Last Updated July 17th
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 73 terns and 8 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. The previous week we conducted a boat survey of the tern and gull colonies on Rock Island (located on the mid-Columbia River in the John Day Pool). During this survey, 26 adult terns and five tern chicks were counted on the colony. Significant mortality of nesting terns and gulls was observed since our last visit to the colonies a few weeks ago. We suspect that the mortality was cause by an avian predator, perhaps a great horned owl, and not a mammalian predator. 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. For the week, 49% of the identifiable fish delivered to the Crescent Island tern colony (n = 153) were salmonids. The majority of the non-salmonid prey items delivered to the Crescent Island colony were centrarchids (i.e., bass and sunfish; 40%). Year to date, 73% of the identifiable fish delivered to the Crescent Island tern colony (n = 2,168) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 66% salmonids in the diet by this time last year.
All chicks captured for banding were released unharmed.
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.
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.
This past week at East Sand Island, a total of 2 colony disturbances were observed (all causes) at a rate of 0.2 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. 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 <1% 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. To date, there have been no signs of mammalian predators on any of the tern colonies monitored as part of this study.
On 12 July, David Nuzum (ODFW), Charlie Bruce (ODFW), and Chris Carey (ODFW) assisted with the tern banding activities on East Sand Island, for which we are grateful. On 13 July, Anne Mary Myers (ODFW), Eric Baker (The Oregonian), Betsy Glenn (OSU), and Jen Gervais (OSU) assisted with the tern banding activities on East Sand Island. Our thanks goes out to them as well. |
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The high and low on-colony counts for the past week on East Sand Island were 12,325 terns and 8,150 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. 
On 12-13 July, a total of 448 tern chicks that were 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 chicks that were banded, 413 chicks were also banded with a unique engraved alphanumeric plastic leg band. Banded fledglings will provide important data on survivorship, dispersal patterns, and recruitment of young terns to breeding colonies in future years. 
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.