Investors are abandoning an exchange-traded fund tracking long-term U.S. Treasury bonds even as it rallies and are piling into shorter-duration ETFs as benchmark yields continue their downward trek. The $9.9 billion iShares 20+ Year Treasury Bond ETF, known by its ticker TLT, is on pace for its worst month of outflows on record. Investors have pulled more than $1.47 billion out of TLT in March, already topping the record $1.37 billion in outflows seen in November 2017. Ironically, the fund is one of the top-performing fixed income ETFs this month, with its shares rising 4.6 percent, according to Bloomberg data.