The first two companies to present at this afternoon's Vertical Social Networking session proved that niche social networks can be exciting, even for people outside of their respective niches. On paper, a social network for bird watchers sounds like a joke. But the founders of Birdpost wowed the TechCrunch50 audience by presenting not only a very well-designed site but one that thoroughly addressed a real problem for certain people, that of locating rare birds. Like Wikipedia, Birdpost intends to unleash knowledge traditionally locked up in the heads of a small group of experts. While in the case of bird watching the group is highly focused, the founders insist that 45 million Americans would actually be interested in their knowledge.