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
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
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
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.