A geometric model for initial orientation errors in pigeon navigation

All mobile animals respond to gradients in signals in their environment, such as light, sound, odours and magnetic and electric fields, but it remains controversial how they might use these signals to navigate over long distances. The Earth's surface is essentially two-dimensional, so two stimuli are needed to act as coordinates for navigation. However, no environmental fields are known to be simple enough to act as perpendicular coordinates on a two-dimensional grid. Here, we propose a model for navigation in which we assume that an animal has a simplified ‘cognitive map’ in which environmental stimuli act as perpendicular coordinates. We then investigate how systematic deviation of the contour lines of the environmental signals from a simple orthogonal arrangement can cause errors in position determination and lead to systematic patterns of directional errors in initial homing directions taken by pigeons. The model reproduces patterns of initial orientation errors seen in previously collected data from homing pigeons, predicts that errors should increase with distance from the loft, and provides a basis for efforts to identify further sources of orientation errors made by homing pigeons.     

Effect of air pollution on olfactory function in residents of Mexico City

To our knowledge there has been no study of the effect of everyday air pollution on olfactory function. It was therefore the aim of this study to compare the olfactory performance of long-term residents of Mexico City, an environment with high air pollution, with the olfactory performance of residents of the Mexican state of Tlaxcala, a region geographically similar to Mexico City but with low air pollution. Healthy volunteers [82 Mexico City subjects (MEX), 86 Tlaxcala subjects (TLX)] 20-63 years of age and balanced for age and gender between the two localities were tested for the perception of the odors of everyday beverages presented in squeeze bottles. When tested with ascending concentrations of stimuli in a three-way oddball paradigm, residents of Tlaxcala detected the odors of instant coffee and of an orange drink at significantly lower concentrations than residents of Mexico City. They also performed significantly better in discriminating between the two similar-smelling Mexican beverages horchata and atole in an oddball test. Significant differences between the two populations in overall olfactory performance were apparent in three of the four age classes (20- to 29-, 30- to 39-, and 40- to 49-year-old subjects) but not in the 50-63 years age class. About 10% of MEX subjects compared to about 2% of TLX subjects were judged to have poor olfactory function; all were from the older age classes (mean age: 48.6 years). Thus, air pollution in Mexico City appears to have a substantial impact on olfactory function even in young and middle-aged residents.     

Flight-induced increase in circulating levels of melatonin in the homing pigeon

• 1.1. Homing pigeons, receiving regular flight-training for participation in racing competitions, were flown from their usual release site, 48 km away from “home”.
• 2.2. On their return “home” within 60–80 min, blood samples for the measurement of melatonin were taken within 1–3 min of arrival.
• 3.3. Post-flight circulating levels of melatonin were found to be about 82% higher than those of the resting control pigeons without any change in plasma osmolality.
• 4.4. This daytime increase in circulating levels of melatonin suggests that melatonin, by virtue of its known hypothermic effect of facilitating peripheral heat dissipation, could prevent excessive flight-induced hyperthermia.
• 5.5. It is also suggested that the flight-induced increase in plasma levels of melatonin is consistent with the known analgesic and metabolic effects of the hormone.

     

Cellular basis for response diversity in the olfactory periphery

An emerging idea in olfaction is that temporal coding of odor specificity can be intrinsic to the primary olfactory receptor neurons (ORNs). As a first step towards understanding whether lobster ORNs are capable of generating odor-specific temporal activity and what mechanisms underlie any such heterogeneity in discharge pattern, we characterized different patterns of activity in lobster ORNs individually and ensemble using patch-clamp recording and calcium imaging. We demonstrate that lobster ORNs show tonic excitation, tonic inhibition, phaso-tonic excitation, and bursting, and that these patterns are faithfully reflected in the calcium signal. We then demonstrate that the various dynamic patterns of response are inherent in the cells, and that this inherent heterogeneity is largely determined by heterogeneity in the underlying intrinsic conductances.     

Detection of changes in atmospheric pressure by the homing pigeon,Columba livia

Summary Homing pigeons were tested for their ability to detect air pressure changes in an otherwise constant environment chamber. Ten of 12 birds tested did respond to the pressure changes. The 50% threshold of detection was 10 mm H₂O or less, which is approximately equivalent to a change in altitude of 10 m or less. Performance was better in a chamber with artificial background noise than in an abnormally quiet chamber.We thank Drs. D. R. Griffin, K. Adler, and J. Hatch for reading and criticizing an early draft of this paper. This work was supported by an NSF Graduate Fellowship to M. Kreithen, a grant from the Cornell Office of Sponsored Research, and NSF Research Grants GB 13046 X and GB 35199 X to W. T. Keeton.     

The ontogeny of the homing pigeon navigational map: evidence for a sensitive learning period

Homing pigeons can learn a navigational map by relying on the heterogeneous distribution of atmospheric odours in the environment. To test whether there might be a sensitive period for learning an olfactory-based navigational map, we maintained a group of young pigeons in an aviary screened from the winds until the age of three to four months post-fledging. Subsequently, the screens were removed and the pigeons were exposed to the winds and the environmental odours they carry for three months. One control group of pigeons was held in a similar aviary but exposed to the winds immediately upon Hedging, while another control group of pigeons was allowed free-flight. When the pigeons from the three groups were released from two distant release sites at about six months of age post-fledging, the two control groups were found to be equally good at orientating and returning home, while the experimental pigeons held in the shielded aviary for the first three months post-fledging were unable to orientate homeward and they were generally unsuccessful in returning home. This result supports the hypothesis that environmental experience during the first three months post-fledging is critical for some aspect of navigational map learning and that navigational map learning displays sensitive period-like properties.     

Degenerative and regenerative processes in the olfactory system of homing pigeons.

Experimental resection of the olfactory nerve in the homing pigeon induces a total degeneration of the nerve and olfactory epithelium. The orthograde degenerative process starts before the retrograde one. Ten days after resection, new neurons begin to differentiate from the basal cells. The axon forms earlier than the distal dendritic process, and the speed of growth increases slowly. The regenerated axons only reach the bulb in the 5th month. Two months after resection the olfactory epithelium is similar to that of the intact control side. The ultrastructural features of the mucosa and olfactory axons are similar to those of normal ones.     

A measurement error model for time-series studies of air pollution and mortality

One barrier to interpreting the observational evidence concerning the adverse health effects of air pollution for public policy purposes is the measurement error inherent in estimates of exposure based on ambient pollutant monitors. Exposure assessment studies have shown that data from monitors at central sites may not adequately represent personal exposure. Thus, the exposure error resulting from using centrally measured data as a surrogate for personal exposure can potentially lead to a bias in estimates of the health effects of air pollution. This paper develops a multi-stage Poisson regression model for evaluating the effects of exposure measurement error on estimates of effects of particulate air pollution on mortality in time-series studies. To implement the model, we have used five validation data sets on personal exposure to PM10. Our goal is to combine data on the associations between ambient concentrations of particulate matter and mortality for a specific location, with the validation data on the association between ambient and personal concentrations of particulate matter at the locations where data have been collected. We use these data in a model to estimate the relative risk of mortality associated with estimated personal-exposure concentrations and make a comparison with the risk of mortality estimated with measurements of ambient concentration alone. We apply this method to data comprising daily mortality counts, ambient concentrations of PM10measured at a central site, and temperature for Baltimore, Maryland from 1987 to 1994. We have selected our home city of Baltimore to illustrate the method; the measurement error correction model is general and can be applied to other appropriate locations.Our approach uses a combination of: (1) a generalized additive model with log link and Poisson error for the mortality-personal-exposure association; (2) a multi-stage linear model to estimate the variability across the five validation data sets in the personal-ambient-exposure association; (3) data augmentation methods to address the uncertainty resulting from the missing personal exposure time series in Baltimore. In the Poisson regression model, we account for smooth seasonal and annual trends in mortality using smoothing splines. Taking into account the heterogeneity across locations in the personal-ambient-exposure relationship, we quantify the degree to which the exposure measurement error biases the results toward the null hypothesis of no effect, and estimate the loss of precision in the estimated health effects due to indirectly estimating personal exposures from ambient measurements.     

Molecular biological approaches to the olfactory system: olfactory marker protein as a model

Detailed exploration of the chemistry of proteins and nucleicacids and of the mechanisms regulating gene expression havebecome commonplace with the advent of recent advances in molecularbiology. The olfactory system is an attractive model in whichto study a wide variety of cellular- and neurobiological questions.Thus, the application to this system of molecular biologicaltechniques should open wide areas for study. Our initial effortshave been directed at the olfactory marker protein (OMP). Wehave determined almost the complete amino acid sequence, isolated,characterized and sized the mRNA and demonstrated its translationin vitro. In addition, cloning of the cDNA for this proteinis underway. In this paper we present an overview of our initialefforts in the use of this technology as well as some indicationof the results which may be expected from its application inthe future.     

Neurodevelopmental involvement in schizophrenia: the olfactory epithelium as an alternative model for research

It has been suggested that disturbances during neurodevelopment may play a crucial role in the etiology of schizophrenia (SZ). This premise is supported by brain imaging, epidemiological, and pathological studies as well as the discovery of susceptibility genes for SZ that appear to be implicated in development of the central nervous system. Here, we discuss the limitations of the current methods and models for studying the neurodevelopmental implications in SZ. We agree with the proposal that the olfactory epithelium, in which neurodevelopment continues throughout life, might represent an alternative model for understanding the pathophysiology of the disorder.     

Patterns of understory diversity in mixed coniferous forests of southern California impacted by air pollution

The forests of the San Bernardino Mountains have been subject to ozone and nitrogen (N) deposition for some 60 years. Much work has been done to assess the impacts of these pollutants on trees, but little is known about how the diverse understory flora has fared. Understory vegetation has declined in diversity in response to elevated N in the eastern U.S. and Europe. Six sites along an ozone and N deposition gradient that had been part of a long-term study on response of plants to air pollution beginning in 1973 were resampled in 2003. Historic ozone data and leaf injury scores confirmed the gradient. Present-day ozone levels were almost half of these, and recent atmospheric N pollution concentrations confirmed the continued air pollution gradient. Both total and extractable soil N were higher in sites on the western end of the gradient closer to the urban source of pollution, pH was lower, and soil carbon (C) and litter were higher. The gradient also had decreasing precipitation and increasing elevation from west to east. However, the dominant tree species were the same across the gradient. Tree basal area increased during the 30-year interval in five of the sites. The two westernmost sites had 30-45% cover divided equally between native and exotic understory herbaceous species, while the other sites had only 3-13% cover dominated by native species. The high production is likely related to higher precipitation at the western sites as well as elevated N. The species richness was in the range of 24 to 30 in four of the sites, but one site of intermediate N deposition had 42 species, while the easternmost, least polluted site had 57 species. These were primarily native species, as no site had more than one to three exotic species. In three of six sites, 20-40% of species were lost between 1973 and 2003, including the two westernmost sites. Two sites with intermediate pollution had little change in total species number over 30 years, and the easternmost site had more species in 2003. The easternmost site is also the driest and has the most sunlight filtering to the forest floor, possibly accounting for the higher species richness. The confounding effects of the precipitation gradient and possibly local disturbances do not show a simple correlation of air pollution with patterns of native and invasive species cover and richness. Nevertheless, the decline of native species and dominance by exotic species in the two westernmost polluted sites is cause for concern that air pollution is affecting the understory vegetation adversely.