Well, Tumblr does not gives you an all-in-one package blog. If you need some website analytics for your blog you will need to setup this on your own. Apparently setting up Google Analytics on tumblr is very easy and can be done in 2 simple steps :-
1) Create a Google Analytics account using your Gmail ID.
Choose an Account name, enter your website address. For Example, http://techstreak.tumblr.com.
After registration you will get a Tracking ID. Copy this ID and click on the bottom Save link.
2) Now, go to your blog customization page and look for ‘Google Analytics ID’ field. Simply copy paste the Tracking ID here and Save. That’s it you are done.
You should be able to see traffic stats under Real-Time(BETA) in google analytics home.
In case you are using old version of google analytics, go here.