Loft features influence the processing of navigational information by pigeons

The present study evaluates the impact of lofts on the development of the navigational system of pigeons. A series of results obtained between 2000 and 2004 were analyzed. The H-loft was placed 10 m above the ground, with a ring format and seven windows all around it as well as three external aviaries that allowed birds to have a wide view of the outdoors and of the sky and knowledge of the wind dynamics. The L-loft was placed at ground level, with a single window transformed into an external aviary. The L-loft was protected from the wind by surrounding trees, reducing the ability of the pigeons to access the wind dynamics and also restricting their access to information regarding the outside area and the sky. In a preliminary analysis, we found the parameter of “vanishing time” to differ significantly between lofts in two of the five age classes. A thorough analysis of this parameter throughout the ontogenetic development of the birds demonstrated a pronounced improvement in the information-processing system with age, with adults vanishing quicker than younger birds, although an impairment of development occurred during the third month of age, perhaps due to a reorganization of the system. This result was obtained when the effect of lofts was considered in the different age classes. Results suggest that loft features are an important factor in the ability of the young pigeons to exploit navigational cues.     

Loft features reveal the functioning of the young pigeon’s navigational system

It is thought that young homing pigeons are able to use information acquired en route for their initial homeward orientation. However, the cues involved and mechanisms utilised are under discussion. Blocking light-dependent route-specific information during the first leg of an outward journey detour, together with analysis of pigeons that were raised under different loft conditions, allowed us to correctly evaluate the functioning of this mechanism and, more generally, the navigational map of birds. Pigeons from the same stock were raised and kept in two different lofts. The birds in the experimental groups were transported to the release sites via detours, and light-dependent information was denied during the first half of the outward journey (no compass information was available). Control birds were transported by the most direct route and had access to all available information. In general, the results showed that the low-loft birds preferred to use magnetic compass cues, whereas the high-loft birds preferred to use navigational map cues to collect information of the first part of the outward journey. The impairments observed in the homing performances of the experimental groups highlight the reliability of information collected inside the map area. Relevant to an understanding of the route-reversal mechanism was the evidence that this mechanism is able to function in the absence of compass information (birds raised in a wind-exposed loft show a detour effect). In systems where directional information could be provided by multiple sources, processing and extracting accurate course trajectories through a common mechanism may prove more efficient and reliable.     

Young convict cichlids use visual information to update olfactory homing cues

In this study, we tested the tendency of young cichlids to orient towards their parents using chemical cues. Convict cichlids have biparental defence of their free-swimming young. If young become separated from their family they must rejoin their family within minutes to have any chance of survival. Here, we used a dichotomous Y-maze to test if displaced convict cichlid young can use chemical cues to orient to their family. First, we showed that young preferentially orient toward water taken from their home tank versus blank water taken from a tank that contained no fish. Second, we showed that young prefer home tank water to water from a tank containing another family of convict cichlids. In a third experiment, we placed young convict cichlids in a small aquarium inserted within a larger aquarium. The large aquarium contained either their parents or no fish. The small insert aquarium contained blank water from a tank that had never contained fish. After 20 min in the insert tank, young convict cichlids were placed in the Y-maze and given a choice between either their home tank water or water from the insert tank. Convict cichlids that did not see their parents during the 20-min conditioning period oriented strongly toward chemical cues of their home tank water. Young that saw their parents during the 20-min conditioning period oriented strongly toward the chemical cues of the insert tank. These data indicate that young convict cichlids use visual cues to learn and reset the smell of “home” in less than 20 min.     

Heterospecific call recognition and phonotaxis in the orientation behavior of the marbled newt,Triturus marmoratus

The role of acoustic cues as reference cues for orientation by amphibians has been demonstrated in anurans, the only amphibian group that engages in acoustic communication, but not in urodeles. Orientation responses of marbled newts, Triturus marmoratus, were studied to determine whether heterospecific calls elicited positive phonotaxis. The orientation tests consisted in presenting either a familiar acoustic stimulus, the advertisement calls of natterjack toads (Bufo calamita), or a control stimulus, the advertisement calls of European green toads (Bufo viridis) that the newts would not be expected to recognize. Marbled newts and natterjack toads occur in simpatry, but T. marmoratus and B. viridis are allopatric species. Thus, T. marmoratus is distributed over the northern half of the Iberian Peninsula, whereas B. viridis occurs in the Balearic Islands, but not over the Iberian Peninsula. Newts were released in a circular arena while a recorded chorus of natterjack toads or European green toads played outside the arena to determine whether they displayed positive phonotactic orientation. Our results show that marbled newts performed positive phonotaxis when exposed to the breeding calls of natterjack toads, but not to those of European green toads. Newts chose a compass course in the direction of the advertisement calls of B. calamita. Acoustic information might improve orientation accuracy. This study is the first to provide evidence of heterospecific call recognition and positive phonotactic response in urodeles.Communicated by W. Wiltschko     

Non-migratory breeding by isolated green sea turtles (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) in the Indian Ocean: biological and conservation implications

Green sea turtles (Chelonia mydas) are renowned for their long-distance migrations but have less fame for short-distance migrations or non-migratory behavior. We present satellite telemetric evidence from Cocos (Keeling) Islands, Indian Ocean for the first predominantly non-migratory green sea turtle (C. mydas) population. The mean migration distance from the nesting beach to the foraging grounds was 35.5 km with a maximum mean transit time of 3.4 days. The behavior of this population has major implications for our general understanding of green turtle behavior and their life cycle and for conservation. Firstly, these results indicate a level of juvenile or adult non-breeding homing behavior from the open ocean to foraging grounds adjacent to their natal nesting beach. Secondly, a non-migratory breeding phase reduces the consumption of reproductive energy utilized, potentially resulting in higher fecundity for this population. Thirdly, the close proximity of the nesting and foraging habitats allows for uniformity in management and conservation strategies rarely possible for wide-ranging green turtle populations.     

Orientation behavior of homing pigeons at the Gernsheim anomaly

Pigeons were released at four release sites within the Gernsheim anomaly, a magnetic 'hill' with a peak 199 nT above the regional reference field and gentle 'slopes' to all sides, situated 44 km south of the Frankfurt loft. Local magnetic conditions at the sites differed in total intensity and in direction and steepness of the intensity gradient. At all sites, the pigeons were well oriented, showing counterclockwise deviations from the home directions that were most pronounced in the western part of the anomaly. There was no systematic difference in orientation behavior or homing performance between the sites within the anomaly and a control site outside. No effect of the local gradient direction was found, nor did the difference in intensity between home loft and the release site affect behavior. This argues against the use of magnetic navigational factors. However, pigeons released for the first time within the anomaly tended to have longer mean vectors with increasingly steeper gradients, which could mean that the birds might somehow have realized the anomalous nature of the local magnetic conditions and ignored them, relying on non-magnetic cues instead.Communicated by R. Gibson     

Acoustic orientation in the palmate newt, Lissotriton helveticus

Experiments reported here were carried out to investigate the use of acoustic cues by palmate newts (Lissotriton helveticus) for orientation and to study whether this behavior is learned, or whether two populations of palmate newts that cohabit with different frog species (Iberian green frog, Rana perezi, and European common brown frog, Rana temporaria) show different phonotactic preferences. The orientation tests consisted of presenting a control stimulus (white noise), a sympatric acoustic stimulus (calls of R. perezi or R. temporaria, depending on the origin of newts), or an allopatric stimulus (calls of natterjack toads, Bufo calamita, or R. perezi). Newts were released in a circular arena, while the acoustic stimuli were presented outside of the circular arena in four different compass orientation directions (0, 90, 180 and 270°). In this study, we show that L. helveticus performed positive phonotaxis toward the calls of R. perezi only when both species shared habitat, orienting randomly when R. perezi was absent from the newt’s natal population. Newts from both populations oriented randomly when exposed to the allopatric and control acoustic stimuli. These results suggest, for the first time, that recognition of the sympatric heterospecific calls could be learned. However, newts sharing the breeding pond with a population of R. temporaria oriented randomly when exposed to the calls of this species. The fact that the breeding seasons of R. temporaria and L. helveticus do not overlap in time does not allow the use of R. temporaria calls as a guidance mechanism for migrating individuals of L. helveticus.     

Repeated training does not improve the path integrator in desert ants

Desert ants, Cataglyphis fortis, return to their nest by means of path integration vectors. By using the reversal of these vectors, they approach previously visited feeding sites again. They adjust these vectors whenever outbound and inbound vector are set into conflict or when they make use of external cues. Here, we examine the influence of repeated training on the accuracy, precision, and straightness of outbound and inbound vectors. We trained desert ants to forage to and fro between their nest and a feeder and made sure that they relied exclusively on their path integrator. Neither the ants’ outbound nor their inbound runs, which, in general, are straighter than the outbound runs, become more accurate, precise, or straighter during repeated training. Hence, repeated training does not improve the path integrator in desert ants.     

Magnetic compass mediates nocturnal homing by the alpine newt, Triturus alpestris

Experiments were carried out to investigate the use of magnetic compass cues in the nocturnal homing orientation of the alpine newt Triturus alpestris. Tests were carried out at a site 9 km to the east–northeast of the breeding pond. Newts were tested at night in an outdoor circular arena that provided an unimpeded view of celestial cues, in one of four symmetrical alignments of an earth-strength magnetic field. In tests carried out under partly cloudy skies newts exhibited homeward magnetic compass orientation. Because the moon was visible in some trials, but obscured by clouds in others, we investigated whether the presence of the moon contributed to the scatter in the distribution of magnetic bearings. When the moon was visible, the distribution of magnetic bearings was more scattered than when the moon was obscured by clouds, although in neither case was the distribution significant due, in part, to the small sample sizes. Moreover, when the moon was visible, newts oriented along a bimodal axis perpendicular to the moon azimuth, suggesting that the presence of the moon may have affected the newts behavior. To provide a more rigorous test of the role of magnetic compass cues when celestial cues were unavailable, nocturnal tests were carried out during the following migratory season under total overcast. In the absence of celestial compass cues, the distribution of magnetic bearings exhibited highly significant orientation in the homeward direction. These findings indicate that newts are able to orient in the homeward direction at night using the magnetic compass as the sole source of directional information. Moon light altered the newts behavior. However, this apparently resulted from the asymmetrical distribution of moon light in the testing arena, rather than the use of an alternative compass.     

Do bearing magnets affect the extent of deflection in clock-shifted homing pigeons?

When released after clock-shift, homing pigeons fail to orient towards the home direction but display a consistent deflection of their initial orientation due to the difference between the real sun azimuth and the computed azimuth according to the subjective time of each single bird. It has been reported that the size of the observed deflection is frequently smaller than expected and a discussion on the possible factors affecting the size of deflection has emerged. Some authors have proposed that the major factor in reducing the deflection after clock-shift is the simultaneous use of both the magnetic and the sun compasses, giving true and erroneous information, respectively, about the home direction. Therefore, a magnetic disturbance, by impeding the use of the geomagnetic information in determining the home direction, is presumed to increase the size of the deflection up to the levels of the expectation. To test this hypothesis, we released three groups of clock-shifted birds from unfamiliar locations (unmanipulated pigeons, pigeons bearing magnets on their head, and pigeons bearing magnets on their back) together with a group of unshifted control birds. As no difference in the orientation of the three groups emerged, we were not able to confirm the hypothesis of the role of the magnetic compass in reducing the expected deflection after clock-shift.Communicated by W. Wiltschko