Malheur National Wildlife Refuge
Pacific Region

Caspian Terns are using the Nesting Island

Caspian Terns have returned to the nesting island for a second year. Caspian Terns began nesting and raising chicks on a one-acre rock fill island located on the south-central side of Malheur Lake in 2012. The island was designed, funded and constructed by the U.S. Army Corps of Engineers in 2012 to encourage nesting of migrating Caspian terns on Malheur Lake rather than in the Columbia River estuary. Terns on the Columbia River typically feed on threatened or endangered juvenile salmon moving into the Pacific Ocean; however terns ending their northward migration on Malheur Lake have access to an abundance of invasive common carp while nesting. Encouraging terns to remain on Malheur Lake is also expected to benefit the terns by reducing the exposure of part of their population to catastrophic events such as predators, storms and disease.

An adult tern shades a young chick under its wing

An adult tern shelters a young chick under its wing to shade it from the summer heat - 2012. Photo Credit USFWS


caspian tern with 2 eggs layed in early May

Caspian tern on nesting island on Malheur Lake with two eggs in May 2012. Photo Credit Nicole Cook

A series of tern decoys and a sound system emitting tern calls were agaun installed on the island in April 2013 to encourage the terns to remain in the area. Terns began investigating the island soon after it was ready and breeding behavior was observed by the beginning of May. Caspian terns scrap shallow indentations in the fine gravel of the island surface for nests. A single nest containing one eggs was documented by observers in late April 2013 from Bird Research Northwest.

Caspian terns are 4-5 years old before they begin breeding; they lay 2-3 eggs and will incubate the eggs for 20-22 days. The adults will feed the juvenile birds small fish for 5-7 months after they fledge from the nest.


Data for the 2012 Breeding Season

Hundreds of banded Caspian Terns from other colonies in the Pacific Northwest discovered the new island.

Most breeding began later than elsewhere in the region and continued into October

232 breeding pairs were observed on the island.

195 young terns fledged (84% success rate per breeding pair).

Nesting continued into October 2012 - beyond the period of regular colony monitoring.

The maximum colony count peaked at 1323 Caspian Tern adults on August 24, 2012.

Counts of over 1000 adults were observed from August 17 - September 9, 2012.

A total of 347 banded Caspian Terns were observed on the island - these terns were initially banded at 9 locations in California, Oregon and Washington.

Observations of foraging activities indicate that terns were venturing as far as Moon Reservoir (31 miles northwest of the island) and 25 miles south to Boca Lake in the Blitzen Valley to feed.


Diet Composition of Terns on Malheur Island 2012. Nate Banet
Fish Family
Proportion of Diet
Catfish 7.2 %
Invasive Carp and Minnows 90.5 %
Trout 0.6 %
Sucker 0.3 %
Sunfish and Bass 0.3 %
Unidentified 0.4 %
Total Observation 2748



a caspian tern flies into the island with a fish in its mouth a young tern practices running and flapping wings
A Caspian tern flies onto the island with a small fish to feed to its chick. Ninety percent of the fish being brought to feed chicks are invasive carp or native tui chubs. Photo Credit USFWS 2012. Two young terns run across the island flapping their wings as they begin learning to fly. These two chicks hatched in the beginning of June 2012 and were flying within a couple of weeks. Photo Credit USFWS.

Observations of tern activity on the nesting island will continue through the end of September and will include monitoring subsequent nests, recording the number of chicks hatched and when they fledge from the nest, identifying the number and types of fish eaten, as well as recording information from banded terns. Colored leg bands provide information about where individual birds were banded, the year they were banded and contain a numeric code for individual birds. The oldest banded Caspian tern lived for 26 years!


Caspian tern with leg bands used to identify where and when it was banded caspian tern with small fish in its mouth
Banded Caspian tern. Photo Credit Nicole Cook 2012
A Caspian tern returns to the nesting island with a small fish. Photo Credit Nicole Cook 2012


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A web camera has been set up so that the public can also observe what is happening on the island.


Last updated: May 6, 2013