A comparison of the effect of long daily photoperiods on the pattern of energy storage in migratory and non-migratory finches

Abstract

Caged white-crowned sparrows, Zonotrichia leucophyrs gambelli, when subjected to long daily photoperiods in mid-winter, deposit large amounts of subcutaneous and visceral fat and develop migratory behavior comparable to natural vernal migratory behavior. The altered metabolic state involved in this deposition of fat is characterized by a reduction in glycogen content of the pectoral muscles and liver and a suppression of the diurnal glycogen cycle in these organs. There is also a marked increase in the fat content of these tissues so that the total mobilizable energy in them is considerably greater than in the short-day winter birds. The thigh muscles show a similar reduction in glycogen content but only a very slight increase in fat content. This change in the pattern of energy storage may be regarded as one feature of the scheme which produces the metabolic alterations necessary for sustained migratory flight. The wintering population of the Oregon Junco, Junco oreganus montanus, in southeastern Washington responds, although less extensively, to long daily photoperiods. This may be correlated with its more restricted migratory movements. The non-migratory English sparrow, Passer domesticus, when subjected to long daily photoperiods, shows no such alteration in the pattern of energy storage in pectoral muscle and liver; rather there is a tendency toward a lower level of energy storage. Although Zonotrichia leucophrys gambelii in mid-winter have much less glycogen in pectoral muscle and liver than the indoor caged birds, the pattern of energy storage may be consistent with that of the latter in experimentally induced migratory state if the restricted flight activity of the latter, the precapture activity of the former, and possible differences in temporal pattern of food intake are taken into consideration. The relatively small amount of glycogen available, and the extensive storage of fat, suggest that there must be very extensive use of fat or fatty acids directly by the pectoral muscles during flight.