Factors reducing the expected deflection in initial orientation in clock-shifted homing pigeons

Is There Visual Lateralisation of the Sun Compass in Homing Pigeons?

Functional lateralisation in the avian visual system can be easily studied by testing monocularly occluded birds. The sun compass is a critical source of navigational information in birds, but studies of visual asymmetry have focussed on cues in a laboratory rather than a natural setting. We investigate functional lateralisation of sun compass use in the visual system of homing pigeons trained to locate food in an outdoor octagonal arena, with a coloured beacon in each sector and a view of the sun. The arena was rotated to introduce a cue conflict, and the experimental groups, a binocular treatment and two monocular treatments, were tested for their directional choice. We found no significant difference in test orientation between the treatments, with all groups showing evidence of both sun compass and beacon use, suggesting no complete functional lateralisation of sun compass use within the visual system. However, reduced directional consistency of binocular vs. monocular birds may reveal a conflict between the two hemispheres in a cue conflict condition. Birds using the right hemisphere were more likely to choose the intermediate sector between the training sector and the shifted training beacon, suggesting a possible asymmetry in favour of the left eye/right hemisphere (LE/RH) when integrating different cues.

In Situ Clock Shift Reveals that the Sun Compass Contributes to Orientation in a Pelagic Seabird

Compass orientation is central to the control of animal movement from the scale of local food-caching movements around a familiar area in parids [1] and corvids [2, 3] to the first autumn vector navigation of songbirds embarking on long-distance migration [4-6]. In the study of diurnal birds, where the homing pigeon, Columba livia, has been the main model, a time-compensated sun compass [7] is central to the two-step map-and-compass process of navigation from unfamiliar places, as well as guiding movement via a representation of familiar area landmarks [8-12]. However, its use by an actively navigating wild bird is yet to be shown. By phase shifting an animal's endogenous clock, known as clock-shifting [13-15], sun-compass use can be demonstrated when the animal incorrectly consults the sun's azimuthal position while homing after experimental displacement [15-17]. By applying clock-shift techniques at the nest of a wild bird during natural incubation, we show here that an oceanic navigator-the Manx shearwater, Puffinus puffinus-incorporates information from a time-compensated sun compass during homeward guidance to the breeding colony after displacement. Consistently with homing pigeons navigating within their familiar area [8, 9, 11, 18], we find that the effect of clock shift, while statistically robust, is partial in nature, possibly indicating the incorporation of guidance from landmarks into movement decisions.

Asymmetric visual input and route recapitulation in homing pigeons

Pigeons (Columba livia) display reliable homing behaviour, but their homing routes from familiar release points are individually idiosyncratic and tightly recapitulated, suggesting that learning plays a role in route establishment. In light of the fact that routes are learned, and that both ascending and descending visual pathways share visual inputs from each eye asymmetrically to the brain hemispheres, we investigated how information from each eye contributes to route establishment, and how information input is shared between left and right neural systems. Using on-board global positioning system loggers, we tested 12 pigeons' route fidelity when switching from learning a route with one eye to homing with the other, and back, in an A-B-A design. Two groups of birds, trained first with the left or first with the right eye, formed new idiosyncratic routes after switching eyes, but those that flew first with the left eye formed these routes nearer to their original routes. This confirms that vision plays a major role in homing from familiar sites and exposes a behavioural consequence of neuroanatomical asymmetry whose ontogeny is better understood than its functional significance.

Pigeon navigation: exposure to environmental odours prior to release is sufficient for homeward orientation, but not for homing

The role of environmental olfactory information in pigeon navigation has been extensively studied by analysing vanishing bearing distributions and homing performances of homing pigeons subjected to manipulation of their olfactory perception and/or the olfactory information they were exposed to during transportation and at the release site. However, their behaviour during the homing flight remains undocumented. In this experiment we report the analysis of tracks of birds made anosmic at the release site by washing their olfactory mucosa with zinc sulfate. We thus can assess the role of local odours at the release site as well as the role of environmental odours perceived on the way, far from the release site. We observed that pigeons transported and kept at the release site in purified air and made anosmic at the release site were unable to orient towards home and were impaired at homing. By contrast, pigeons allowed to smell environmental odours during transportation and at the release site, although made anosmic prior to release, displayed unimpaired homeward orientation, but nevertheless showed impaired homing performance. These results are consistent with the view that local odours at the release site are critical for determining the direction of displacement (olfactory map) and suggest that pigeons consult the olfactory map also during their homing flight in order to be able to find their way home.

Olfaction and topography, but not magnetic cues, control navigation in a pelagic seabird: displacements with shearwaters in the Mediterranean Sea

Pelagic seabirds wander the open oceans then return accurately to their habitual nest-sites. We investigated the effects of sensory manipulation on oceanic navigation in Scopoli’s shearwaters (Calonectris diomedea) breeding at Pianosa island (Italy), by displacing them 400 km from their colony and tracking them. A recent experiment on Atlantic shearwaters (Cory’s shearwater, Calonectris borealis) breeding in the Azores indicated a crucial role of olfaction over the open ocean, but left open the question of whether birds might navigate by topographical landmark cues when available. Our experiment was conducted in the Mediterranean sea, where the availability of topographical cues may provide an alternative navigational mechanism for homing. Magnetically disturbed shearwaters and control birds oriented homeward even when the coast was not visible and rapidly homed. Anosmic shearwaters oriented in a direction significantly different from the home direction when in open sea. After having approached a coastline their flight path changed from convoluted to homeward oriented, so that most of them eventually reached home. Beside confirming that magnetic cues appear unimportant for oceanic navigation by seabirds, our results support the crucial role of olfactory cues for birds’ navigation and reveal that anosmic shearwaters are able to home eventually by following coastal features.

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.

Route following and the pigeon's familiar area map

Homing pigeons (Columba livia) have been the central model of avian navigation research for many decades, but only more recently has research extended into understanding their mechanisms of orientation in the familiar area. The discovery (facilitated by GPS tracking) that pigeons gradually acquire with experience individually idiosyncratic routes home to which they remain faithful on repeated releases, even if displaced off-route, has helped uncover the fundamental role of familiar visual landmarks in the avian familiar area map. We evaluate the robustness and generality of the route-following phenomenon by examining extant studies in depth, including the single published counter-example, providing a detailed comparison of route efficiencies, flight corridor widths and fidelity. We combine this analysis with a review of inferences that can be drawn from other experimental approaches to understanding the nature of familiar area orientation in pigeons, including experiments on landmark recognition, and response to clock-shift, to build the first detailed picture of how bird orientation develops with experience of the familiar area. We articulate alternative hypotheses for how guidance might be controlled during route following, concluding that although much remains unknown, the details of route following strongly support a pilotage interpretation. Predictable patterns of efficiency increase, but limited to the local route, typical corridor widths of 100-200 m, high-fidelity pinch-points on route, attraction to landscape edges, and a robustness to clock-shift procedures, all demonstrate that birds can associatively acquire a map of their familiar area guided (at least partially) by direct visual control from memorised local landscape features.

Homing pigeons respond to time-compensated solar cues even in sight of the loft

The sun has long been thought to guide bird navigation as the second step in a two-stage process, in which determining position using a map is followed by course setting using a compass, both over unfamiliar and familiar terrain. The animal’s endogenous clock time-compensates the solar compass for the sun’s apparent movement throughout the day, and this allows predictable deflections in orientation to test for the compass’ influence using clock-shift manipulations. To examine the influence of the solar compass during a highly familiar navigational task, 24 clock-shifted homing pigeons were precision-tracked from a release site close to and in sight of their final goal, the colony loft. The resulting trajectories displayed significant partial deflection from the loft direction as predicted by either fast or slow clock-shift treatments. The partial deflection was also found to be stable along the entire trajectory indicating regular updating of orientation via input from the solar compass throughout the final approach flight to the loft. Our results demonstrate that time-compensated solar cues are deeply embedded in the way birds orient during homing flight, are accessed throughout the journey and on a remarkably fine-grained scale, and may be combined effectively simultaneously with direct guidance from familiar landmarks, even when birds are flying towards a directly visible goal.

Evidence for discrete landmark use by pigeons during homing

Considerable efforts have been made to investigate how homing pigeons (Columba livia f. domestica) are able to return to their loft from distant, unfamiliar sites while the mechanisms underlying navigation in familiar territory have received less attention. With the recent advent of Global-Positioning-System (GPS) data-loggers small enough to be carried by pigeons, the role of visual environmental features in guiding navigation over familiar areas is beginning to be understood, yet surprisingly, we still know very little about whether homing pigeons can rely on discrete, visual landmarks to guide navigation. To assess a possible role of discrete, visual landmarks in navigation, homing pigeons were first trained to home from a site with four wind turbines as salient landmarks as well as from a control site without any distinctive, discrete landmark features. The GPS-recorded flight paths of the pigeons on the last training release were straighter and more similar among birds from the turbine site compared to the control site. The pigeons were then released from both sites following a clock-shift manipulation. Vanishing bearings from the turbine site continued to be homeward oriented as 13 of 14 pigeons returned home. By contrast, at the control site the vanishing bearings were deflected in the expected clock-shift direction and only 5 of 13 pigeons returned home. Taken together, our results offer the first strong evidence that discrete, visual landmarks are one source of spatial information homing pigeons can utilize to navigate when flying over a familiar area.

How habitat features shape ground squirrel (Urocitellus beldingi) navigation

The purpose of this investigation was to determine whether Belding's ground squirrels (Urocitellus beldingi) from areas rich in beacons perform differently in a task of spatial memory compared with squirrels from beacon-thin areas. To assess the role of environmental experience in spatial memory, wild-born squirrels with several days of experience in the field were compared with squirrels born in a lab and with no experience in their original habitat. Over two summers, squirrels captured from beacon-dense and beacon-thin areas were tested in a radial maze interspersed with beacons, using number of trials to criterion as a measure of spatial memory. To evaluate the effect of landmark navigation, in year 2 juveniles were prevented from seeing outside the maze area. In both years squirrels from beacon-dense populations reached criterion faster than squirrels from beacon-thin populations, and a weak rearing effect was present in 1 year. Despite sex differences in adult spatial skills, no differences were found between males and females in the maze. This demonstrates variation in the navigation strategies of young U. beldingi, and highlights the need to evaluate spatial preferences as a function of population or ecology in addition to species and sex.

Orientation of lizards in a Morris water-maze: roles of the sun compass and the parietal eye

The present study examined for the first time whether a Morris water-maze can be used to explore compass and other orientation mechanisms in the ruin lizard Podarcis sicula. In the open field, during sunny days, lizards were individually trained to swim from the center of the water maze onto a hidden platform (the goal), positioned at the periphery of the maze in a single compass direction. The goal was invisible because it was placed just beneath the water surface and the water was rendered opaque. The results showed that lizards learn to swim directly towards the hidden goal under the sun in the absence of visual feature cues. We further examined whether the observed orientation response would be due to lizards learning the spatial position of the goal relative to the sun's azimuth, i.e. to the use of a time-compensated sun compass. Lizards reaching learning criteria were subjected to 6 h clock-shift (fast or slow), and tested for goal orientation in the Morris water-maze. Results demonstrated that the learned orientation response is mediated by a time-compensated sun compass. Further investigations provided direct evidence that in ruin lizards an intact parietal eye is required to perform goal orientation under the sun inside a Morris water-maze,and that other brain photoreceptors, like the pineal or deep brain photoreceptors, are not involved in orientation.

Pigeons combine compass and landmark guidance in familiar route navigation

How do birds orient over familiar terrain? In the best studied avian species, the homing pigeon (Columba livia), two apparently independent primary mechanisms are currently debated: either memorized visual landmarks provide homeward guidance directly, or birds rely on a compass to home from familiar locations. Using miniature Global Positioning System tracking technology and clock-shift procedures, we set sun-compass and landmark information in conflict, showing that experienced birds can accurately complete their memorized routes by using landmarks alone. Nevertheless, we also find that route following is often consistently offset in the expected compass direction, faithfully reproducing the shape of the track, but in parallel. Thus, we demonstrate conditions under which compass orientation and landmark guidance must be combined into a system of simultaneous or oscillating dual control.