Last Updated May 2nd
Caspian Tern Colony Counts East Sand Island The high and low on-colony counts for the week on East Sand Island were 9,800 terns (28 April) and 2,500 terns (24 April), respectively. The high and low counts for this week are 10% and 47% lower, respectively, than during this week last year. The weather in the estuary this past week improved compared to previous weeks; clear skies and calmer winds prevailed throughout the week.
Three surveys of the upper estuary were conducted this past week (26, 27, and 29 April) looking for nesting terns at dredge disposal sites. An unusually high number of terns was observed in the upper estuary this past week, with nearly 1,900 terns counted during an aerial survey from Rice Island to Tenasillahe Island on 27 April. It is likely that this increase in number of terns in the upper estuary is in response to the arrival of out-migrating juvenile salmonids to the estuary this past week. Of these terns, 116 were spotted in the upland area of Pillar Rock Sands and 148 terns were on the upland portion of Miller Sands Spit. Resource managers were informed of the situation and on 29 and 30 April a USACE contractor (Ken Larson) deployed stakes fixed with brightly colored flagging to dissuade terns from nesting at these potential colony sites. This effort seems to have been effective in dissuading terns from roosting at these two sites, at least in the short-term. 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.
During aerial surveys conducted along the southern Washington coast this past week (27 April), 54 terns and 363 terns were counted on islands in Willapa Bay and Grays Harbor, respectively. These birds were observed roosting below the high tide line, with the exception of 46 terns that were counted on an upland site near the Westport Airport in Grays Harbor. This site is unlikely to be suitable for nesting terns due to its proximity to the mainland; mammalian predators from the mainland likely have access to this site during low low tides. The number of terns counted in Willapa Bay and Grays Harbor is higher than has been observed in recent years during this time of year. We will continue to fly periodic surveys in these areas looking for nesting terns. Up-river Sites (Crescent Island, Three Mile Canyon Island, Miller Rocks) The high and low on-colony counts for the week on Crescent Island were 709 terns (24 April) and 547 terns (28 April), respectively. These counts are similar to those recorded at this colony last year during the comparable week. The first tern egg was laid at the Crescent Island colony on 16 April, four days later than was observed the previous year. Three surveys were conducted this week (19, 21, and 26 April) looking for nesting terns on islands on the mid Columbia River from The Dalles Dam to Priest Rapids Dam and off the Columbia River in Potholes Reservoir. Caspian terns continue to show interest in nesting on Rock Island within the Blalock Islands, 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 an island within the Blalock Islands again this year. Nesting terns were not observed at any other sites on the mid-Columbia (Miller Rocks, Three Mile Canyon Island, Sand Island, Nelson Island, Fencepost Island, Richland Island, Island 18, and Johnson Island). Four Caspian terns were seen loafing on the shore of Cabin Island (located near Priest Rapids Dam) but there was no evidence of tern nesting. We will continue to fly periodic surveys in these areas looking for nesting terns.
For the week, 95% of the identifiable fish delivered to the Crescent Island tern colony (N = 174) were salmonids. Year to date, 75% of the identifiable fish delivered to the Crescent Island tern colony (N = 421) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 85% salmonids in the diet by this time last year.
On 26 April and 27 April, net pens were deployed in Burbank and Peninsula Slough, respectively, 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 Wildlife Refuge, 8 km northeast of Crescent Island) and the first year in Peninsula Slough (also McNary Wildlife Refuge, 6 km northeast of Crescent Island). 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. The net pen frames were fitted with wire spike strips to prevent avian predators from roosting on the net pen frames and to deter predators other than terns from foraging on the fish held in the net pens. Juvenile rainbow trout in two different size classes (mean fork length 10 cm and 17 cm, respectively) were PIT-tagged and placed in the net pens, with approximately equal numbers of both size classes within each net pen. All fish were certified, disease-free triploids (sterile as adults) obtained from the Trout Lodge Hatchery, WA. The net pens will be monitored 8 hrs/day, 7 days/week until a minimum of 100 fish have been removed from each net pen by Caspian terns. Mesh netting will be placed over the net pens after each observation period to prevent terns and other predators from feeding on fish held in the pens when observers are not present. Following the breeding season and after all the terns have left the colony, the Crescent Island tern colony will be scanned for PIT tags by NOAA Fisheries. The number of PIT tags that are removed from the net pens by terns and subsequently detected on the Crescent Island tern colony will be used to address the research objectives listed above. Caspian terns showed interest in the fish held within the Burbank Slough net pen, although no fish were removed by terns this week. No terns were observed foraging in or near the Peninsula Slough net pen. We will continue to monitor bird activity at the net pens in the coming weeks. Predator Activity On 24 April, a great horned owl was observed roosting on East Sand Island. 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. Owls, which hunt at night, 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 to prevent the colony from abandoning (in 2003 the owl left the island on its own). This year as in previous years, there is considerable evidence that the owl has been preying on adult terns at night. Efforts are underway to try to remove the owl from the island as soon as possible.
At East Sand Island, a total of 5 colony disturbances were observed at a rate of 0.5 disturbances/hr of observation. This past week bald eagle activity near the tern colony has declined from what was observed in previous weeks. Generally, disturbances at the tern colony are 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. This past week, gull kleptoparasitism rates at East Sand Island were 4% of all known fates of fish delivered by terns. At Crescent Island, gull kleptoparasitism rates were 6% 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.
This past week, Brendan Courtot, a former field crew leader, Ram Papish, Amanda Gladics, Steve Kress, and Elissa Wolfson visited East Sand Island. Steve Kress is the Director of the National Audubon Society’s Seabird Restoration Program and a pioneer in the use of social attraction and habitat improvement to restore extirpated seabird colonies. Also this past week, Gary Miller and Ken Gustafson assisted research activities in the Columbia River estuary (thank you, Gary and Ken!). Ken Larson, a USACE contractor, visited Miller Sands Spit and Pillar Rock Sands in order to dissuade terns from nesting at these sites (see above). |
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The first tern egg was laid at the East Sand Island tern colony on 26 April. This is the latest first-egg date that we have recorded at the East Sand Island tern colony since 1999, and was 12 days later than the first-egg date last year. This delay in nesting chronology at East Sand Island is likely due to poor weather conditions (heavy rain and high winds), frequent disturbance by bald eagles, and an apparent shortage of available forage fish early in the season. Conditions in the estuary improved this past week; not only has the weather improved, but eagle disturbances have declined and forage fish availability has apparently increased with the arrival of out-migrating juvenile salmonids to the estuary. Consequently, the terns at the colony on East Sand Island appear to be settling in more as evidenced by an increase in nesting behavior (i.e., scrape digging, copulation, and courtship feeding) and the onset of egg-laying.
For the week of 24 April – 30 April, 66% of the identifiable fish delivered to the East Sand Island colony (N = 348) were salmonids. This dramatic increase in salmonids in the diet of East Sand Island terns is apparently associated with the onset of the juvenile salmonid out-migration through the Columbia River estuary. The majority of the non-salmonid prey items being delivered to the East Sand Island colony were smelt (10%). During this same week last year, clupeids (herring and sardines) and anchovies made up a combined 46% of the East Sand Island terns diet compared to only 7% this year. Year to date, 41% of the identifiable fish delivered to the East Sand Island tern colony (N = 1,056) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 29% salmonids in the diet by this time last year. 
In addition, there considerable evidence that there is currently a raccoon on East Sand Island. Although the raccoon has not been seen, fresh raccoon scat and tracks have been found away from the tern colony, and we found evidence that the raccoon had depredated a Canada goose nest near our camp. Live traps have been set in order to attempt to capture and remove the animal before it causes significant disturbance to the tern colony, which we suspect has not happened yet.