Adsense > Performance Reports > Products: AdSense API Referral Bounty - What does it mean?

[Pwn B]

An item, "AdSense API Referral Bounty", shows up as a product in the performance reports of Google Adsense.

It reflects thousands of pageviews with zero earnings. What are these types of adverts, where are they shown and why doesn't it perform as good as "AdSense for Content"?

Thanks

Pwn B