NEW YORK ( TheStreet) -- Since the financial crisis, nervous investors have been pouring into bond funds. But the flight to fixed income could produce dismal results. The problem is that most bond funds drop when interest rates rise, and many economists expect that rates will climb in coming years.Investors recently got a taste of how hazardous rising rates can be. During the past month, rates on 10-year Treasuries climbed 0.30 of a percentage point to 2.28%, and long government funds lost 2.8%, according to Morningstar. For protection, investors should diversify portfolios. One strategy is to add high-yield funds, which invest in junk or corporate bonds that are rated below-investment grade. High-yield funds showed their resilience in the past month, returning 1.0% and outpacing most bond categories. The strong showing was not unusual. Junk bonds often climb as the outlook for the economy improves and the risk of defaults declines. Can high-yield funds continue rallying? Yes, argues Tom O'Reilly, portfolio manager of Neuberger Berman High Income Bond ( NHINX). O'Reilly says that the bonds are currently undervalued because investors remain wary about defaults. The default rate peaked in 2009 when 10% of junk bonds collapsed. Now most of the shakiest bonds have been eliminated. The survivors have been strengthening their balance sheets and refinancing debt. The ratings agencies have been upgrading many issues. With the economy improving last year, only 1.8% of junk bonds defaulted, a rate that is below historical averages. O'Reilly figures that the default rate this year will be 1.5%. Despite the healthy performance, investors are pricing bonds as if they will suffer a default rate of 6%, he says. As the year progresses, investors will become less nervous and bid up prices to account for the modest default rate. That should enable the funds to return 8% to 12% for the year, O'Reilly says. Most of the return of junk bonds this year should come from their relatively rich yields. The bonds yield 6% to 8%, a fat payout at a time when money-market funds yield next to nothing.