Last Updated June 15th
Note: The following data are preliminary and may change upon further review. East Sand Island
During an aerial survey the previous week (3 June), no aggregations of terns were observed on upland areas of dredged material disposal islands in the upper estuary ( Rice Island, Miller Sands Spit, and Pillar Rock Sands). 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; occasionally, we may check these dredged material disposal islands, but 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 are nesting at two sites on islands in Potholes Reservoir near Moses Lake.
For the week, 65% of the identifiable fish delivered to the Crescent Island tern colony (N = 226) were salmonids, a lower percentage as compared to the previous week (72%). Most of the non-salmonids observed being delivered to the Crescent Island colony were centrarchids (e.g., bass, sunfish; 17%) and cyprinids (e.g., northern pikeminnow, peamouth; 11%). Year to date, 74% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,774) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 72% salmonids in the diet of Crescent Island terns by this time last year.
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, 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. No disturbance events were observed during disturbance observation periods at the East Sand Island or Crescent Island tern colonies this past week. During plot watches, no nest predation was observed at the East Sand Island tern colony this past week. One tern chick was depredated by a California gull at the Crescent Island tern colony this past week, or 0.1 nest depredations/hr of observation. This past week, gull kleptoparasitism rates at East Sand Island were 3% of all known fates of fish elivered by terns. At Crescent Island, gull kleptoparasitism rates were 16% 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.
On 1 June, 40 recently-hatched Caspian tern chicks were collected from the East Sand Island colony for captive-rearing experiments. These experiments were designed to evaluate the Quantitative Fatty Acid Signature Analysis method for nondestructive determination of diet composition in piscivorous waterbirds. We will also use these captive-reared chicks to better understand PIT tag passage rates in Caspian terns. The tern chicks are being raised on different diets of forage fish, and fat will be biopsied from the chicks periodically to validate the use of this method to detect dietary differences among free-ranging Caspian terns. So far, all captive chicks are displaying healthy appetites and thriving, with the exception of one chick that suffered from a congenital developmental abnormality.
There were no visitors to either the East Sand Island or Crescent Island tern colonies this past week. |
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The high and low on-colony counts for the week on East Sand Island were 16,649 terns (10 June) and 10,149 terns (10 June), respectively. The annual photo census of the Caspian tern colony on East Sand Island was conducted on 17 May. Once the aerial photos are counted (Fall 2004) we will be able to accurately estimate colony size and determine whether there has been a significant change in colony size since 2003. 
For the week of 7 June – 13 June, 18% of the identifiable fish delivered to the East Sand Island tern colony (N = 361) were salmonids,