Few lakes in California can match Clear Lake’s abundance of bird life. There are literally thousands of birds depending on the resources of the lake to survive. However, if the lake’s fish population plummets that can have a dramatic impact on the birds.
There is an old saying among wildlife biologists that “food is the engine that drives the train.” What they mean is that if the food supply drops, the birds will either move on to another area or starve to death. This certainly applies to many of the water birds at Clear Lake. For example, two years ago there were more than 1,000 white pelicans at the lake. This year that number is fewer than 50. The same applies to the western grebes. At one time Clear Lake played host to up to 60,000 grebes but now there are fewer than 1,000.
Gulls, cormorants and other fish-eating birds are also way down in numbers. A possible reason for the decline in all these bird populations is the lack of small bait fish. A good example is the pelican, which requires approximately four pounds of fish a day to sustain itslef. If sufficient food isn’t available the birds move on to other bodies of water. I was on the lake Sunday and didn’t see a single grebe nest. When the food supply is down the grebes won’t nest and even if they do nest it’s rare for the eggs to hatch. I also counted only five pelicans between Rocky Point and Lakeside County Park. I also didn’t see any silverside minnows or threadfin shad.
Thousands of birds pass through the lake every year. If there is an abundant supply of food they will stay. If not, they move on. There have been very few shad in recent years at Clear Lake where the silverside minnow population is also down considerably. The result is that most of the water bird populations are way down. Last year a number of grebes built nests but abandoned their eggs. The theory is that because there was little feed the grebes abandoned their nests because they wouldn’t be able to feed their young after they hatched. According to biologists who monitored the grebes, only a few young were observed on the entire lake.
Extensive studies conducted at Clear Lake in 1950 showed that the primary food source for western grebes was the bluegill minnow. Few bass were found in their stomachs. Of course, that was before threadfin shad or silverside minnows were introduced into the lake, which in turn resulted in a grebe population explosion.
Threadfin shad and silverside minnows consume various species of plankton and there has been little or none of that plankton found at the lake the last two years. This type of plankton is made up of small crustaceans and is one of the primary food sources for all the juvenile species of fish in the lake, including bass. When the plankton population is down so is the population of small fish. In turn, the birds that feed on the small fish have to migrate to other lakes to find food.
Threadfin shad are a good example. When the shad were numerous in the lake, the plankton counts were very high and the grebe population and the populations of other fish-eating birds peaked. The shad population crashed a number of years ago and the bird population has declined considerably.
Clear Lake is a good example of a complex ecosystem where each species depends upon another species to survive. If one link in the food chain is broken, it has an impact on the entire chain. Many locals and tourists complain when the lake is cloudy because of the algae. They want clear water. Whereas the swimmers and some of the boaters like the gin-clear water, the creatures living in the lake prefer cloudy water rich in nutrients. A clear lake also means an explosion of weeds, which also makes many of the lake users unhappy.
Actually, there is little that man can do or should do to change this 2 million-year-old lake. Clear Lake was here long before humans and will be here long after we are all gone.
