Fermi's Paradox and The Zoo Hypothesis

Today I read about the Zoo Hypothesis, which essentially posits that ETIs are shielding us from discovering their existence. It's an interesting thing to consider. Read more about it here:

Spatio-temporal constraints on the zoo hypothesis, and the breakdown of total hegemony

Duncan H. Forgan (2011).
International Journal of Astrobiology, Volume 10, Issue04, October 2011 pp 341-347
http://journals.cambridge.org/action/displayAbstract?aid=8361227

Reading this abstract of course led me to looking up the Fermi Paradox. Interesting page found at this link:

http://www.fermisparadox.com/

The Fermi Paradox calculates that there are three base reasons why a civilization would expand beyond it's planet, the reasons being exploration, colonization, and survival. 

Taking Drake's equation into account, the probability of a galaxy having at least one intelligent species is there, though quite minute, and as we are one of many galaxies, it stands to reason there is a possibility of intelligent life elsewhere. The likelihood of that species expanding and colonizing and thus taking over neighbouring clusters, while also a possibility, could take millions of years; However, when you consider that the universe is billions of years old, this seems a small amount of time by comparison.

There could also be hundreds of galaxies in our area with no intelligent life whatsoever, but it's a bit of a Schroedinger's Cat paradox - they could both be there and not there, but we wouldn't know.

Enrico Fermi postulated in 1950 that since only one ETI could likely spread in that relatively short period of time, how is it that we have never seen these extraterrestrial entities and that our radio telescopes never collected unidentifiable signals from said populace?

Which of course leads us back to the Zoo Hypothesis, a rather soft answer to this question. 

Food for thought...