When Does Previewing the Landscape Affect Pigeon Homing?

The importance of visual landmarks during homing in pigeons (Columba livia) remains a contentious issue. Three experiments which explore the role of visual landmarks at release sites are reported here. The effects of releasing homing pigeons after a 5-minute period in either a clear or an opaque sided release box were investigated. In the clear sided box pigeons were able to observe local surroundings at a release site, but this view was obstructed in the opaque sided box. In experiment 1 pigeons were released from familiar locations close to home (between 2 and 5.6 km): being unable to view landmarks prior to release significantly slowed homing speeds. In experiment 2 pigeons were released at familiar locations further from home (between 8.4 and 10 km): being unable to view landmarks prior to release did not significantly affect homing speeds. In experiment 3 pigeons were trained to home from distant release sites but were tested at closer, unfamiliar sites located on the likely homing routes used by the pigeons in training. No significant difference in homing speeds were observed when pigeons were released from either the clear or opaque sided box. The significance of these results for understanding the role of visual landmarks within a pigeon's familiar area is discussed.     

Experimental life cycle of Ascaridia columbae in intravenously infected pigeons, Columba livia.

The fate and routes of migration of infective larvae of Ascaridia columbae were studied in intravenously (i.v.) infected pigeons. Larvae were able to complete a trachael migration, and arrived at the small intestine where they established a patent infection. Granulomas were observed and histopathologically described in the lungs of i.v. infected birds.     

Spontaneous and deferred imitation in the pigeon

Experimentally-naive pigeons were placed on one side of a clear partition. A pigeon on the other side received food for pecking a ping-pong ball, pulling a rope, or pecking a plastic disk. When given access to a similar object, each naive pigeon pecked or pulled at a low rate for several sessions and two continued to do so forseveral sessions in the absence of the leader. In a second experiment, the latter effect was demonstrated after a delay of 24 hours, even though the naive pigeons had never had access to the object in the presence of the model. A third experiment demonstrated that the effect on the follower was not due merely to the presence of or activity of another pigeon and was at least somewhat specific to the behavior of the model.     

Pigeon homing: The influence of topographical features in successive releases at the same site

A new device, the direction-recorder, offered the possibility to extend earlier studies of homing behaviour of pigeons when relevant topographical elements (mountains and large tracts of water) interpose between the release site and the home loft. Three series of experiments were carried out at three different sites to investigate intraindividual and interindividual variability in subsequent tosses from the same locality. Two release sites were chosen behind a mountain chain with respect to home; at the third site homeward directed route crosses the sea. From our results it turns out that homing pigeons may adopt different strategies. Moreover, a wide intraindividual variability was observed in repeated tosses at the same site; some pigeons remained faithful to the first route, whereas other birds tried successive new routes which, in most cases, were significantly shorter than previous ones. This result indicates that pigeons try, and are actually able, to improve their performance in subsequent releases from the same site.     

The effect of modifying the glucosinolate content of leaves of oilseed rape (Brassica napus ssp. oleifera) on its interaction with specialist and generalist pests

Twenty eight Brassica napus lines were developed which had contrasting leaf glucosinolate profiles to those found in commercial oilseed rape cultivars. The lines varied both in the total amount of aliphatic glucosinolates and in the ratio of different side chain structures. The lines were used in field experiments to assess the manner by which glucosinolates mediate the interactions between Brasssica and specialist pests (Psylliodes chrysocephala and Pieris rapae) and generalist pests (pigeons and slugs). Increases in the level of glucosinolates resulted in greater damage by adult flea beetles (P. chrysocephala) and a greater incidence of Pieris rapae larvae, but reduced the extent of grazing by pigeons and slugs. Decreasing the side chain length of aliphatic glucosinolates and reducing the extent of hydroxylation of butenyl glucosinolates increased the extent of adult flea beetle feeding. The implications of modifying the glucosinolate content of the leaves of oilseed rape and the role of these secondary metabolites in plant/herbivore interactions are discussed.     

Development of the navigational map in homing pigeons: effects of flight experience on orientation performance

Experiments have shown that pigeons, Columba livia, are able to develop navigational abilities even if reared and kept confined in an aviary, provided that they are exposed to the natural winds. In contrast, pigeons reared in a wind-screened aviary do not learn to navigate. Pigeons kept confined in a screened aviary when young do not learn to navigate even if, once they become adult, the screens are removed and the birds are exposed to natural winds for a period sufficiently long for map learning. In all of these experiments, pigeons were kept confined until the day of test release. In the present study we found that pigeons reared in a wind-screened aviary developed navigational abilities if, once adult, they were allowed to perform spontaneous flights around the loft. Nevertheless, their navigational performance never reached the level of controls.Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

Fragmental regulation of vestibuloocular responses

Intact pigeons were exposes to whole body centric and eccentric horizontal rotations in darkness during angular velocity trapezoids. The overall nystagmus alteration patterns were analysed. In 10 pigeons, all nystagmus alterations may be explained on the basis of the dynamics of peripheral otolith activity and central effects that are the same for all combinations of interacting inputs (type 1 patterns), whereas in other pigeons part of the nystagmus alterations were connected with some central effects that were individually specific and touch upon the responses to separate combinations of interacting input (type 2 patterns). It was observed the transformation of type 2 to type 1-patterns during the reiterated rotational trails and light nembutal anesthesia. A fragmentary control of the vestibulo-ocular responses seems to exist. This implies that the CNS is able to discern numerous kinds of bilaterally organized interacting inputs arising during different otolith membrane shifts.     

Relevance of visual cues for orientation at familiar sites by homing pigeons: an experiment in a circular arena

Whether pigeons use visual landmarks for orientation from familiar locations has been a subject of debate. By recording the directional choices of both anosmic and control pigeons while exiting from a circular arena we were able to assess the relevance of olfactory and visual cues for orientation from familiar sites. When the birds could see the surroundings, both anosmic and control pigeons were homeward oriented. When the view of the landscape was prevented by screens that surrounded the arena, the control pigeons exited from the arena approximately in the home direction, while the anosmic pigeons' distribution was not different from random. Our data suggest that olfactory and visual cues play a critical, but interchangeable, role for orientation at familiar sites.     

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.     

The social transmission of a food-finding technique in pigeons: what is learned?

Experimentally-naive pigeons (Columba livia) were exposed to varying amounts of socially transmitted information needed for solving a food-finding problem. Observer pigeons that saw a trained bird (model) piercing the paper covering a food box and eating were able to solve the problem faster and more efficiently than pigeons that only saw the model eating but not piercing. This result held whether observer performance was simultaneous or deferred with respect to the model's demonstration. Pigeons that saw the model piercing but not eating showed almost no tendency to copy. These results suggest that copying was dependent upon observer recognition of the fact that the model was getting a food reward, and that pigeons were capable of learning aspects of the piercing technique by observation rather than by trial and error.     

Study of the role of pigeons in the dissemination of Cryptococcus neoformans in nature.

Cryptococcus neoformans was recovered from droppings collected within the first 24 h from pigeons experimentally fed with a dose of 5 X 10(6) cells. The fungus proved to multiply well though differently in the sterilized pigeon and chicken excreta seeded with the organism. In both unsterile types of droppings no viable cells of C. neoformans were detected after 4 weeks incubation. Isolated bacterial flora from the intestinal contents of apparently healthy pigeons showed a complete inhibitory effect on the growth of C. neoforms in vitro. It has been concluded that pigeons do not favor multiplication of the fungus in their gut and consequently they do not seem to play an active biological role in dissemination of C. neoformans in nature.     

Protecting buildings against feral pigeons

Feral pigeons (Columba livia, Gmelin 1789) cause different problems for building owners when using structures for daytime perching, sleeping, and breeding. Problems include fouling of building facades and pavements, transmission of allergens and pathogenic microorganisms, and infestations with ectoparasites emanating from breeding sites. Owners are primarily interested in keeping away unwanted pigeons from their property. Pest control companies offer different deterrent systems, of widely varying efficacy, for proofing buildings against feral pigeons. A better solution is avoiding attractive structures during building design or subsequent alterations of existing structures used by feral pigeons. With our study, we elaborate the relevant structural data to help to maintain a building free of pigeons. We performed experiments with free ranging feral pigeons in a feral pigeon loft in the City of Basel, Switzerland. The maximum outlet width a pigeon is not able to pass through is 4 cm; the respective outlet height is 5 cm and a pigeon-safe square opening is not larger than 6 × 6 cm. The maximum ledge width a pigeon is not able to sit on is 4 cm. The pigeon-safe angle of inclination for smooth construction materials (tinplate, glass, plastics) is 25°, for medium rough materials (wood, plane concrete) 35°, and for rough materials (sandstone, rough concrete) at least 50°. Additionally, we studied the behavioral strategies used by feral pigeons to surmount our experimental constructional restrictions, ledge width, and ledge inclinations. Our data provide the essential data to prevent feral pigeons from using building structures.     

Shivering thermogenesis in leg and breast muscles of galliform chicks and nestlings of the domestic pigeon.

We studied the ontogeny of shivering thermogenesis in breast and leg muscles of precocial galliforms (domestic fowl, grey partridge, and Japanese quail) and the altricial domestic pigeon using electromyography (EMG) and indirect calorimetry. Galliforms were able to increase heat production by shivering in leg muscles at the youngest age studied (1-2 d). Pectorals contributed to heat production from days 7-10 onward, but in the partridge and especially in the fowl, shivering by the pectorals was weaker than in the quail. In the pigeon, shivering began in pectorals and legs at 2 and 4 d of age, respectively, and pectorals had clearly the predominant role in thermogenesis. Despite the early beginning of electrical signs of shivering, significant thermogenesis did not appear in the pigeon before the age of 6 d. All galliforms shivered in bursts, like pigeons aged 2-4 d. From the age of 6 d onward, continuous shivering became predominant in the pigeon. In pectorals of 2-6-d-old pigeons, shivering did not increase linearly during decreasing ambient temperature, as in other muscles and species, but started abruptly, at full intensity. Furthermore, in 2-4-d-old pigeons, cooling induced movement activity in legs. The median frequency of shivering EMGs varied (1) with maturation of the muscle, (2) with size of the adult bird, and (3) between altricials and precocials.     

Selective stimulus control in discrimination of lateral mirror images by pigeons

Four monocularly and two binocularly viewing pigeons were trained to peck a key when it displayed one stimulus (S+) but not to peck when it displayed another stimulus (S−). S+ and S− were a lateral mirror-image pair of two-coloured stimuli. When tested for transfer with the untrained eye open, two of the monocular birds pecked more during S− than S+, the other two continuing to favour S+. During generalization tests on the wavelength dimension all monocular birds pecked much more often during one S+ colour than during the other. The colour controlling pecking was that displayed on the side of the key facing the open eye during S+ presentations. Both binocular birds developed asymmetrical responses to the key, one favouring the left, the other the right side of the key. Generalization tests on the wavelength dimension showed selective control by the colour displayed on the favoured side of the key during S+ presentations. The results are interpreted as supporting the view that pigeons learn to discriminate lateral mirror images by developing asymmetrical observing responses that convert the left-right difference between the mirror images into a difference more easily discriminable.     

Characterizing the effects of d-amphetamine on temporal discrimination

Although the effects of dopamine agonists on temporal discrimination have been widely studied, conclusions as to their behavioral and neurophysiological effects are difficult due to a number of discrepant findings in the literature. This study examined whether a previously unexplored procedural difference could account for some of these discrepancies. In three experiments, pigeons categorized the duration of temporal samples during two variants of the interval-bisection procedure. In the position variant, responses to a side key that corresponded to the sample duration produced food. In the color-matching variant, responses to the key color that corresponded to the sample duration produced food. Across experiments, d-amphetamine produced a general disruption of temporal discrimination not accompanied by over or underestimation of time in both procedures. This effect occurred whether pigeons were exposed to both procedures within session (Experiment 1) or across conditions (Experiments 2 and 3) and whether the pigeons were drug experienced (Experiments 1 and 2) or naïve (Experiment 3). Analyses of the cumulative normal functions fitted to the proportion-long response data indicated that d-amphetamine produced its effects by selectively decreasing stimulus control, rather than by affecting timing.     

The key mimetic features of hoverflies through avian eyes

Batesian mimicry occurs when a palatable species (the mimic) gains protection from predators by resembling an unpalatable or otherwise protected species (the model). While some mimetic species resemble their models closely, other species ('imperfect mimics') are thought to bear only a crude likeness. In an earlier study, pigeons (Columba livia) were trained to recognize wasp images in one experiment and non-mimetic (NM) fly images in another by rewarding the pigeons for pecking on the respective image types. These pigeons were subsequently presented with different images, including seemingly wasp-like hoverfly species, and the recorded peck rates on these images were used as a measure of the pigeons' perception of the hoverflies' mimetic similarity. To identify a candidate set of morphological features that the pigeons used when assessing this mimetic similarity, we first extracted a range of biometrical measurements from images originally presented to the pigeons. We then repeatedly optimized an empirical model in an attempt to match the recorded pigeon peck rates while using as few biometrical features as input as possible. Our models were able to fit the pigeon peck rates with considerable accuracy even while excluding many input features. Antennal length, a feature commonly used to discriminate between flies and wasps, was regularly retained as an input variable, but overall a different set of biometrical features was important for predicting the peck rates of pigeons rewarded for identifying wasps compared to those rewarded for identifying NM flies. In highlighting the importance of specific biometrical features in promoting mimicry and the irrelevance of others, our optimized models provide an explanation as to why certain species that appear to be poor mimics to humans are judged to be good mimics by birds.     

The formation and execution of sequential plans in pigeons (Columba livia)

The ability to formulate and execute plans is a hallmark of human behaviour. Here we present evidence of planning in pigeons. Subjects were trained to respond to three geometric shapes in a prescribed order. Probe trials were then introduced in which, following a response to the first item, the on screen positions of the second and third item were exchanged. If subjects were planning a sequence of responses at the outset of a trial, we would expect reaction time to the second item to increase, reflecting the updating of a predetermined response plan. This is exactly what was found. Subjects also responded correctly on trials in which, following a response to the first item, stimuli were covered by opaque white squares. Together these results suggest pigeons are able to plan one step ahead on the simultaneous chaining paradigm.     

Evaluation of the antiparasitic activity of the chitosan-silver nanocomposites in the treatment of experimentally infested pigeons with Pseudolynchia canariensis

This study aimed to evaluate the efficacy of chitosan-silver nanocomposites in the treatment of experimentally infested pigeons with Pseudolynchia canariensis (P. canariensis) with evaluation of different immunological parameters before and after treatment. Therefore, fourteen birds were divided into 2 groups; group1(infested group including 12 birds) which subdivided into 6 sub-groups experimentally infested pigeons 2 pigeons each, and five group of them were treated with chitosan-silver nanocomposites and sub-group number 6 was treated with deltamethrin while, group 2 including two pigeons were kept as control negative ones. P. canariensis flies distributed under the wing and /or under the tail in infested group and these pigeons showed significantly lower RBCs and higher WBCs than that in non-infested pigeons. The cell mediated immune response against experimentally infested pigeons with P. canariensis was studied. P. canariensis infestation in pigeons have a negative impact on pigeon’s blood parameters, increase TNF-α and IL-1β cytokines levels. This study cleared out the role of P. canariensis in the induction of a case of oxidative stress indicated by high level of nitric oxide and malondialdehyde (MDA) with low antioxidant capacity in shape of reduced zinc concentration in the sera of experimentally infested pigeon. Chitosan-silver nanocomposite has a promising effect in the elimination of P. canariensis infestation in pigeons.     

Pigeon Homing: The Navigational Map Developed in Adulthood is Based on Olfactory Information

Homing pigeons raised in a shielded aviary and kept confined until the day of the test releases are not able to navigate even if, once adult, the screens are removed and the birds are exposed to natural winds for a sufficiently long period for map learning. However, pigeons raised in the same condition but, once adult, allowed to perform spontaneous flights around the loft are able to develop navigational abilities which, however, never reach the level of controls. In the present study, we show that the navigational map learned by the adult birds, which had the possibility to perform spontaneous flights, is based on olfactory information.     

Local cutaneous water barrier in cold- and heat-acclimated pigeons (Columba livia) in relation to cutaneous water evaporation

The thermoregulatory function of the skin differs in adult cold-acclimated and heat-acclimated rock pigeons (Columba livia). In general, the cutaneous evaporative cooling mechanism is not activated by appropriate stimuli in cold-acclimated pigeons in contrast to heat-acclimated pigeons. We studied with electron microscopy whether the differences in the function of the skin are reflected in the structure of the epidermal water barrier of these two extreme acclimation states. The epidermis of cold-acclimated pigeons is attenuated, and the underlying dermis lacks any intimate vascularization. Both the extracellular and the intracellular domains in the stratum corneum contain organized lamellar lipids. At the stratum transitivum-stratum corneum interface, multigranular body secretion is indicated by the highly convoluted cell membranes and membraneous sacculae enclosing the multigranular bodies. Alternatively, multigranular bodies retain in the corneocytes, and the lipoid material originated from them is reprocessed to broad lamellae. The keratohyalin (KH) granules are spotlike and oriented as cortical bands beneath the plasma membrane. In heat-acclimated pigeons, the epidermis displays modified patches side by side with basic structural type of epidermis. The modified areas are characterized by hypertrophy and abundance of dermal capillaries adjacent to the hypertrophied patch. No lamellar lipids are discerned in the dilated extracellular space. The structure of multigranular bodies is abnormal, and the numbers of lipid droplets in the outer viable epidermis and stratum corneum are decreased. The transitional cells contain stellate KH granules, which form a network throughout the cell. It is concluded that cold-acclimated pigeons have a lamellar, extracellular water barrier, the cutaneous water evaporation is minimized, and heat is stored in the body core. Acclimation to heat leads to formation of structurally heterogeneous skin. The structurally modified skin patches show disruption of the barrier-forming machinery in the multigranular bodies and marked reorganization of fibrillar proteins and electron-dense KH masses in the transitional layer. Thus water barrier adjustments in cold- and heat-acclimated pigeons manifest the dynamic function of avian skin as a thermoregulatory organ.