Body Composition, Lipid Reserves and Caloric Densities of Summer Birds in a Northern Deciduous Forest

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Abstract
Specimens of 16 passerine bird species [Empidonax minimus, Sitta carolinensis, Turdus migratorius, Hylocichla mustelina, Catharus guttata, C. ustulata, C. fuscescens, Vireo olivaceus, V. philadelphicus, Dendroica caerulescens, D. virens, Seiureus aurocapillus, Setophaga ruticilla, Piranga olivaceus, Pheucticus ludovicianus, Junco hyemalis] collected in midsummer in the Hubbard Brook forest ecosystems in central New Hampshire [USA] were analyzed for major chemical constituents (water, lipid, lean dry matter, ash) and for caloric value. Bird tissue contained on the average 66% water, while the ash content of lean dry tissue was 13.00 .+-. 0.12% as measured in the bomb calorimeter and 14.22 .+-. 0.15% by combustion in a muffle furnace. Ether-extractable lipid averaged 0.165 .+-. 0.007 g/g lean dry weight, a very low value indicating that these birds in summer have no lipid reserve to meet environmentally caused metabolic emergencies. Caloric densities of lean dry tissue, extracted lipids and of whole birds averaged 4616 .+-. 12, 8908 .+-. 28 and 5239 .+-. 29 cal/g dry weight, respectively.