This study was designed to answer the question, "Is there a genetic correlation with population density" An answer to this question was sought by comparing the frequency of a few genetic markers in populations of different density. New biochemical and morphological genetic markers were described. By electrophoresis of samples of blood plasma, two variable zones were found on starch gel stained for serum esterases. The number and position of the bands seen in each of these zones (Rg and Ng) were probably controlled by codominant alleles at an autosomal locus. Genetic variation in the pigmentation of the adults' plumage and the colour of the chicks' down was also found. The frequency of these genetic markers was compared in populations differing in mean territory size, breeding density, brood size, and breeding success. More heterozygote- chicks, lightly coloured chicks, and lightly pigmented adults were found in a population with a higher breeding density, brood size, and breeding success; this suggested that there was a genetic correlation with density between areas Since heterozygotes and light-coloured chicks were also more frequent amongst the larger broods of chicks, there was some evidence that a genetic correlation with breeding density existed both within and between areas. Although the food on these high and low-density populations also differed, the variation in the quality and quantity of food did not consistently explain the variation in the breeding density and breeding success.