Final Hierarchy Image

Clouds image by - mistagregory
Retrieved from http://en.wikipedia.org/wiki/File:Overcast_skies_from_Tropical_Storm_Danny.jpg

City Silhouette image by - JEFFSTER
Retrieved from http://www.newyorker.com/online/photocontests/eustace_tilley_2011/entry514034452?nextprev=true

Pigeons retrieved from
- http://www.pigeon-bg.com/index.php?show=about_me&flag=2
- http://sc.wikipedia.org/wiki/File:Rock_Pigeon-Mindaugas_Urbonas-2.jpg
- http://www.mdahlem.net/omnbirds/11/rockdove.php
- http://birdsculpture.blogspot.co.nz