I don't know if the article is true or not, but this guy has been studying them, he claims the information about intruders comes from banding information. I did see a loon stalking a Merganzer duck and her babies last summer. I noticed the loon swimming very low in the water then saw the duck and her baby high tail it out of there. The duck wanted nothing to do with loon. I've always wondered what happened to the Merganzer duck broods which start out with about 10 babies in the beginning of the summer and are usually down to 1 or 2 by the end.
Mr. Walcott is into loons, read here for another discovery on the male loon yodel:
http://news.nationalgeographic.com/n...0411_loon.html
".... a new study has found that when a male loon .... changes territories to find a new mate, he changes his call, too. Why this happens is a mystery."