A large fraction of the images in Snapshot Serengeti are “blank”, i.e. they have no animals in them. This is because grass waving in front of the camera traps can cause them to fire. While doing some work on trying to remove the blank images in order to make the project more efficient, we stumbled upon an interesting phenomenon. It looked like the fewer blank images a volunteers saw, the fewer classifications they performed in total! This led to Zooniverse web scientist Alex Bowyer setting up an experiment to test this hypothesis. His very interesting and intriguing finding reads:
What we have shown in this experiment, is that reducing the percentage of “blank” images that a user sees in their session will reduce the length of time they spend providing voluntary classifications. This is very important for citizen science researchers to understand, since a common approach is to remove blanks in order to optimise for efficiency and not waste volunteers’ time. What we have shown is that optimising for user experience, not efficiency, is critical if each user’s contribution is to be maximised.
This continuing research is now going to look at other factors that might motivate volunteers to stay longer, such as variety and complexity. Read his full write-up of this experiment and its results at www.mico-project.eu/why-citizen-science-researchers-shouldnt-remove-mundane-images.
Daily Zooniverse 
I’m curious, is removing the blanks eliminating the sense of a hunt? If the animals are already “caught”, we just have to do the follow up paperwork?
I think that’s exactly right Janet. There is a lot of research from gambling, psychology and elsewhere that shows that something that a rewarding event that occurs rarely and unpredictably can motivate people to keep going “in search of the prize”. Didn’t quite follow your question at the end, sorry…
All successful hunts produce joy at the capture, then followup work – wrapping the capture up and carrying it home is not all that much fun at all. Yet that is all that the 100% animal group is left to do.
Fewer blanks leave a greater concentration of pix with animals …fine. But if those pix are of wide open plains and near microscopic animals my eyes and patience give out sooner.
Interesting idea Judy – that the blanks give some “rest and relaxation” in between harder tasks. We’re also going to look at varying the complexity of the images you are presented with, so that hard/tiny images would happen less often; we think this will let people keep going for longer.