The social transmission of spatial information in homing pigeons

We adapted a technique to explore the social transmission of spatial information in homing pigeons Columba livia. Five demonstrator pigeons were first trained to find a food goal within an indoor arena. This arena consisted of nine lidded cups laid out within a 12x12 grid on the floor. The task was to find the goal cup and flip the lid to obtain the food hidden within. Once the demonstrators had reached criterion the experiment proper began. During stage 1 of the experiment, 10 target birds, which had not previously been trained to find the goal, were introduced to the spatial task either in isolation or paired with a demonstrator. We measured how long they took to complete the task, the number of squares crossed on the grid, and the number of incorrect lids flipped. In stage 2, the target birds were introduced to the arena a second time, by themselves, and we compared the performance of the birds in the two treatments. The pigeons that had been introduced to the task with a demonstrator in stage 1 walked further and made more incorrect choices when searching for the food goal in stage 2 than the pigeons that were introduced to the task alone. This indicates that pigeons learn a spatial, food-finding task more effectively when performing the task alone than when accompanied by a knowledgeable conspecific. We discuss possible reasons for this in the light of previous experiments. Copyright 1999 The Association for the Study of Animal Behaviour.     

Effects of stimulus size and spatial organization on pigeons’ conditional same-different discrimination

In two experiments, we explored the effects of varying the size and the spatial organization of the stimuli in multi-item arrays on pigeons’ same-different discrimination behavior. The birds had previously learned to discriminate a simultaneously presented array of 16 identical (Same) visual items from an array of 16 nonidentical (Different) visual items, when the correct choice was conditional on the presence of another cue: the color of the background (Castro et al., in press). In Experiment 1, we trained pigeons with 7-item arrays and then tested them with arrays containing the same item, but in a variety of sizes. In Experiment 2, we tested the birds with the items grouped in novel locations: the top, the bottom, the left, or the right portions of the display area, which generated different vertical and horizontal alignments. Accuracy scores revealed virtually perfect stimulus generalization across various item sizes and spatial organizations. Reaction times revealed that the birds perceived different sizes of a single icon as the same stimulus (Experiment 1) and that the birds processed vertical arrangements faster than horizontal arrangements (Experiment 2). These results suggest that the pigeons noticed both physical and spatial changes in the stimuli (as shown by their reaction times), but that these changes did not disrupt the birds’ discriminating the sameness or differentness of the multi-item arrays (as shown by their accuracy scores).     

The Effects of Zinc Sulphate Anosmia on Homing Pigeons,Columba livia,in a Homing and a Non-homing Experiment

There is debate over whether homing pigeons, Columba livia, use olfactory information as part of their navigational map. Antagonists of the theory argue that homing deficits noted in anosmic pigeons may be due to a non-specific impairment in general information processing. In Experiment I, we present data from a modest investigation describing the typical navigational deficits that occur following zinc sulphate-mediated anosmia. Our results are consistent with previous experiments that noted impairments in homing performance from unfamiliar locations of anosmic pigeons. Experiment II is a critical experiment that involved a spatial working memory paradigm; this paradigm consisted of testing zinc sulphate-treated birds in a forced-choice alternation task in a T-maze. This experiment allowed us to determine whether anosmic pigeons were impaired in memory performance, a robust measure of general information processing. There were no differences between the last day of training and a subsequent-test day when pigeons received an intranasal injection of zinc sulphate. This experiment suggests that zinc sulphate anosmia does not impair general information processing, supporting the hypothesis that homing pigeons use olfactory cues when homing from unfamiliar locations.     

Effects of demanding foraging conditions on cache retrival accuracy in food-caching mountain chickadees (Poecile gambeli)

Birds rely, at least in part, on spatial memory for recovering previously hidden caches but accurate cache recovery may be more critical for birds that forage in harsh conditions where the food supply is limited and unpredictable. Failure to find caches in these conditions may potentially result in death from starvation. In order to test this hypothesis we compared the cache recovery behaviour of 24 wild-caught mountain chickadees (Poecile gambeli), half of which were maintained on a limited and unpredictable food supply while the rest were maintained on an ad libitum food supply for 60 days. We then tested their cache retrieval accuracy by allowing birds from both groups to cache seeds in the experimental room and recover them 5 hours later. Our results showed that birds maintained on a limited and unpredictable food supply made significantly fewer visits to non-cache sites when recovering their caches compared to birds maintained on ad libitum food. We found the same difference in performance in two versions of a one-trial associative learning task in which the birds had to rely on memory to find previously encountered hidden food. In a non-spatial memory version of the task, in which the baited feeder was clearly marked, there were no significant differences between the two groups. We therefore concluded that the two groups differed in their efficiency at cache retrieval. We suggest that this difference is more likely to be attributable to a difference in memory (encoding or recall) than to a difference in their motivation to search for hidden food, although the possibility of some motivational differences still exists. Overall, our results suggest that demanding foraging conditions favour more accurate cache retrieval in food-caching birds.     

Does Seed‐Caching Experience Affect Spatial Memory Performance by Pinyon Jays?

Food‐storing birds use spatial memory to find previously cached food items. Throughout winter, pinyon jays (Gymnorhinus cyanocephalus) rely heavily on cached pinyon pine (Pinus edulis) seeds. Because of a recent severe drought, pinyon pine trees had not produced a significant seed crop for several years. Therefore, 1‐ and 2‐yr‐old birds never had the opportunity to cache and recover seeds and birds 4 or more years of age had not recovered seeds in 3 yr. This study examined whether natural but extreme variability in experience might result in differences in abstract spatial memory ability during a non‐cache recovery test of spatial memory. Three groups of jays were tested for spatial memory ability in an open room analog of the radial arm maze. Two of the groups were 8 mo old: young/minimally experienced birds which had 2 mo of experience in the wild, while young/experienced birds had 5 mo of experience in their natural habitat. The third group, adult, consisted of birds more than 3 yr old, with at least 3 yr of experience in their natural habitat. This was the only group with experience caching pine seeds. All three groups performed equally and well above chance. This suggests that spatial memory is fully developed by 8 mo of age and is not affected by extensive experience in the wild.     

The effects of cue competition on timing in pigeons

We studied the effects of cue competition on timing in both overshadowing and blocking operant procedures with pigeons. A white center key delivered reward when pecked 30 s after a red or green sidekey was presented and 10 s after presentation of the alternate color on the other sidekey. In Experiment 1, key presentations were concurrent during training trials for overshadow-condition pigeons, while side key presentations were separated across training trials for control birds. In Experiment 2, half of the birds (Blocking group) were given pre-exposure trials to either the 10-s or 30-s sidekey condition. Both blocking-condition and control birds were then given trials of concurrent side key presentations. Peak time curves were compared between experimental and control conditions. The results showed blocking of timing accuracy of a long (30-s) stimulus by a short (10-s) stimulus, but no evidence for overshadowing of timing accuracy.     

Rats (Rattus norvegicus) and pigeons (Columbia livia) are sensitive to the distance to food,but only rats request more food when distance increases

Three experiments investigated foraging by rats and pigeons. In Experiment 1, each response on a manipulandum delivered food to a cup, with the distance between the manipulandum and the cup varying across conditions. The number of responses made before traveling to collect and eat the food increased with distance for rats, but not for pigeons. In Experiment 2, two manipulanda were placed at different distances from a fixed food source; both pigeons and rats preferentially used the manipulandum closest to the food source. Experiment 3 was a systematic replication of Experiment 1 with pigeons. In different conditions, each peck on the left key increased the upcoming hopper duration by 0.5, 1.5 or 2.5 s. Completing a ratio requirement on the right key of 1, 4, 8, 16 or 32 pecks, depending on the condition, then produced the food hopper for a duration that depended on the number of prior left pecks. As the ratio requirement increased on the right key, pigeons responded more on the left key and earned more food. Overall, the results replicate previous research, underlining similarities and differences between these species. The results are discussed in terms of optimal foraging, reinforcer sensitivity and delay discounting.     

The effects of hippocampal lesions in homing pigeons on a one-trial food association task

The role of the avian hippocampal formation in a one-trial food association task was investigated across various retention intervals. Control pigeons, lesioned controls, and pigeons with hippocampal formation lesions were allowed to find food hidden in one of four uniquely decorated bowls in a specific location in a room. After retention intervals of 10 min, 1 h, 7 h, and 24 h, pigeons were placed back in the room with the same bowl in the same location (unmanipulated trials) or with the previously rewarding bowl in a new location and a different bowl in the previously rewarding location (test trials). Although all groups chose the correct bowl during unmanipulated trials, hippocampal formation lesioned birds' choices to the bowl in the correct location decreased compared to the combined controls during the test trials. The results suggest that hippocampal formation lesions do not impair long-term memory of a goal after one experience but significantly decrease the use of spatial information to return to that goal. Accepted: 18 September 1999     

Food, audience and sex effects on pinyon jay (Gymnorhinus cyanocephalus) communication

Pinyon jays (Gymnorhinus cyanocephalus) have a complex social system that may require a complex communication system. They need to interact with multiple flock members, and they form life-long pair-bonds. We researched whether pinyon jays would selectively vocalize depending on the presence or absence of food and certain flock members. We recorded the vocalizations of nine pinyon jays (four pair-bonds and one single male) in response to different audience types. The calls of the test bird were recorded after it was given either an empty food cup or one containing 50 pinyon pine (Pinus edulis) seeds, and the bird was in the presence of one of the following audience types: (1) two males and two females including subject's mate; (2) two males and two females excluding subject's mate; (3) four males excluding mate; (4) three females excluding mate; and (5) no audience. Birds gave fewer calls when there was food. When alone, birds called in a manner that may maximize long-distance transmission. Trends indicate that birds call differently to their mate. A sex effect was also found in that males and females called in a distinct manner, possibly reflecting differences in dominance status. Overall, birds responded to the presence or absence of an audience.     

Not just passengers: pigeons,Columba livia,can learn homing routes while flying with a more experienced conspecific

For animals that travel in groups, the directional choices of conspecifics are potentially a rich source of information for spatial learning. In this study, we investigate how the opportunity to follow a locally experienced demonstrator affects route learning by pigeons over repeated homing flights. This test of social influences on navigation takes advantage of the individually distinctive routes that pigeons establish when trained alone. We found that pigeons learn routes just as effectively while flying with a partner as control pigeons do while flying alone. However, rather than learning the exact route of the demonstrator, the paired routes shifted over repeated flights, which suggests that the birds with less local experience also took an active role in the navigational task. The efficiency of the original routes was a key factor in how far they shifted, with less efficient routes undergoing the greatest changes. In this context, inefficient routes are unlikely to be maintained through repeated rounds of social transmission, and instead more efficient routes are achieved because of the interaction between social learning and information pooling.     

Gaze direction - a cue for hidden food in rooks (Corvus frugilegus)?

Other individual's head- and eye-directions can be used as social cues indicating the presence of important events. Among birds, ravens and rooks have been shown to co-orient with conspecifics and with humans by following their gaze direction into distant space and behind visual screens. Both species use screens to cache food in private; also, it had been suggested that they may rely on gaze cues to detect hidden food. However, in an object-choice task, ravens failed to do so, and their competitive lifestyle may have prevented them from relying on these cues. Here we tested closely related and cooperative rooks. Food was hidden in one of two cups and the experimenter gazed at the baited cup. In a second experiment, we aimed to increase the birds’ motivation to choose correctly by increasing the investment needed to obtain the reward. To do so, the birds had to pull on a string to obtain the cup. Here, the birds as a group tended to rely on gaze cues. In addition, individual birds quickly learned to use the cue in both experiments. Although rooks may not use gaze cues to find hidden food spontaneously, they may quickly learn to do so.     

Clark's Nutcrackers Nucifraga columbiana Remember the Size of Their Cached Seeds

Clark's nutcrackers ( Nucifraga columbiana ) hide thousands of seeds in subterranean caches that they later recover using spatial information about cache location. In two experiments, we tested whether nutcrackers also remember another type of information regarding their caches – the size of the seeds in each cache. We videotaped birds during cache recovery and then measured their bill gape during probing behaviour as captured on the videotape. In experiment one, six birds each experienced two treatments: one that allowed them to cache and then recover large seeds, and the other, an identical treatment using small seeds. During this experiment, all six birds used a wider gape when attempting to recover seeds during the large-seed treatment than during the small-seed treatment, and gape width was significantly correlated with seed size. During experiment two, we presented birds with both large and small seeds within the same caching session. We also increased the retention interval between caching and recovery. These modifications increased the difficulty of the task. Six of the seven birds used a wider gape during seed recovery when digging for caches that contained large seeds than they did when searching for small seeds. The ability to remember the size of seeds placed within caches may serve to increase the likelihood of speedy and successful recovery. It also allows the birds another level of organization of their food supply. These are the first experiments to suggest that Clark's nutcrackers remember more about their caches than location alone.     

Foraging success in junco flocks and the effects of social hierarchy

The relative advantages of flocking for socially dominant and subordinate dark-eyed juncos (Junco hyemalis) were investigated in a laboratory experiment. Success in finding seeds hidden in an artificial tree was determined for all individuals hunting alone. When hunting alone, birds who spread their searching more evenly over the habitat had a greater chance of finding the food source. Flocks of four were housed together and subsequently each flock formed a dominance hierarchy social structure. High-ranking individuals obtained more seeds when in flocks than when hunting as isolates. In numbers of seeds obtained, socially low-ranking birds gained no advantage in comparison to their performance as isolates. In our experiment, the primary advantage of flocking for low-ranking individuals was the reduced chance of obtaining no food at all.     

Re-orienting in space: do animals use global or local geometry strategies?

Here we compare whether birds encode surface geometry using principal axes, medial axes or local geometry. Birds were trained to locate hidden food in two geometrically identical corners of a rectangular arena and subsequently tested in an L-shaped arena. The chicks showed a primary local geometry strategy, and a secondary medial axes strategy, whereas the pigeons showed a medial axes strategy. Neither species showed behaviour supportive of the use of principal axes. This is, to our knowledge, the first study to directly examine these three current theories of geometric encoding.     

Functional organization of the avian auditory field L

Summary The 2-deoxyglucose (2DG) autoradiographic method is used to analyse the functional organization of the auditory forebrain nucleus, field L, in parrots, ducks, pigeons, gulls and passerine birds. The data are compared to earlier studies in domestic and Guinea fowls. In all birds field L is a trilaminar structure, placed at the border between neostriatum mediale and caudale. The orientation and spatial extent within the forebrain, however, shows considerable variability. There is a close spatial relationship between field L and the overlying hyperstriatum ventrale, which is a secondary auditory center receiving input from field L. Stimulation with tones produces stripe like patterns of metabolic activity which are continuous across the layers of field L and the hyperstriatum ventrale. In all birds the position of the stripes in both areas shift in medio-lateral direction with decreasing tone frequency. In none of the birds the representation of frequencies above 3 kHz cover more than 20% of the neuronal space. Thus, high frequency hearing is underrepresented. Frequencies between 500 Hz and 3 kHz with somewhat variable representation, cover most of the neuronal space. Fowls and pigeons appear to have a low frequency specialization in field L.Abbreviations 2DG 2-deoxyglucose - FM frequency modulated     

How does time since feeding affect the fuels pigeons use during flight?

Time between meals can vary from multiple hours to days within and among species. We investigated the effects of time since feeding on lipid, protein, and carbohydrate oxidation in flying pigeons (Columba livia) by interpreting changes in blood plasma metabolite concentrations and mass during flight. Five pigeons were flown or rested for 4 h after food deprivations of 2, 12, 24, and 48 h. After flight, blood plasma concentrations of uric acid and beta-hydroxybutyrate were elevated over control and preflight values, indicating elevated protein and lipid catabolism during flight. Lipid oxidation, as indicated by changes in beta-hydroxybutyrate concentration, increased more in unfed flying pigeons compared with recently fed flying pigeons and with resting controls. Protein oxidation, as indicated by changes in uric acid concentrations, also positively covaried with feeding time; the covariation was mostly caused by increases in 48-h food-deprived pigeons. Unfed birds lost less mass during a 4-h flight than recently fed birds. We reasoned that recently fed pigeons oxidized more glycogen in flight than pigeons not recently fed; calculated glycogen stores explained 72%-117% of mass loss differences between 2- and 48-h-fed pigeons. Thus, time since feeding was an important determinant of the fuels pigeons used in flight.     

Sun compass orientation in seed-caching scrub jays (Aphelocoma coerulescens)

Summary In their natural environment, scrub jays harvest pinyon pine seeds and store them in subterranean caches. In our tests, the birds performed this behavior in an octagonal outdoor aviary with sand-filled cups inserted in the floor. For caching, only 12 such cups in a 90° sector were available, while for the recovery session 4 to 6 days later all 48 cups in the entire aviary were open. In control tests, the birds concentrated their search in the sector where the seeds had been cached. When the internal clock of the birds was shifted 6 h between caching and recovery, they preferentially probed in the adjacent 90° sector. This indicated that they used sun compass information to relocate their caches, largely ignoring visual cues from surrounding landmarks.The dominant role of the sun compass which has a parallel in the orientation of homing pigeons, may reflect a general tendency to prefer compass information in spatial orientation tasks; it is in agreement with the model that birds generally have a directionally oriented view of space.Abbreviations OR Original caches - SH shifted caches     

The potential of seed‐eating birds to spread viable seeds of weeds and other undesirable plants

The potential for seed‐eating birds to spread viable seeds was investigated using captive‐feeding trials to determine seed preference, passage time through the gut, and viability of passed seeds for bronzewing pigeons (Phaps chalcoptera), peaceful doves (Geopelia striata), crested pigeons (Ocyphaps lophotes), Senegal doves (Streptopelia senegalensis), zebra finches (Taeniopygia guttata), black ducks (Anas superciliosa) and wood ducks (Chenonetta jubata). Test seeds were bladder clover (Trifolium spumosum), crimson clover (Trifolium incarnatum), gorse (Ulex europaeus), canola (Brassica napus) and red panicum (Setaria italica). Their consumption was compared with that of commercial seed mixes. Although all test seeds were recognizable foods, their consumption usually decreased in the presence of other foods, except for canola, where consumption rates were maintained. Hard‐seeded bladder clover was the only species where viable seeds were passed by obligate seedeaters. In contrast, viable seeds of canola and gorse were passed by seed‐eating omnivorous/herbivorous ducks, although the germination of passed seeds (42%) was reduced significantly compared with that of untreated control seed (67%). Field validation with wild, urban bronzewings and Australian magpies (Gymnorhina tibicen) offered canola and commercial seed yielded similar outcomes, with a range of viable seeds recovered from magpie soft pellets. Mean seed passage time in captive birds ranged from 0.5 to 4.3 h for all test seeds and commercial seed mixes, suggesting that these bird species may potentially disperse seed over moderate distances. Despite the low probability of individual birds spreading viable seed, the high number of birds feeding in the wild suggests that the potential for granivorous and seed‐eating omnivorous birds to disperse viable seeds cannot be discounted, particularly if exozoochorous dispersal is also considered.     

Do release-site biases reflect response to the Earth's magnetic field during position determination by homing pigeons?

How homing pigeons (Columba livia) return to their loft from distant, unfamiliar sites has long been a mystery. At many release sites, untreated birds consistently vanish from view in a direction different from the home direction, a phenomenon called the release-site bias. These deviations in flight direction have been implicated in the position determination (or map) step of navigation because they may reflect local distortions in information about location that the birds obtain from the geophysical environment at the release site. Here, we performed a post hoc analysis of the relationship between vanishing bearings and local variations in magnetic intensity using previously published datasets for pigeons homing to lofts in Germany. Vanishing bearings of both experienced and naïve birds were strongly associated with magnetic intensity variations at release sites, with 90 per cent of bearings lying within ±29° of the magnetic intensity slope or contour direction. Our results (i) demonstrate that pigeons respond in an orderly manner to the local structure of the magnetic field at release sites, (ii) provide a mechanism for the occurrence of release-site biases and (iii) suggest that pigeons may derive spatial information from the magnetic field at the release site that could be used to estimate their current position relative to their loft.     

The Orientational Consequences of Flocking Behaviour in Homing Pigeons,Columba livia

Two experiments are described which investigate the orientational consequences of flocking in homing pigeons Columba livia. Previous experiments have shown that homing pigeons placed inside a clear-sided release box for 5 min before release from a familiar site have enhanced ground homing speed compared with those placed in an opaque-sided box. It is assumed that previewing the surrounding landscape allows for faster homing since a bird denied this information must accumulate the knowledge on release. In experiment 1, using the same technique developed in these experiments but releasing the birds in pairs we showed that within familiar areas, homing pigeons can exploit a partner that has acquired more information, allowing them to home more quickly. In experiment 2 we attempted to test three potential strategies which may occur during homing flights. The results do not conclusively distinguish between these three mechanisms but suggest that orientation of the pairs of birds is most likely to have resulted from a compromise of individual tendencies, or from following the best homer, but not from following a ‘governing leader’. The consequence of these mechanisms is discussed.