Nightly Unrest in Caged Migratory Sparrows under Outdoor Conditions

Abstract

The phenomenon of nocturnal activity, or Zugunruhe, in caged migratory birds has been known and studied in Europe for some time and has been regarded, as the German name indicates, as an expression of the migratory urge. In America this nightly unrest has only recently begun to be investigated. Eyster (1952, 1954) found that it occurred in three species of migratory fringillids, Junco hyemalis, Zonotrichia albicollis, and Zonotrichia leucophrys, under conditions of temperature and photoperiod simulating those at which these birds normally migrate and that it did not occur in the nonmigratory Passer domesticus under the same conditions. Eyster described the effects of temperature on the daily activity rhythms of these birds, finding that the activity levels generally were depressed by either very high or very low temperatures and that between the extremes the level increased directly with the temperature. A decrease in the activity levels at the time of molt was also found. Eyster concluded that nightly unrest is an indicator of the migratory condition and that it can be equated with the actual nocturnal migratory behavior pattern exhibited by wild birds. Farner and co-workers (1953a, 1954) have demonstrated the presence of nightly unrest in a migratory race of the white-crowned sparrow, Zonotrichia leucophrys gambelii, during the spring migration period under outdoor conditions and have correlated it with changes in body weight, fat deposition, molt and testicular development. In the nonmigratory Clark nutcracker, Nucifraga columbiana, nightly unrest was found not to occur at any time of the year (1953a). Another important discovery by these workers is that high environmental temperatures induce nightly unrest in the white-crowned sparrow even at short photoperiods (1953b). This appears to weaken the supposition that nightly unrest is strictly associated with true migratory behavior and Farner et al. state (1954) that the investigation of Zugunruhe as a tool in the study of the physiology of migration must be applied very cautiously. The investigations of Zugunruhe in Europe have been extensively reviewed by Palmgren (1944, 1949), Farner (1950), Eyster (1954) and others. These studies have also indicated some discrepancies between nightly unrest and actual migratory activity. In most of the species investigated the unrest begins in the spring at about the normal time of migration but continues throughout the breeding period, often until the onset of the post-nuptial molt. In the fall the unrest again appears at about the normal migration time but in many cases continues far into the winter. Many of the investigations were conducted under unnatural or unstated conditions of temperature and photoperiod and the results are thus difficult to interpret. The present study was undertaken in connection with an experimental investigation of the role of the gonads in the physiology of migration in the white-throated sparrow. It was desired to use nightly unrest as one indicator of the migratory condition, but since there was considerable question of its reliability as such, it was decided to investigate it in newly captured migrating birds under outdoor conditions. This study was begun In the fall of 1951, and in the early spring of 1952 it was enlarged to a more intensive investigation of the relation of seasonal changes in activity to those in body weight, molt, and later, fat deposition and energy intake, under outdoor conditions. It was believed that the climatic conditions to which the birds were exposed at Champaign, Illinois, would not be greatly different from those to which wild birds are exposed and that any physiological changes caused by these conditions would be similar to those of wild birds. Thus the exact relationships of nightly unrest with the migratory periods, and with other presumed indicators of the migratory condition, could be determined. For comparison with the white-throated sparrow, two other species, the tree sparrow and the slate-colored junco, with different migratory habits, were also studied. Observations were made on birds confined in individual activity cages in an outdoor aviary in the fall of 1951, and continuously from March, 1952 until the end of July, 1953. In 1951 only the activity was studied; beginning in 1952 regular observations were also made on body weight and molt. Fat deposition was studied for the tenmonth period from October, 1952 through July, 1953, and food consumption (metabolized energy 'Contribution from the Department of Zoology, University of Illinois, Urbana, Illinois, and the Department of Biology, Fisk University, Nashville, Tennessee.