Kenneth P. Able

The Development of Orientation and Navigation Behavior in Birds

The complex mechanisms of orientation and navigation in birds develop through the interaction of experience with the relevant stimuli and the underlying genetic substrate. Many migratory species show site fidelity, homing to previously occupied breeding and overwintering localities. The ability to do this requires experience at the site and involves a process like imprinting that seems to take place at least twice during a birds first year of life. On the first migration, birds fly directions and distances that are apparently genetically programmed and are sufficient to bring them within the winter range of their population. Little else is known concerning the genetic basis of orientation behavior. The sun, stars, and earths magnetic field provide compasses for migratory and homing orientation. The ontogeny of each sort of compass involves experience-dependent modification during at least the first few months of a birds life. The sun compass is learned by observation of the suns arc in concert with the birds biological clock. There is some evidence that the magnetic field may also be involved in calibrating the sun compass of the homing pigeon. The star compass is established through visual observation of the axis of stellar rotation during the birds first summer. The pole point is defined as north, but the biological basis of this rule is unknown. The sensory basis of the magnetic compass is also unknown, but it is subject to modification by visual cues, probably stars. In this article we discuss the varying degrees of plasticity in the ontogeny of these mechanisms within the evolutionary context of the spatial and temporal variability of the relevant orientation cues. There appears to be a trend in which information flows from more reliable to les reliable cue-systems during development. In addition to a compass, goal-directed orientation, or navigation, requires some means of assesing location relative to the goal. Homing pigeons apparently utilize sensory information acquired during the displacement journey in this context, but such input does not seem to be necessary. The ability to navigate using only those cues available at the release point is thought to be based on a map of some sort. The bases of this map remain controversial: current investigations are focused on odors and magnetic gradients, but these are not mutually exclusive possibilities, nor are they the only ones. In both of the above cases, there is evidence of experiential effects, and we believe that an ontogenetic approach may elucidate the essentials of these mechanisms. Studies of the ontogeny of bird navigation are also likely reveal important things about the development of behavior in general.

Status signalling in dark-eyed juncos, Junco hyemails: plumage manipulations and hormonal correlates of dominance

Status signalling in dark-eyed juncos was investigated by using plumage manipulations and observing interactions within pairs of birds. Plumage manipulations included darkening of the hood and mantle and the addition of white tail feathers to mimic the appearance of adult males. Plumage characteristics predicted dominance relationships within pairs of first-year males when body size and prior residence in cages was controlled. These characteristics were also strong enough to reverse previously established intra-class relationships within pairs of first-year males and first-year and adult females. The results fail to support the incongruence hypothesis (Rohwer: Behaviour, 1977, 61, 107–129; Rohwer &Rohwer: Anim. Behav., 1978, 26, 1012–1022). In contrast to recent studies using exogenous testosterone to investigate dominance behaviour, circulating plasma levels of testosterone were measured and a comparison made between those of dominants and those of subordinates. Plasma levels of corticosterone were also analysed as a measure of stress. No correlation between either hormone and dominance status was found. Hypotheses are proposed to explain the absence of a relationship between circulating levels of testosterone and winter aggression in flocking birds.

Age-related dominance in male dark-eyed juncos: effects of plumage and prior residence

Abstract Age-related differences in dominance ability and the effect of prior residence on age-related dominance were investigated in captive male dark-eyed juncos, Junco hyemalis . To determine if adults and first-winter birds differed in their intrinsic dominance ability, pairs of adult and first-winter birds of equal body size and winning experience were established. Because plumage influences status, young birds were experimentally darkened to match their older cage-mates. Adult and first-winter males became dominant with equal frequency. Because of this result and the fact that adults are usually dominant in the field, the effect of prior residence on age-related dominance was also investigated. When given prior residence, birds of either age-class won significantly more interactions against intruders. Although first-winter residents (without darkened plumage) dominated intruding adults, they won significantly fewer interactions than did resident adults against intruding adults. This difference in relative dominance success may be due to age-related plumage differences. In the absence of advantages based on prior residence or winning experience, both adult and first-winter birds may rely on plumage differences to settle contests with others of their age class. Prior residence confers an advantage on both adult and first-winter birds. In nature, however, adults are more likely to experience this advantage as a consequence of earlier arrival at migration stopover sites and of site fidelity to the wintering grounds.

Wind drift, compensation, and the use of landmarks by nocturnal bird migrants

Abstract In this paper we describe fall nocturnal migration at three localities in eastern New York, one adjacent to the Hudson River, the other two 30 km to the west in a topographically more uniform area. Migrants at both study areas moved southwest in winds not out of the west and were, therefore, seemingly unaffected by the river. In west winds, however, birds away from the river moved south-southeast whereas those in the vicinity of the river flew a track west of south paralleling the river. In addition, a relative increase in the number of migrants along the river compared to away was observed in west winds as birds presumably became concentrated near the river. We conclude that on most autumn nights migrants passing through this area have a preferred track direction toward the southwest and in strong winds from the west and northwest they are drifted. Upon reaching the vicinity of the Hudson River, some birds alter their headings yielding a track direction that closely parallels the river resulting in at least a partial compensation for wind drift. No alternative hypothesis is consistent with all the data.

Differential migration and an endocrine response to stress in wintering dark-eyed juncos (Junco hyemalis).

The dark–eyed junco (Junco hyemalis) exhibits differential migration in autumn that, in general, results in females overwintering south of males, and young within each sex overwintering north of older birds. Individuals overwintering at higher latitudes face less predictable and more challenging environmental conditions. Rapid increases in circulating levels of the energy-regulating glucocorticosteroid, corticosterone, occur in response to environmental stressors. To establish whether the strength of acute corticosterone secretion was correlated with the probability of encountering poor environmental conditions, we compared the corticosterone stress response (e.g. initial plasma concentrations at the time of capture and 30 min later) in dark–eyed juncos overwintering in Mississippi (MS), USA, near the southern limit of their wintering range, with juncos overwintering in New York (NY), USA, near the northern limit of their wintering range. During two winters, 22 males and one female were sampled in NY; 13 males, 12 females and one bird of undetermined sex were sampled in MS. Not unexpectedly, NY birds carried greater fat reserves that resulted in a significantly higher value of energetic condition (mass corrected for wing cord cubed). There was no difference between the two winters sampled at either site, nor was there an effect of sex on patterns of corticosterone secretion in MS birds. With sexes pooled, MS and NY birds had similar baseline corticosterone levels. However, as predicted, NY birds exhibited significantly higher corticosterone concentrations 30 min after capture. These results support the hypothesis that birds wintering in less predictable, more extreme environments show a higher amplitude corticosterone response, which may enable them to adjust their behaviour and physiology more rapidly in response to environmental stressors such as storms. Adrenocortical sensitivity may be a part of the physiological milieu associated with differential migration in juncos; whether it results from endogenous differences in the migratory programmes of individuals or from acclimatization to local environmental conditions remains to be determined.

Ontogeny of migratory orientation in the savannah sparrow, Passerculus sandwichensis: calibration of the magnetic compass

Abstract The ontogeny of magnetic orientation was examined in the savannah sparrow by manipulating the early experience of hand-raised birds with visual and magnetic cues. Tests of magnetic orientation were performed indoors in orientation cages covered by translucent sheets so that the birds could see nothing outside the cages. Control birds, raised entirely indoors, oriented in a magnetic north-northwest to south-southeast axis during autumn migration. Birds raised outdoors, exposed to clear daytime skies in a normal magnetic field, showed north-south magnetic orientation. Three groups were given experience with the natural sky only within a set of coils that shifted magnetic north clockwise to geographical east-southeast: one group saw only the daytime sky, one group saw only the clear night sky, and the third saw both day and night skies. The birds of all three groups oriented magnetic northeast-southwest, significantly different from the controls. Magnetic northeast-southwest corresponded approximately to geographical northwest-southeast within the magnetic coils in which the birds obtained their visual experience. The differences in the orientation directions chosen by the groups show that the primary magnetic compass may be calibrated early in life by some reference to geographical directions. Experience with either the clear daytime or night sky was sufficient to effect this modification. Celestial rotation, which provides a source of geographical directions both day and night, is proposed to be that geographical reference. At night the birds presumably used the stars to assess celestial rotation. In the daytime sky, both the sun itself and patterns of polarized skylight provide a means of determining geographical north. Experiments designed to determine which of these two visual cues was the relevant stimulus in the calibration of the magnetic compass were inconclusive.

Maps in birds: representational mechanisms and neural bases

The often extraordinary navigational behavior of birds is based in part on their ability to learn map-like representations of the heterogeneous distribution of environmental stimuli in space. Whether navigating small-scale laboratory environments or large-scale field environments, birds appear to be reliant on a directional framework, for example that provided by the sun, to learn how stimuli are distributed in space and to represent them as a map. The avian hippocampus plays a critical role in some aspects of map learning. Recent results from electrophysiological studies hint at the possibility that different aspects of space may be represented in the activity of different neuronal types in the avian hippocampus.

Persistence of circannual cycles in a migratory bird held in constant dim light

Summary1.Most studies of long-term endogenous cycles in birds have been performed in light:dark (L:D) cycles. In this study, male dark-eyed juncos (Junco hyemalis) were held in constant dim light (1−3 lx) and constant temperature for up to 3 years. Testicular cycles, molt, migratory fattening and nocturnal migratory activity (Zugunruhe) were monitored continuously.2.Birds exhibited up to 3 cycles of gonadal growth and regression, spring pre-migratory fattening, molt, and spring and fall Zugunruhe. The annual cycle events maintained appropriate sequential relationships. The amplitude of successive testicular cycles did not decrease.3.The annual cycles of individual birds drifted out of phase with one another, i.e., they appeared to free-run. Cycle lengths were quite variable: 6 to 20 months based on the interval between testicular maxima, and from 6 to 21 months based on the interval between the onset of post-nuptial molts. The cycles had a mean duration of 13.7 months (SD = 4.2 months) between testicular maxima, and 15.0 months (SD = 3.8 months) between the onset of post-nuptial molts. Therefore they may be considered circannual.4.These data provide the strongest evidence for the existence of endogenous, free-running long-term rhythms in birds. They are consistent with a hypothesis in which annual cycles are based on a self-sustaining circannual oscillator upon which seasonal changes in daylength act as a Zeitgeber.

Mechanisms of dusk orientation in white-throated sparrows (Zonotrichia albicollis): Clock-shift experiments

SummarySeveral species of night migrating birds, especially North American emberizines, exhibit markedly different orientation behaviour when tested in circular cages under clear skies at dusk as compared with tests performed after complete darkness. During the period between sunset and the first appearance of stars, birds tend to show high levels of well-oriented hopping; birds deprived of exposure to clear skies at dusk hop less and their activity is usually not oriented. There is evidence that visual cues available during the dusk period, but not later, are responsible for this difference, but details of the orientation mechanisms involved are unclear. We performed 3-h fast and slow clock shifts on white-throated sparrows (Zonotrichia albicollis) to address two questions concerning migratory orientation at dusk: (1) Is the better orientation of sparrows tested at dusk a function of the visual cues available at that time, or does it result from circadian changes in motivation?; and (2) Is the dusk orientation based on a time-compensated sun compass?Sparrows subjected to a 3-h slow clock shift were tested with controls on clear, moonless nights beginning immediately after lights-off in the clock shift room and thus about 3.5 h after local sunset. Individuals of both groups performed poorly oriented hopping typical of tests performed after complete darkness. The pooled data from each group were not significantly oriented. These results show that the visual cues available shortly after sunset, not temporal changes in the motivation of the birds, are responsible for the qualitative differences in orientation.Birds exposed to a 3-h fast clock shift were tested with controls on clear evenings between sunset and the first appearance of stars. Both groups showed well-oriented hopping. The mean direction of the pooled tests of controls was 325°, a typical spring orientation direction for this species. The mean direction of the pooled tests of the clock shifted birds (274°) was significantly different from that of controls and the 51° counterclockwise shift is consistent with that predicted by a time-compensated sun compass model.

The flight behaviour of individual passerine nocturnal migrants: A tracking radar study

Abstract Nocturnal passerine migrants were tracked with a small automatic tracking radar during spring migration in eastern New York. Climbing, descending and markedly non-linear tracks were selected for analysis because they may reveal relationships not evident in normal straight and level tracks. Climbing individuals ascended at 1 to 2 vertical metres per second by heading into the wind and increasing their ascent angles while air speed tended to remain constant. Within individual tracks, birds flew slower when flying downwind than when flying into the wind and changes in air speed were performed over periods of a few seconds. A small amount of data suggested that this behaviour did not occur under overcast skies. Both the direction and speed of the wind force were important in predicting air speed. Multiple regression analysis indicated that faster flying birds were more likely to fly in winds of high speed and at large angles into the wind.