Last Updated July 25th
Caspian Tern Colony Counts East Sand Island The first fledgling was observed on the East Sand Island tern colony on 6 July, 8 days later than the first fledgling was observed on the East Sand Island colony last year. As a result of a large number of failed nesting attempts early in the season (due to gull predation on tern eggs) and the subsequent re-nesting of failed breeders, the nesting at the East Sand Island tern colony is more asynchronous than in most previous years.
We have discontinued regular monitoring of Rice Island and the other upper estuary dredge disposal islands for early signs of nesting (e.g., nest scrape digging) because the chances of Caspian terns initiating nesting in the upper estuary this late in the season are essentially nil. The high and low on-colony counts for the week on Crescent Island were 63 terns and 0 terns, respectively. The first fledgling was observed on Crescent Island on 1 July which was 17 days later than was observed last year. Earlier counts of incubating or brooding adult terns on the Crescent Island colony indicate that about 355 pairs of Caspian terns attempted to nest at the colony this year. This represents about a 21% decline in the size of the colony compared to 2006, when about 450 pairs nested on Crescent Island. Based on numbers of tern chicks counted on the Crescent Island colony in recent weeks, it appears that tern productivity this year will be only fair. Rock Island (located on the mid-Columbia River in the John Day Pool) was visited on 16 July. No terns were observed on the island during this visit. Significant mortality of nesting terns and gulls was observed during a previous visit to the island on 7 July. We suspect that the mortality was cause by an avian predator, perhaps a great horned owl or peregrine falcon, and not a mammalian predator. During our visit to the colony on 7 July, 26 adult terns and five tern chicks remained on the Rock Island tern colony. Based on our observations, it is uncertain whether or not any young successfully fledged from the Rock Island tern colony in 2007; at best productivity was poor. In 2006, the Rock Island Caspian tern colony failed due to mink predation on all tern eggs and chicks produced at the colony. Nesting Caspian terns have not been observed at other potential colony sites along the mid-Columbia River so far this year. Avian predation rates often vary by salmonid species, run-type, stock, and rearing type (hatchery vs. wild). Furthermore, predation rates for specific groups of fish can vary greatly from one year to the next. Despite this well-documented variation, few data are available to determine which biotic and abiotic factors account for differences in smolt vulnerability to avian predators. One method to evaluate the potential intrinsic and extrinsic factors affecting relative vulnerability of smolts to avian predation is to PIT-tag smolts and subsequently recover their tags on bird colonies following the breeding season. Relative Vulnerability - Steelhead Tagging Study This year, we initiated a pilot study whereby run-of-the-river steelhead smolts encountered at the juvenile fish facilities at Lower Monumental and Ice Harbor dams on the lower Snake River are PIT-tagged, weighed, measured, photographed (for condition scoring), and released back into the river to resume their out-migration. Following the breeding season, PIT tags will be recovered from various bird colonies in order to test hypotheses concerning how differences in smolt morphology, condition, abundance, origin, river conditions, and dam operations are associated with differences in smolt vulnerability to avian predation. In total, 7,107 steelhead were PIT-tagged at either Lower Monumental or Ice Harbor dams as part of this study. In the coming weeks we will begin our effort to recover PIT tags at various bird colonies on the Columbia Plateau to determine which biotic and abiotic factors account for differences in smolt vulnerability to avian predators.
There were no disturbances 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 1% of all known fates of fish delivered by terns. Gull kleptoparasitism was not observed during fish watch at the Crescent Island tern colony 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. To date, there have been no signs of mammalian predators on any of the tern colonies monitored as part of this study.
Twelve educators from around the Pacific Northwest visited East Sand Island on 17 July. Patrick Willis (Portland), Emily Sandford (Olympia), Cory Samia (Portland), Forest Schoner (Rogue River), Casey Ralston (Seattle), Joy Tally (North Bend), Giovannina Savers (Seattle), Julie Hahn (Bellevue, WA), James Byrne (Longview, WA), Orlay Johnson (Seattle), Mary Lou Pelletier (Olympia), and Lee Cain (Astoria) were in Astoria for the Northwest Aquatic and Marine Educators (NAME) conference this past week and East Sand Island was one of their stops. |
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The high and low on-colony counts for the past week on East Sand Island were 12,645 terns and 6,835 terns, respectively. The annual photo census of the Caspian tern colony on East Sand Island was conducted on 23 May. Once the aerial photos are counted (Fall 2007) we will be able to accurately estimate colony size and determine whether there has been a significant change in colony size since 2006. 
For the week of 16 July – 22 July, 8% of the identifiable fish delivered to the East Sand Island colony (n = 350 prey items) were salmonids. As was the case the previous seven weeks, anchovies were the most prevalent prey type in the tern diet this past week (50% of identifiable prey items). Year to date, 32% of the identifiable fish delivered to the East Sand Island tern colony (n = 4,958) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 34% salmonids in the diet by this time last year.