In the range of a budgie's breast, there is a bone that is called
sternum, and it's an evolutionary specialty
of birds. Its cross section is similar to the Mercedes Benz "star".
One part of the sternum points out of the bird's body. At this breast
bone, the flight muscles that stretch over a budgie's breast are fixed.
If vets want to test the nourishing condition of a bird, they touch the breast searching for the sternum. A normally nourished budgie who is in good condition shows trained muscles and only little fat, thus the breast bone is evenly perceptible.
Those budgies who are in bad nourishing conditions, don't have enough flight muscles and their sternum is clearly perceptible as a sharp edge. In worst cases, the breast bone is even visible for layman while shift the bird's feathers sideward carefully. The photo above shows a budgie whose sternum builds an extreme edge since the bird was seriously ill and thus life-threateningly starving.
Birds who are overweighed can be recognized by their big breast. It is nearly impossible to feel their sternum which is completely covered by adipose tissue.
Link tip: Do you want to discuss with experts and other bird owners about your bird's health? Then please feel free to visit the English forum 
of 
. Of course you will meet me there, too. My nickname is "Feenseeschwalbe".
All photos and the text on this page are protected by the copyright law. In case you'd like to use photos or texts for your own non-commercial purpose, please contact the author.