I'd wager the U. S is seen as more of a safe haven than Spain, hence further scope to fall in my viewWell if I was to look at the chart in this article Link I would guess the Spanish 10 Yr. I describe it as domino because investors want to match their maturity needs first, 5yr, 10yr etc.
I am assuming institutional longterm bond investors are insruance companies / pension funds needing to match long term liabilities so they are seeking a relatively low risk yield, they Target the least risky countries first. Those yields start declining, they now have to shorter maturity or change country. That is why the riskiest debt in Europe is now pretty much the only yielding positive.
The U.S is a different kettle but is already seeing yields moving down.