USA: what do fish-eating birds eat in Montana?

This video is about American White Pelicans in migration.

From Montana Fish, Wildlife & Parks (USA):

The Birds At Canyon Ferry Reservoir

What kind of fish do fish-eating birds munch on?

A recent survey at Canyon Ferry Reservoir near Helena provided a fascinating look at their diet.

“We looked at 5 islands,” says Eric Roberts, Fish, Wildlife and Parks fisheries technician.

“One pelican island, three cormorant islands, and one mixed.”

Roberts looked at stomach samples from 52 cormorants and 12 pelicans.

The samples were regurgitated contents from young birds. And you wondered where all the good jobs went.

“For cormorants, stonecats made up the largest portion of the diet, with 77% of the observed samples containing stonecats,” Roberts reports.

“Longnose dace were the second most abundant and were present in 27% of the samples.

After that were trout (observed in 23% of the samples), suckers (23%), crayfish (13%), and sculpins (11%).

The low frequency of trout in the diet, leads Roberts to speculate that since rainbows were last stocked into Canyon Ferry – May 11 – they have dispersed throughout the reservoir, making them harder for cormorants to find.

As for pelicans, the bird many anglers view with disdain, Roberts says: “Carp and crayfish continue to be their primary food item.

We saw one adult trout, but we didn’t see any evidence of stocked trout in the pelican diet.

We do know that pelicans will eat stocked fish right after they come off the hatchery truck, but pelicans are such opportunistic grazers, that I think that the fish are only vulnerable for a short period of time.

Once the fish start to disperse the pelicans just aren’t that effective at catching them.”

One final curious note is the absence of perch in the diet.

“When we first did diet surveys in 2003, perch were present in 80% of the samples,” Roberts says.

“Since perch numbers have crashed in the reservoir, perch are practically non-existent in the diet samples.”