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Shore Birds—Jennifer Griem

On a balmy night in 1996, biologist Jennifer Griem found
herself observing a late night beach phenomenon unique to
southern California: a grunion run. Grunion are small fish
who spawn once every two weeks during the summer months by
temporarily beaching themselves. Taking advance of the
highest high tides, the grunion lay their eggs in the
sand, where they incubate until they are washed back into
the ocean two weeks later. As impressive as the grunion
spectacle was, Griem was more fascinated by the array of
birds she observed lining up for an easy grunion meal:
Great Blue Herons, Night Herons, Western Gulls and Snowy
Egrets.
NOVA: What's so interesting about a bunch of birds
taking advantage of a grunion run?
JG: Of the four bird species that feed on the grunion,
there's only one that's truly nocturnal—the Night Heron.
The other three are usually daytime feeders, but they come out
at night for grunion runs. So we're seeing daytime feeders
coming out and engaging in nocturnal behavior, which is very
interesting. It prompted me to get going and do some
population counts and some correlations between grunion runs
and the appearance of birds on the beach.
NOVA: Tell me about the technology that you used.
JG: Well, I had a pair of binoculars, which is pretty
standard. The other instrument I used was an ITT night vision
scope. It was a monocular, so I looked through it with only
one eye. It takes whatever small amount of light is on the
beach and it multiplies it so that you see very
clearly—almost like it's daylight. It's the same
technology that the military uses for their night
exercises.
NOVA: Where did you get it?
JG: We got ours at a marine store, because it was
waterproof, but they have them at hunting stores, too. I think
the one we got was over $1000, which is fairly expensive, but
it works tremendously well. It enabled me to identify the
birds, to species, at night—by their silhouette and
their markings. And it enabled me to do accurate counts
without having to get too close to them and scare them away.
It was a real useful piece of equipment.
NOVA: What did the night vision scope enable you to learn
about the birds and their relationship with the grunion that
you otherwise would have missed?
JG: I learned that the birds are present not only during
grunion runs, but
before grunion runs. Like a half an hour before the
fish even show up, they're there waiting. And they're not
there on nights when the fish are not supposed to come. They
actually know when the fish are coming.
(back)
Photos: (1,3) Karen Martin, Pepperdine University; (2)
Stephen Davis, Pepperdine University.
Night Vision
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