Nesting behaviour influences species-specific gas exchange across avian eggshells

Carefully controlled gas exchange across the eggshell is essential for the development of the avian embryo. Water vapour conductance (GH2O) across the shell, typically measured as mass loss during incubation, has been demonstrated to optimally ensure the healthy development of the embryo while avoiding desiccation. Accordingly, eggs exposed to sub-optimal gas exchange have reduced hatching success. We tested the association between eggshell GH2O and putative life-history correlates of adult birds, ecological nest parameters and physical characteristics of the egg itself to investigate how variation in GH2O has evolved to maintain optimal water loss across a diverse set of nest environments. We measured gas exchange through eggshell fragments in 151 British breeding bird species and fitted phylogenetically controlled, general linear models to test the relationship between GH2O and potential predictor parameters of each species. Of our 17 life-history traits, only two were retained in the final model: wet-incubating parent and nest type. Eggs of species where the parent habitually returned to the nest with wet plumage had significantly higher GH2O than those of parents that returned to the nest with dry plumage. Eggs of species nesting in ground burrows, cliffs and arboreal cups had significantly higher GH2O than those of species nesting on the ground in open nests or cups, in tree cavities and in shallow arboreal nests. Phylogenetic signal (measured as Pagel's λ) was intermediate in magnitude, suggesting that differences observed in the GH2O are dependent upon a combination of shared ancestry and species-specific life history and ecological traits. Although these data are correlational by nature, they are consistent with the hypothesis that parents constrained to return to the nest with wet plumage will increase the humidity of the nest environment, and the eggs of these species have evolved a higher GH2O to overcome this constraint and still achieve optimal water loss during incubation. We also suggest that eggs laid in cup nests and burrows may require a higher GH2O to overcome the increased humidity as a result from the confined nest microclimate lacking air movements through the nest. Taken together, these comparative data imply that species-specific levels of gas exchange across avian eggshells are variable and evolve in response to ecological and physical variation resulting from parental and nesting behaviours

Computer Assisted Interpretation of Multi-channel Airborne Electromagnetic Measurements

This paper was published in Geophysics, 38, No. 6, December, 1973. This paper appeared as Research in Applied Geophysics as Report No. 3, Geophysics Laboratory, University of Toronto.Recent improvements of the INPUT airborne electromagnetic system have made possible a more quantitative approach to interpretation. The necessary interpretational aids can be obtained in two ways: either by correlating the system and ground EM measurements, or by devising computational or analog quantitative models. Both approaches have been explored. In the former, the system decay rate can be correlated with the apparent conductivity‐thickness (σt) estimated by ground surveys. In the latter, four quantitative models were investigated, vertical half‐plane, vertical ribbon, dipping half‐plane, and homogeneous half‐space. Nomograms have been constructed which make it possible to determine σt, conductor depth, and dip for sheet‐like conductors, and conductivity for a homogeneous half‐space. Field examples show that this procedure can be used satisfactorily in the routine interpretation of records obtained by this system

Computer Anomaly Recognition and Classification

This paper was presented at the 40th Annual Meeting of the Society of Exploration Geophysicists in New Orleans, on November 11, 1970 (Mining Session, paper M-20). This paper appeared as Research in Applied Geophysics as Report no. 1, Geophysics Laboratory, University of Toronto.A study has been made of computer methods of anomaly recognition and classification, suitable for application in multichannel airborne electromagnetic methods. Synthetic and real data from the Barringer INPUT System have been used in all experiments. A variety of processing methods, including multichannel Fourier filtering, have been tried with varying success. The best procedure found so far involves the following steps. First, the profiles are scanned to find local maxima, which may indicate an anomaly. Then the width and area of these tentative anomalies are estimated and unimportant peaks discarded. This process can be done on each channel separately, or on a summation profile, where each point is a weighted sum of the corresponding points on the six channels. The decay rate of anomaly amplitude from channel 1 to 6 is next determined by fitting an exponential to the six values. The ratio, sum of the six traces divided by the decay rate, seems to be a food indication of the conductor quality and importance. Theoretically, the dependence of the INPUT data on flight altitude depends on anomaly decay rate, and therefore one can only introduce flight height correction to the anomaly amplitude at this point. However, it might be more convenient to introduce a constant third power correction as the first step of the described process. As a final step all parameters are employed in the correlation of several neighboring profiles