Feather sequence studies

Future progress will most likely depend on further correlation between evidence from electron microscopy. X-ray diffraction, sequence analysis, and solution studies. A promising line of investigation is the study of the fibrous material regenerated from solutions of feather proteins (Woodin, 1956 Fraser and MacRae, 1959, 1963 Filshie et al., 1964). An example of fibrils obtained in this way is shown in Fig. 16. 

Hg levels in birds have been smdied more often than levels in reptiles and mammals. The only published study that deals with the Hg distribution in tissues of birds from Mexico compared levels between migratory and resident avifauna. For resident birds, the sequence of Hg concentrations detected in different tissues was as follows liver > feathers > heart > muscle > viscera. For migratory birds, the descending order of Hg levels was feathers > liver > muscle > heart > viscera. The highest values for Hg in the liver (5.08 pg g dry wt) were recorded in the olivaceous cormorant (Phalacrocorax olivaceus) the highest Hg concentration in feathers (3.57 pg g" dry wt) was detected in the American avocet (Recurvirostra ameri-cana). It has been established that Hg levels of 5.0 pg g dry wt in feathers may cause adverse reproductive effects (Eisler 1987). Liver levels above 3.0 pg g dry wt may cause sublethal effects to these birds (Hui et al. 2(X)1). 

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