Partial experience with the arc of the sun is sufficient for all-day sun compass orientation in homing pigeons, Columba livia

The sun compass revisited

Many animals, and birds in particular, are thought to use directional information from the sun in the form of a time-compensated sun compass, with predictably deviated orientation under clock shift being regarded as the litmus test of this. We suggest that this paradigm obscures a number of other ways in which solar-derived information could be important in animal orientation. We distinguish between the known use of the sun's azimuth to provide absolute geographical direction (compass mechanism) and its possible use to detect changes in heading (heading indicator mechanism). Just as in an aircraft, these two kinds of information may be provided by separate mechanisms and used for different functions, for example for navigation versus steering. We also argue that although a solar compass must be time-referenced to account for the sun's apparent diurnal movement, this need not entail full time compensation. This is because animals might also use time-dependent solar information in an associatively acquired, and hence time-limited, way. Furthermore, we show that a solar heading indicator, when used on a sufficiently short timescale, need not require time compensation at all. Finally, we suggest that solar-derived cues, such as shadows, could also be involved in navigation in ways that depend explicitly upon position, and are therefore not strictly compass-related. This could include giving directionality to landmarks, or acting as time-dependent landmarks involved in place recognition. We conclude that clock shift experiments alone are neither necessary nor sufficient to identify the occurrence of all conceivable uses of solar information in animal orientation, so that a predictable response to clock shift should not be regarded as an acid test of the use of solar information in navigation.

Directional compass preference for landing in water birds

Introduction

Landing flight in birds is demanding on visual control of velocity, distance to target, and slope of descent. Birds flying in flocks must also keep a common course of landing in order to avoid collisions. Whereas the wind direction may provide a cue for landing, the nature of the landing direction indicator under windless conditions has been unknown. We recorded and analysed landing directions of 3,338 flocks in 14 species of water birds in eight countries.

Results

We show that the preferred landing direction, independently of the direction from which the birds have arrived, is along the north-south axis. We analysed the effect of the time of the year, time of the day (and thus sun position), weather (sunny versus overcast), light breeze, locality, latitude, and magnetic declination in 2,431 flocks of mallards (Anas platyrhynchos) and found no systematic effect of these factors upon the preferred direction of landing. We found that magnetic North was a better predictor for landing direction than geographic North.

Conclusions

In absence of any other common denominator determining the landing direction, the alignment with the magnetic field lines seems to be the most plausible if not the only explanation for the directional landing preference under windless and overcast conditions and we suggest that the magnetic field thus provides a landing direction indicator.

Behavioural and physiological mechanisms of polarized light sensitivity in birds

Polarized light (PL) sensitivity is relatively well studied in a large number of invertebrates and some fish species, but in most other vertebrate classes, including birds, the behavioural and physiological mechanism of PL sensitivity remains one of the big mysteries in sensory biology. Many organisms use the skylight polarization pattern as part of a sun compass for orientation, navigation and in spatial orientation tasks. In birds, the available evidence for an involvement of the skylight polarization pattern in sun-compass orientation is very weak. Instead, cue-conflict and cue-calibration experiments have shown that the skylight polarization pattern near the horizon at sunrise and sunset provides birds with a seasonally and latitudinally independent compass calibration reference. Despite convincing evidence that birds use PL cues for orientation, direct experimental evidence for PL sensitivity is still lacking. Avian double cones have been proposed as putative PL receptors, but detailed anatomical and physiological evidence will be needed to conclusively describe the avian PL receptor. Intriguing parallels between the functional and physiological properties of PL reception and light-dependent magnetoreception could point to a common receptor system.

EEG responses to visual landmarks in flying pigeons

BACKGROUND

GPS analysis of flight trajectories of pigeons can reveal that topographic features influence their flight paths. Recording electrical brain activity that reflects attentional processing could indicate objects of interest that do not cause changes in the flight path. Therefore, we investigated whether crossing particular visual landmarks when homing from a familiar release site is associated with changes in EEG.

RESULTS

Birds carried both data-loggers for recording GPS position and EEG during flight. First, we classified characteristic EEG frequencies of caged birds and found five main bands: A: 0-3, B: 3-12, C: 12-60, D: 60-130, and E: 130-200 Hz. We analyzed changes in these activity bands when pigeons were released over sea (a featureless environment) and over land. Passing over the coastline and other prominent landmarks produced a pattern of EEG alterations consisting of two phases: activation of EEG in the high-frequency bands (D and/or E), followed by activation of C. Overlaying the EEG activity with GPS tracks allowed us to identify topographical features of interest for the pigeons that were not recognizable by distinct changes of their flight path.

CONCLUSIONS

We provide evidence that EEG analysis can identify landmarks and objects of interest during homing. Middle-frequency activity (C) reflects visual perception of prominent landmarks, whereas activation of higher frequencies (D and E) is linked with information processing at a higher level. Activation of E bands is likely to reflect an initial process of orientation and is not necessarily linked with processing of visual information.

Honeybees can learn the relationship between the solar ephemeris and a newly-experienced landscape

Many species learn the sun's daily pattern of azimuthal movement (the solar ephemeris function) for use in sun-compass orientation. In honeybees, this learning is accomplished with much innate guidance and yields stubborn, imprinting-like retention of certain aspects of the stored information. One such case involves the failure of transplanted bees to update their memories of the relationship between the solar ephemeris and a new landscape, even after many days' experience at the new site. In the present study, I ask whether the bees in previous transplantation experiments failed to update their memories of the relationship between the sun and landscape because the source and recipient landscapes were (rotated) panoramic twins of each other, each dominated by a conspicuous treeline. To test this hypothesis, I transplanted bees from their natal site at the bottom of a valley to a panoramically different, treelined site and later tested the bees' knowledge of the sun's course in relation to the treeline. The test involved observing the bees' communicative dances under overcast skies at a second treeline that was a mirror image of the first. The cloudy-day dances show that the bees had indeed learned the relationship between sun's pattern of movement and the (panoramically novel) treelined site, indicating that the bees' memory of the relationship between the ephemeris function and the landscape is not incapable of revision as the earlier results had suggested. I discuss these results in the context of a brief summary of our current understanding of solar ephemeris learning in bees.

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.

Participation of the homing pigeon thalamofugal visual pathway in sun-compass associative learning

The ascending thalamofugal visual pathway in pigeons (Columba livia) terminates in the telencephalic wulst. Characterizing the role of this pathway in visually guided behaviour has remained a challenge. To determine whether this pathway, and in particular the wulst, may participate in sun-compass-guided behaviour in homing pigeons, intact, ectostriatum-lesioned or wulst-lesioned pigeons were trained to use their sun compass to locate the direction of a food reward in an outdoor, octagonal arena. Control and ectostriatum-lesioned pigeons learned the task well, and orientated appropriately during the first trial of the last three training sessions and after a phase-shift manipulation. In contrast, the wulst-lesioned pigeons learned the task but they took more sessions to learn, and their directional choices were more scattered during the first trial of the last three training sessions and after the phase-shift manipulation. A subsequent regression analysis indicated that deeper layers of the wulst might have made more of a contribution to the observed behavioural impairments. The data indicate that the homing pigeon wulst participates in visually guided behaviour when the sun compass is used to learn the directional location of a goal.

The ontogeny of the homing pigeon navigational map: evidence for a sensitive learning period

Homing pigeons can learn a navigational map by relying on the heterogeneous distribution of atmospheric odours in the environment. To test whether there might be a sensitive period for learning an olfactory-based navigational map, we maintained a group of young pigeons in an aviary screened from the winds until the age of three to four months post-fledging. Subsequently, the screens were removed and the pigeons were exposed to the winds and the environmental odours they carry for three months. One control group of pigeons was held in a similar aviary but exposed to the winds immediately upon Hedging, while another control group of pigeons was allowed free-flight. When the pigeons from the three groups were released from two distant release sites at about six months of age post-fledging, the two control groups were found to be equally good at orientating and returning home, while the experimental pigeons held in the shielded aviary for the first three months post-fledging were unable to orientate homeward and they were generally unsuccessful in returning home. This result supports the hypothesis that environmental experience during the first three months post-fledging is critical for some aspect of navigational map learning and that navigational map learning displays sensitive period-like properties.