Last Updated May 23th
Caspian Tern Colony Counts East Sand Island
The annual photo census of the Caspian tern colony on East Sand Island is scheduled for 24 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.
Three surveys of the upper estuary were conducted this past week (15, 17, and 19 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, Rice Island, Grassy Island, Fitzpatrick Island, Welch Island, Tenasillahe Island, Puget Island, Wallace Island, and Browns Island. As was reported last week, 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. Washington Coast (Willapa Bay, Grays Harbor) During aerial surveys conducted along the southern Washington coast this past week (17 May), 89 Caspian terns and 42 Caspian terns were counted on islands in Willapa Bay and Grays Harbor, respectively. These birds were all observed roosting below the high tide line. The number of terns counted in Willapa Bay was higher than was observed on our census conducted on 27 April (54), while the count of terns in Grays Harbor was lower than was observed during that same census (363). We will continue to fly periodic surveys in these areas looking for nesting terns.
The high and low on-colony counts for the week on Crescent Island were 735 terns (20 May) and 506 terns (16 May), respectively. Counts of incubating or brooding adult terns on the Crescent Island colony indicate that about 450 pairs of Caspian terns are attempting 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 Surveys conducted in previous weeks have shown that Caspian terns continue to show interest in nesting on Rock Island in the Blalock Islands group, which is located in John Day pool between the towns of Boardman and Irrigon, Oregon. Eighty Caspian terns were counted on Rock Island during an aerial survey on 26 April. During boat surveys of this island on 19 and 21 April, we observed some nest scrapes but no tern eggs were present. 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). It appears that terns may attempt to nest on Rock Island again this year. Nesting Caspian terns have not been observed at other potential colony sites along the Mid-Columbia River so far this year. Inland Washington Sites off the Columbia River (Sprague Lake and Banks Lake) This past week, 7 adult terns were observed on Harper Island in Sprague Lake (approximately 50 miles east of Moses Lake on I-90). During a survey of Banks Lake (just above Dry Falls Dam near Coulee City) this past week, 65 adult terns were counted on Dry Falls Island. No terns were observed on Goose Island, an island in Banks Lake that has had tern nesting in previous years. No nests were observed on Harper Island, suggesting that the terns may have already failed there, while 20 active nests were discovered on Dry Falls Island. Caspian terns have nested on Sprague Lake and Banks Lake in previous years and appear to be nesting there again this year.
For the week of 15 May – 21 May, 69% 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 (10%), clupeids (herring and sardines; 8%), and anchovies (6%). Year to date, 56% of the identifiable fish delivered to the East Sand Island tern colony (N = 2,106) 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, 75% of the identifiable fish delivered to the Crescent Island tern colony (N = 161) were salmonids. Year to date, 79% of the identifiable fish delivered to the Crescent Island tern colony (N = 903) 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, 14 trout were removed from the Burbank Slough net pen by Caspian terns; to date a total of 21 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 6 trout total since the study began. We will continue to monitor bird activity at the net pens in the coming weeks.
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 Crescent Island, no colony disturbances were observed this past week. This past week, gull kleptoparasitism rates at East Sand Island were 6% of all known fates of fish delivered by terns. At Crescent Island, gull kleptoparasitism rates were 4% 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 19 May, Troy Guy (NOAA Fisheries) visited East Sand Island. This past week, Gary Miller assisted with research activities in the Columbia River estuary (thank you, Gary!). |
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The high and low on-colony counts for the week on East Sand Island were 14,645 terns (18 May) and 10,885 terns (16 May), respectively. Clear skies and calm-moderate winds have prevailed at East Sand Island over the past several weeks. This past week, we have observed a continued expansion in the area used by nesting terns to the lower regions of the colony, northeast of the core colony area. This was the area that seemed to be most affected by the great horned owl before it was captured and removed from the island. The counts of incubating terns on our plots for sampling productivity suggest that most breeding adult terns have laid eggs and are incubating. We have yet to observe the first tern chick on the East Sand Island colony; the first tern chick was observed last year on 16 May. 
At East Sand Island, a total of 10 colony disturbances were observed at a rate of 0.9 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.