Monday, January 12, 2015

Bird of the Day: Ospreys at Merced Falls

Ospreys are great hunters of fish. There is a pretty good spot in our area to see them at work. It's along the Merced River near the village of Merced Falls. This is the place where the Merced emerges from the foothills onto the floor of the San Joaquin Valley. There are four reservoirs along this stretch, huge New Exchequer Dam, forming McClure Lake, and three much smaller dams, McSwain, Merced Falls, and Crocker-Huffman. The smaller lakes are wide and shallow, offering some good fishing possibilities for the Osprey population. We saw them at work yesterday, not so much fishing, but enjoying the fruits of their labor. Every Osprey we saw had a fish (there were at least three of them). To judge from the picture above, they saw us too.

It was easy to see why the fishing was good. Merced Falls lake was way down so the water was shallow, and the resident fish had much less shelter to hide in. In the picture below all the rocks in the background are usually submerged.

The Merced River is currently the southernmost Sierra Nevada River that supports salmon, but as of 2007, they were not able to get past Crocker-Huffman dam about three miles downstream of our location. There was a feasibility study in 2007 that explored the possibility extending their range, but I don't know if anything was done about it. I'm sure the Ospreys would be in favor of it!

Ospreys (Pandion haliaetus) are well-adapted to fishing, able to dive as much as three feet into the water to capture their prey (fish makes up 99% of their diet). They have barbs on their feet that allow them to grip their slippery targets.

The widespread use of DDT in the 1950s and 1960s nearly did in the Osprey. Their population crashed, and it was only after the use of the pesticide was banned that their numbers began to climb again. According to the Cornell Bird site, there are about 500,000 across North and South America.

There is a huge Osprey nest on a post near the reservoir. We'll be keeping an eye on developments there during the spring!

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