Conditioning the pecking motions of pigeons

The spatio-temporal courses of head and neck motions of pigeons while pecking at small grains are described. Single and serial pecks are distinguished but the inter- and intraindividual variability of the peck kinetics is stressed. Pigeons were then trained with instrumental conditioning procedures to speed-up their pecking. A partial reinforcement schedule where pigeons had to peck repeatedly before receiving reward led to a mild shortening of inter-peck intervals at lower reinforcement rates but surprisingly, a lengthening at higher rates. A schedule where short inter-peck intervals were differentially rewarded yielded a pronounced abbreviation of the inter-peck intervals, but this was achieved by a reduction of the movement path rather than an increase in motion velocity. A schedule whereby increased approach velocities were differentially rewarded yielded marked movement accelerations. When pigeons were rewarded for diminished approach speeds they also showed significant movement decelerations. Finally, it is shown that pigeons could learn to reliably abort their peck approach movement when a visual stimulus signalling a penalty was occasionally presented during the approach movement. The proportion of successful peck interruptions decreased as these interruption signals occurred later during the approach phase. It is concluded that the pecking of pigeons is neither an innately fixed nor a visually ballistic movement. It is instead a multiply controlled and flexibly adaptable response pattern.     

Orientation of anosmatic pigeons

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

Transverse patterning in pigeons

The ability of pigeons to form configural stimulus representations was assessed in two operant discrimination experiments. In Experiment 1 the transverse patterning problem of Spence (1952) was trained. In Phase 1, subjects had to choose stimulus A on A + B — trials; B + C — trials were added in Phase 2. In Phase 3, the first two pairs were combined with C + A — trials. The success of the subjects was simulated by a model assuming that elemental and configural stimulus representations coexist in a stable proportion, even in the phases of the experiment which do not require configural stimulus representations for successful solution. Experiment 2 replicated the first two phases of Experiment 1, but trained A + C — in Phase 3. Comparison of the results of this experiment with simulations of the model showed that elemental and configural stimulus representations coexisted in similar proportions as in Experiment 1, even though they were not necessary for successful task solution.     

Regulation of the hypothalamic-pituitary-adrenal axis in free-living pigeons

We studied feral free-living pigeons (Columba livia) to determine whether either unstressed or stress-induced corticosterone release was altered during a prebasic molt. The pigeons were at various stages of molt throughout the study, but corticosterone responses in molting and nonmolting birds did not differ. This was further reflected in equivalent adrenal responses to exogenous adrenocorticotropic hormone (ACTH), suggesting equivalent steroidogenic capacity of adrenal tissues during both physiological states. There was a slight change, however, in pituitary regulation during molt. Whereas exogenous arginine vasotocin (AVT) elevated corticosterone levels in nonmolting birds, during molt an equivalent dose of AVT was ineffective, suggesting that the pituitary is less sensitive to an AVT signal during molt. AVT also appears to be more effective than corticotropin-releasing factor at eliciting ACTH release in pigeons. Overall, these data indicate that pigeons regulate their corticosterone release differently during molt than other avian species studied to date.     

Echoic memory in pigeons

It is unknown whether birds are able to retain the memory of purely sensory auditory information such as white noise over an extended period of time. In a Pavlovian heart rate conditioning paradigm, four pigeons were trained to associate a mild electric shock with periodic random waveforms, and no shock with aperiodic noise. Periodic waveform detection requires echoic memory, i.e., the online retention of a waveform pattern over a limited time. Starting with 40ms, the waveform period was increased after successful learning until no significant stimulus discrimination could be found. Significant discrimination was achieved at periods of up to 2560ms. This is the first demonstration that echoic memory performance in birds is clearly superior to cats and gerbils, and comparable to naive human performance.     

Iron metabolism in pigeons.

Several haematological parameters such as haemoglobin concentration, haematocrit, erythrocyte number, reticulocyte concentration, plasma iron and total iron binding capacity were determined in 118 urban pigeons of both sexes. No statistically significant sex differences among these parameters were found. In 36 specimens (23 males and 13 females), the plasma iron turnover was determined using 59Fe. The results obtained in this species, expressed per 100 ml-1 blood. day-1 and Kg-1 body weight. day-1, were compared with those of turkeys, ducks and chickens calculated from earlier papers. The highest values versus body weight were observed in pigeons. Organ (liver, spleen, tibia, heart, leg muscle, ribs, sternal keel, gonads and blood) distribution of 59Fe intravenous injection was analyzed during a period from 5 min up to 120 days (19 different times) in groups of 4 pigeons. At the 6 h period, the organs retained the highest dose (20% of total Fe injected), but by the 2nd day period, the radioiron in the blood represented about 98% of the total injected. A fast iron uptake by the circulatory blood was checked and compared with that of other species (domestic fowl, ducks and turkeys). The reticulocyte count in pigeons normally ranged from 4 to 12%, which was consistent with these results. A linear decreasing radioactivity in blood, with an inflexion point on the 40th day was observed. An inverse correspondence between blood and liver was found. Content in other organs decreased uniformly with time, except the heart where the iron content was practically constant during the whole time. Ribs and sternal keel are erythropoietic organs in young pigeons.     

Visual stimulus compounding with pigeons

Eight pigeons responded to successively presented color and line stimuli correlated with different likelihoods of reinforcement (100, 50 and 10%). An intertriai interval was included during training for half of the birds. In Experiment 1, tests with superimposed compounds resulted in variable responding, but overall, rates of responding were intermediate to the rates controlled by the individual component stimuli. In Experiments 2a and 2b, tests with compounds of spatially separated stimuli yielded rates of responding that were intermediate to, and in some cases lower than, responding controlled by the individual component stimuli. These results suggest limitations to the generality of additive models of stimulus compounding when visual stimulus combinations are employed.     

Response of the hypothalamo-corticotropic system to metyrapone in pigeons

Chronic catheterization and miniature recording device allowed plasma corticosterone (B) and hypothalamic multiunit activity (MUA) to be simultaneously obtained from freely behaving, awake pigeons, before and for 4 hrs after intravenous injection of metyrapone. Injection of vehicle (tartric acid : 100 mg/4 ml/kg) led to MUA and B profiles quite similar to stress-induced responses, i.e., a rapid and sustained rebounding increase in hypothalamic firing rate and, shifted by 5-10 min, in plasma B. These responses were progressively attenuating for 90-120 mn. Metyrapone administration induced first a rapid and short MUA and B increase. Then both parameters drastically decreased near zero for about 2 hrs and were slowly restored to initial values within 3-4 hrs. It is suggested that metyrapone treatment inhibited both peripheral (B synthesis) and central (hypothalamic neurons) levels of the corticotropic axis.