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Fewer Cormorants Nest at East Sand Island, Observers Document Bald Eagle Predation on Eggs by Staff Columbia Basin Bulletin, July 20, 2018

As of early July some 6,500 double-crested cormorants were nesting on East Sand Island in the lower Columbia River estuary and even more were seen nesting on nearby bridges, according to a recent report by the U.S. Army Corps of Engineers.

Rather than lethally remove or cull the cormorants this year, the Corps decided to enter the second phase of its five-year cormorant management program by hazing the birds and removing a limited number of eggs at the island as a way to keep the number of nesting pairs under control.

As another control measure, the Corps' contractor, Wildlife Services, which in past years was responsible for the lethal culling of cormorants, fenced off a nesting area on East Sand Island -- a 1.3 acre plot -- in which they hope the cormorants will nest. Birds not in the confines of the fence are hazed.

Cormorants feed on juvenile salmon and steelhead, some of which are listed under the federal Endangered Species Act.

The Corps said earlier this year that it would like to see up to 5,900 breeding pairs to fit into the fence line near the western end of island (see CBB, May 4, 2018, "Cormorants Return To East Sand Island But No Lethal Removal This Year; Hazing, Egg Take". The Corps would like to limit the population to these breeding pairs, about 12,000 birds.

The Corps began culling, harassing and egg oiling of the birds and their nests in 2015, but for the past two years cormorants were late to nesting, requiring the Corps to suspend the operations designed to reduce the number of breeding pairs in the lower river.

The Corps' June 27 to July 5 management report shows that the island had 6,538 individual double-crested cormorants, 3,586 nests and, also crowded onto the island, 208 Brandt's cormorant nests as of June 19.

But that's just a partial story of the number of cormorants in the lower Columbia River this spring and summer. The Corps reports that the Lewis & Clark Bridge, which crosses Youngs Bay between Astoria and Warrenton, Oregon, had 217 cormorants and 159 nests as of July 5. The more than 4-mile long Astoria-Megler Bridge, which crosses the Columbia River between Oregon and Washington, had 3,167 cormorants and 1,452 nests at one point on the bridge as of June 28, and 2,751 birds and 1,498 nests as of July 5 at another bridge site.

Nesting is not without incident, especially from persistent predation on cormorant eggs by bald eagles.

BAEA (bald eagle) "pressure was persistent and intense for most of the visit," said an observer on June 27. "A group of 6 BAEA (3 adults, 3 juveniles) landed on the colony pushing a large portion of the colony off their nests. They proceeded to eat eggs throughout this portion of the colony up to within about 6 feet of the blind, moving north along the fence and out to the edge of the flat sand where it drops off to the cove beach. There was no way to enumerate egg loss as it was immense and widespread. Many clutches between 1-4 were observed losing all eggs. The nests within a few feet of the fence appeared to hold onto their clutches. This first disturbance event lasted just over an hour (65 min) followed by a break in predation that lasted approximately 37 min with 4 of the eagles loafing on the cove beach and 1 juvenile remaining stationary on the colony."

This event was followed by another period of predation by 5 eagles (2 adults, 3 juveniles that were observed for 43 minutes. Observers during these two events saw a total of 8 individual eagles. During these disturbances many Western gulls followed the eagles throughout the colony picking up egg remains left behind.

In 2016, culling was suspended in mid-May and Wildlife Services didn't resume until October 3. By mid-July 2016, some 15,300 cormorants were seen "loafing" on the island. By August about 23,000 were on the island and by September many were rebuilding nests and laying eggs. The agency still managed to cull nearly 3,000 of the cormorants in 2016, almost all of those by the end of October.

However, last year Wildlife Services suspended culling April 27 and never resumed, killing just 248 cormorants and no nests were destroyed. The Corps said that as many as 40 eagles were harassing the sea birds, keeping them from nesting on the island and driving them to other areas, such as local bridges, and Willapa Bay and Grays Harbor in western Washington State.

The U.S. Fish and Wildlife Service issued its fourth depredation permit to the Corps April 19. The permit allows the collection of up to 500 cormorant eggs on East Sand Island, as well as up to 250 eggs on sites in the upper estuary at "dredged material placement sites," which are areas where the Corps places sandy dredged materials from its dredging operations that keep the Columbia River shipping channel at a 43-foot average depth.

Management activities this year are supplemented with limited egg take, as necessary and within the limit authorized by USFWS, to support maintenance of a breeding colony with no more than 5,900 breeding pairs on East Sand Island, the Corps said.

Related Sites:
Corps Decides Not to Cull Estuary Cormorants In 2018, Will Continue Hazing, Egg Removal by Staff, Columbia Basin Bulletin 3/16/18
Estuary Cormorants Nesting In Low Numbers; Corps Unsure If Culling Will Resume Before Season Ends by Staff, Columbia Basin Bulletin 9/22/17
Due To Low Numbers Of Estuary Cormorants Showing Nesting Activity, Culling Remains Suspended by Staff, Columbia Basin Bulletin 8/11/17
Corps Continues Suspension Of Culling Salmon-Eating Cormorants In Estuary by Staff, Columbia Basin Bulletin 7/7/17
With Cormorant Nesting On East Sand Island Stalled, Boat-Based Shooting Of Birds Suspended by Staff, Columbia Basin Bulletin 6/16/17
Third Year Of Shooting Salmon-Eating Cormorants, Oiling Nests: Goal Is To Kill 2,409 Birds by Staff, Columbia Basin Bulletin 4/28/17
Court Allows Continued Culling Of Cormorants In Columbia Estuary To Reduce Predation On Salmonids by Staff, Columbia Basin Bulletin 9/9/16