In the past few weeks I have been slowly adding new channels and putting adsense on pages that have existed for years and already rank well in Google. Each time I do this, the ads on the new channel appear to be very targeted to the content of the page and the ads on the channel have a high click through ratio.
After a day or so I notice that the CTR, the clicks, and the dollar value of the clicks has dropped. I check and find that the ads now being served up are now poorly targeted.
I can understand why Google would initially serve targeted ads as the pages are well known to Google already but find it strange that this honeymoon only lasts for a day. It is almost as if once the page is crawled for adsense purposes the opinion of the page changes. Is this normal adsense behavior?