NEW YORK ( TheStreet) -- Struggling to obtain income, investors have raced to buy high-yield bonds. High-yield funds have returned 7.9% this year, compared to a gain of 3.7% for the Barclays Capital Aggregate bond index, according to Morningstar. Attracted by the strong returns, investors have poured $16 billion into high-yield funds this year, a big gain for a category with $227 billion in total assets.Now some analysts worry that too much cash is rushing into high-yield bonds, which are rated below-investment grade. Fund companies apparently share the concern, and they have shut portfolios to new investors. Funds that closed recently include T. Rowe Price High-Yield ( PRHYX) and Vanguard High-Yield Corporate ( VWEHX). Should you avoid high-yield bonds entirely? Not necessarily. Default rates are low, and the bonds pay competitive yields. But to limit risks, consider funds that hold short-term high-yield securities. Bonds with maturities of two or three years have tiny default rates, and they yield 3% to 5% -- a rich payout at a time when 3-year Treasuries yield 0.28%. When interest rates rise, many bonds sink. But short-term securities often prove resilient. Funds that hold short-term high-yield bonds include Intrepid Income ( ICMYX), RiverPark Short-Term High Yield ( RPHYX) and Thornburg Strategic Income ( TSIAX). Intrepid Income ranks as one of the most cautious funds in the high-yield category. Besides buying short-term securities, the portfolio managers avoid the shakiest issues in the high-yield universe. "We are trying to offer a higher-quality alternative that is somewhere between investment-grade funds and typical high-yield funds," says portfolio manager Ben Franklin. When the Intrepid managers can't find bargains, they hold cash. In June 2008, the fund had 33% of assets in cash. That helped to limit losses when markets collapsed later in the year. But the high-quality securities lagged in 2009 when the market soared. The fund currently yields 4.4%, compared to a yield of 5.7% for the average high-yield fund. Another stable choice is RiverPark Short-Term High Yield. The fund has an average maturity of five months, and most holdings recently had maturities of 60 days or less. RiverPark yields 3.7%. "We are trying to provide higher yields on cash for investors who have a time horizon of at least three or four months," says portfolio manager David Sherman.