Caspian Tern Colony Preparations

At East Sand Island, habitat improvements were accomplished by the USACE during April 1-4. Similar to last year, roughly 6.5 acres of suitable bare sand habitat was prepared at the eastern end of East Sand Island. Tern decoys (100) and a sound system were deployed in the center of the colony area to attract nesting terns to the site. On April 9, a camp was set up on East Sand Island and will be continuously occupied by two colony monitors throughout the tern breeding season.

The former tern colony area on Rice Island (roughly 7 acres) is completely vegetated and is unsuitable for tern nesting.

Caspian Tern Colony Counts

East Sand Island

The high and low on-colony counts for the week on East Sand Island were 2,388 terns (April 13) and 708 terns (April 9), respectively. During the period when habitat work was being done on East Sand Island (April 1 - 4), terns were continuously roosting on portions of the colony site. Early breeding behaviors (i.e., scrape digging, courtship feeding, copulation) increased in frequency at the colony site throughout the week.

On the night of April 12 a rainstorm caused standing water to form on part of the colony (roughly 5% of the colony area had standing water). This temporarily displaced about 50-100 terns that had been roosting and setting up territories to other areas on the colony. The areas with standing water dried out by April 14, at which time the terns returned to those areas.

Rice Island and Other Upper Estuary Islands

During this past week, no terns were observed roosting or attempting to nest in upland areas on Rice Island, Miller Sands Spit, or Pillar Rock Sands. Furthermore, no terns were observed roosting on the beaches surrounding these islands, which had been observed in previous years at this time.

Given that the entire former colony area on Rice Island is now vegetated, we do not expect that terns will attempt to nest at the former colony site on Rice Island in 2003. We will continue to monitor Rice Island and other upper estuary dredge disposal islands for early signs of nesting (e.g., scrape digging) and will promptly inform resource managers of any such activity.

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 146 terns (April 12) and 19 terns (April 8), respectively. Terns have not been observed on Three Mile Canyon Island so far this season, where mink predation caused complete colony failure in 2000 and 2001 (no terns attempted to nest there in 2002).

Diet Composition

For the week of April 7 - 13, 14% of the identifiable fish delivered to the East Sand Island colony (N = 183) were salmonids. The majority of the prey items being delivered to the East Sand Island colony were smelt (50%).

For the week, 50% of the identifiable fish delivered to the Crescent Island tern colony (N = 44) were salmonids. Most of the non-salmonids observed at Crescent Island were cyprinids (e.g., northern pikeminnow, peamouth; 25%) and bass (18%).

Predator Activity

At East Sand Island, bald eagles and peregrine falcons have been observed at the colony throughout the week, frequently causing terns to take flight (0.80 disturbances/hr of observation). Generally, these disturbances are short, causing terns to flush for only 10-15 seconds before returning to the colony.

Bald eagles have also caused disturbances at the Crescent Island tern colony (0.20 disturbances/hr of observation). The terns seemed to be more settled on the Crescent Island colony this year as compared to this same time period last year, returning to the colony site within 10-15 seconds following disturbances. We expect the number of eagle disturbances to terns on Crescent Island will decline once migratory waterfowl in the vicinity of Crescent Island leave the area.

This past week, gull kleptoparasitism rates were low at East Sand Island (7% of all known fates of fish delivered by terns). At Crescent Island, no kleptoparasitism was observed this past week.

To date, there have been no signs of mammalian predators on any of the tern colonies monitored as part of this study.

Media & Other Visitors

During April 1 - 4, USACE personnel (lead by Geoff Dorsey) were on East Sand Island to prepare suitable tern nesting habitat.

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