My grading system. Pretend you are looking at a cross-section through a breast. The blue line is the sternum with the keel atop it. Pectorals are red. Note the notch at the top of the keel in Plump; see cuckoo and grouse In hand, the most unmistakable sign of starvation in birds is the wasting of the pectorals, the great flight muscles on the breast that are from 15% to over 20% of the body weight. They are in two layers, with the top layer, the pectoralis major, producing the powerful downstrokes of the wings, while the smaller layer actually on the sternum, the pectoralis minor (also known as the supracoracoideus muscle) produces the much easier upstroke. The latter passes through the triosseal canal at the shoulder to insert on the humerus, and sometimes when one of those three bones making up the canal is damaged, the canal is obliterated. This limits or even prevents the upstroke. When no food comes in, the body makes up for the lack by burning its own stored fat for energy. When that is used up, it begins to burn muscle, and this can be read by a careful examination of the breast, using some sort of grading system. When the bird is on its back, the breast feathers are blown aside or lightly dampened to expose the pectorals, which except in aquatic birds, have very little feather cover growing on them. Evaluating them thoroughly must be done with both eyes and fingers (see below). Note the colour too. Twice I have found one pectoral a healthy dark wine colour, while the other was palest puce from traumatic ischaemia—reduced or absent blood circulation. Checking both sides at about the level of the middle of the keel is the best place to assess the health of the muscle mass. This is not a scientific measurement, but a subjective observation that requires understanding of the anatomy; this is best acquired by repeated post-mortems. After many of them, I learned that different species have slightly different shaped sternums, different heights of keels, as well as different depths of the pectorals themselves. For example, pigeons have very deep keels and deep, strong pectorals compared to Great Horned Owls, and vegetarians such as Ruffed Grouse are nearly always so plump that the keel-bone is in a depression. Some birds with low keels are hard to evaluate. I also found correlations between the pectoral muscle, the body weight, and the amount or absence of body fat, and often if there was some body fat internally, the bird was not severely starved. Finally I drew the diagram of imaginary cross-sections of birds through the middle of their chests. Though I tried, I never did find a way to photograph them well--the closest might be the skinned pigeon on page 1. Note some factors that can confuse: Pectoral swellings caused by injection, hematoma, or deep caseation (hardened infection) or necrotic muscle. Injections cause bleeding, bruising and even ischemia in the muscle. To see for yourself, cut open the pectorals after an injection given for death, and check the injection site. Pectorals that have suffered a blow may lose their blood supply and become necrotic, then harden and push out of the skin of the breast as new muscles grow beneath to replace the dead ones Air from a ruptured airsac pushing up under the skin (subcutaneous emphysema) when under the sternal skin, looks plump to the eye, but collapses to a finger-touch. Onesided pectoral atrophy, in which one of the pectoral muscles wastes away due to destruction of the branch of the brachial nerve that serves it. The other, unaffected, pectoral may be quite plump. This bird will have had a one-sided wing paralysis that will not recover. Keel depth varies in species. The loss on an emaciated Screech Owl does not look as dangerous as on an emaciated pigeon, who has much deeper pectoral muscle and therefore a deeper keel for the muscle to attach to. Having a fair idea of the state of the nutrition directs what should be done next. If there is "reasonable" flesh or more, there is no rush to feed (except Sharp-shins, wrens, kinglets and other very high-metabolism birds, even if they are plump). When there is emaciation looming, the weakened bird may need help getting food in, or may be dying and no amount of feeding will help.