Once again Clear Lake has proved just how environmentally dynamic it is.
It was just a few weeks ago that the lake was teeming with bird life. White pelicans could be seen soaring by the hundreds over the surface of the water. Western and eared grebes were everywhere, feeding on the small bait fish. Now they are all gone.
What happened?
It”s the old story of food being the primary attraction for all wildlife and once the food source disappears the birds move on to new locations. It”s either that or starve.
The most noticeable disappearance is that of the white pelicans. The number of white pelicans on the lake numbered close to a thousand during the fall and into early winter. Today there are probably fewer than 50. In fact, last week a person called me and said that when he was returning to Lake County from Sacramento on Highway 20 he saw a huge flock of white pelicans heading east. They were headed toward the Sacramento Valley.
The reason the pelicans were at Clear Lake in the first place was because of the abundance of bait fish. The lake was literally awash with inland silverside minnows and a good population of threadfin shad. A pelican is a large bird and requires about 3 pounds of fish per day to sustain its self. The pelicans would herd the minnows into the shallows and then scoop them up with their large bills.
Grebes also fed on the minnows, but like the pelicans most of the grebes have left the lake for more fertile waters.
This past summer and fall saw more silverside minnows than anytime in recent history. A good example was when the county”s Vector Control was running seine nets to capture the minnows. The nets were so full of the small minnows that it was a struggle just to get the nets into the boat. The silversides also play an important role as a food fish for the small bass, crappie, bluegill and catfish.
Silversides are not native to the West but were introduced into Clear Lake in 1967 to control the Clear Lake gnat and to control blue-green algae blooms. Within two years their population exploded and they became the most numerous fish in the lake.
The reason the silversides have disappeared from the shallow water is because the recent cold spells have dropped the water temperatures to below 45 degrees. That drop in water temperature has forced the silversides to migrate to the deeper water where they aren”t available to the birds. Silversides can survive cold temperatures, however, they are considered a short-lived fish and most don”t live more than a year. Even though they don”t live very long they do reproduce in massive numbers.
As for the other primary bait fish in the lake, the threadfin shad, its population did increase somewhat this past fall but it never reached the numbers of two years ago. Cold water will kill shad and I”m sure the past few weeks has seen a die-off of a good number of the shad.
Whereas the pelicans and grebes may be leaving the lake there is a bird that is arriving in large numbers. The ruddy duck population grows daily and now approaches several thousand birds. Ruddy ducks are deep divers and will feed off aquatic insects and vegetation in water as deep as 20 feet.
The ruddy duck population normally peaks in February and it could be as high as 10,000 or more birds. The past two years has seen a large die-off of the ruddy ducks due to avian cholera. These ducks are susceptible to cholera because they stay in very tight flocks. The few birds that arrive with the cholera virus can in turn infect hundreds more. The ruddy ducks will migrate north in March.
At any given time Clear Lake plays host to a wide variety of birds and that”s what makes a visit out on the lake so exciting. You never know what you will here.
