Information foraging is a theory that applies the ideas from optimal foraging theory to understand how human users search for information. The theory is based on the assumption that when searching humans utilize "built-in" food foraging mechanisms that evolved to help our animal ancestors find the prey. Better understanding of human search behaviour can improve the usability of the web-sites.
In 1970s a theory was developed by anthropologists and ecologists to explain animal foraging strategies. It suggested that animals constantly consider the available food and the cost of obtaining it, deciding to stay for a while or move on to the next food patch.
In the early 1990s Peter Pirolli and Stuart Card from PARC noticed the similarities between users' information searching patterns and animal food foraging strategies. Working together with psychologists on analysing users' actions, the information landscape that they navigated (links, descriptions, and other data) they showed that information seekers do indeed use the same strategies as food foragers.
Informavores constantly make decisions on what kind of information to look for, whether to stay at the current site, trying to find additional information or move to another site, which link to follow, and when to finally stop the search. While humans don't feel much evolutionary pressure to improve their Web use, basic laziness, which is a survival-related trait, forces them to optimise their searching behaviour and, simultaneously, to minimize the thinking required.
The most important concept in the information foraging theory is "information scent". Like animals rely on scents to indicate the chances of finding prey in current area and guide them to other promising patches, humans rely on various cues in the information environment to get similar answers. Human users estimate how much useful information are they likely to get on a given path and then compare the efforts with the expected outcome. When the information scent stops getting stronger (i.e. when users stop finding useful additional information and don't expect to find it soon), people move to a different information source.
Some tendencies in users' behaviour are easily understood from the information foraging theory standpoint. On the Web, each site is a patch and information is the prey. Leaving a site has always been easy, but finding a good one was not. Google has changed this fact by reliably providing relevant links and altered the searching strategies of the users. When users expect that sites with lots of information are easy to find, they have less incentive to stay in one place. The growth of broadband connections had a similar effect. With dial-up, connecting to Internet was difficult and users spend bigger chunks of time online. But always-on connections encourage "information snacking" — short online visits to get specific answers.
Jakob Nielsen considers information foraging to be "the most important concept to emerge from Human-Computer Interaction research since 1993". By applying the information foraging theory, Web sites can be made more intuitive, user-friendly and effective.
Sources:
http://useit.com/alertbox/20030630.html
http://www.usatoday.com/tech/news/2001-05-15-web-usability-research.htm
http://www.wordspy.com/words/informationforaging.asp