Among the more popular birds that migrate to Clear Lake is the grebe. Their mating dance, during which they race across the surface of the lake and dive in perfect unison, is a photographer”s dream.
Ten years ago the Western and Clark grebe population on Clear Lake numbered in the tens of thousands, however, that population has dwindled the last three years and is now just a shadow of what it used to be.
The primary reason grebes migrate to Clear Lake is because of the lake”s abundant food source and the ideal nesting conditions. Grebes construct their nests from tules and other aquatic weeds and build the floating nests on weed mats. The female then lays from three to five eggs and both the male and female tend the nest and sit on the eggs. The eggs are hatched in 23-25 days. The young leave the nest shortly after being hatched but stay with their parents for up to three months. The young ride on the backs of their parents. One unusual trait is that the adult will often extend out its foot, providing a step so the young can climb on their back.
A grebe”s diet is mostly fish and at Clear Lake that means silverside minnows, threadfin shad, baby bass, crappie, bluegill and other small minnows. They catch their fish by stabbing it with their long and sharp bills. They also normally eat their prey while underwater but will often bring a minnow to the surface to offer it to their mate and young ones.
There is an old saying among wildlife biologists that “food is the engine that drives the train,” and that certainly applies to grebes. When the grebe population peaked a few years ago at Clear Lake there literally were billions of silverside minnows and threadfin shad. One could see large groups of grebes diving and feeding on the schools of fish. Two years ago the shad population crashed and the silverside minnow population has also declined. The reason given for the decline was the tiny fish had exhausted its primary food source, which is plankton. As the baitfish disappeared, so did the grebes. They had the choice to stay at Clear Lake and starve or find a new lake.
Only a small population of grebes migrated to Clear Lake last year and there was very limited nesting. So far this year there are grebes on the lake but I haven”t received a single report of a baby grebe sighting. They did nest and lay eggs but after a few days the birds abandoned their nests and eggs. The big mystery is why the grebes have abandoned their nests and eggs. There have been reports of more than 100 nests being abandoned near Long Tule Point. At first it was thought that possibly boaters and fishermen had disturbed the nesting grebes, but the weeds are so thick boats can”t get within a few hundred yards of the nesting birds.
According to professor and biologist Floyd Hayes, the grebes can nest as late as October and there are several areas where there are colonies of birds attempting to nest. However, the same thing happened last year and the end result was there were very few baby chicks observed.
There are several theories on why grebes abandon their eggs. Human disturbance will cause the grebes to leave. Predators such as gulls, coots and other predator birds will often eat the eggs. A study done in Utah showed that the California gull and coots (mud hens) prey heavily on grebe nests. Otters will also eat the eggs and young chicks. But it is highly unusual to not have even a single egg hatch out of dozens. One theory is that Mother Nature plays a major role. If the food source isn”t there (young fish) to rear the young chicks, the birds won”t sit on their eggs and hatch them. This occurs to other animals in the wild. When the food source is poor, deer have been known to abort their fawns. The same applies to most wild animals.
Hopefully the grebes that are currently on their nests will hatch out the young. However, if they also abandon the nests the mystery will remain. Boaters are being asked to stay clear of any grebe nests and to not disturb them.
