. The book of birds, common birds of town and country and American game birds . ung. Field observations of the food habitsof birds serve a useful purpose, but theyare rarely accurate enough to be fully re-liable. The presence of certain birds ina corn or wheat field or in an orchard isbv no means proof, as is too often as-sumed, that they are devastating the grainor fruit. They may have been attractedby insects which, unknown to the farmeror orchardist. are fast ruining his it has been found necessary to ex-amine the stomachs and crops of l)irds toascertain definitely what and how m
. The book of birds, common birds of town and country and American game birds . ung. Field observations of the food habitsof birds serve a useful purpose, but theyare rarely accurate enough to be fully re-liable. The presence of certain birds ina corn or wheat field or in an orchard isbv no means proof, as is too often as-sumed, that they are devastating the grainor fruit. They may have been attractedby insects which, unknown to the farmeror orchardist. are fast ruining his it has been found necessary to ex-amine the stomachs and crops of l)irds toascertain definitely what and how muchthey eat. ASTOXISIIIXG CAPACITY OF BIRDS STOM-ACHS RV TI-STS The Biological Survey has in this wayexamined upward of birds, most ofwhich have been obtained during the lastJ5 Years from scientific collectors, for ourbirds arc too useful to be sacrificed whenit can possibly be avoided, even for thesake of obtaining data upon which to baselegislation for their protection. It is interesting to observe that hungrybirds—and birds are hungry most of the. BorealRegion AuslraJRegion Trail-iv i^^,Region > ZONE MAP OF NORTH AMERICA After U. S. Biological Survey 0 500 Statute Milesy/ir doited parts of the Austml Zones east of tfie Great Plainf: indicateejtent q/the (f these Zones, knowmvspecti vet i/nstJieAtleyliaCarolinian and Awtrtiviparian Faunas. The iindotted parts of the same zonesarv knoum as the Transition. Upper Sonoi-an and flower SoTioran. MAP SHOWING THE BIRD ZONES Witli their unparalleled facilities for locomotion over both land and water, birds are morewidely distributed than any other vertebrates, yet their comparatively delicate organizationsare highly sensitive to many conditions of life. The most important factor in determiningthe breeding range of birds is, of course, the one of climate, expressed mainly through tem-perature and to a lesser degree through rainfall. The zone map shows that North America is divide
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