DuckDuckGo either sells or partners with Yahoo?
duckduckgo.com
duckduckgo.com
This is just speculation, not news. Alternative headline: "duckduckgo.com/$engine/ redirects to that search engine".
Yahoo search engine is only a few points behind Bing right now anyway (at least in US), and those were lost because they partnered with Bing in the first place, and those people decided that they might as well use Bing, the source, now.
Bing's market share grew mainly because they managed to partner or capture most other niche search engines out there (by getting them to use the Bing API). It didn't take anything away from Google, nor did it replace others on its own. It's actually other engines like Yandex and Baidu that are growing faster than Bing.