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Oak savanna, once widespread across central North America, has functionally vanished from most of its range due to land conversion or fire suppression and subsequent afforestation. Savanna-associated bird species have exhibited population declines as a result. One of the few areas containing remnant oak savanna is the vast Cross Timbers ecoregion of the south-central Unites States. Previous research in the Midwest showed some bird species exhibited higher rates of nest success (i.e., lower predation of eggs and nestlings) in restored savannas than in closed-canopy forests. Our objective was to quantify patterns of avian nest success across a gradient from open-canopy oak savanna to closed-canopy forest in the Cross Timbers ecoregion of southeastern Kansas. Daily nest survival rates for four common bird species--mourning dove (Zenaida macroura), yellow-billed cuckoo (Coccyzus americanus), brown thrasher (Toxostoma rufum), and northern mockingbird (Mimus polyglottos)-- were modeled against covariates of woodland structure along the habitat gradient. Tree density and canopy cover had no significant effects on daily nest survival rate, but daily survival rates of brown thrasher and northern mockingbird nests showed positive trends with increasing shrub density. We expect restoration of oak savanna habitat would have little effect on nest survival of some common bird species in the naturally heterogeneous Cross Timbers ecoregion., INTRODUCTION Oak-prairie savanna habitat in the Midwestern United States has largely disappeared (Nuzzo, 1986: Henderson, 1995; Noss et al., 1995). Land conversion and degradation due to fire suppression have been [...]

We review the taxonomic history, external morphology, anatomy, behavior, distribution, and zoogeography of the Blue-headed Quail-Dove (Starnoenas cyanocephala), which is endemic to Cuba, and conclude that it is completely unlike any other New World member of the Columbidae. It presents a mosaic of characters shared with various genera in Australasia but is perhaps most similar to the Australian genus Geophaps and related terrestrial pigeons. The Blueheaded Quail-Dove should be placed in its own subfamily, Starnoenadinae, until its relationships with Australasian genera can be refined by additional data including molecular. We recommend that the English name be changed to Blue-headed Partridge-Dove. Received 9 October 2015. Accepted 17 November 2015. Key words: anatomy, behavior, Columbidae, Geophaps, Geotrygon, paleontology, Starnoenadinae, zoogeography., Received wisdom often distorts our perception of relationships among various groups of birds until new information or more critical evaluation of old evidence dispels the inaccuracy of current knowledge. A [...]

In Experiment 1, 2 groups of pigeons were trained to respond to either a 4-item (A[right arrow]B[right arrow]C[right arrow]D) or 5-item (A[right arrow]B[right arrow]C[right arrow]D[right arrow]E) list. After learning their respective list, half of the subjects were trained on a positive pair with reinforcement provided when pairs were responded to in the order true to that of the original sequence (4-item: B[right arrow]C; 5-item: B[right arrow]D). The remaining subjects were trained on a negative pair with reinforcement provided for responding to the pairs in the order opposite to that learned in the original sequence (4-item: C[right arrow]B; 5-item: D[right arrow]B). Subjects in the positive pair condition learned their respective pair faster than did subjects in the negative pair condition. In Experiment 2, after reaching criterion on a 4-item list, subjects received 16 BC probe trials spread across 4 sessions of training. Subjects performed significantly above chance on the probe trials. The performance of our subjects in Experiments 1 and 2 demonstrates that, similar to monkeys, pigeons form a representation of the lists that they learn. Keywords: serial order, representation, chaining theory DOI: 10.1037/a0020926

A basic tenet of principles of associative learning applicable to models of spatial learning is that a cue should be assigned greater weight if it is a better predictor of the goal location. Pigeons were trained to locate a goal in an acute corner of an isosceles trapezoid arena, presented on a slanted floor with 3 (Experiment 1) or 2 (Experiment 2) orientations. The goal could be consistently determined by the geometric shape of the arena; however, its position with respect to the slope gradient varied, such that slope position was not a good predictor of the goal. Pigeons learned to solve the task, and testing on a fiat surface revealed successful encoding of the goal relative to the geometric shape of the arena. However, when tested in the arena placed in a novel orientation on the slope, pigeons surprisingly made systematic errors to the other acute--but geometrically incorrect--mirror image corner. The results indicate that, for each arena orientation, pigeons encoded the goal location with respect to the slope. Then, in the novel orientation, they chose the corner that matched the goal's position on the slope plus local cue (corner angle). Although geometry was 2 times (Experiment 2) or even 3 times (Experiment 1) as predictive as slope, it failed to control behavior during novel test trials. Instead, searching was driven by the less predictive slope cues. The reliance on slope and the unresponsiveness to geometry are explained by the greater salience of slope despite its lower predictive value. Keywords: goal location, slope or geographical slant, geometric shape, cue salience, Columba livia DOI: 10.1037/a0019234

Animals that travel together in groups display a variety of fascinating motion patterns thought to be the result of delicate local interactions among group members (1-3). Although the most informative way of investigating and interpreting collective movement phenomena would be afforded by the collection of high-resolution spatiotemporal data from moving individuals, such data are scarce (4-7) and are virtually non-existent for long-distance group motion within a natural setting because of the associated technological difficulties (8). Here we present results of experiments in which track logs of homing pigeons flying in flocks of up to 10 individuals have been obtained by high-resolution lightweight GPS devices and analysed using a variety of correlation functions inspired by approaches common in statistical physics. We find a well-defined hierarchy among flock members from data concerning leading roles in pairwise interactions, defined on the basis of characteristic delay times between birds' directional choices. The average spatial position of a pigeon within the flock strongly correlates with its place in the hierarchy, and birds respond more quickly to conspecifics perceived primarily through the left eye--both results revealing differential roles for birds that assume different positions with respect to flock-mates. From an evolutionary perspective, our results suggest that hierarchical organization of group flight may be more efficient than an egalitarian one, at least for those flock sizes that permit regular pairwise interactions among group members, during which leader-follower relationships are consistently manifested., Collective movement phenomena in animals include many spectacular and familiar examples: among birds, seemingly instantaneous changes in a flock's direction of motion, the abrupt splitting of a flock, or a [...]

Long-distance dispersal (LDD) of plants remains as a little-understood, key ecological process. We present evidence indicating that granivorous pigeons may disperse large amounts of viable seeds when they die with seeds in their crops at long distance from the parent plant. Research was conducted in Eared Dove (Zenaida auriculata) breeding colonies in central Argentina where breeding populations may reach over 8000 doves/ha. We measured (a) crop seed viability and germination rate from dead doves and (b) daily travel distance from the breeding colonies to the feeding grounds. Seed viability was over 50% in fresh adult and nestling samples. Seed-germination rate ranged between 35% and 65%, even in corpses left on the ground for 30 days. Maximum doves' daily flight distance from the breeding colonies was 117 km. The estimated annual seed deposition per hectare resulting from crop spillage in two breeding colonies was 10.95 and 9.66 Mg, respectively. Significant ecological implications of dove-crop spillage include seed dispersal among fragments, rapid colonization of new habitats including islands, and dispersal of large volumes of weed and transgenic material. A preliminary assessment of dispersal kernel generated by crop spillage in colonial Eared Doves is included. Key words: Cordoba province, Argentina; Croton; dove weeds; Eared Dove breeding colonies; long-distance dispersal; pigeons; transgenic material dispersal; weed dispersal; Zenaida auriculata.

Three pigeons were trained in a successive same/different (S/D) procedure using compound auditory stimuli (pitch/timbre combinations). Using a go/no-go procedure, pigeons successfully learned to discriminate between sequences of either all same (AAAA ... or BBBB ...) or all different (ABCD ...) sequences consisting of 12 sounds. Both pitch and timbre were subsequently established as controlling dimensions. Transfer tests with novel stimuli revealed a generalized basis for the discrimination (novel pitch/timbre combinations, novel pitches, novel instruments, and complex natural & man-made sounds). These results indicate for the first time that pigeons can learn generalized same/different discriminations in a nondominant modality. When combined with earlier visual results, they support a qualitative similarity among birds and primates in their capacity to judge this type of fundamental stimulus relation across different modalities. Keywords: audition, relational discrimination, same-different discrimination, pigeon, birds

Three experiments assessed the relation between the differential outcomes effect and resistance to change of delayed matching-to-sample performance. Pigeons produced delayed matching-to-sample trials by responding on variable interval schedules in two components of a multiple schedule. In the same-outcome component, the probability of reinforcement was the same for both samples (.9 in Experiments 1 and 2, .5 in Experiment 3); in the different-outcomes component, the probability of reinforcement was .9 for one sample and .1 for the other. In all three experiments, the forgetting functions in the different-outcomes component were higher and shallower than in the same-outcomes component. When total reinforcement was greater in the same-outcomes component (Experiments 1 and 2), resistance to disruption by prefeeding, intercomponent food, extinction, or flashing lights typically was greater in that component. In Experiment 3, when total reinforcement was equated, resistance to disruption was similar across components. Thus, the level and slope of forgetting functions depended on differential reinforcement correlated with the samples, but the resistance to change of forgetting functions depended on total reinforcement in a component. Both aspects of the results can be explained by a model of delayed matching to sample performance. Keywords: delayed matching to sample, differential outcome effect, probability of reinforcement, resistance to change, pigeons

Byline: R. Tabassum, S. Hussain, H. Kali and S. Abbas ABSTRACT An experiment was carried out to estimate the effect of different energy levels of diets on weight of body [...]

Microbiological characterization of the bacteriocyte-associated symbiotic bacterium in slender pigeon louse, Columbicola columbae is presented using molecular phylogenetic analyses and histological techniques.

Sexual size dimorphism is a conspicuous trait of many wild bird species. Differences in body size between the sexes might reflect selective pressures and trade-offs to optimize performance. Here, we analyze the size dimorphism of the Galapagos Dove (Zenaida galapagoensis) using principal component and discriminant analyses with samples obtained from six islands: Santiago, Santa Fe, Santa Cruz, Espanola, Genovesa, and Wolf. We also reanalyze published morphological data but also including additional samples from Wolf Island to account for morphological differences among islands. Males were significantly larger than females. Discriminant analyses correctly classified 98% of males and 100% of females, and cross-validation of the model correctly classified 97% of males and 98% of females. We created two sexual size dimorphism indices using wing chord and tarsus as body-size surrogates. Significant differences were found in the sexual size dimorphism index for both measurements among islands. Significant differences in sexual size dimorphism among islands might indicate the role of different selective pressures acting on individual islands (e.g., competition, predation, resources, sexual selection), which might result in life history variation of the species among islands. For the first time, we provide significant morphological evidence supporting the classification of the Galipagos Dove into two subspecies: Z. g. galapagoensis and Z. g. exsul. Key words: Galapagos, morphology, sexual size dimorphism. Zenaida galapagoensis. El dimorfismo sexual de tamano es una caracteristica comun de muchas especies de aves. Las diferencias en el tamano corporal entre machos y hembras puede reflejar la accion de factores de seleccion y soluciones de costo-beneficio que actuan para optimizar el rendimiento de las aves en su ambiente. Analizamos el dimorfismo de tamano de Zenaida galapagoensis por medio de anilisis de componentes principales y anilisis de discriminacion utilizando muestras colectadas en seis islas: Santiago, Santa Fe, Santa Cruz, Espanola, Genovesa y Wolf. Tambien reanalizamos informacion morfologica previamente publicada, en donde incluimos muestras provenientes de la isla Wolf la cual no estuvo comprendida en el esudio anterior, para analizar diferencias morfologicas entre las islas. Los machos fueron significativamente mas grandes que las hembras. El analisis de discriminacion clasifico correctamente el 98% de los machos y el 100% de las hembras, el analisis de validacion del modelo de discriminacion clasifico correctamente el 97% de los machos y el 98% de las hembras. Creamos un indice de dimorfismo sexual de tamano utilizando la cuerda alar y el tarso como medidas de tamano corporal. Se encontraron diferencias significativas en el dimorfismo sexual de tamano entre algunos pares de islas para ambas medidas. Diferencias significativas en el dimorfismo sexual de tamano pueden indicar la accion de diferentes presiones selectivas en diferentes islas (e.g., competicion, depredacion, recursos, seleccion sexual), lo cual puede crear variaciones en la biologia de la especie entre las distintas islas. Por primera vez, proveemos resultados morfologicos significativos que apoyan la separacion de Z. galapagoensis en dos subespecies: Z. g. galapagoensis y Z. g. exsul.

The present experiments examined whether pigeons can sum symbols that are associated with various temporal consequences in a touch screen apparatus. Pigeons were trained to discriminate between two visual symbols that were associated with 0, 1, 2, 3, 4, or 5 s either of delay to 4 s of hopper access (delay group) or duration of hopper access (reward group). In Experiment 1, the pigeons in both groups learned to select the symbol associated with the more favorable outcome, and they successfully transferred this discrimination to novel symbol pairs. However, when tested with 2 pairs of symbols associated with different summed durations, they responded on the basis of a simple response rule rather than the sum of the symbol pair. In Experiment 2, the reward group was presented with four symbols at once and was allowed to successively choose one symbol at a time. All pigeons chose the symbols in order from largest to smallest. This indicates that pigeons formed an ordered representation of symbols associated with different time intervals, even though they did not sum the symbols. Keywords: pigeons, symbol use, temporal representation, summation, ordinality

Experiment 1 showed that the Hick--Hyman law (W. E. Hick, 1952; R. Hyman, 1953) described the effects of anticipated reinforcement, a form of incentive, on pigeons' (Columba livia) reaction time to respond to a target spatial location. Reaction time was an approximately linear function of amount of information interpreted as probability of reinforcement, implying that pigeons processed incentive at a constant rate. Experiment 2 showed that the Hick--Hyman law described effects of incentive even when it varied from moment to moment in a serial reaction time task similar to that of M. J. Nissen and P. Bullemer (1987), and processing information about target spatial location modulated absolute reaction time and not rate of processing incentive. The results support mental continuity and provide comparative support for the idea of the economics of information in economic theory about the incentive value of information. Keywords: incentive, anticipated reinforcement, Hick--Hyman law, reaction times, pigeons

Absolute pitch (AP) is the ability to classify individual pitches without an external referent. The authors compared results from pigeons (Columba livia, a nonsongbird species) with results (R. Weisman, M. Njegovan, C. Sturdy, L. Phillmore, J. Coyle, & D. Mewhort, 1998) from zebra finches (Taeniopygia guttata, a songbird species) and humans (Homo sapiens) in AP tests that required classification of contiguous tones into 3 or 8 frequency ranges on the basis of correlations between the tones in each frequency range and reward. Pigeons' 3-range discriminations were similar in accuracy to those of zebra finches and humans. In the more challenging 8-range task, pigeons, like zebra finches, discriminated shifts from reward to nonreward from range to range across all 8 ranges, whereas humans discriminated only the 1st and last ranges. Taken together with previous research, the present experiments suggest that birds may have more accurate AP than mammals. Keywords: absolute pitch, comparisons with humans and songbirds, frequency-range discriminations, pigeons, zebra finches

Adult humans (Homo sapiens) and pigeons (Columba livia) were trained to discriminate artificial categories that the authors created by mimicking 2 properties of natural categories. One was a family resemblance relationship: The highly variable exemplars, including those that did not have features in common, were structured by a similarity network with the features correlating to one another in each category. The other was a polymorphous rule: No single feature was essential for distinguishing the categories, and all the features overlapped between the categories. Pigeons learned the categories with ease and then showed a prototype effect in accord with the degrees of family resemblance for novel stimuli. Some evidence was also observed for interactive effects of learning of individual exemplars and feature frequencies. Humans had difficulty in learning the categories. The participants who learned the categories generally responded to novel stimuli in an all-or-none fashion on the basis of their acquired classification decision rules. The processes that underlie the classification performances of the 2 species are discussed. Keywords: adult humans, categorization, decision rule, pigeons, prototype effect

Past evidence that pigeons may adopt a single-code/default strategy to solve duration sample discriminations may be attributable to the similarity between the intertrial interval (ITI) and the retention interval. The present experiments tested whether pigeons would adopt a single-code/default strategy when possible ITI-retention-interval ambiguity was eliminated and sample salience was increased. Previous studies of duration sample discriminations that have purported to show evidence for the use of a single-code/default coding strategy have used durations of 0, 2, and 10 sec (Zentall, Klein, & Singer, 2004). However, the results of Experiment 1 suggest that the use of a 0-sec sample may produce an artifact resulting in inadvertent present/absent sample matching. In Experiment 2, when pigeons were trained with three nonzero duration samples (2, 8, and 32 sec), clear evidence for the use of a single-code/default strategy was found.

We investigated whether pigeons are able to discriminate color photographs of male and female pigeons, using a categorical discrimination procedure. In Experiments 1 and 2B, 10 out of 14 pigeons learned the discrimination. Of these, 5 pigeons showed transfer to novel stimuli, demonstrating the categorical nature of the trained discrimination. Experiment 3 showed that the discriminative behavior was based primarily on the body, as opposed to the head and the neck region. In 1 out of 3 pigeons, the discriminative behavior was maintained by the black-and-white photographs. The results suggest that some pigeons have the ability to discriminate the sex of conspecifics without behavioral cues.

The authors examined how pigeons (Columbia livia) perform on 2-dimensional maze tasks on the LCD monitor and whether the pigeons preplan the solution before starting to solve the maze. After training 4 pigeons to move a red square (the target) to a blue square (the goal) by pecking, the authors exposed them to a variety of detour tasks having lines as a harrier. A preview phase was introduced, during which the pigeons were not allowed to peck at the monitor. Results of a set of experiments suggest that our pigeons successfully learned to solve these tasks, that they came to take an efficient strategy as the barriers became complex, and that they possibly preplan its solution, at least on familiar, well-practiced tasks. Keywords: pigeons, maze, navigation, preplanning Supplemental materials: http://dx.doi.org/10.1037/0735-7036.120.4.358.supp

A study on blind imitation behavior of pigeons based on food reward experiment is presented

Four pigeons were given repeated reversal training and testing with photographs of human faces constituting two categories structured by family resemblances, each consisting of a prototype, good exemplars, and poor exemplars. Each of the good exemplars (AM, BM, and CM) was created by 50% morphing of the prototype (M) and one of the poor exemplars (A, B, and C, respectively) and thus was physically similar to the prototype and to the corresponding poor exemplar. The pigeons were first trained and tested for the formation of two (AM, BM, and CM) classes. Then, the stimulus sets were extended to include (1) M and the poor exemplars that were not physically similar to one another and (2) 50% morphs of the poor exemplars (AB, BC, and CA). In the sequentially introduced training and test phases, we successfully tracked expansion of the functional equivalence classes consisting of exemplars that had little similarity but could be linked together through other members of the class.

Pigeons trained in a conditional discrimination procedure to respond to a visual array made a left or right choice, depending on which of two numbers of elements (i.e., anchor numerosities) the array contained. They were then tested with novel arrays at these anchor numerosities, as well as at interpolated and extrapolated numerosities. Various control conditions showed that the birds' discrimination performance was primarily based on stimulus numerosity, and not on other factors, such as brightness or area. Results from a series of tests, spanning a wide range of numerosities, conformed to scalar principles. Psychometric functions showed superposition, indicating that Weber's law applies to numerosity discrimination. The subjective midpoint between anchor values was at the geometric mean. Variability about this bisection point increased in proportion to the numerical value of the mean.

Success in tasks requiring categorization of pictorial stimuli does not prove that a subject understands what the pictures stand for. The ability to achieve representational insight is by no means a trivial one because it exceeds mere detection of 2-D features present in both the pictorial images and their referents. So far, evidence for such an ability in nonhuman species is weak and inconclusive. Here, the authors report evidence of representational insight in pigeons. After being trained on pictures of incomplete human figures, the birds responded significantly more to pictures of the previously missing parts than to nonrepresentative stimuli, which demonstrates that they actually recognized the pictures' representational content. Keywords: picture-object recognition, categorization, representation, pigeon

Abstract This article deals with the aesthetics of the sounds of ring-necked doves and African ground hornbills among the Wawanji people of the Iringa region in the southern highlands of [...]

A go/no-go procedure was used to train pigeons to discriminate pictures of human faces differing only in shape, with either static images or movies of human faces dynamically rotating in depth. On the basis of experimental findings in humans and some earlier studies on three-dimensional object perception in pigeons, we expected dynamic stimulus presentation to support the pigeon's perception of the complex morphology of a human face. However, the performance of the subjects presented with movies was either worse than (AVI format movies) or did not differ from (uncompressed dynamic presentation) that of the subjects trained with a single or with multiple static images of the faces. Furthermore, generalization tests to other presentation conditions and to novel static views revealed no promoting effect of dynamic training. Except for the subjects trained on multiple static views, performance dropped to chance level with views outside the training range. These results are in contrast to some prior reports from the literature, since they suggest that pigeons, unlike humans, have difficulty using the additional structural information provided by the dynamic presentation and integrating the multiple views into a three-dimensional object.

Initial-link response allocation in concurrent chains becomes less extreme as the absolute duration of the initial links increases (Fantino, 1969). The present study asked whether initial-link duration affected how quickly response allocation reached asymptote (i.e., acquisition of preference). Six pigeons were trained on a concurrent-chains procedure in which the terminal links were fixed-interval (FI) 8 sec FI 16 sec or FI 16 sec FI 8 sec and were reversed every 20 sessions. Across conditions, all possible combinations of transitions between variable-interval (VI) 8-sec (short) and VI 24-sec (long) initial-link schedules were studied. Overall, the rate of acquisition was faster when the durations of the initial links preceding the reversal were short rather than long, and when the durations of the initial links following the reversal were long rather than short. By contrast, initial-link duration had no effect on acquisition or asymptotic measures of temporal control of terminal-link responding. These results support the core principle of delay-reduction theory (Fantino, 1969) that the impact of a conditioned reinforcer varies directly with initial-link duration, but also suggest that temporal learning during the terminal links proceeds independently of initial-link duration.

When Pavlovian stimuli activate representations of food, do these representations resemble memories of food consumed in the recent past or expectancies of food that is imminent? In Experiments 1A and 1B, this question was addressed by training pigeons on a symbolic matching-to-sample task involving different grains as memory cues or as expectancy cues for correct choices. Autoshaping trials involving these same grains were interspersed among matching-to-sample trials, as were test trials involving the substitution of autoshaping stimuli for cues in the matching-to-sample task. Control over choices transferred to autoshaping stimuli in both experiments, suggesting that associatively activated representations of food resemble both memories and expectancies. In Experiment 2, pigeons were trained on a symbolic matching-to-sample task in which food and no-food memory cues (i.e., the samples) were juxtaposed with no-food and food expectancy cues. Subsequently, autoshaping stimuli, which activated representations of food and no food, were substituted for the samples. Choices by the pigeons indicated that associatively activated representations of food-related events resemble expectancies more closely than they do memories.

The adaptive basis of plumage color has received much attention, including the finding that color can reveal information about parasite loads to potential mates. A related possibility, that color may be a direct defense against parasites, has received less attention. Melanin makes feathers tough and more resistant to wear and tear. Melanin may also make feathers more difficult for feather-feeding parasites to eat. We explored the role of melanin as a possible ectoparasite defense using Rock Pigeons (Columba livia) and their feather-feeding lice (lnsecta: Phthiraptera). Rock Pigeons are an ideal species for such work because of the extreme variation in the feathers of different color morphs, ranging from melanin-rich black to melanin-free white individuals. We tested the effect of melanin on lice in several ways. First, we compared the natural louse loads of free-ranging pigeons to see whether the more melanistic color morphs had fewer lice. We also did laboratory assays in which we measured the survival and reproductive success of pigeon lice forced to feed on feathers with different amounts of melanin, and we compared the quantities of feather material consumed by these lice. Finally, we tested the habitat and feeding preferences of lice exposed to feathers with different amounts of melanin. None of our tests revealed any effect of melanin on lice. We conclude that melanin is not, at least in Rock Pigeons, a defense against feather lice. Received 1 September 2004, accepted 26 June 2005. Key words: Columba livia, Columbiformes, ectoparasites, plumage color, preening, Rock Pigeon. La base adaptativa del color del plumaje ha recibido mucha atencion, incluyendo el descubrimiento de que el color puede revelar informacion sobre la carga parasitaria de las potenciales parejas. La posibilidad de que el color pueda ser una defensa directa contra los parasitos ha recibido menos atencion. La melanina hace que las plumas sean duras y mas resistentes al uso y a desgarrarse y tambien puede hacer que las plumas sean mas dificiles de comer para los parasitos que se alimentan de ellas. Exploramos el rol de la melanina como una posible defensa contra los ectoparasitos usando a Columba livia y a los piojos que se alimentan de sus plumas (Insecta: Phthiraptera). C. livia es una especie ideal para este trabajo debido a la variacion extrema del color de las plumas de las distintas formas, que van desde individuos negros ricos en melanina hasta individuos blancos libres de melanina. Evaluamos el efecto de la melanina sobre los piojos de distintas maneras. Primero, comparamos las cargas naturales de piojos de palomas libres para ver si las formas con mas melanina tenian menos piojos. Tambien realizamos ensayos de laboratorio en donde medimos la supervivencia y el exito reproductivo de piojos forzados a alimentarse de plumas con diferentes cantidades de melanina y comparamos las cantidades de material de las plumas consumidas por estos piojos. Finalmente, evaluamos las preferencias de habitat y alimenticias de los piojos expuestos a plumas con diferentes cantidades de melanina. Ninguna de nuestras pruebas revelo un efecto de la melanina sobre los piojos. Concluimos que la melanina no es una defensa contra los piojos de las plumas, al menos en C. livia.

Eight pigeons were trained and tested in a simultaneous same/different task. After pecking an upper picture, they pecked a lower picture to indicate same or a white rectangle to indicate different. Increases in the training set size from 8 to 1,024 items produced improved transfer from 51.3% to 84.6%. This is the first evidence that pigeons can perform a two-item same/different task as accurately with novel items as training items and both above 80% correct. Fixed-set control groups ruled out training time or transfer testing as producing the high level of abstract-concept learning. Comparisons with similar experiments with rhesus and capuchin monkeys showed that the ability to learn the same/different abstract concept was similar but that pigeons require more training exemplars. Keywords: same/different, abstract-concept learning, identity, higher order rule learning, pigeon

We conducted four experiments in order to investigate whether pigeons' responses to a recently attended (i.e., recently pecked) location are inhibited. In Experiments 1 and 2, stimulus displays were similar to those used in studies of inhibition of return (IOR) with humans; responses to cued targets tended to be facilitated rather than inhibited. In Experiments 3 and 4, birds were presented with stimulus displays that mimicked clusters of small grains and were relatively localized, which should have been more appropriate for detecting IOR in pigeons. The results from these experiments again provided evidence for facilitation of responding to cued targets, rather than for IOR.

We explored response rate as a possible mediator of learned stimulus equivalence. Five pigeons were trained to discriminate four clip art pictures presented during a 10-sec discrete-trial fixed interval (FI) schedule: two paired with a one-pellet reinforcer, which supported a low rate of responding, and two paired with a nine-pellet reinforcer, which supported a high rate of responding. After subjects associated one stimulus from each of these pairs with a discriminative choice response, researchers presented two new clip art stimuli during a 10-sec FI: one trained with a differential reinforcement of low rate schedule (DRL) after the FI and the other trained with a differential reinforcement of high rate schedule (DRH) after the FI. Each of the stimuli that were withheld during choice training was later shown to see if the choice responses would transfer to these stimuli. The results suggest that response rate alone does not mediate learned stimulus equivalence.

In two experiments, pigeons' responding on an extraneous task was explicitly reinforced during delayed matching-to-sample trials. In Experiment 1, red or green sample stimuli were followed by retention intervals of 0.2, 1, 4, or 12 sec, during which pecks to a white center key were reinforced with 2.5-sec access to wheat according to extinction, variable-interval 30-sec, and variable-interval 15-sec schedules in different conditions. A proportion of .2, .5, .7, or .9 of subsequent red or green choice responses that matched the sample were reinforced with 3-sec access to wheat. The result was that increasing center key reinforcement, or reducing reinforcer probability, lowered overall accuracy. Initial discriminability fell, but with no change in the rate of forgetting. In Experiment 2, initial discriminability was affected by extraneous reinforcers that were contingent on center key pecking, but not by noncontingent reinforcers. A plausible conclusion is that initial discriminability decreases when reinforcers strengthen competing behaviors.

The potential to augment Breeding Bird Survey, (BBS) Washington Call Count, and Washington and Oregon Mineral-Site were investigated to provide more precise population indices for the Pacific Coast band-tailed pigeon and augment to BBS to index the Interior or 'Four Corners' population. Mineral-site surveys provide the greatest potential to monitor breeding populations and detect short-term trends in the Pacific Coast population.

Using field-implanted subcutaneous radio transmitters, we monitored the breeding biology of White-winged Doves (Zenaida asiatica) in a recently colonized urban area (Waco, Texas). We implanted transmitters in June 2002 (n = 39; 16 males, 23 females) and February and March 2003 (n = 40; 17 males, 17 females, 6 unknown sex), and tracked radio-tagged doves every 3rd day until transmitters no longer functioned (90-120 days). We tracked 26 doves to 36 nests in nine tree species. The maximum number of nesting attempts was four. Nest success of first and second nesting attempts was 62 and 24%, respectively, and overall nest success for both years combined was 52%. Mean nest height as a proportion of tree height ranged from 0.31 to 0.75. Urban White-winged Doves had an extended breeding season; nesting attempts occurred both before and after the traditional dove breeding period in native brush habitats of the lower Rio Grande Valley of Texas. Field-implantation of subcutaneous radio transmitters was a viable technique for monitoring nesting activities of White-winged Doves. Received 20 Art gust 2004, accepted 13 March 2005., Over the last 40 years, the distribution of White-winged Doves (Zenaida asiatica) has undergone substantial change (Schwertner et al. 2002). Until the mid-1970s, the breeding range in Texas was limited [...]

We report the first successful demonstration of a simultaneous, two-item same-different (S/D) discrimination by 6 pigeons, in which nonpictorial color and shape stimuli were used. This study was conducted because the majority of recently successful demonstrations of S/D discrimination in pigeons have employed displays with more than two items. Two pairs of stimulus items were simultaneously presented on a touch screen equipped computer monitor. Pigeons were reinforced for consistently pecking at either the same (i.e., identical) or the different (i.e., nonidentical) pair of items. These pairs were created from combinations of simple colored shapes drawn from a pool of six colors and six shapes. After acquiring the discrimination with item pairs that differed redundantly in both the shape and the color dimensions, the pigeons were tested for transfer to items that varied in only one of these dimensions. Although both dimensions contributed to the discrimination, greater control was exhibited by the color dimension. Most important, the discrimination transferred in tests with novel colored, shaped, and sized items, suggesting that the mechanisms involved were not stimulus specific but were more generalized in nature. These results suggest that the capacity to judge S/D relations is present in pigeons even when only two stimuli are used to implement this contrast.

The effects of identical context on pattern recognition by pigeons for outline drawings of faces were investigated by training pigeons to identify (Experiment 1) and categorize (Experiment 2) these stimuli according to the orientation of the mouth--an upright U shape representing a smiling mouth or an inverted U shape representing a sad mouth. These target stimuli were presented alone (Pair 1), with three dots in a triangular orientation to represent a nose and eyes (Pair 2), and with the face pattern surrounded by an oval (Pair 3). In Experiment 1, the pigeons trained with Pair 1 were most accurate, those trained with Pair 2 were less so, and those trained with Pair 3 failed to acquire the discrimination within eighty 100-trial sessions. The same ordering was found in Experiment 2 for pigeons trained on the three pairs simultaneously. The authors suggest that a contrasting finding in humans, the face superiority effect, might be due to a gain in discriminability resulting from recognition of the pattern as a face. An exemplar model of information processing that excludes linguistic coding accounts for the present results.

Pigeons were trained in a within-subjects design to discriminate durations of a filled interval (2s and 8s of light) and durations of an empty interval (2s and 8s bound by two 500 ms light markers). Filled intervals required a response to one set of comparisons (e.g., blue vs. yellow), whereas empty intervals required a response to a different set of comparisons (e.g., red vs. green). Psychophysical testing indicated that empty intervals were judged to be longer than equivalent durations of a filled interval. This finding was replicated when the anchor durations used during training were changed to 1s and 4s, or 4s and 16s. The difference between the point of subjective equality (PSE) for the empty intervals and the PSE for filled intervals increased as the magnitude of the anchor duration pairs increased. In addition, the difference limens (DL) for empty intervals were smaller than those for filled intervals, and the) also increased as the magnitude of anchor duration pairs increased. An analysis of the Weber fractions (WF; i.e., DL/PSE) provided evidence for superimposition of the empty and filled timing functions across the different sets of anchor durations. These results suggest that the accumulation of subjective time was greater for empty intervals than for filled intervals. Within the framework of scalar timing theory, this difference in timing appeared to be the result of a clock rate difference rather than a switch latency difference.

Pigeons were trained initially with 2- and 8-sec empty or filled intervals as sample stimuli. Interval onset and termination was signaled by 1-sec start and stop markers. Following retention and psychophysical testing, both groups were trained with the alternative type of interval, and the tests were repeated. Group empty-first demonstrated a choose-long effect with both empty and filled intervals. Group filled-first demonstrated a weak (and nonsignificant) choose-short effect with filled intervals and a robust choose-long effect with empty intervals. Both groups tended to time the markers and to add that duration to the sample duration only on filled-interval trials, Initial training with empty intervals alters the way pigeons process temporal information on filled-interval trials, whereas initial training with filled intervals has little effect on the processing of temporal information on empty-interval trials.

Pigeons responded in a serial response time task patterned after that of M. J. Nissen and P. Bullemer (1987) with humans. Experiment 1 produced global facilitation: Response times in repeating lists of locations were faster than when locations were random. Response time to a spatial location was also a function of both that location's 1st- and 2nd-order local predictability, in rough agreement with the Hick-Hyman law, according to which response time is a linear function of amount of information. Experiment 2 showed that both local and global facilitation is limited to moderate response-to-stimulus intervals of about 0.50 to 2.00 s. Experiment 3 showed that response time did not depend on global statistical information. Overall, local and global performances depended on local statistical information, but global performance did not depend on global information. Local facilitation was interpreted in plain English as anticipating.

The bidirectional control procedure was used to determine whether pigeons (Columba livia) would imitate a demonstrator that pushed a sliding screen for food. One group of observers saw a trained demonstrator push a sliding screen door with its beak (imitation group), whereas 2 other groups watched the screen move independently (possibly learning how the environment works) with a conspecific either present (affordance learning with social facilitation) or absent (affordance learning alone). A 4th group could not see the screen being pushed (sound and odor control). Imitation was evidenced by the finding that pigeons that saw a demonstrator push the screen made a higher proportion of matching screen pushes than observers in 2 appropriate control conditions. Further, observers that watched a screen move without a demonstrator present made a significantly higher proportion of matching screen pushes than would be expected by chance. Thus, these pigeons were capable of affordance learning.

Three experiments examined the pigeon's ability to adapt to the specific tasks of identification and categorization of complex visual stimuli by attending to information at different levels of abstraction. In Experiment 1, pigeons were successively trained to discriminate first between pairs of human faces from the same sex and then between male and female faces. A final test revealed that the associations formed in the first training phase did not survive categorization training, indicating that the pigeons used item-specific information to discriminate faces of the same sex, but shifted their attention to category-level information for discriminating between the male and female categories. Two further experiments disproved alternative explanations. The results support the feature-learning account of open-ended categorization in animals.

In Experiment 1, 12 pigeons (Columba livia) were trained on a simultaneous matching-to-sample task with 2 stimuli and then tested with 2 novel stimuli. Half of the birds were trained with a fixed ratio schedule requirement of 1 (FR1) or 20 (FR20) pecks on the sample stimulus. None of the birds showed any evidence of concept-mediated transfer. In Experiment 2, 12 pigeons were trained with 3 stimuli and then tested with the same novel stimuli used in Experiment 1. Half of the birds in each group were trained with either an FR1 or FR20 requirement on the sample stimulus. Two of the FR20 birds showed high levels of transfer to the novel stimuli similar to that of monkeys in a previous study.

In the present experiment, we investigated whether pigeons rely exclusively on elemental information or whether they are also able to exploit configural information in a people-present/people-absent discrimination task. Six pigeons were trained in a go/no-go procedure to discriminate between 800 color photographs characterized by the presence or absence of people. The people-present stimuli were designated as positive, and the people-absent stimuli were designated as negative. After training and a subsequent generalization test, the pigeons were presented with both familiar and novel people-present stimuli containing human figures that were distorted in one of seven different ways. All the pigeons learned the initial discrimination and also showed generalization to novel stimuli. In the subsequent test, performance on all types of distorted stimuli was diminished in comparison with that on the intact original pictures from which they had been derived. At the same time, however, peck rates clearly exceeded the level of responding found for regular people-absent stimuli. This result strongly suggests that responding was controlled by both the constituting target components and their spatial relations and, therefore, points to the dual importance of elemental and configural information.

Pigeons pecked keys on concurrent-chains schedules that provided a variable interval 30-sec schedule in the initial link. One terminal link provided reinforcers in a fixed manner; the other provided reinforcers in a variable manner with the same arithmetic mean as the fixed alternative. In Experiment 1, the terminal links provided fixed and variable interval schedules. In Experiment 2, the terminal links provided reinforcers after a fixed or a variable delay following the response that produced them. In Experiment 1 3, the terminal links provided reinforcers that were fixed or variable in size. Rate of reinforcement was varied by changing the scheduled interreinforcer Interval in the terminal link from 5 to 225 sec. The subjects usually preferred the variable option In Experiments I and 2 but differed in preference in Experiment 3. The preference for variability was usually stronger for lower (longer terminal links) than for higher (shorter terminal links) rates of reinforcement. Preference did not change systematically with time in the session. Some aspects of these results are inconsistent with explanations for the preference for variability in terms of scaling factors, scalar expectancy theory, risk-sensitive models of optimal foraging theory, and habituation to the reinforcer. Initial-link response rates also changed within sessions when the schedules provided high, but not low, rates of reinforcement. Within-session changes in responding were similar for the two initial links. These similarities imply that habituation to the reinforcer is represented differently in theories of choice than are other variables related to reinforcement.

Most species of birds have a uropygial gland, also known as a preen gland, which produces oil that birds spread through their plumage when preening. The plumage of waterfowl deprived of uropygial oil becomes brittle and is subject to breakage. For other groups of birds, however, the importance of preen oil remains unclear. Previous workers have argued that preen oil may serve little or no function in Columbiforms (pigeons and doves). We tested that assertion by removing uropygial glands from Rock Doves (Columba livia) and assessing their plumage condition after several months. The results of that experiment showed significant degradation of plumage in the absence of oil. Our results are the first rigorous demonstration that preen oil is important for plumage condition in nonwaterfowl. We tested one possible function of preen oil--that it has insecticidal properties and that reduction in plumage condition on birds without glands is due to an increase in ectoparasites. We tested that hypothesis for feather-feeding lice (Phthiraptera:Ischnocera) using both in vitro and in vivo experiments. Lice raised in an incubator died more rapidly on feathers with preen oil than on feathers without oil, which suggests that preen oil may help combat lice. However, removal of the preen gland from captive birds had no significant effect on louse loads over the course of a four-month experiment. Although the results of our in vivo experiments suggest that preen oil may not be an important defense against lice, further experiments are needed. We also consider the possibility that preen oil may protect birds against other plumage-degrading organisms, such as bacteria and fungi. Received 25 April 2002, 5 February 2003.

The Puerto Rican Plain Pigeon (Columba inornata wetmorei) was listed as endangered in 1970. Transect-survey and nest-monitoring data were collected to estimate reproductive parameters and to assess effects of weather, food, predation, and habitat. We monitored 377 of 423 nests found in east-central Puerto Rico during February-September 1986-2000. The largest sampling effort was conducted in May-June 1998, and 131 nests were found along 8,460 m, resulting in a nest density (D) of 5.26 per hectare or 356 nesting pairs (N) in the surveyed area (a = 67.7 ha). Nest spatial distribution was highly clumped (b = 3.2) and transect surveys were highly variable (CV = 40%). Thus, 34,000 m needed to be surveyed for a desired coefficient of variation (CV[D]) of 20%. Nest density varied widely during May-June 1986-2000. With a CV about the trend line of 121%, from 18 to 28 years of data would be needed to detect an increase or a decrease (r) of 5-10% in log-transformed nest density estimates through linear regression analysis (alpha = 0.15 and power = 0.80). Whereas food abundance had positive and significant relationships with nest density and number of fledglings produced, predator density had negative and significant relationships with nesting success and the number of fledglings produced. Predation accounted for 79% of nest losses (n = 183). Mayfield's estimates of nesting success averaged 40% and an average of 0.5 fledglings were produced per nesting pair. Because Plain Pigeons are able to produce fledglings from three or more broods per year and have extended nesting seasons (with a nest density peak usually occurring in May-June), we hypothesized that hatch-year and after-hatch-year survival rates of 50-65% and a yearly productivity of 1.4-2.0 fledglings per nesting pair were enough to offset mortality. Our optimism is tempered by the fact that Plain Pigeons have not been reported nesting outside east-central Puerto Rico, where rapid destruction and fragmentation of second-growth forests, catastrophic weather, food availability, nest predation, illegal hunting and poaching of nestlings may interact and cause an irreversible population decline. Managers should focus on conserving and restoring second-growth forest fragments to provide food and cover throughout the year. Additional recommendations are given based on the results of our study, which was part of a larger study of factors affecting the reproduction of columbids on Puerto Rico and its territories. Received 30 October 2001, accepted 17 November 2002.

In 3 experiments, pigeons acquired a discrimination between patterns comprising the same features. Thus vertical green bars beside horizontal red bars might have signaled food, and horizontal green bars beside vertical red bars might have signaled no food. The solution of this discrimination can be explained by assuming each pattern is represented either by a template or by structural features that are sensitive to combinations of color and line orientation. The 1st explanation predicts subjects should react to a training pattern rotated 90[degrees]in the same way as the pattern on which it is based. The 2nd explanation predicts these patterns should be treated as if they signal opposing outcomes. The experiments confirmed the 2nd of these predictions.

The Plain Pigeon (Columba inornata) was listed as endangered in Puerto Rico in 1970. During 1986-1992 and 1997-2001, we collected point transect survey data to estimate density, population size, and rate of change. Density and population size estimates increased between 1986-1992 and 1997 2001. With a mean density of 0.25 ± 0.06 SE individuals/ha and a mean population size in the area of the surveys of 3,746 ± 892 SE individuals during 1997-2001, we believe that the status of the Plain Pigeon is not as precarious as it was during 1986-1992, when mean density was 0.02 ± 0.003 SE individuals/ha and mean population size in the area of the surveys was 218 ± 42 SE individuals. However. Plain Pigeons are not widely distributed and the loss and fragmentation of second growth forests combined with the effects of hurricanes and other factors may cause their extinction. Because Plain Pigeons have a spatially clumped distribution, we recommend sampling at least 1,195 points during peak nesting activity (March through June) throughout the island, with at least 526 points covering areas of abundance in eastcentral Puerto Rico, to monitor population changes and evaluate the effectiveness of management actions. Received 24 June 2002, accepted 11 December 2002., Plain Pigeons (Columba inornata) are endemic to the Greater Antilles, where they are threatened or endangered mainly by habitat loss and hunting (Wiley 1985, Perez-Rivera 1990, Strong and Johnson 2001). [...]

The authors taught pigeons to discriminate displays of 16 identical items from displays of 16 nonidentical items. Unlike most same-different discrimination studies--where only stimulus relations could serve a discriminative function--both the identity of the items and the relations among the items were discriminative features of the displays. The pigeons learned about both stimulus identity and stimulus relations when these 2 sources of information served as redundant, relevant cues. In tests of associative competition, identity cues exerted greater stimulus control than relational cues. These results suggest that the pigeon can respond to both specific stimuli and general relations in the environment.

Hungry pigeons received food periodically, signaled by the onset of a keylight. Key pecks aborted the feeding. Subjects responded for thousands of trials, despite the contingent nonreinforcement, with varying probability as the intertrial interval was varied. Hazard functions showed the dominant tendency to be perseveration in responding and not responding. Once perseveration was accounted for, a linear operator model of associative conditioning further improved predictions. Response rates during trials were correlated with the prior probabilities of a response. Rescaled range analyses showed that the behavioral trajectories were a kind of fractional Brownian motion.