re: Satsuma under attack

Here are pics of my satsuma tree fruit that is being destroyed. In the first pic, the satsuma on the left still has fruit in it, but the top 1/4 looks like it was cut off. Fruit is still on the inside.

Can squirrels do this, or is the consensus is that it's rats?

My next door neighbor who is an MD is having the same issues with his tree in his yard. He said that he thinks it is some kind of citrus disease. He claims that he had one that was discolored, and picked it off the tree, and he noticed that it was very light, didn't weigh much. He got a knife and cut it in half and there was very little rind on the inside. But he can't come up with an explanation of why some of them are bored out with just the skin left.

Any ideas?