Accoring to webmasters tools (sitemaps), the number of pages for one of my sites in the Google index has been steadily declining over the last few days. In the space of a week the number of pages has dropped from over 1000 to just over 400. Why might this be? Has anyone else experienced something similar recently?
I had the same thing happen to a site that was hit by Panda. About a month after the initial traffic drop, the number of reported indexed pages went down to almost zero, but the pages were actually still in the search index. I made incremental improvements to the crawl-ability of the site, and after a few months, the number of reported pages went back up to original levels. There was no way to tell if the improvements affected that number, but overall traffic has improved.
Edit: The main improvements I made: