Ms. Witter et Ic. Cuthill, THE ECOLOGICAL COSTS OF AVIAN FAT STORAGE, Philosophical transactions-Royal Society of London. Biological sciences, 340(1291), 1993, pp. 73-92
Avian fat storage is associated with both benefits and costs. Although
the benefits of maintaining higher energetic reserves have long been
considered, the associated costs have received far less attention. Spa
tial and temporal patterns of fat storage, together with experimental
data, indicate that birds are capable of actively regulating their ene
rgetic reserves at levels below physiological or environmental maxima.
This regulation implies that fat storage entails a cost. Evidence of
potential costs are reviewed and discussed under the following heading
s: mass-dependent metabolism, mass-dependent predation risk, mass-depe
ndent risk of injury, mass-dependent foraging, pathological costs and
reproductive costs. Although the evidence that fat storage is costly i
s convincing, key empirical data are lacking. We indicate the sorts of
data which need to be gathered and suggest ways in which this might b
e done. We go on to discuss the interaction of these costs and their r
elevance to between-individual patterns of fat storage and the interpr
etation of 'condition indices'. Because many of the purported costs of
fat storage are dependent upon changes in body mass, or wing loading,
our review is also relevant to other phenomena which may involve mass
-dependent costs, such as gonadal hypertrophy, transport of food items
and primary moult.