How desert ants cope with enforced detours on their way home

Summary We ask whether desert ants (Cataglyphis fortis) perform path integration on their homeward as well as on their outward journey. If path integration does occur on the return journey, then, after an enforced detour, the ant's trajectory should point directly at its nest. To test whether this is so, ants were trained to forage at a spot 25 m from their nest. As an ant began its return journey to the nest, it was caught and transported to a test area where it was released either 2 m or 12 m from a wide barrier which obstructed its homeward path. The direction of the ants' trajectory after detouring around the barrier corresponded closely to that predicted on the assumption that the home vector is accurately updated during the detour.     

Homing by path integration in a new environment

Path integration was tested in golden hamsters, Mesocricetus auratus, within a new environment and in darkness. From the exit of its home cage, the subject was lured over a certain distance into the experimental arena, and then startled by a sudden noise to induce instantaneous homing. The subjects in experiment 1 had previously been tested within an identical arena in another building; they started the outward journey from a peripheral nest. Upon hearing the sound, all subjects returned in the correct direction to the arena border. In experiments 2 and 3, experimentally na?ve subjects started the outward trip from a central nest exit. Both groups initially oriented correctly, but only a few of subjects returned to the nest. According to computational considerations, experiment 1 required mainly the calculation of the homing direction, while experiments 2 and 3 required a homing vector. Furthermore, the experienced subjects may have been helped by their homing experience in the same type of arena, while the na?ve subjects may not have ‘trusted’ self-generated vector information sufficiently to follow it to the goal in an uncharted environment. Thus, the performance, but not the computation of self-generated vector information, may depend on the animal's experience. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Trail‐following and trail‐searching behaviour in homing of the intertidal gastropod mollusc,Onchidium verruculatum

When uncovered by the tide, Onchidium verruculatum leaves its place of hiding, grazes on the rock surface, and thèn returns to its own home. Onchidium will follow its own mucus trail, most frequently towards the origin. This behaviour explains homing when the outward path is partly or completely retraced. Sometimes, however, homing occurs without contact with the outward trail. It was observed that trails were followed more closely at low humidities than at high humidities. No evidence was found for any method of orientation other than detection of chemical trials: when displaced onto sand Onchidium tend simply to crawl in a spiral until they contact their own trail. In addition to being a safe retreat, the home provides a fixed starting point to feeding excursions : this may facilitate re‐location of preferred feeding areas.     

Garden ant homing behavior in a maze task based on local visual cues

Although it has been shown that visual cues play an essential role in navigation by the garden ant Lasius niger, no previous studies have addressed the way in which information from local visual cues is acquired and utilized in navigation. We found that in the absence of pheromone trails, ants whose homing motivation was triggered by feeding returned to the nest following local visual cues. In our experiments, the ants travelled through a maze to reach a feeder. They explored the maze and sometimes became trapped in its dead ends. We found that the ants more effectively used visual cues during their homeward journey if they experienced a dead end during their outward journey. This result suggested that the ants used the information acquired from visual cues during the outward journey to avoid a dead end on their return journey.     

Short-distance homing in the golden hamster after a passive outward journey

The golden hamster carries food back to its nest along a direct path. In a situation combining a passive outward journey with the elimination of visual and various other exteroceptive cues, the subjects continued to return to their nest site and were not influenced by alterations of the earth's magnetic field. Experiments in which the animals started their hoarding trips from a changing point of departure, or were transferred to an unfamiliar experimental space, suggest that they orientate by path integration and that they assess the angular, but not the linear component of a passive outward journey.     

Search strategies of ants in landmark-rich habitats

Search is an important tool in an ant’s navigational toolbox to relocate food sources and find the inconspicuous nest entrance. In habitats where landmark information is sparse, homing ants travel their entire home vector before searching systematically with ever increasing loops. Search strategies have not been previously investigated in ants that inhabit landmark-rich habitats where they typically establish stereotypical routes. Here we examine the search strategy in one such ant, Melophorus bagoti, by confining their foraging in one-dimensional channels to determine if their search pattern changes with experience, location of distant cues and altered distance on the homebound journey. Irrespective of conditions, we found ants exhibit a progressive search that drifted towards the fictive nest and beyond. Segments moving away from the start of the homeward journey were longer than segments heading back towards the start. The right tail distribution of segment lengths was well fitted by a power function, but slopes less than −3 on a log-log plot indicate that the process cannot be characterized as Lévy searches that have optimal slopes near –2. A double exponential function fits the distribution of segment lengths better, supporting another theoretically optimal search pattern, the composite Brownian walk.     

Homing in the Mangrove Swimming Crab Thalamita crenata (Decapoda: Portunidae)

On the Kenyan coast, Thalamita crenata confines itself to a defined system of crevices and forages, swimming in a few cm of water, within a radius of about 5 m from its shelter. A field study was designed to analyse this crab's ability to find its shelter after being moved away from it. Crabs were displaced, being kept under water, with full vision of the sky and landscape and released 5 m away from their refuges, at a maximum depth of 50 cm. They were able to return to their shelters within 1 h and followed initial directions which were well orientated towards home. T. crenata was still well orientated and successful in returning home during nocturnal displacements and even after trials in which the landscape was altered. Only blind crabs were neither initially orientated towards home nor successful in returning within two tidal cycles of their release. The hypothesis that this swimming crab could use orientating information obtained during the outward displacement was then tested. Specimens were dislocated following a non-linear outward path, without vision of the surrounding landscape; other crabs were carried to a false release point and then carried in a closed container to the actual release point. Finally, three kinds of detour experiments were performed. In all these trials the directions chosen by the crabs were still clustered around the home direction and homing success was again high. These results exclude homing mechanisms based on random search strategies or on egocentric mechanisms, such as path integration. The most probable hypothesis is that T. crenata organizes some visual cues in a map-like arrangement and, detecting these cues from any release point within its home range, uses this map to return home.     

Short-range Homing in Fiddler Crabs (Ocypodidae, Genus Uca): A Homing Mechanism not Based on Local Visual Landmarks

This field study investigated the spatial strategies and homing ability of two East African fiddler crabs, Uca lactea annulipes and Uca vocans hesperiae, using various experimental procedures. A clear-cut spatial segregation between the two species was observed, with U. l. annulipes occupying areas even a few centimetres above U. v. hesperiae . Females of both species were extremely faithful to their holes while the males exhibited behavioural differences. U. l. annulipes males were quite faithful to their holes; in contrast, U. v. hesperiae males, during a single low tide, visited several holes which they did not defend. Two displacement experiments were conducted in order to identify the stimuli that fiddler crabs use in their homing. In the 'dislocation experiment', the crabs were moved (by hand) 1 or 2 m away from their refuge and released. None of these crabs returned to its burrow and, moreover, the initial directions they followed were not homeward orientated. In the 'translation experiment', the crabs were passively translated while actively feeding. When the crabs attempted to go 'home' after the translation, they darted along a straight path that led them to points that would have corresponded to their homes if the translation had not taken place. After this first response crabs then commenced searching strategies that led half of them home. Short-range homing seems to depend strongly on information actively gathered during the outward journey, other than local visual landmarks.     

The Role of “Outward-Journey Information” in Homing Experiments with Pigeons: New Data on Ontogeny of Navigation and General Survey

Potentially, homing from distant areas can be based on two different principles of navigation: (1) A path-integration mechanism records and integrates an animal's motions during the outward trip; it is independent of location-specific stimuli. (2) Site localization, by contrast, is performed by deducing the animal's position in relation to home from such stimuli. Hence the first mechanism entirely depends on an uninterrupted flow of “outward-journey information”. The second mechanism may but need not be independent of stimuli recorded during the outward journey. Homing of pigeons is evidently based on site localization. Empirical findings do not support the idea that in experiments using passive displacement path integration is involved in addition or alternatively. Also, there is no reason to assume that very young pigeons transitionally, for only few weeks, apply such a method (as has been concluded by Wiltschko & Wiltschko 1982, 1985, etc.). It is shown that very young pigeons require local olfactory signals for initial homeward orientation as do older birds (Fig. 1). They are not generally better at homeward orientation than older inexperienced pigeons and show similar deviations from home and preferences for a particular compass direction (Table 1, Fig. 2). Olfactory signals appear to be gathered, as good as conditions allow, during any stage of a homing experiment. No fundamental difference can be recognized between olfactory “outward-journey information”, “release-site information”, etc. Signals received at different times and sites before release may contribute by varying proportions to the initial-orientation patterns observed under varying circumstances.     

Landmark cues can change the motivational state of desert ant foragers

Desert ants of the genus Cataglyphis rely on path integration vectors to return to the nest (inbound runs) and back to frequently visited feeding sites (outbound runs). If disturbed, e.g., experimentally displaced on their inbound runs, they continue to run off their home-bound vector, but if disturbed in the same way on their outbound runs, they do not continue their feeder-based vector, but immediately switch on the home-bound state of their path integration vector and return to the nest. Here we show that familiar landmarks encountered by the ants during their run towards the feeder can change the ants’ motivational state insofar that the ants even if disturbed continue to run in the nest-to-feeder direction rather than reverse their courses, as they do in landmark-free situations. Hence, landmark cues can cause the ants to change their motivational state from homing to foraging.     

Testing the nest-homing abilities of a phytotelm-breeding frog, Chirixalus eiffingeri (Rhacophoridae)

We conducted a manipulative experiment to assess the homing of female Chirixalus eiffingeri to the nest. There were three experimental treatments and a control. For the control treatment, bamboo stumps were cut off at the base and reattached. In the first experimental treatment, when stumps were displaced 1 m, the proportion of stumps attended by females and the growth of tadpoles did not differ from the results of the control treatment, suggesting the 1-m stump displacement did not affect the nest homing of female frogs. In the second experimental treatment, when a bamboo stump was displaced 1 m and a new bamboo stump with tadpoles was put in its place, some females fed tadpoles in the displaced stump (3/12), but some fed tadpoles in the stump (3/12) at the original site. This finding suggests that the addition of a new stump confused the female frogs spatially, which resulted in females feeding the tadpoles in either stump. In the third experimental treatment, when a bamboo stump was displaced 1 m and a new stump without tadpoles was added at the original site, some female frogs fed tadpoles in the displaced stump (5/12) but some laid trophic eggs in the stump (4/12) at the original site, also indicating the female frogs were confused spatially. The overall results support the hypothesis that females rely on the spatial distribution of a nest stump, relative to other bamboo stumps, for nest homing to feed their offspring, and that stump location is an important cue to the nest homing of females.     

Path integration controls nest-plume following in desert ants

The desert ant Cataglyphis fortis is equipped with sophisticated navigational skills for returning to its nest after foraging. The ant's primary means for long-distance navigation is path integration, which provides a continuous readout of the ant's approximate distance and direction from the nest. The nest is pinpointed with the aid of visual and olfactory landmarks. Similar landmark cues help ants locate familiar food sites. Ants on their outward trip will position themselves so that they can move upwind using odor cues to find food. Here we show that homing ants also move upwind along nest-derived odor plumes to approach their nest. The ants only respond to odor plumes if the state of their path integrator tells them that they are near the nest. This influence of path integration is important because we could experimentally provoke ants to follow odor plumes from a foreign, conspecific nest and enter that nest. We identified CO(2) as one nest-plume component that can by itself induce plume following in homing ants. Taken together, the results suggest that path-integration information enables ants to avoid entering the wrong nest, where they would inevitably be killed by resident ants.     

Orientation of anosmatic pigeons

Summary Test releases performed at five symmetrically arranged sites around the loft, at a distance of 78–99 km from it, showed that 1) anosmatic birds transported without alteration of the earth's magnetic field were completely random-oriented, 2) anosmatic birds transported in a container inside which the intensity of the magnetic field was strongly reduced were unable to orientate homewards and mostly departed according to a preferred compass direction, 3) control birds, which could smell, and were transported without alteration of the magnetic field, were homeward oriented and performed better in homing than both experimental groups. The conclusion is that anosmatic birds are unable to detect home direction at unfamiliar sites and that magnetic stimuli perceived during the outward journey are unable to substitute olfactory cues.Abbreviation PCD preferred compass direction Supported by a grant from the Consiglio Nazionale delle Ricerche     

Ant navigation en route to the goal: signature routes facilitate way-finding of Gigantiops destructor

We investigated in laboratory conditions how foragers of the tropical ant Gigantiops destructor develop individually distinctive landmark routes. Way-finding along a familiar route involved the recognition of at least two locations, nest and feeding site, and the representation of spatial relations between these places. Familiar visual landmarks were important both at the beginning and at the end of the foraging journey. A motor routine guided the ants at the start of their foraging path towards the first landmarks, which they learnt to pass consistently on the same side, before taking the next direction. At the last stage of the route, landmark recognition allowed them to pinpoint their preferred feeding site without using distant cues or odometric information. By contrast, ants en route to the goal were not systematically guided by a stereotyped sequence of snapshots recalled at each corresponding stage of the route. Each ant slalomed in an idiosyncratic distinctive way around different midway landmarks from a foraging excursion to the next, which induced a variability of the path shapes in their intermediate parts. By reducing the number of landmark recognition-triggered responses, this economical visuomotor strategy may be helpful in the Amazonian forest where many prominent landmarks are alike.     

Experience Based Use of Landmark and Vector Based Orientation During Homing by the Ant Formica cunicularia (Hymenoptera: Formicidae)

Homing paths of Formica cunicularia foragers from an artificial food reward were analyzed on a familiar terrain and in displacement experiments on a familiar and an unfamiliar terrain. Foragers were tested either when relatively new to a foraging route (untrained group) or after a day’s experience with it (trained group). Untrained foragers followed direct homing paths to the nest site when tested in the familiar terrain but followed tortuous paths when displaced to the unfamiliar terrain. Trained foragers behaved similarly to untrained ones when tested from the food reward to the nest site in the familiar terrain but their behavior changed in displacements. Irrespective of the familiarity of the displacement site, these foragers followed paths taking them to the expected nest sites. The results showed that foragers did not rely on chemical cues for homing and revealed that untrained foragers disregarded path integration and were directed to the nest site when it is in their visual panorama. On the contrary, trained foragers may have relied on path integration on familiar and unfamiliar terrain. The results also demonstrated that experience greatly affected the preferential use of visual and vector based cues by foragers during homing.     

Path integration in desert ants, Cataglyphis: how to make a homing ant run away from home

Path integration is an ant's lifeline on any of its foraging journeys. It results in a homebound global vector that continually informs the animal about its position relative to its starting point. Here, we use a particular (repeated training and displacement) paradigm, in which homebound ants are made to follow a familiar landmark route repeatedly from the feeder to the nest, even after they have arrived at the nest. The results show that during the repeated landmark-guided home runs the ant's path integrator runs continually, so that the current state of the homebound vector increasingly exceeds the reference state. The dramatic result is that the homing ants run away from home. This finding implies that the ants do not rely on cartographic information about the locations of nest and feeder (e.g. that the nest is always south of the feeder), but just behave according to what the state of their egocentric path integrator tells them.     

Does pigeon homing depend on stimuli perceived during displacement?

Summary In order to test whether stimuli perceived during passive displacement are important for the subsequent homing, pigeons were transported in an apparatus designed to prevent them from receiving relevant information: The experimental birds were continuously rotated quite rapidly (1.5 cps, radial acceleration about 4 g); in addition, they were exposed to an artificial magnetic field and supplied with bottled air. Control birds were transported in open-air cages on top of the van with free view to all sides.Five pairs of releases from equal distances in opposite directions were conducted. Experienced birds were released at distances of about 15, 90, and 300 km from the loft, inexperienced birds at distances of about 180km. In each pair of releases both groups of pigeons were significantly homeward oriented. Neither in initial orientation nor in homing performance nor in the distribution of recoveries were the experimental birds inferior to the controls or in any perceptable way different from them.It is concluded that homing of passively displaced pigeons is not primarily based on information gathered during the outward journey.Abbreviations EP experimental pigeon(s) - CP control pigeon(s) The possibility to maintain our pigeon loft in a building that belongs to the Zoological Institute (Prof. M. Lindauer) of the University of Würzburg is gratefully acknowledged.     

Conditions for landmark-based navigation in the house mouse, Mus musculus

I investigated whether mice, after learning to home by relying on visual extra-arena landmarks, still required instantaneous access to such cues for successful navigation. Two groups of lactating mice were trained to retrieve their pups from the centre of a circular arena back to their peripheral nest. On test trials, mice from one group were allowed to view distal visual cues while moving from the nest towards the centre, and mice from the other group were allowed to view distal visual cues when homing from the centre towards the nest. The results indicate that viewing the visual cues when homing is necessary for landmark-based navigation.     

Marine turtles use geomagnetic cues during open-sea homing

Marine turtles are renowned long-distance navigators, able to reach remote targets in the oceanic environment; yet the sensory cues and navigational mechanisms they employ remain unclear [1, 3]. Recent arena experiments indicated an involvement of magnetic cues in juvenile turtles' homing ability after simulated displacements [4, 5], but the actual role of geomagnetic information in guiding turtles navigating in their natural environment has remained beyond the reach of experimental investigations. In the present experiment, twenty satellite-tracked green turtles (Chelonia mydas) were transported to four open-sea release sites 100-120 km from their nesting beach on Mayotte island in the Mozambique Channel; 13 of them had magnets attached to their head either during the outward journey or during the homing trip. All but one turtle safely returned to Mayotte to complete their egg-laying cycle, albeit with indirect routes, and showed a general inability to take into account the deflecting action of ocean currents as estimated through remote-sensing oceanographic measurements [7]. Magnetically treated turtles displayed a significant lengthening of their homing paths with respect to controls, either when treated during transportation or when treated during homing. These findings represent the first field evidence for the involvement of geomagnetic cues in sea-turtle navigation.     

Predator-induced plasticity in nest visitation rates in the Siberian jay (Perisoreus infaustus)

Bird nestlings may be at risk not only from starvation but alsofrom predators attracted to the nest by parental feeding visits.Hence, parents could trade reduced visitation rates for a lowerpredation risk. Here, through field data and an experiment,we show plasticity in daily patterns of nest visitation in theSiberian jay, Perisoreus infaustus, in response to predatoractivity. In high-risk territories, jay parents avoided goingto the nest at certain times of the day and compensated by allocatingmore feeding effort to periods when predators were less active.Such modifications in provisioning routines allowed parentsin high-risk habitat to significantly lower the risk of providingvisitation cues to visually oriented corvid nest predators.These results indicate that some birds modify their daily nestvisitation patterns as a fourth mechanism to reduce predator-attractingnest visits in addition to the clutch size reduction, maximizationof food load-sizes, and prevention of allofeeding suggestedby Skutch.