WEEKLY UPDATE 8/26 – 9/1/2019
9/1/19 ›
This completes our regular weekly reporting of field research activities on East Sand Island for 2019
8/26 – 9/1/19 ›
Count for the week of 465 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 8/27; the number of Caspian terns present on the one-acre colony area during the day this week was lower than the count the previous week (1,466); the estimated number of tern nests with contents (either eggs or chicks) on the one-acre colony area decreased this week to about 214, compared to about 365 the previous week; about 97% of these tern nests contained chicks, and the rest contained only eggs; as in previous weeks, western/glaucous-winged gulls continued to depredate tern eggs and chicks during disturbances to the tern colony that caused nesting adult terns to flush; western/glaucous-winged gulls were also observed depredating some Caspian tern chicks in the absence of any colony disturbances
8/26 – 9/1/19 ›
Counts of the number of Caspian tern individuals nesting and/or prospecting at the three apparent satellite tern colonies off of the main tern colony were not conducted this week, as there did not appear to be any individuals exhibiting nesting behaviors
8/26 – 9/1/19 ›
No bald eagle caused disturbances to the tern colony were observed this week; during the week, we continued to observe evidence of depredated juvenile and adult Caspian terns and gulls, mostly the apparent result of avian predation
WEEKLY UPDATE 8/19 – 8/25/2019
8/19 – 8/25/19 ›
Count for the week of 1,466 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 8/22; the number of Caspian terns present on the one-acre colony area during the day this week was lower than the count the previous week (2,273); the estimated number of tern nests with contents (either eggs or chicks) on the one-acre colony area decreased this week to about 365, compared to about 641 the previous week; about 95% of these tern nests contained chicks, and the rest contained only eggs; as in previous weeks, western/glaucous-winged gulls continued to depredate tern eggs and chicks during disturbances to the tern colony that caused nesting adult terns to flush; western/glaucous-winged gulls were also observed depredating some Caspian tern chicks in the absence of any colony disturbances
8/19 – 8/25/19 ›
Counts of the number of Caspian tern individuals nesting and/or prospecting at the three apparent satellite tern colonies off of the main tern colony were also obtained from the photo mosaic taken by UAS; the satellite colony on the upper beach just to the south of the one-acre colony area had no terns present, which was a decrease compared to the count from the previous week (28 individuals); the satellite colony on the upper beach to the southwest of the one-acre colony area had a total of 22 tern individuals, which was a significant decrease compared to the count from the previous week (66 individuals); the newer satellite tern colony on the south beach west of the passive dissuasion had a total of 23 individuals, which was a significant decrease from the count the previous week (54 individuals); the combined total number of Caspian terns counted in the three satellite colonies this week was 45 individuals, compared to 148 individuals counted in all three satellite colonies the previous week
8/19 – 8/25/19 ›
Bald eagle pressure on the Caspian tern colony declined this week compared to the previous week, with no bald eagle caused disturbances to the tern colony observed this week; during the week, we continued to observe evidence of depredated juvenile and adult birds (i.e. terns, gulls, and cormorants), mostly the apparent result of avian predation
8/22/19 ›
Boat-based survey to count California brown pelicans roosting on East Sand Island revealed 3,285 pelicans on the island, the majority on the western half of the island, particularly on the rocks south of the cormorant colony area; there has been no evidence of nesting by California brown pelicans on East Sand Island so far this season
WEEKLY UPDATE 8/12 – 8/18/2019
8/12 – 8/18/19 ›
Count for the week of 2,273 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 8/15; the number of Caspian terns present on the one-acre colony area during the day this week was lower than the count the previous week (3,148); the estimated number of tern nests with contents (either eggs or chicks) on the one-acre colony area decreased this week to about 641, compared to about 1,400 the previous week; about 69% of these tern nests contained chicks, and the rest contained only eggs; as in previous weeks, western/glaucous-winged gulls continued to depredate tern eggs and chicks during disturbances to the tern colony that caused nesting adult terns to flush; western/glaucous-winged gulls were also observed depredating some Caspian tern chicks in the absence of any colony disturbances
8/12 – 8/18/19 ›
Counts of the number of Caspian tern individuals nesting and/or prospecting at the three apparent satellite tern colonies off of the main tern colony were also obtained from the photo mosaic taken by UAS; the satellite colony on the upper beach just to the south of the one-acre colony area had a total of 28 tern individuals, which was a slight increase compared to the count from the previous week (23 individuals); the satellite colony on the upper beach to the southwest of the one-acre colony area had a total of 66 tern individuals, which was a significant decrease compared to the count from the previous week (119 individuals); the newer satellite tern colony on the south beach west of the passive dissuasion had a total of 54 individuals, which was a significant decrease from the count the previous week (151 individuals); the combined total number of Caspian terns counted in the three satellite colonies this week was 148 individuals, compared to 292 individuals counted in all three satellite colonies the previous week
8/12 – 8/18/19 ›
Bald eagle pressure on the Caspian tern colony was similar this week compared to the previous week, with only one observed disturbance to the tern colony caused by bald eagles; during the week, we continue to observe evidence of depredated juvenile and adult birds (i.e. terns, gulls, and cormorants), mostly the apparent result of avian predation
WEEKLY UPDATE 8/5 – 8/11/2019
8/5 – 8/11/19 ›
Count for the week of 3,148 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 8/6; the number of Caspian terns present on the one-acre colony area during the day this week was lower than the count the previous week (4,347); the estimated number of tern nests with contents (either eggs or chicks) on the one-acre colony area decreased this week to about 1,400, compared to about 2,001 the previous week; about 65% of these tern nests contained chicks, and the rest contained only eggs; as in previous weeks, western/glaucous-winged gulls continued to depredate tern eggs and chicks during disturbances to the tern colony that caused nesting adult terns to flush; western/glaucous-winged gulls were also observed depredating some Caspian tern chicks in the absence of any colony disturbances
8/5 – 8/11/19 ›
Counts of the number of Caspian tern individuals nesting and/or prospecting at the three apparent satellite tern colonies off of the main tern colony were also obtained from the photo mosaic taken by UAS; the satellite colony on the upper beach just to the south of the one-acre colony area had a total of 23 tern individuals, which was a slight decrease compared to the count from the previous week (37 individuals); the satellite colony on the upper beach to the southwest of the one-acre colony area had a total of 119 tern individuals, which was a slight decrease compared to the count from the previous week (136 individuals); the newer satellite tern colony on the south beach west of the passive dissuasion had a total of 151 individuals, which was a slight decrease from the count the previous week (164 individuals); the combined total number of Caspian terns counted in the three satellite colonies this week was 292 individuals, compared to 337 individuals counted in all three satellite colonies the previous week
8/5 – 8/11/19 ›
Bald eagle pressure on the Caspian tern colony was similar this week compared to the previous week, with only one observed disturbance to the tern colony caused by bald eagles; during the week, we continue to observe evidence of depredated juvenile and adult birds (i.e. terns, gulls, and cormorants), mostly the apparent result of avian predation
WEEKLY UPDATE 7/29 – 8/4/2019
8/1/19 ›
First Caspian tern fledgling of the season observed on the designated one-acre tern colony area on East Sand Island
7/29 – 8/4/19 ›
Count for the week of 4,347 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 8/1; the number of Caspian terns present on the one-acre colony area during the day this week was similar to the count the previous week (4,360); the estimated number of tern nests with contents (either eggs or chicks) on the one-acre colony area decreased this week to about 2,001, compared to about 2,867 the previous week; about 63% of these tern nests contained chicks, and the rest contained only eggs; as in previous weeks, western/glaucous-winged gulls continued to depredate tern eggs and chicks during disturbances to the tern colony that caused nesting adult terns to flush; western/glaucous-winged gulls were also observed depredating some Caspian tern chicks in the absence of any colony disturbances; Caspian terns attempting to nest on the westernmost portion of the one-acre colony area remained more prone to frequent flushes from their nests and egg loss than terns nesting in the central and eastern portions of the colony
7/29 – 8/4/19 ›
Counts of the number of Caspian tern individuals nesting and/or prospecting at the three apparent satellite tern colonies off of the main tern colony were also obtained from the photo mosaic taken by UAS; the satellite colony on the upper beach just to the south of the one-acre colony area had a total of 37 tern individuals, which was a slight increase to the count from the previous week (18 individuals); the satellite colony on the upper beach to the southwest of the one-acre colony area had a total of 136 tern individuals, which is a slight decline in the number of individuals counted during the previous week (148 individuals); the satellite tern colony on the south beach west of the passive dissuasion had a total of 164 individuals this week, an increase from the count the previous week (52 individuals); the combined total number of Caspian terns counted in the three satellite colonies this week was 337 individuals, compared to 217 individuals counted in all three satellite colonies the previous week
7/29 – 8/4/19 ›
Bald eagle pressure on the Caspian tern colony declined this week compared to the previous week, with zero bald eagle caused disturbances to the tern colony observed this week; during the week, we continue to observe evidence of depredated juvenile and adult birds (i.e. terns, gulls, and cormorants), mostly the result of avian predators
WEEKLY UPDATE 7/22 – 7/28/2019
7/22 – 7/28/19 ›
Count for the week of 4,360 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 7/25; the number of Caspian terns present on the one-acre colony area during the day this week was slightly lower than the count the previous week (4,773); the estimated number of tern nests with contents (either eggs or chicks) on the one-acre colony area decreased this week to about 2,867, compared to about 3,780 the previous week; about 62% of these tern nests contained chicks, and the rest contained only eggs; as in previous weeks, western/glaucous-winged gulls continued to depredate tern eggs and chicks during disturbances to the tern colony that caused nesting adult terns to flush; western/glaucous-winged gulls were also observed depredating some Caspian tern chicks in the absence of any colony disturbances; Caspian terns attempting to nest on the westernmost portion of the one-acre colony area remained more prone to frequent flushes from their nests and egg loss than terns nesting in the central and eastern portions of the colony
7/22 – 7/28/19 ›
Counts of the number of Caspian tern individuals nesting and/or prospecting at the three apparent satellite tern colonies off of the main tern colony were also obtained from the photo mosaic taken by UAS; the satellite colony on the upper beach just to the south of the one-acre colony area had a total of 18 tern individuals, similar to the count from the previous week (16 individuals); the satellite colony on the upper beach to the southwest of the one-acre colony area had a total of 148 tern individuals, which is a slight decline from the count during the previous week (157 individuals); the satellite tern colony on the south beach west of the passive dissuasion had a total of 52 individuals this week, a significant decline from the count the previous week (308 individuals); thus, the combined total number of Caspian terns counted in the three satellite colonies this week was 217 individuals, compared to 480 individuals counted in all three satellite colonies the previous week
7/22 – 7/28/19 ›
Bald eagles continue to cause disturbances to nesting terns on the one-acre main colony area, with the frequency of these disturbances increasing slightly this week compared to the previous week; during the week, we continue to observe evidence of depredated juvenile and adult birds (i.e. terns, gulls, and cormorants), mostly the result of avian predators; a night-time disturbance to the tern colony by a great horned owl was suspected this week
WEEKLY UPDATE 7/15 – 7/21/2019
7/15 – 7/21/19 ›
Count for the week of 4,773 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 7/18; the number of Caspian terns present on the one-acre colony area during the day this week was similar to the count the previous week (4,859); the estimated number of tern nests with contents (either eggs or chicks) on the one-acre colony area decreased this week to about 3,780, compared to about 4,100 the previous week; like the previous week, about half of these tern nests contained chicks, and the other half contained only eggs; bald eagle disturbances to the tern colony were slightly down this week compared to the previous week, but western/glaucous-winged gulls still depredated a significant number of tern eggs and chicks on the one-acre main colony
7/15 – 7/21/19 ›
Counts of the number of Caspian tern individuals nesting and/or prospecting at the three apparent satellite tern colonies on East Sand Island off the main tern colony were also obtained from the photo mosaic; the satellite colony on the upper beach just to the south of the one-acre colony area had a total of 16 tern individuals, which is no change from the previous week; the satellite colony on the upper beach to the southwest of the one-acre colony area had a total of 157 tern individuals, a decrease in the number of individuals counted compared to the previous week (341 individuals); the new apparent satellite tern colony on the south beach west of the passive dissuasion had a total of 308 individuals this week, a decrease in the number of individuals counted compared to the previous week (444 individuals); thus, the combined total number of Caspian terns counted in the three satellite colonies this week was 480 individuals, compared to 801 individuals counted in all three satellite colonies the previous week
7/15 – 7/21/19 ›
Bald eagles continue to cause disturbances to nesting terns on the one-acre main colony area, although the frequency of these disturbances has declined dramatically as compared to earlier in the season; during the week, evidence was found of depredated juvenile ring-billed gulls (13) and one adult Caspian tern, mostly the result of avian predators; no night-time disturbances to the tern colony by great horned owls were detected this week
WEEKLY UPDATE 7/8 – 7/14/2019
7/8 – 7/14/19 ›
Count for the week of 4,859 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 7/12; the number of Caspian terns present on the one-acre colony area during the day this week was lower than the previous week (6,081); the estimated number of tern nests with contents (either eggs or chicks) on the one-acre colony area decreased this week to about 4,100, compared to about 4,600 the previous week; about half of these tern nests contained chicks, and the other half contained only eggs; disturbances to the tern colony by bald eagles continued this week, but eagle disturbances were less frequent and were not associated with the high level of tern nest failures (caused by gull depredation of tern eggs) that was observed earlier this season
7/8 – 7/14/19 ›
Counts of the number of Caspian tern individuals nesting and/or prospecting at the two apparent satellite tern colonies off the main tern colony on East Sand Island were obtained from UAS aerial photography; the satellite colony on the upper beach just to the south of the one-acre colony area had a total of 16 tern individuals, a dramatic decline from the previous week when 207 individuals were counted; the satellite colony on the upper beach to the southwest of the one-acre colony area had a total of 341 tern individuals, which is an increase in the number of individuals compared to the previous week, when 250 individuals were counted; a new apparent satellite tern colony began to form on the south beach west of the passive dissuasion this week, including terns that were sitting tight in nest scrapes, and 444 Caspian tern individuals were counted in this incipient satellite colony; in total, 801 tern individuals were counted in the three satellite colonies this week
7/8 – 7/14/19 ›
Bald eagles continue to cause disturbances to nesting terns on the one-acre main colony area, although the frequency of these disturbances has declined dramatically as compared to earlier in the season; during the week, evidence was found of depredated ring-billed gull chicks (18) and an adult ring-billed gull (1), all apparently the result of avian predators; river otter tracks were observed on the north beach, near the Caspian tern colony area on 7/11 and 7/14; no night-time disturbances to the tern colony by great horned owls were detected this week
7/11/19 ›
Boat-based survey to count California brown pelicans roosting on East Sand Island revealed ca. 1,625 pelicans on the island, the majority on the south beach near the one-acre East Sand Island tern colony; no adult brown pelicans in breeding plumage were observed this week, and no brown pelicans were observed carrying potential nesting material this week; monitoring for potential nesting by brown pelicans will continue in the coming weeks
WEEKLY UPDATE 7/1 – 7/7/2019
7/1 – 7/7/19 ›
Count for the week of 6,081 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 7/2; the number of Caspian terns present on the one-acre colony area during the day this week (6,081) was higher than the previous week (ca. 5,370); the estimated number of tern nests with contents (either eggs or chicks) increased this week to about 4,600, compared to about 3,400 the previous week; tern eggs continue to hatch, and the number of tern chicks present on the main colony increased throughout the week; disturbances to the tern colony by bald eagles continued this week, but eagle disturbances were less frequent and were not associated with the high level of tern nest failures (caused by gull depredation of tern eggs) that was observed earlier this season
7/1 – 7/7/19 ›
Counts of the number of Caspian tern individuals nesting and/or prospecting at two of the three apparent satellite tern colonies off the main tern colony on East Sand Island were also obtained from UAS aerial photography; the satellite colony on the upper beach just to the south of the one-acre main colony area had a total of 207 tern individuals, which is an increase compared to the count on 6/28 (134 individuals), but a decrease from the count on 6/21 (461 individuals); the satellite colony on the upper beach to the southwest of the one-acre colony area had a total of 250 tern individuals, which is an increase compared to the count on 6/28 (140 individuals), but a decrease from the count 6/21 (971 individuals); the area on the southeast tip of East Sand Island where a satellite tern colony was present in previous weeks has been filled with passive dissuasion by the USACE dissuasion team, and this satellite colony appears to have been abandoned
7/1 – 7/7/19 ›
The diet composition of Caspian terns nesting on East Sand Island continued to shift, with juvenile salmonids representing less that 10% of prey items, and marine forage fishes (for example, anchovies and herring) representing more than 50% of prey items
7/1 – 7/7/19 ›
For the first time this season, California brown pelicans roosting on East Sand Island were observed handling potential nest material (sticks and vegetation); no other pre-nesting behavior by brown pelicans has been observed so far this season
7/1 – 7/7/19 ›
Bald eagles continue to cause disturbances to nesting terns on the one-acre main colony area, although no eagles were observed chasing adult terns with bill-load fish this week; during the week, evidence was found of depredated ring-billed gull chicks (3) and an adult Caspian tern (1), all the result of avian predators; mink tracks were observed on the north beach, west of the Caspian tern colony area on 7/3; no night-time disturbances to the tern colony by great horned owls were detected this week
WEEKLY UPDATE 6/24 – 6/30/2019
6/24 – 6/30/19 ›
Count for the week of ca. 5,370 Caspian tern individuals on the designated one-acre East Sand Island tern colony based on a ground count conducted from a nearby blind on 6/27; the estimated number of Caspian terns present on the one-acre colony area during the day this week (ca. 5,370) was lower than the previous week (6,020); the estimated number of terns sitting on eggs and/or young chicks increased this week to 3,395, compared to 2,906 tern nests with eggs/chicks the previous week; tern eggs continue to hatch, and the number of tern chicks present on the main colony increased throughout the week; there continues to be disturbance to the tern colony caused by bald eagles, but these disturbances were less frequent and are not associated with the high level of tern nest failure (caused by gull depredation of tern eggs) that was observed earlier in the season
6/24 – 6/30/19 ›
The number of Caspian tern individuals nesting and/or prospecting at two of the three apparent satellite tern colonies off of the main tern colony on East Sand Island was estimated based on a ground count conducted from a nearby blind on 6/27; a total of 390 tern individuals were counted on potential satellite colony locations just before a hazing bout conducted by USACE dispersed the terns from those locations
6/24 – 6/30/19 ›
Bald eagles continue to cause 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; no night-time disturbances to the tern colony by great horned owls were detected this week
WEEKLY UPDATE 6/17 – 6/23/2019
6/21/19 ›
First Caspian tern chicks of the season observed on the designated one-acre tern colony area on East Sand Island
6/21/19 ›
Boat-based survey to count California brown pelicans roosting on East Sand Island revealed ca. 1,400 pelicans on the island, the majority on the south beach near the one-acre East Sand Island tern colony; no nesting activity by California brown pelicans has been detected on East Sand Island so far this breeding season
6/17 – 6/23/19 ›
Count for the week of 6,020 Caspian tern individuals on the one-acre East Sand Island tern colony, based on a direct count from aerial photography taken by UAS on 6/21; the number of Caspian terns present on the one-acre colony area during the day this week (6,020) was slightly higher than the previous week (5,767); the estimated number of terns sitting on eggs and/or chicks increased slightly this week to 2,906, as compared to 2,378 tern nests with eggs the previous week; despite an increase in the frequency of bald eagle disturbance to the colony this week as compared to the previous two weeks, the number of terns nest with eggs did not decline, but instead has remained stable or is increasing, suggesting that the tern colony may produce some fledglings this season
6/17 – 6/23/19 ›
The number of Caspian tern individuals nesting and/or prospecting at two of the three apparent satellite tern colonies off of the main tern colony on East Sand Island was estimated from aerial photos taken by UAS on 6/21; the satellite colony on the upper beach just to the south of the one-acre colony area had a total of 461 tern individuals; the satellite colony on the upper beach to the southwest of the one-acre colony area had a total of 971 tern individuals; although terns were present on a potential satellite tern colony on the southeast tip of East Sand Island, aerial photos of that area were not taken due to a high level of disturbance from bald eagles on the eastern tip of the island
6/17 – 6/23/19 ›
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; no night-time disturbances to the tern colony by great horned owls were detected this week
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
