A partnership between Oregon State University, Real Time Research, and the USGS - Oregon Cooperative Fish and Wildlife Research Unit

Columbia River Estuary

WEEKLY UPDATE 6/10 – 6/16/2019

6/10 – 6/16/19 ›

Count for the week of 5,767 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 6/14; the number of Caspian terns present on the one-acre colony area during the day this week (5,767) was similar to the previous week (5,499); the estimated number of terns sitting on eggs decreased slightly this week to 2,378, as compared to 2,917 tern nests with eggs the previous week; the frequency of eagle disturbance to the colony and gull depredation of tern eggs continues to decline from what was observed earlier in the season suggesting that the tern colony may produce some fledglings this season

6/10 – 6/16/19 ›

Two satellite Caspian tern colonies (i.e. areas away from the one-acre designated tern colony area where terns are engaged in nesting behaviors and have laid and are incubating eggs) were present on East Sand Island this week; a total of 1,176 Caspian terns were counted in aerial photography of the two satellite tern colonies taken on 6/14, up from 838 terns counted on three satellite colonies on 6/8; efforts by the Corps to dissuade terns from nesting at a satellite colony discovered last week on the southeast tip of East Sand Island were successful, as there were no terns present at that location during the aerial survey on 6/14

6/10 – 6//19 ›

Bald eagles caused frequent daytime disturbances to nesting terns on the one-acre colony area, including chasing adult terns with bill-load fish and flying low over the tern colony looking for terns with bill-load fish; also, night-time colony disturbances were observed and depredations of nesting terns by a great horned owl were observed this week

WEEKLY UPDATE 6/3 – 6/9/2019

6/4/19 ›

Aerial survey of the Columbia River estuary, Willapa Bay, and Grays Harbor to search for nesting Caspian terns at sites other than the managed colony on East Sand Island; Caspian tern nesting behavior was not observed at any location other than on East Sand Island; a total of about 180 Caspian terns were observed at loafing sites in the Columbia River estuary away from East Sand Island, including 80 loafing terns on Rice Island; a total of about 250 Caspian terns were observed loafing in Willapa Bay, and a total of about 43 Caspian terns were observed loafing in Grays Harbor

6/3 – 6/9/19 ›

Count for the week of 5,499 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 6/8; the number of Caspian terns present on the one-acre colony area during the day this week (5,499) was similar to the previous week (5,153); the estimated number of terns sitting on eggs increased again this week to 2,917 tern nests with eggs compared to 1,939 tern nests with eggs last week; colony status this week suggested that the tern colony may produce fledglings this season, as it did last season; similar to the previous week, the magnitude of eagle disturbance to the tern colony and the rate at which gulls are depredating tern eggs were not as great as earlier in the nesting season, when it appeared that the tern colony might completely fail

6/3 – 6/9/19 ›

This week it became clear that three satellite Caspian tern colonies are forming on East Sand Island outside of the one-acre designated tern colony area; all three satellite colonies appear to include tern nests with eggs, but it is too early to estimate how many tern pairs might be nesting in each satellite colony; a total of 838 Caspian terns were counted in aerial photography of the three satellite tern colonies this week, suggesting that the numbers of Caspian terns attempting to nest outside the one-acre colony area are now significant

6/3 – 6/9/19 ›

Bald eagles caused frequent daytime disturbances to nesting terns on the one-acre colony area, including chasing adult terns with bill-load fish and flying low over the tern colony looking for terns with bill-load fish; also, colony disturbances were observed and depredations of nesting terns by a great horned owl was observed this week

WEEKLY UPDATE 5/27 – 6/2/2019

5/27 – 6/2/19 ›

Count for the week of 5,153 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 5/30; the number of Caspian terns present on the one-acre colony area during the day this week increased compared to the previous week; 1,939 tern nests with eggs were estimated on the tern colony by the end of the week (6/2), a large increase compared to the previous week when only an estimated 247 nests with eggs were present on-colony; this increase was related to lower rates of disturbance to the tern colony by bald eagles and, consequently, lower rates of gull depredation of tern eggs; developments this week suggest that some nesting attempts by terns on East Sand Island this season may succeed in producing young, as they did in 2018, if eagle disturbances and egg predation rates by gulls continue to wane; the decline in both eagle disturbance rates to the tern colony and gull predation rates on tern eggs coincided with a sharp decline in the proportion of juvenile salmonids in the tern diet, but whether this is coincidence or a cause-effect association is unclear

5/27 – 6/2/19 ›

Bald eagles caused frequent daytime disturbances to nesting terns on the one-acre colony area, including chasing adult terns with bill-load fish and flying low over the tern colony looking for terns with bill-load fish; also, colony disturbances were observed and depredations were suspected on nesting terns and gulls by a great horned owl and a peregrine falcon this past week

WEEKLY UPDATE 5/20 – 5/26/2019

5/20 – 5/26/19 ›

Count for the week of 4,279 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 5/22; the number of Caspian terns present on the one-acre colony area during the day this week did not increase compared to the previous week, when numbers were down from three weeks ago; only 247 tern nests with eggs were estimated to remain on the tern colony by the end of the week (5/26), a decline compared to the previous week when an estimated 540 nests with eggs were present on-colony; this decline was caused by high rates of disturbance to the tern colony by bald eagles and high rates of gull depredation of tern eggs during those disturbances; these trends suggest that all early nesting attempts by terns may fail this season, as they did in 2011 and 2017, if eagle disturbances and egg predation by gulls continue unabated; the magnitude of eagle disturbance to the tern colony and the rate at which gulls are depredating tern eggs is somewhat unexpected, given that river discharge into the Columbia River estuary is similar to the average for this time of year, and forage fish availability to the terns does not seem to be limiting

5/20 – 5/26/19 ›

Bald eagles caused frequent daytime disturbances to nesting terns on the one-acre colony area, including chasing adult terns with bill-load fish and flying low over the tern colony looking for terns with bill-load fish; as many as 114 western/glaucous-winged gulls were counted this week on the one-acre tern colony area, including several nesting pairs of gulls; gull predation rates on tern eggs continued to be high this week, raising the possibility that the combination of intense eagle disturbance and high gull predation rates on tern eggs might cause the tern colony to fail to raise any young terns this season

WEEKLY UPDATE 5/13 – 5/19/2019

5/13 – 5/19/19 ›

Estimate for the week of ca. 4,400 Caspian tern individuals and 540 active nests on the one-acre East Sand Island tern colony, based on ground-based counts on 5/19 from an observation blind adjacent to the colony; poor weather prevented taking aerial photography of the colony with UAS this week; the estimate of numbers of terns on-colony was less than the UAS-based count the previous week (5,194 individuals); terns observed on-colony were mostly engaged in courtship and nesting behaviors (i.e. digging nest scrapes, copulation, courtship feeding, egg-laying); early in the week, about 75% of the colony area had active tern nests with 1- to 2-egg clutches, excluding the western-most part of the colony, which was devoid of active tern nests; due to a large number of flushes of the tern colony caused by bald eagles, egg depredation rates by western/glaucous-winged gulls increased later in the week, and the number of tern eggs and active tern nests on-colony declined appreciably by the end of the week; by 5/19, most tern nests that were still active contained just 1 egg, although a handful of active tern nests still contained 2 eggs; the majority of tern nests with eggs were concentrated in the central and northern portions of the eastern half of the colony area

5/13 – 5/19/19 ›

Bald eagles caused frequent daytime disturbances to nesting terns on the one-acre colony area, including chasing adult terns with bill-load fish and flying low over the tern colony looking for terns with bill-load fish; as many as 107 western/glaucous-winged gulls were counted this week on the one-acre tern colony area, including several nesting pairs of gulls; gull predation rates on tern eggs were particularly high this week, raising the possibility that the combination of intense eagle disturbance and high gull predation rates on tern eggs might cause the tern colony to fail this season

5/18 – 5/19/19 ›

Boat-based surveys to count California brown pelicans roosting on East Sand Island revealed 89 pelicans on the island the morning of 5/18 and 226 pelicans on the island the evening of 5/19; no nesting activity by California brown pelicans has been detected on East Sand Island so far this breeding season

WEEKLY UPDATE 5/6 – 5/12/2019

5/7/19 ›

First California brown pelicans (5) observed in the Columbia River estuary by the field crew this season; by the end of the week, 200 individual brown pelicans were counted on the southeast beach of East Sand Island

5/6 – 5/12/19 ›

Count for the week of 5,194 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS; terns observed on-colony were mostly engaged in courtship and nesting behaviors (i.e. digging nest scrapes, copulation, courtship feeding, egg-laying); the rate of egg-laying increased on the colony area this week, with the majority of nests containing 1 or 2 eggs; disturbances to the tern colony by bald eagles continued to be frequent, with large numbers of tern eggs being depredated by gulls during colony flushes

5/6 – 5/12/19 ›

Bald eagles caused frequent daytime disturbances to nesting terns on the one-acre colony area; there were no other signs of predators observed on East Sand Island this week

WEEKLY UPDATE 4/29 – 5/5/2019

4/29/19 ›

First Caspian tern eggs (3) observed on the designated one-acre tern colony area on East Sand Island, and all were quickly depredated by gulls during a flush of the colony caused by a bald eagle; it is possible, perhaps likely, that egg laying by terns on the one-acre colony area occurred late last week, but any eggs were quickly depredated by gulls before they could be observed by our field crew

4/29 – 5/5/19 ›

Count for the week of 4,528 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS; terns observed on-colony were mostly engaged in courtship and nesting behaviors (i.e. digging nest scrapes, copulation, courtship feeding, egg-laying); by the end of this week there was at least one tern nest on-colony that contained more than one egg

4/29 – 5/5/19 ›

Signs of multiple predators observed on East Sand Island; bald eagles caused frequent daytime disturbances to nesting terns on the one-acre colony area; river otter tracks were observed on the north beach east of the one-acre tern colony area; two peregrine falcons observed flying over the east end of the island on 5/1

WEEKLY UPDATE 4/22 – 4/28/2019

4/22 – 4/28/19 ›

Count for the week of 3,079 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS; terns observed on-colony were engaged in pre-nesting behaviors (i.e. territory defense, digging nest scrapes, copulation, courtship feeding); Caspian terns began to spend the night on the prepared one-acre colony area for the first time this season on 4/24; it is possible, perhaps likely, that egg laying by terns on the one-acre colony area has commenced; however, any eggs that were laid were likely depredated by gulls

4/22 – 4/28/19 ›

Signs of multiple predators observed on East Sand Island; bald eagles causing frequent daytime disturbances to nesting terns on the one-acre colony area; mink tracks were observed on the south beach west of the one-acre tern colony area

WEEKLY UPDATE 4/15 – 4/21/2019

4/15 – 4/21/19 ›

Count for the week of an estimated 2,470 Caspian tern individuals on the one-acre East Sand Island tern colony; this estimate was based on rough counts from the ground by the field crew; terns observed on-colony were engaged in pre-nesting behaviors (i.e. territory defense, digging nest scrapes, copulation, courtship feeding); although Caspian terns have established nest scrapes and territories on the one-acre colony area, they have not spent the night on the prepared colony area so far this breeding season

4/15 – 4/21/19 ›

Signs of multiple predators observed on East Sand Island; bald eagles causing frequent daytime disturbances to nesting terns on the one-acre colony area; a river otter was observed east of the tern colony on 4/19, causing a small disturbance to nesting western/glaucous-winged gulls

WEEKLY UPDATE 4/8 – 4/14/2019

4/8/19 ›

OSU field crew installed six trail cameras to monitor brown pelican use of the island for loafing and possible nesting

4/11/19 ›

First Caspian terns (232) observed on the designated one-acre tern colony area on East Sand Island

4/8 – 4/14/19 ›

High count for the week of an estimated 791 Caspian tern individuals on the one-acre East Sand Island tern colony; terns observed on-colony were engaged in pre-nesting behaviors (i.e. territory defense, digging nest scrapes, copulation, courtship feeding)

4/8 – 4/14/19 ›

Signs of multiple predators observed on East Sand Island; bald eagles and a red-tailed hawk were observed occasionally flying over island

UPDATE 3/16 – 4/7/2019

3/16/19 ›

First visit by the OSU field crew to East Sand Island

3/17/19 ›

As many as 14 bald eagles observed on or near the one-acre tern colony area on East Sand island

3/21/19 ›

On-site meeting with OSU and the Corps’ Fisheries Field Unit to discuss the location, shape, and surface preparation for the one-acre Caspian tern colony area on East Sand Island

3/21/19 ›

Corps’ Fisheries Field Unit began placement of tern nest dissuasion materials (i.e. stakes, rope, and flagging) outside the designated one-acre tern colony area

3/22/19 ›

Corps’ Fisheries Field Unit completed delineation and began preparation of bare-ground substrate on one-acre tern colony area at East Sand Island

3/22/19 ›

Large numbers of ring-billed gulls began consistently attending their colony site on the upper section of the northeast beach on East Sand Island

3/26/19 ›

First Caspian terns sighted in the Columbia River estuary by project staff in 2019; several individuals seen flying over East Sand Island

3/28/19 ›

River otter tracks seen on east beach of East Sand Island

4/1/19 ›

First Caspian terns (20 individuals) observed on East Sand Island (loafing on the northeast beach)

4/2/19 ›

River otter scat observed west of the one-acre tern colony area on East Sand Island

4/4/19 ›

OSU field crew set up grids and productivity plots on the one-acre tern colony area used to collect data on nesting terns

4/4/19 ›

Harbor seal carcass washed up on the southeast beach on East Sand Island attracting scavenging bald eagles to the vicinity of the one-acre tern colony area

The weekly update of events at various piscivorous waterbird colonies in the Columbia River estuary

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