I don't understand the whole concept of vulturing. Ferrer seems to be the first name that springs to peoples' minds when discussing this topic. However anyone with a shred of common sense would see its obvious why Ferrer plays the 250s and 500s he chooses to.
Pre Aussie Open, Auckland and Chennai generally have the weakest fields out of the 5 events, yet they all offer the same amount of points. Prize money is only significantly higher in Doha, but that event typically attracts Federer, Nadal, Murray and Tsonga who would all be a massive threat to Ferrer on hardcourt. Why increase the risk of going out in a QF when your chances of winning a title (and same number of rankings points) is increased by taking part in another event?
Same applies to Ferrer playing in South America rather than Europe/Asia post Aussie Open. Fields in Rotterdam and Dubai are generally stacked, plus they are also on hardcourts, not clay where Ferrer feels most comfortable.
Queen's & Halle are also stacked WRT to draw, whereas Rosmalen is relatively much weaker, yet offers the same number of ranking points.
Also, if none of the top players played these weaker field events, they may aswell stick the events on the Challenger tour and only hold one tourney a week on the ATP tour.
Bingo. That's exactly why Ferrer is a vulture, because he enters tournaments with weak fields, often in the same week where top players are battling it out ie. 8 of the top 10 players went to Dubai (Nadal didn't play that week) and Ferrer to Acapulco to prey on a week field.
It is a smart choice ranking point wise, but one that only a point vulture would make.