Seven decades of research on the “cognitive map,” the allocentric representation of space, have yielded key neurobiological insights, yet field evidence from free-ranging wild animals is still lacking. Using a system capable of tracking dozens of animals simultaneously at high accuracy and resolution, we assembled a large dataset of 172 foraging Egyptian fruit bats comprising >18 million localizations collected over 3449 bat-nights across 4 years. Detailed track analysis, combined with translocation experiments and exhaustive mapping of fruit trees, revealed that wild bats seldom exhibit random search but instead repeatedly forage in goal-directed, long, and straight flights that include frequent shortcuts. Alternative, non–map-based strategies were ruled out by simulations, time-lag embedding, and other trajectory analyses. Our results are consistent with expectations from cognitive map–like navigation and support previous neurobiological evidence from captive bats.

Introduction: When birds fly in cluttered environments, they must tailor their flight to the gaps that they traverse. We trained budgerigars, Melopsittacus undulatus, to fly through a vertically oriented gap of variable width, to investigate their ability to perform evasive manoeuvres during passage.

Magnetite-containing structures in the upper beak of birds have been described as putative magnetoreceptors [1-4], but so far, all positive evidence indicating their influence on behavior has come from laboratory studies using rather unnatural stimuli (e.g., [5-7]). Here, we demonstrate these receptors' possible role in a natural situation: we released pigeons with these receptors deactivated by a local anesthetic within and outside a magnetic anomaly, together with untreated control birds. Within the anomaly, the untreated birds showed unusually long vanishing intervals and scattered bearings, indicating confusion by the anomalous magnetic conditions. Anesthesia of the beak suppressed this adverse effect. Outside the anomaly, in contrast, the treatment had little effect. These findings indicate that the receptors in the beak mediate magnetic "map" information and that this information is normally included in the navigational process yet can be replaced by nonmagnetic factors at most sites.

Pigeons released away from their loft usually fly around at the release site for a while before they finally leave. Visual observations had suggested that the moment when the birds decide to head home is associated with a certain change in flying style. To see whether this change is also reflected by GPS-recorded tracks, a group of pigeons equipped with flight recorders was released at two sites about 10 km from their home loft. The initial part of their flight paths was analyzed in order to find objective criteria indicating the point of decision. We selected the highest increase in steadiness as the best estimate for the moment of decision. This criterion allows us to divide the pigeons' paths in two distinct phases, an initial phase and the homing phase, with the moment of decision, on an average, 2 min after release. The moment of decision marks a change in behavior, with a significant increase in steadiness and flying speed and headings significantly closer to the home direction. The behavior of the individual birds at the two sites was not correlated, suggesting no pronounced individual traits for the length of the initial phase. The behavior during this phase seems to be controlled by flight preparation, exploration, and non-navigational motivations rather than by navigational necessities alone.

No abstract

No abstract

It is essential for birds to be agile and aware of their immediate environment, especially when flying through dense foliage. To investigate the type of visual signals and strategies used by birds while negotiating cluttered environments, we presented budgerigars with vertically oriented apertures of different widths. We find that, when flying through narrow apertures, birds execute their maneuvers in an anticipatory fashion, with wing closures, if necessary, occurring well in advance of the aperture. When passing through an aperture that is narrower than the wingspan, the birds close their wings at a specific, constant distance before the aperture, which is independent of aperture width. In these cases, the birds also fly significantly higher, possibly pre-compensating for the drop in altitude. The speed of approach is largely constant, and independent of the width of the aperture. The constancy of the approach speed suggests a simple means by which optic flow can be used to gauge the distance and width of the aperture, and guide wing closure.

Tracks of pigeons, recorded with the help of GPS-receivers from two sites 30 km north and south of the Frankfurt loft, were analyzed in view of an influence of irregular fluctuations of the geomagnetic field. The data obtained were correlated with indices characterizing different aspects of these fluctuations. We found the best correlations with the index quantifying the average amplitude of the magnetic disturbance, and with an index that quantifies the average variability of the magnetic field on the day of release: stronger and more variable fluctuations lead to a counter-clockwise shift of the mean headings during the initial phase at the release site and the following departure phase, but not during the final homing phase leading to the loft. The steadiness of flight was not affected during the initial phase; however, during the later parts of the homing flight, stronger fluctuations, as well as higher variability in the magnetic field led to a marked decrease in steadiness. This continuing effect of magnetic fluctuations indicates that magnetic factors not only affect the beginning, but remain an integral part of the pigeons' navigational processes during the entire homing flight.