Last Updated July 19th
Note: The following data are preliminary and may change upon further review.
Caspian Tern Colony Counts East Sand Island The first fledgling (i.e., young-of-the-year capable of flight) was observed at the East Sand Island colony on 23 June. Nesting success at the East Sand Island tern colony appears somewhat lower than in recent years. This agrees with reports from throughout the coastal Pacific Northwest of poor ocean conditions and very poor nesting success by fish-eating seabirds. A second aerial photo census of the colony was conducted on 7 July. Once these aerial photos are counted (Fall 2005) we will be able to accurately estimate the number of young terns fledged from the East Sand Island colony this year.
The first fledgling (i.e., young-of-the-year capable of flight) was observed at the Crescent Island tern colony on 22 June. Nesting success at the Crescent Island tern colony appears to be lower this year compared to last. This agrees with the lower nesting success observed at the East Sand Island Caspian tern colony this year. Nesting Caspian terns have not been observed at former colony sites along the Mid-Columbia River at Three Mile Canyon Island (John Day Pool), Miller Rocks (The Dalles Pool), and Cabin Island (Priest Rapids Pool). A small, new Caspian tern breeding colony has been discovered on Rock Island in the Blalock Islands, John Day pool (between the towns of Boardman and Irrigon, Oregon). On 5 July, there were 3 adults and one black-capped fledgling observed on the island. This one fledgling appears to be the only young tern raised at this colony this year; as many as six breeding pairs were observed during previous visits to the island. Nesting Caspian terns shared the island with nesting California gulls and Forster’s terns (ca. 60 pairs).
For the week of 11 July – 17 July, 3% of the identifiable fish delivered to the East Sand Island colony (N = 354) were salmonids. The majority of the prey items being delivered to the East Sand Island colony were anchovies (61%) and surfperch (26%). Year to date, 25% of the identifiable fish delivered to the East Sand Island tern colony (N = 5,010) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 17% salmonids in the diet at this time last year. In the last seven weeks the percent salmonids in the diet of East Sand Island Caspian terns has declined to the levels seen last year at this time, suggesting that there has been an influx of anchovies and other marine forage fishes into the estuary concurrent with the decline in out-migrating salmonid smolts. For the week, 25% of the identifiable fish delivered to the Crescent Island tern colony (N = 177) were salmonids, a significant drop in the salmonid percentage from previous weeks. This likely reflects a decline in availability of out-migrating smolts near the Crescent Island colony. Year to date, 69% of the identifiable fish delivered to the Crescent Island tern colony (N = 2,855) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 71% salmonids in the diet at this time last year. Chick Banding
Two mortalities of tern chicks occurred during the above-mentioned banding operations. The banded fledglings that survived will provide important data on subadult survivorship, dispersal patterns, and recruitment of young terns to breeding colonies in future years.
At East Sand Island, four colony disturbances were observed at a rate of 0.5 disturbances/hr of observation. Generally, disturbances of the East Sand Island tern colony by bald eagles have been more frequent and more intense than last year, including observations of eagles roosting on the colony and preying on adult Caspian terns on or near the colony. During these eagle disturbances, a large proportion of the adult terns on the colony may flush, leaving tern eggs and chicks vulnerable to predation by gulls nesting near the tern colony. Gull predation on Caspian tern eggs and chicks at the East Sand Island colony has been more frequent this year than in any other year since the colony was established in 1999. At Crescent Island, no colony disturbances were observed 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 2% 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 12-13 July, Troy Guy (NOAA), Melissa Carper (NOAA), Charlie Bruce (ODFW), Chris Carey (ODFW), Katie Dugger (OSU), Dave Craig ( Willamette University), Paul Swenson ( Willamette University), Jacquelyn Grace ( Willamette University), Sharnelle Fee ( North Coast Rehabilitation Center) and Cheryl ( North Coast Rehabilitation Center) assisted with the tern banding activities on East Sand Island, for which we are grateful. |
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The high and low on-colony counts for the week on East Sand Island were 7,200 terns (11 July) and 1,810 terns (17 July), respectively. The annual photo census of the Caspian tern colony on East Sand Island was conducted on 17 May. Visual estimates of colony size from the ground suggest that the East Sand Island colony has declined somewhat since the 2004 nesting season. Once these aerial photos are counted (Fall 2005) we will be able to accurately estimate colony size and determine whether there has been a significant decline in colony size since 2004. 
On 12 – 13 July, a total of 250 Caspian tern chicks 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 250 banded chicks, 209 chicks were also banded with a unique color combination of plastic leg bands. The smaller number of young terns banded at East Sand Island this season compared with previous years reflects the lower nesting success this year.