digiscoped photo
Swarovski ATS80HD
Canon SD1100 IS

On perched birds, brood patches are
difficult to see because they are mostly
covered by surrounding feathers. Even on
birds in the hand, banders blow on the feathers
in order to reveal the entire brood patch.

See interesting and informative
articles on brood patches at
http://www.stanford.edu/group/stanfordbirds/text/essays/Brood_Patches.html
and in Frank Gill's Ornithology textbook.