A gathering of geese

On Thursday I noticed a tremendous gathering of geese at the college between the soccer field and Lake Banet. I tried to sneak up on them to get a good picture, but there were so many of them that there was no way to capture the number that were there. Below you can see a small part of the gaggle.

I do not know if I was the one who disturbed them or something else did, but suddenly they all took flight. The hundreds of big birds in the air all at once was an even more impressive sight, but again, not one that I could adequately capture in a photo.

Why are they concentrated at SJC and what do all these geese eat? I suspect that they are doing a good job of fertilizing the small soccer field that is to the south of the varsity field.