Last Updated July 7th
Note: The following data are preliminary and may change upon further review.
| Caspian Tern Colony Counts East Sand Island
For the past three weeks the median count of adult terns on the East Sand Island colony has remained near the maximum for the year. In previous years the median counts of terns at East Sand Island have declined sharply after mid-June. The relatively high number of terns remaining at the East Sand Island colony into July is likely due to the abundance of marine forage fish at the mouth of the Columbia River, particularly anchovies (R. Emmett, NOAA Fisheries, pers. comm.). The high availability of marine forage fish may have (1) attracted greater numbers of non-breeders and failed breeders from other sites to East Sand Island than in previous years, (2) caused terns currently nesting on East Sand to spend less time foraging and more time on colony than in previous years, and (3) caused failed breeders from East Sand Island to remain on the colony longer than in previous years. The aerial photo census of the East Sand Island tern colony was conducted on May 23. Once the aerial photos are counted (Fall 2003) we will be able to accurately estimate colony size and determine whether there has been a significant change in colony size since 2002. A second aerial photo census of the colony will be conducted in early July in order to estimate the number of young terns fledged from the East Sand Island colony this year. Rice Island and Other Upper Estuary Islands Our weekly surveys for nesting terns on Pillar Rock Sands, Miller Sands Spit, Rice Island, and other upper estuary dredged material disposal islands have concluded for the season. These dredge material disposal islands will only be checked occasionally for the remainder of this season, as we do not anticipate the formation of new colonies at this late date. Washington Coast (Willapa Bay, Grays Harbor) Our aerial surveys for nesting terns along the southern Washington coast have concluded for the season; we do not anticipate the formation of new colonies at this late date. Up-river Sites (Crescent Island, Three Mile Canyon Island, Miller Rocks)
No terns have been observed at the former colony on Three Mile Canyon Island so far this season; mink predation caused complete colony failure in 2000 and 2001 (no terns attempted to nest there in 2002).
For the week of June 30 – July 6, 8% of the identifiable fish delivered to the East Sand Island tern colony (N = 352) were salmonids, an increase in the percentage as compared to the previous week (6%). Other major prey items being delivered to the East Sand Island colony included anchovy (46%) and clupeids (e.g., herring; 24%). Year to date, 29% of the identifiable fish delivered to the East Sand Island tern colony (N = 4,404) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 38% juvenile salmonids in the diet of terns on East Sand Island by the same date in 2002. For the week, 65% of the identifiable fish delivered to the Crescent Island tern colony (N = 150) were salmonids, an increase in the percentage as compared to the previous week (57%). Most of the non-salmonids observed being delivered to the Crescent Island colony were bass (19% of total diet) and cyprinids (e.g., northern pikeminnow, peamouth; 11% of total diet). Year to date, 69% of the identifiable fish delivered to the Crescent Island tern colony (N = 1,672) were salmonids (this cumulative percent is an average of the previous weeks’ percentages). This compares to 75% juvenile salmonids in the diet of terns on Crescent Island by the same date in 2002.
On July 3, a total of 21 tern chicks that were near fledging were banded at the Solstice Island tern colony, located in the Potholes Reservoir in central Washington. Each chick was banded with a numbered U.S. Geological Survey metal leg band and unique color combination of plastic leg bands. No mortality or injuries occurred
to the banded tern chicks during the above-mentioned banding operations.
These banded fledglings will provide important data on survivorship, dispersal
patterns, and recruitment of young terns to breeding colonies in future
years. Net Pen Feasibility Study The net pen feasibility study was concluded on June 6. This study demonstrated conclusively that Caspian terns can learn to forage for fish confined to a net pen that is equipped with deterrents that prevent other avian predators from using the net pen.
Radio-Tagging On May 13 and 14, a total of 12 adult Caspian terns were captured and radio-tagged at the Crescent Island tern colony. These radio-tagged terns will help determine the foraging patterns of terns nesting on Crescent Island (see previous weekly report for further details on the radio-tagging operation). Resightings of Radio-Tagged Terns One radio-tracking flight that was not completed due to high winds was conducted this past week (June 30). The area surveyed included the lower Columbia River from one mile below McNary Dam to the Snake River confluence and the Walla Walla River from the Columbia River confluence to river mile 1. Five of the 12 radio-tagged terns (42%) were detected during the morning flight and of these, 2 were on the Crescent Island tern colony (40%) and 3 were on the mainstem Columbia River downstream of Crescent Island (60%). All five of these terns are confirmed breeders on Crescent Island based on our colony observations from the blind. This past week, one tern that was radio-tagged on Crescent Island on May 13th was observed at the East Sand Island tern colony, two terns have lost their transmitters, and four terns (2 of which are confirmed nesters on Crescent Island) were not detected at the areas surveyed. We plan to conduct one radio-tracking flight per week for the remainder of the breeding season.
Disturbance rates at the East
Sand Island tern colony were higher this week (0.4 disturbances/hr of
observation) compared to the previous week (0.3 disturbances/hr of observation).
The disturbances to the East Sand Island tern colony this past week were
either of an unknown cause (50%), caused by bald eagles (25%), or caused
by the researchers (25%) when they went on to the beach adjacent the colony
in order to collect dead chicks to estimate chick mortality prior to chick
banding. There were no disturbances observed at the Crescent Island tern
colony this past week. At East Sand Island, gull kleptoparasitism rates this past week were 1% of all known fates of fish delivered by terns, an increase in the kleptoparasitism rate compared to the previous week (0% of all known fish fates). At Crescent Island, gull kleptoparasitism rates this past week were 39% of all known fates of fish delivered by terns, an increase in the kleptoparasitism rate compared to the previous week (22% of all known fish fates).
There were no visitors to the East Sand Island tern colony this past week. |
|
Site developed and maintained by Real Time Research, Inc. |
|
Comments about the site? Contact clientservices@realtimeresearch.org |
The
high and low on-colony counts for the week on East Sand Island were 14,650
terns (June 30) and 11,795 terns (July 3), respectively. This represents
a 19% increase in the median count of terns on the East Sand Island colony
from last week to this week. 
The
high and low on-colony counts for the week on Crescent Island were 183
terns (June 30) and 161 terns (July 1), respectively. This represents
a 46% decrease in the median count of terns on the Crescent Island colony
from last week to this week. The aerial photo census of the Crescent Island
tern colony was conducted on May 21. Once the aerial photos are counted
(Fall 2003) we will be able to accurately estimate colony size and determine
whether there has been a significant change in colony size since 2002.
On
July 2, a total of 100 tern chicks that were near fledging were banded
at the Crescent Island tern colony. Each chick was banded with a numbered
U.S. Geological Survey metal leg band and a unique color combination of
plastic leg bands.