Last Updated July 13th
Note: The following data are preliminary and may change upon further review. East Sand Island Our weekly boat-based surveys to monitor Pillar Rock Sands, Miller Sands Spit, Rice Island, and other upper estuary dredged material disposal islands looking for early signs of nesting (e.g., scrape digging) have been discontinued for this year. No active Caspian tern nests (nest scrapes containing eggs) were detected at any of these upper estuary sites this year, and we do not anticipate the formation of any new colonies this late in the season. We have detected no Caspian terns attempting to nest at other colony sites on the Mid-Columbia River, Lower Snake River, or Lower Yakima River this breeding season. Caspian terns were nesting at two sites on islands in Potholes Reservoir near Moses Lake; terns nesting at one of these sites (Solstice Is.) failed due to rising water levels that flooded low lying nests and black-crowned night-heron predation on the remaining nests (C. Moranto, University of Washington, pers. comm.). Nesting success at the other colony on Potholes Reservoir (Goose Is.) was also low this year.
For the week, 78% of the identifiable fish delivered to the Crescent Island tern colony (N = 200) were salmonids, a higher percentage as compared to the previous week (64%). Most of the non-salmonids observed being delivered to the Crescent Island colony were centrarchids (e.g., bass, sunfish; 14%). Year to date, 73% of the identifiable fish delivered to the Crescent Island tern colony (N = 2,700) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 69% salmonids in the diet of Crescent Island terns by this time last year.
No mortality or major injuries occurred to the banded tern chicks during the above-mentioned banding operations. These banded fledglings will provide important data on survivorship, dispersal patterns, and recruitment of young terns to breeding colonies in future years.
Earlier this season, a net pen was deployed near Crescent Island and stocked with approximately 1,000 PIT-tagged juvenile rainbow trout to investigate (1) PIT tag deposition rates at the Crescent Island tern colony, (2) vulnerability of fish in different size classes to tern predation, and (3) gull kleptoparasitism rates on fish captured by terns at the net pen. The net pen and the surrounding slough were monitored 8 – 15 hrs/day, 7 days/week, from 24 April to 4 June. A net was placed over the net pen after each observation period to prevent terns and other predators from feeding on fish held in the pen when observers were not present. On 26 April, Caspian terns began foraging on fish within the net pen. During the 40-day study period, a total of 94 PIT-tagged trout were removed from the net pen by Caspian terns during 207 attempts (i.e., plunge dives into the net pen). No other predators were observed removing PIT-tagged trout from the net pen, with the exception of Forster’s terns, which removed a total of 43 fish from the net pen. Following the breeding season and after all the terns and gulls have left their respective colonies, the Crescent Island tern and gull colonies will be scanned for PIT tags by NOAA Fisheries. The number of PIT tags that were removed from the net pen by terns and subsequently detected on the Crescent Island tern and gull colonies will be used to address the research objectives listed above.
At East Sand Island, four colony disturbances were observed at a rate of 0.3 disturbances/hr of observation. Generally, these disturbances were short, causing terns to flush for only 10-30 seconds before returning to the colony. There were no disturbances observed at the Crescent Island tern colony this past week. During plot watches, no nest predation was observed at the East Sand Island or Crescent Island tern colonies 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 8% 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 Californiagull. So far this season there have been no signs of mammalian predators on any of the tern colonies monitored as part of this study.
Susan Barnes (ODFW), Charlie Bruce (ODFW), David Craig (Willamette U.), Charnelle Fee (North Coast Wildlife Rehabilitation Center), Troy Guy (NOAA Fisheries), Samantha Lantz (Willamette U.), Alex Moculeski, Diane Moculeski, Jason Podabrshy (Portland State U.), Brad Ryan (NOAA Fisheries), Joel Shinn (Willamette U.), Matthew Shinn (Willamette U.), Amy Vasereno (Willamette U.), and Jen Zamon (NOAA Fisheries) visited the East Sand Island tern colony this past week. |
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The first fledgling (i.e., young-of-the-year capable of flight) was observed at the East Sand Island colony on 19 June. Nesting success at the East Sand Island tern colony appears high so far this year. A second aerial photo census of the Caspian tern colony on East Sand Island was conducted on 3 July. Once these aerial photos are counted and verified we will be able to accurately estimate the number of young terns fledged from the East Sand Island colony this year.
For the week of 5 July 
On 6 – 7 July, a total of 453 Caspian tern chicks near fledging were banded at the East Sand Island tern colony. Each chick was banded with a numbered U.S. Geological Survey metal leg band. Of the 453 banded chicks, 424 chicks were also banded with a unique color combination of plastic leg bands. Of all the tern chicks captured for banding, only 1 (0.2%) had a salmonid smolt PIT tag in it’s digestive track (based on scans of chicks using an electronic PIT tag reader).