Nocturnal Migrant Research Articles

Homing behavior of wood thrushes (Hylocichla mustelina)

Using the wood thrush (Hylocichla mustelina) as an example of a typical nocturnal migrant, we employed radio telemetry to follow breeding birds during the course of homing movements following displacements. Seven thrushes were displaced over distances of 6.5 to 17.3 km in a variety of directions from their nesting territories. The thrushes moved in a series of short flights (mean = 2.1 km) performed primarily at dawn. Consequently, the birds took several days to home from even these relatively short displacements. Thrushes flew under clear and solid overcast skies and even in light rain. The pooled individual flights of the birds were significantly oriented in the homeward direction (Fig. 2). Their orientation relative to home did not improve significantly as they progressed toward the goal. Three of the birds were documented to have returned to their home territories. The detailed tracks of the birds preclude the possibility that they homed by random search.

Skylight polarization patterns at dusk influence migratory orientation in birds

Over 100 animal species are known to be able to perceive the plane of polarization of linearly polarized light; most of these are arthropods but several molluscs and vertebrates, including man, share this ability1,2. At least five aquatic vertebrates (three fish, a salamander and a larval frog) are capable of oriented movement based on the E-vector of linearly polarized light3–9. Pigeons (Columba livia) have been conditioned to discriminate between rotating and stationary polarized light and between widely separated stationary E-vectors10,11, but the behavioural significance of this ability remains unknown. I report here that the migratory orientation of the white-throated sparrow (Zonotrichia albicollis), a nocturnal migrant, is affected by manipulations of the axis of skylight polarization. These data provide the first evidence that polarized light may be a relevant cue in migratory orientation.

The sun as a cue in the orientation of the white-throated sparrow, a nocturnal migrant

The sun as a cue in the orientation of the white-throated sparrow, a nocturnal migrant

Sunset and the orientation of a nocturnal migrant bird

THE information required for compass orientation among migratory birds is potentially available in the form of numerous environmental stimuli or cues1. Most passerine migrants complete their annual migrations at night, and their orientation is though to depend on a star compass or one based on geomagnetic stimuli1. The pioneering work of Kramer2 suggested that the setting sun may play a part in the migratory orientation of birds, but this possibility attracted little attention until more recently1. I present here the first experimental evidence that directional information at the time of sunset plays a crucial part in the compass orientation of a nocturnal migrant Passerculus sandwichensis, the savannah sparrow.

Daily rhythm of plasma corticosterone binding activity in the white-throated sparrow, Zonotrichiaalbicollis

There is a bimodal daily rhythm of plasma corticosterone binding activity (CBA) in the white-throated sparrow, Zonotrichia albicollis , in the spring migratory condition. Low levels occurred at the beginning (0500) and at the end (2100) of a 16-hour daily photoperiod. Peak CBA occurred at 0900 and 0100, as did peak locomotor activity in this nocturnal migrant. Comparisons of CBA with total plasma corticosteroid concentrations from a previous study of the same group of birds indicate a positive correlation during most of the day but not during the early hours of darkness. The daily rhythm of locomotor activity may account for the rhythm of CBA which, in turn, may be partially responsible for the daily rhythm of plasma corticosteroid concentration.

Sun Compass Orientation in a Nocturnal Migrant, the White-Throated Sparrow

Migratory birds are known to be capable of using several environmental cues for orientation (see Emlen 1975 for a recent review). The sun is a potentially important source of compass information and many vertebrates possess sun compasses that are timecompensated via the internal clock. Nocturnal migrants cannot refer directly to the sun during migratory flight, but solar cues could be useful in determining take-off directions or in correcting for inflight displacements. A logical first step in analyzing the potential role of the sun in the orientation of nocturnal migrants is to determine if a functional sun compass exists in a spectrum of these species. Here we report the ability to perform sun compass orientation in the White-throated Sparrow (Zonotrichia albicollis).

Temporal synergism of corticosterone and prolactin controlling fat storage in the white-throated sparrow, Zonotrichia albicollis

Increases in body fat were induced by daily injections of corticosterone. However, the time of injection is of critical importance. Injections given 6 hr after the onset of a daily photoperiod of 6 hr caused fat increases, whereas injections at 12 or 18 hr after “dawn” were ineffective. In addition to fat increases, injections at 6 hr after “dawn” also induced nocturnal locomotor activity in the white-throated sparrow, a nocturnal migrant. Nocturnal activity was absent in the untreated birds as well as in those receiving corticosterone at 12 or 18 hr after “dawn.” Apparently, the daily variations in responses to corticosterone depend on the circadian release of endogenous pituitary prolactin. In birds kept on continuous light, it was discovered that a temporal synergism of injected corticosterone and injected prolactin can regulate the level of fat stores. Daily injections of prolactin at 4 or 12 hr after corticosterone produced high levels of obesity in lean photorefractory birds after 5 days. Injections at 8 or 20 hr after corticosterone depressed fat stores, and injections at 0 or 16 hr after the adrenal steroid produced intermediate levels of fat. It is concluded that seasonal levels of fat stores are the cumulative results of daily changes that are regulated by a temporal synergism of corticosterone and prolactin.

Diurnal variations of metabolic responses to prolactin in lower vertebrates

Several responses to prolactin are shown to vary diurnally. On 16-hour photoperiods, midday injections induce fattening in the golden topminnow, Fundulus chrysotus, the leopard frog, Rana pipiens, the green anole, Anolis carolinensis, and the white-throated sparrow, Zonotrichia albicollis. Such injections, carried out over a period of 1 week, increase the total body lipid to levels found during the annual cycle when lipid deposits are greatest. Midday injections also promote a catabolic effect in the fish and the bird, and induce nocturnal restlessness in the white-throated sparrow, a nocturnal migrant. On the other hand, early injections (2 hours after the beginning of the photoperiod) cause a loss in fat stores in the fish and the bird and fail to produce nocturnal restlessness in the bird. Early injections, however, promote growth responses (increase in dry nonlipid materials) in all four vertebrates. The fattening and catabolic responses to prolactin injections at midday are still present in unfed fish. The diurnal variation in responses to prolactin offer an explanation for the conflicting and diverse reports regarding the function of prolactin and emphasize the importance of time in understanding the physiology of prolactin.

A possible endocrine basis for migratory behaviour in the White-crowned Sparrow, Zonotrichia leucophrys gambelii

By using hormone preparations, a simulated migratory behaviour has been induced in caged Z. l. gambelii, a nocturnal migrant. Daily injections of prolactin increase nocturnal restlessness in photosensitive birds under outdoor conditions prior to spring migration and also initiate nocturnal locomotor activity in photo-refractory birds held indoors on a long daily photoperiod. These effects are augmented by adrenocortical hormones which, however, are ineffective when administered alone. In addition, metapirone, an inhibitor of adrenocortical synthesis, suppresses nocturnal activity. Simultaneous injections of corticosterone eliminate the metapirone-induced suppression of nocturnal activity. In prolactin-treated birds, there is a reduction of locomotor activity during the last two hours of light that is strikingly similar to the late afternoon reduction in activity as natural Zugunruhe developes. The dual role of prolactin in promoting fattening and nocturnal locomotor activity, and the augmentation of nocturnal activity by adrenocortical hormones have been discussed in regard to their possible involvement in the physiologic events of migration. Assays of pituitary prolactin at several times during the annual cycle appear to be compatible with a hypothesis involving prolactin in the development and maintenance of migratory behaviour.