Cormorant Management

Chicks observed with ages between two to three weeks old

Observations from the island on Sept. 13 show approximately 1,500 double-crested cormorants and approximately 3,000 Brandt's cormorants loafing on the western portion of the island. Chicks of both species were observed and nest chronology estimates their age to be between two and three weeks old. Aerial images taken Sept. 13 show between 140 and 150 active double-crested cormorant nests. A single disturbance event was observed during the survey, when four kayaks approached the island and rounded the western tip into Baker Bay. As the kayaks left the area, the birds resettled into their former loafing spots.

Updated counts show higher numbers; first sign of chicks

Updated information from a detailed analysis of the aerial imagery collected Aug. 14 and 25 reveals a higher number of active nests than was previously estimated through ground surveys. Flight imagery from Aug. 14 shows 260 double-crested cormorant nests and 1,409 Brandt's cormorant nests. Ground surveys had not accounted for the majority of these nests as they were out of view from the blinds from which those surveys had been conducted. The updates numbers are a substantial increase from the approximately 30 double-crested cormorant nests that were visible from the blinds. Aerial images from Aug. 25 shows 306 double-crested cormorant nests and 1,272 Brandt's cormorant nests.

The first observations of chicks for the 2017 season were observed during recent ground surveys of East Sand Island. Five thousand to 6,000 cormorants were observed on the western portion of the island, visible on the shoreline and foraging in open water off the western tip of the island. Both double-crested and Brandt's cormorants were confirmed to have active nests with chicks that were estimated to be about 7 to 10 days old. At least five double-crested cormorant chicks and 26 Brandt's cormorant chicks were observed. Most nests had two chicks, with no observations of nests that had more than two. Aerial imagery conducted Sept. 5 shows about 200 double-crested cormorant nests, suggesting the peak nest count for the 2017 season occurred at the end of August at 306 nests.

Nest estimates unchanged at East Sand Island

Observations from the blind at East Sand Island showed cormorants occupying the same areas on the western portion of the island that they have occupied since late July. About 7,000 cormorants were observed, comprising about 4,000 double-crested cormorants and 3,000 Brandt's cormorants. Nest estimates were unchanged from previous observations of about 30 double-crested cormorant nests and 200 Brandt's cormorant nests.

Final Astoria-Megler Bridge roost survey yields lowest numbers since April

The final Astoria-Megler Bridge roost survey was completed the evening of Aug. 26 and the following morning. The evening survey revealed the lowest totals for individuals and arrivals at the bridge since late April. Three times as many birds commuted from downstream as compared to upstream. Many of the birds observed were juveniles and both double-crested cormorant and Brandt's cormorant chicks were observed under the main portion of the bridge supports. Morning survey totals were very similar to totals recorded the previous evening, with the lowest number of departing birds this season. About 1,400 double-crested cormorants roosted on the bridge overnight.

7,500 double-crested cormorants, no predators observed at East Sand Island

A late-season visit to East Sand Island Aug. 25 showed cormorants distributed at the western portion of the island, with more double-crested cormorants loafing on the beaches and on the upland sand flats adjacent to the jetty. Our best estimate for overall cormorant numbers was about 7,500 — comprising about 6,000 double-crested cormorants and about 1,500 Brandt's cormorants. Though numbers were higher than those seen during the previous visit on Aug. 19, the number of nesting birds did not significantly change, with about 30 double-crested cormorants and about 200 Brandt's cormorants sitting on nests. No breeding behaviors were observed. One Brandt's cormorant was observed delivering nest materials. No avian predators were observed on the western portion of the island during the survey.

3,500 double-crested cormorants, no predators observed at East Sand Island

About 5,000 cormorants were observed on East Sand Island Aug. 19, consisting of approximately 3,500 double-crested cormorants and 1,500 Brandt’s cormorants. No birds were observed conducting breeding displays or bringing nest material to active nests. Active nests were estimated to total approximately 30 double-crested cormorant nests and approximately 200 Brandt’s cormorant nests. There were no observation of predators (e.g. bald eagles) during the site visit.

Lewis and Clark Bridge shows nest decrease with chicks fledging

A survey of the Lewis and Clark Bridge Aug. 17 showed a decrease in the number of double-crested cormorant nests, from 53 nests compared to the previous observation of 147 nests on July 20. Most chicks have fledged from nests but there remained some juveniles estimated to have approximately one more week before fledging.

Numbers remain consistent at East Sand Island

A survey of East Sand Island revealed similar observations relative to the previous week, with approximately 5,000 double-crested cormorants and approximately 2,500 Brandt’s cormorants loafing along the shorelines. Observations of nesting birds estimated that 85 double-crested cormorant nests and 298 Brandt’s cormorant nests are on active nests. In addition to the birds loafing on East Sand Island, there were approximately 4,500 double-crested cormorants observed loafing along the shoreline of Rice Island upstream from Tongue Point. Additional surveys of the Astoria-Megler Bridge revealed a slight decrease in the number of double-crested cormorant nests (412) compared to the previous week’s observation. There was no change in the number of pelagic cormorant nests relative to the previous week (56 active nests), and there were a total of four Brandt’s cormorant nests observed, two more than previously observed. Most chicks have fledged from the nests on the bridge, but there are some juveniles that were still one to two weeks from fledging. Roughly 10,000 double-crested cormorants were observed loafing on the shoreline at Rice Island Aug. 11. It is unknown how many of the birds observed Aug. 11 are the same or different from the birds observed Aug. 9.

Lower numbers at East Sand Island, Astoria-Megler Bridge

A survey of East Sand Island was conducted on Aug. 2, but poor lighting limited visibility and species identification and differentiation. Despite the hazy conditions, about 4,000 to 5,000 were observed loafing along the shorelines of the island. The high number of birds observed July 26 were not present. It is possible that the multitude consisted of birds dispersed from breeding areas outside of the Columbia River estuary who were now queuing up in advance of the fall migration. A survey of the Astoria-Megler Bridge was conducted Aug. 2. Double-crested cormorant nests totaled 477 (down from 654 nests July 26). Pelagic cormorants continue to occupy the bridge and are maintaining 56 active nests, and Brandt’s cormorants are maintaining two active nests.

Evidence of increased presence, nesting at East Sand Island

The team also visited East Sand Island to observe the status of cormorants on the upland portion of the island. As with the previous week, double-crested and Brandt's cormorants were observed in breeding displays, copulating and delivering materials for nest construction. Observations were boat-based, as cormorant use along the beaches and sections of riprap precluded access to the observation blinds for ground-based monitoring. An aerial flight was conducted simultaneously with the boat-based surveys, revealing about 19,700 cormorants (both double-crested and Brandt's) present on the island and beaches, with an estimated 500 exhibiting nesting behaviors July 26 (similar to last week's observations). No bald eagles were observed in the vicinity during the entire survey of East Sand Island.

Nest numbers hold steady at Astoria-Megler Bridge

A roost survey was conducted at the Astoria-Megler Bridge the evening of July 23 and morning of July 24. Double-crested cormorants were observed commuting to the bridge mostly from downstream and most birds departed the bridge in the morning and moved downstream. Approximately 4,500 to 5,000 double-crested cormorants roosted at the bridge overnight. A nest survey of the Astoria-Megler Bridge July 26 showed total nest numbers were lower than but still mostly similar to the previous week's observations, with 654 active nests compared to 787 nests for the previous week. There remained about 65 pelagic cormorants and a single Brandt's cormorant nest on the bridge as well.

Cormorants exhibit breeding behavior at East Sand Island

Following the aerial survey on July 19, a ground survey of East Sand Island on July 21 showed approximately 6,500 double-crested cormorants on shorelines around East Sand Island. Researchers observed breeding behavior from approximately 500 double-crested cormorants and 1,200 Brandt's cormorants, including breeding displays, copulation and nest-building activity with continuous delivery of nesting material. While there were four bald eagles observed in the vicinity, only one eagle was observed near the western portion of island on in-water pilings but they were not on the island as observed previously in the season.

Cormorants observed loafing at East Sand Island

Approximately 6,000 double-crested cormorants were observed loafing on the western shoreline of East Sand Island during an aerial survey on July 19. In addition, a routine survey of the Astoria-Megler Bridge on July 20 showed that double-crested cormorant nests decreased from previous week from 834 to 787 nests — pelagic cormorant nests also decreased to 69 nests. There is still only one confirmed Brandt's cormorant nest on the bridge. Nest observations show chicks with asynchronous age structures, with some birds very young and downy, while others are mobile and ready to fledge. A routine survey of the Lewis & Clark Bridge July 20 shows an estimated 147 double-crested cormorant nests, with some of those nests in new locations not observed during previous surveys.

Nest numbers continue to increase at Astoria-Megler Bridge

An aerial survey of East Sand Island July 10 show an estimated 3,000 to 3,500 loafing on the shoreline, with small numbers on the riprap and above the high tide line. A routine survey of the Astoria-Megler Bridge showed approximately 834 double-crested cormorant nests, again increasing from the previous week. Pelagic cormorant nests increased, as well, to 76 nests, along with a single confirmed Brandt's cormorant nest. Approximately 6,000 adult double-crested cormorants were observed on the bridge.

Nest numbers increasing at Astoria-Megler Bridge

An aerial survey of East Sand Island July 5 shows an estimated 2,000 to 3,000 double-crested cormorants loafing on the shoreline, with small numbers on the riprap and above the high-tide line. A routine survey of the Astoria-Megler Bridge July 4 shows nest numbers continuing to increase (47 nests more than in the previous week's observation). Pelagic cormorant nest numbers showed little changes with 71 nests observed. Chicks appear to be 35 to 40 days old. Upwards of 7,000 adult cormorants were observed on the bridge.

A routine survey conducted at the Astoria-Megler Bridge June 28 showed approximately 3,500 double-crested cormorants and 722 nests. Pelagic cormorants continue to nest on the bridge as well, but in smaller numbers (with 72 nests observed). On June 29, a routine survey of the Lewis & Clark Bridge showed approximately 125 nests with chicks ranging in age between 10 and 30 days old. An aerial survey of the mouth of the Columbia River, Grays Harbor and Willapa Bay shows approximately 3,000 cormorants loafing around the shoreline of Sand Island in Grays Harbor with some small clusters of nesting birds on channel markers in the vicinity of Grays Harbor South Channel.

Fewer bald eagles observed at East Sand Island

Approximately 7,000 to 9,000 individual double-crested cormorants are observed clustered tightly along the shoreline at East Sand Island June 26. While bald eagles are present in fewer numbers to previous visits with 12 observed, no dispersal events are noted during the period of observation.

Cormorants reported at other sites

The Corps receives reports of several thousand cormorants at Grays and Willapa bays over the weekend. Aerial surveys conducted over the Columbia River are unable to find vast numbers of cormorants in the estuary, though about 1,000 to 1,500 are observed at the south shoreline. Nest surveys of the Astoria-Megler Bridge estimate 686 double-crested cormorant nests and 76 pelagic cormorant nests, with some Brandt’s cormorants loafing on the lower portion of the bridge.

Seventh survey conducted at Astoria-Megler Bridge

A seventh survey of the Astoria-Megler Bridge is conducted June 14. Total numbers of double-crested and pelagic cormorants are consistent with previous observations, though nest estimates have increased to 645 for double-crested cormorants and 77 for pelagic cormorants. Nest observations confirm the presence of chicks, with estimated age based on appearance of visible chicks at seven to 10 days old. A roost survey is conducted the evening of June 17 and again on the morning of June 18 with about 10,000 double-crested cormorants on the bridge June 17. Weather conditions limited visibility, though approximately 7,000 cormorants were counted on the bridge structure early next morning.

On-island observations yield evidence of earlier nesting

Between 3,000 to 4,000 cormorants are observed on the north shoreline of East Sand Island in the morning. Seventeen eagles are spotted at the western portion of the island flushing birds on multiple occasions. The Corps determines a brief visit to a small portion of the colony for closer observation is warranted and will have little potential for disturbance to the birds on the beach, due to the lack of activity in the colony area. Two fresh cormorant carcasses are observed during the site visit, along with eggshell fragments throughout the observed area, confirming that cormorants attempted nesting earlier in the season. The survey for eggs was limited to minimize the potential for disturbance. Approximately 4,000 to 5,000 cormorants were observed on the shoreline in the early afternoon after the field crew departed the island.

Fewer bald eagles observed at East Sand Island

Approximately 7,000 to 9,000 are observed clustered tightly along the shoreline at East Sand Island. While bald eagles were present in fewer numbers relative to previous visits, with 12 observed, no dispersal events were noted during the period of observation.

Aerial survey conducted

An aerial survey conducted at East Sand Island reveals about 100 adult double-crested cormorants.

Management actions begin

Preparations of the East Sand Island colony site are completed, with the work crew demobilized and the site ready for occupation. Boat-based culling of adult double-crested cormorants in the lower estuary begins.

Astoria-Megler Bridge roost count conducted

A count at the Astoria-Megler Bridge shows about 10,000 cormorants roosting on the bridge overnight June 9. Photos from East Sand Island taken June 10 show some cormorants in the colony area in the morning, only to disperse soon after.

Third bridge survey conducted at Lewis and Clark Bridge

A third bridge survey for the Lewis and Clark Bridge shows 114 active double-crested cormorant nests with few cormorants observed in vicinity of bridge.

Continued eagle harrassment and dispersals

Field observations show about 8,500 cormorants on the western portion of East Sand Island, including the rock jetty extending west of the nesting area. Twenty-five to 30 eagles were spotted on or near the colony for the majority of the day, causing short-duration dispersals throughout the day and predation of at least two adult cormorants. Photographic evidence indicates that all cormorants were dispersed in the early morning on June 6.

Cormorants return despite continued bald eagle harassment

Double-crested cormorants have returned to East Sand Island, occupying the island throughout the day and night with short-duration disturbances from bald eagles. Aerial and boat-based surveys show more than 10,000 double-crested cormorants in the nesting area, on the rip rap bank on the south or on the beach on the north side of the island. Pressure from bald eagles remains high, with 22 eagles observed throughout the west end of the island.

Cormorant dispersal continues

Double-crested cormorants occupied East Sand Island throughout the day but were dispersed in the evening.

Fourth nest count conducted

A fourth nest count on the Astoria-Megler Bridge shows 404 active double-crested cormorant nests and 57 pelagic cormorant nests.

Aerial and boat-based surveys conducted

Aerial and boat-based surveys show about 6,000 double-crested cormorants in the water near East Sand Island or on the beach on the north side of the island. Pressure from bald eagles remains high with 17 eagles observed on the west end of the island.

Bald eagles disperse all cormorants

Around the middle of the day, all double-crested cormorants are dispersed from the colony site. Clear photographic evidence and real-time observation from blinds show bald eagles played a significant role in the dispersal of cormorants. No eggs were observed in abandoned double-crested cormorant nests.

Third nest count conducted

A third nest count on the Astoria-Megler Bridge shows 394 active double-crested cormorant nests and 55 pelagic cormorant nests.

Cormorants nesting at East Sand Island

Double-crested cormorants have occupied East Sand Island for five days, with short-duration disturbances from bald eagles. Nest-building and breeding behavior have been observed regularly. An estimated 5,422 individual double-crested cormorants and 997 nests are counted from aerial imagery.

Night survey

A night survey of the Astoria-Megler Bridge shows 5,271 double-crested cormorants roosting overnight on the bridge. By morning, about 2,493 remain on the bridge. Of the double-crested cormorants that left by sunrise, 38 percent flew downstream toward the mouth and 62 percent flew upstream.

More cormorants arrive

A large number of double-crested cormorants arrive at East Sand Island. Evidence of regular disturbances from bald eagles are still observed, but the cormorants return to the nesting areas quickly after each disturbance.

Reconnaissance flight, second nest count conducted

A reconnaissance flight over the estuary shows 1,500 to 2,000 double-crested cormorants foraging north of Pillar Rock Island (i.e. about 1,000 cormorants roosting on the beach of Pillar Rock Island, while the remainder roost elsewhere. There are no signs of cormorants nesting in the vicinity.) An estimated total of 3,000 double-crested cormorants are observed foraging in groups around training dikes upstream of Tenasillahe, Puget, Eureka, Crims and Lord Islands, with no evidence of nesting nearby.

A second nest count is conducted, showing 385 active double-crested cormorant nests and 36 pelagic cormorant nests on the Astoria-Megler Bridge.

Some eagles are diverted

As many as 40 bald eagles are observed at the site of the whale carcass placed near East Sand Island two days earlier.

Eagle high-perch trees removed

Three dead trees in the East Sand Island double-crested cormorant colony site used as high perches by bald eagles there are removed in an attempt to alleviate pressure on cormorants attempting to colonize the island.

Alternate food source provided for eagles

NOAA fisheries place a deceased gray whale near East Sand Island to decay naturally following a necropsy — an additional food source nearby may help to draw bald eagles away and allow for double-crested cormorant colony formation on the island.

Nest count conducted

Nest counts are conducted at Astoria-Megler and Longview bridges. Count reveals 258 active double-crested cormorant nests and 23 pelagic cormorant nests at Astoria-Megler Bridge. Sixty-four active double-crested cormorant nests are counted at Longview Bridge.

Night survey

A night survey conducted of the Astoria-Megler Bridge shows 6,090 double-crested cormorants roosting overnight on the bridge. In the morning, approximately 729 double-crested cormorants remained on the bridge. Of the cormorants that left at sunrise, 50 percent flew downstream toward the mouth of the Columbia and 50 percent flew upstream.

Culling is suspended

Culling activity in the estuary is suspended due to lack of colony formation on the island. Photos show daily attempts by double-crested cormorants to initiate nesting are continually interrupted by widespread disturbances by bald eagles. The adaptive management team intends to wait for the colony to form so it can collect a baseline population number before resuming culling activity.