Stomach analysis

Birds may be found dead and the contents of the stomach analyzed. This used to be the main technique for the purpose, but shooting birds solely to determine diet is nowadays usually considered unacceptable. The methods for analyzing stomach contents are similar to those for droppings (10.2.4). The stomach should be removed as soon as possible and placed in alcohol (high concentrations are preferable as water contents of stomachs may be high) because the contents deteriorate rapidly. There may be differential digestibilities of prey types and different passage times, with hard items persisting for longer (Rosenberg and Cooper 1990). Most of the principles that apply to dropping analysis (see 10.2.4) apply to stomach contents, remembering that the tendency of the stomach to retain large hard parts and allow small soft items to pass into the intestines can lead to bias.

In some species, esophageal contents can be quantified and do not suffer from differential digestibilities (Kundle 1982). Some granivorous species have gullets or crops in which food is stored before it enters the stomach and again the contents are unaffected by differential digestion.

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