Prospectus excerpt:  We are offering 1,600,000 shares of 7.25% Series D Cumulative Convertible Perpetual Preferred Shares of Beneficial Interest (the ÙSeries D Preferred Sharesˆ). The annual dividend on each Series D Preferred Share is $3.625 and is payable, when, as and if declared by our board of trustees, quarterly in cash, in arrears, on each January 1, April 1, July 1 and October 1, commencing on July 1, 2011. Each Series D Preferred Share has a liquidation preference of $50.00 per share and is convertible, at the holder?s option at any time, initially into 3.4699 of our common shares (equal to an initial conversion price of approximately $14.41 per share), subject in each case to specified adjustments as set forth in this prospectus supplement. The Series D Preferred Shares are not redeemable by us. If a fundamental change occurs, we may be required to pay a make-whole premium on Series D Preferred Shares converted in connection therewith, through the increase of the applicable conversion rate, as described in this prospectus supplement. On or after April 20, 2018, we may at our option cause all of the outstanding Series D Preferred Shares to be mandatorily converted into that number of common shares for each Series D Preferred Share equal to the then-prevailing conversion rate if the Daily VWAP (as defined herein) of our common shares equals to or exceeds 130% of the then-prevailing conversion price for at least 20 trading days in a period of 30 consecutive trading days, including the last trading day of such 30-day period.