehabilitated for release back into the wild. Data on egg and chick loss associated with this activity were not available at the time of this report and will be made available in a subsequent report. The capture of adult terns for banding and force-feeding at East Sand Island and Crescent Island is now completed for the 2006 breeding season.