High-yield mortgage REITs: Too good to be true?

As bond, CD, and money market interest rates remain mired at rock-bottom levels, investors continue their quest for dividends. One category offers eye-popping yields: mortgage real estate investment trusts, or mREITs (which are required to pass most of their income to shareholders via dividends). Chimera Investment and American Capital Agency each yield more than 19%. And the largest mREIT, Annaly Capital Management -- which we've recommended before -- offers a 15% payout. Are these returns too good to be true?