The Caspian terns were calling as we sauntered along at Harriman State Park

A deep raspy “aaayayaum” sound interrupted my wife and I as we hiked along the shore of Silver Lake at Harriman State Park this week.

“What is that?” she asked as we sauntered along.

“It’s a Caspian tern bragging about the fish it caught – just like most fishermen.”

We watched as eight of the world’s largest terns flew along the shallows of the lake, hunting for small fish swimming near the surface. The serious dives were from 30 to 40 feet above the water that would completely submerge the large birds going for the bigger prize. With each successful catch was followed by the bragging vocalization.

“Don’t talk with your mouth full,” does not apply to these birds.

Every time I deliver fishing flies to the Drift Lodge near Henrys Lake, I will stop at Harriman to try to capture these birds hunting. During their hunting times, they ignore everything except looking for something to eat. Also, I will often also stop at Last Chance to watch them hunt the Henrys Fork of the Snake River and you can occasionally see them perched on a rock in the middle of the water. The west shore of Henrys Lake is also a good place to observe them.

Caspian terns are found on five continents and were named after the Caspian Sea. They enjoy both fresh and saltwater habitats and feed almost exclusively on fish but will sometimes feed on frogs and other amphibians. They are “kleptoparasites” meaning that they will chase and steal fish from smaller species for terns. This happens often at Market Lake Wildlife Management Area where the smaller Forster terns outnumber the Caspians.

After they capture a fish, they will usually swallow it whole, headfirst, while in flight before another kleptoparasite, a Bald eagle, can steal it from them. They have been known to capture fish too large to swallow and have choked to death.

Food is also a major part of the dating scene for Caspians. Once they get to their breeding grounds, a male will capture a fish and fly past a group of terns perched on the shore, bragging about his catch. Several females may follow him and when the chasers are down to one, he will offer the fish to her, bobbing his head in agreement. The pair has bonded and began elaborate aerial displays as they build their nest.

Together, they dig a small depression in the sand, usually on an island where there is very little vegetation. They often gather stones and/or sticks to make a border around the nest to mark it as they often belong to a colony of other Caspians.

Their relationship is an open one, as both will cheat on each other by breeding with others in the colony, but they are good parents. Both are busy defending the nest and chicks once they are hatched. They will feed the kids for almost a year — even after their relationship is over — with the kids going with one or both parents.

It takes three years for the young to become mature and as “teenagers” they gather in colonies of non-breeding groups. Most of the Caspians that summer in Idaho are these loose groups with only three areas known to produce viable nesting. This year, I observed a pair at Market Lake that went through their courting behavior. They may have moved on or they may be nesting as I have not seen them, as a couple, in the last month. We will watch for them to show up with kids before they migrate south.

They are an interesting species to observe, but they are difficult to track as they are nomadic and head for the best fishing areas quickly. It will be fun for me to watch the group at Silver Lake.