Outer Green Island, Maine

SJ Kwiatkowska, Island Supervisor National Audubon Society Seabird Restoration Program

interns
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roseate ternTern Census

The 2016 Gulf of Maine Seabird Working Group (GOMSWG) tern census was conducted on Outer Green Island on 13 June. A total of 1289 Common Tern (Sterna hirundo) nests were counted. The inclusion of 41 productivity study nests (one clutch was laid post census within the GOMSWG window), 24 feeding study nests, and a Lincoln correction index of 1.01 (n=205) resulted in a corrected total of 1367 nests. This is another new record for Outer Green Island, making it the largest tern colony in Casco Bay, Maine for the second year in a row. There were no known Arctic Tern (S. paradisaea) nests on the island this year, but a single pair of three-year old Roseate Terns (S. dougallii) laid a single egg in grid #10 on 26 June. This egg hatched on 20 July, and the chick was still alive and well when researchers left the island on 1 August.

 

Table 1.  GOMSWG annual census on Outer Green Island, 2010-2016

Year

COTE

ROST

ARTE

2010

1151

15

0

2011

1067

0

0

2012

1034

0

0

2013

1143

0

0

2014

1139

0

0

2015

1353

0

0

2016

1367

0*

0

*One ROST nest was laid after 20 June

 

Tern Productivity

The first Common Tern egg was laid on 20 May. The average number of eggs per nest was 2.40 (n=65). The first hatch was on 12 June, and peak hatch lasted approximately from 18-26 June. The average number of eggs hatched per nest was 2.12, and the average number of chicks fledged per nest (productivity) was 1.26.

 

Table 2.  Outer Green Island annual Common Tern productivity, 2010-2016

Year

Mean Clutch

Mean Hatch

Productivity

2010

2.81

2.63

2.09

2011

2.43

1.98

1.77

2012

2.81

2.19

1.42

2013

2.60

2.27

1.15

2014

2.13

1.92

1.42

2015

2.03

1.83

1.36

2016

2.40

2.12

1.26

 

 

Tern Provisioning

Chick provisioning was observed at 23 Common Tern nests (one nest never hatched) this season over 912 nest hours. A total of 1199 feedings to chicks were recorded for an average feeding rate of 1.31 items per hour, which is lower than the 2014 feeding rate of 1.73 items per hour, but higher than the 2015 rate of 0.97 items per hour. The most frequently observed prey item was herring species (Clupeidae sp.), which made up 35% of the observed diet. Hake species (Urophycis sp.) was the second most frequently observed prey item, at 26% of the observed diet.

 

Predation

Early and late in the season, Ruddy Turnstones (Arenaria interpres) were opportunistically depredating eggs.

Two Black-crowned Night Herons (Nycticorax nycticorax) landed and depredated at least two nests, a Peregrine Falcon (Falco peregrinus) predated one or two fledgling terns, and a Bald Eagle (Haliaeetus leucocephalus) landed on the island twice. An American Mink was located and subsequently shot on the island on 16 June 2016 after predating one adult Black Guillemot (Cepphus grylle) in its burrow. Throughout the season, Great Black-Backed Gulls (Larus marinus) and a few Herring Gulls (Larus argentatus) hunted at all times of day in the colony, but increased their predatory activity at dawn and dusk and during poor weather conditions. Deterrence methods included gull walks and lethal control. Two Great Black-Backed Gulls (one adult, one juvenile) were shot. On neighboring Junk of Pork Island, one Great Black-Backed Gull and two Herring Gull nests were destroyed. On Outer Green Island, one Herring Gull nest was destroyed. One Herring Gull was seen with a Common Eider (Somateria mollissima) duckling, and an estimate of 3-10 young terns were predated daily by large gulls during the peak predation period (18 June – 10 July).

 

Weather

The average, high, and low air temperatures and average sea surface temperature (SST) this year are similar to the island averages over the past 15 years. Air temperatures ranged from 42°F to 85°F, with an average temperature of 61.5°F. Sea surface temperatures (SST) ranged from 43°F to 67°F, with an average SST of 55.5°F.  Precipitation was recorded on 24 days this season for a season minimum of 9.9 inches (rainfall was not collected in May).

 

Black Guillemots

This year, one new Black Guillemot burrow was found, raising the island total to 23 burrows. This year, 16 burrows were active, and 10 were followed for growth. Of the 16 active burrows, one burrow had what is considered a supernormal clutch of three eggs. This is the second year in a row of a supernormal clutch size on Outer Green Island. The burrow with three eggs had two eggs for a long period which felt cold, and then a third was found laid in the burrow. None of the eggs hatched, likely due to the disturbance from the American Mink during incubation. Because of the supernormal clutch, the average clutch size was 2.06, the average number of eggs hatched per nest was 1.25, and the estimated productivity (based on healthy chick growth at time of staff departure) was 1.13.

 

HELP KEEP INTERNS ON OUTER GREEN ISLAND
You can see the island from parts of Chebeague!

If you would like to help please contact Steve Kress at Audubon.

outergreen map