The Pelican Puzzle

One would think that one would see, over time, roughly equal numbers of pelicans flying north and south along the Pacific coast. But no. In the past two years I have seen 1,256 pelicans flying north, and only 245... no, 246 pelicans flying south.

Clearly, there must be a pelican source in the south. And a pelican sink in the north. I wonder what they could be...