The Globe and Mail reports in its Wednesday, March 26, edition that recent declines in U.S. yields have fuelled speculation that mortgage portfolio managers and insurance companies buying Treasury securities and interest rate swaps contributed to this drop. A Reuters dispatch to The Globe reports that these purchases, aimed at "convexity" buying, help mitigate the impact of mortgage refinancing as interest rates fall, potentially amplifying the recent decline in Treasury yields amid economic growth concerns. Convexity refers to how small changes in interest rates can significantly impact an asset manager's portfolio or an insurer's balance sheet. Convexity buying seems to have begun earlier this month as yields fell to their lowest levels since late October, down from 15-month highs in February. The U.S. 10-year yield, influential for borrowing costs on homes and businesses, has remained stable near 4.1 per cent since March 4, after a notable decline. However, it dropped 18 basis points from March 13 to 4.17 per cent on March 20. TD Securities' Gennadiy Goldberg says, "There's always convexity hedging going on," citing the amount of uncertainty in markets from mid-January to the end of February and early March.