Abstract
In early May, 1952, the author collected six specimens and three eggs of Sterna fuscata on Marcus I. As compared with 22 Bonin, 3 Palau, 10 Riukiu and 4 Formosan specimens, these and four other Marcus specimens were found to be larger in wing length and culmen. The outermost rectrices reach 200mm in one of the specimens and the breast is slightly purer white than in the Bonin or Palau birds. The author followed Peters ('34) in including the Marcus population in oahuensis, the Hawaiian race, which was not available for study and might still be larger. The birds of the other islands were regarded as nubilosa by their smaller size, though the difference might be found in a larger series. For example, a Bonin specimen has outermost rectrices as long as 199mm, but they do not reach 180mm in the Riukiu or Formosan specimens examined.
Three eggs from Marcus I. were found to be quite different from those obtained in the Riukiu (Yaeyama Group) in their reddish wash on the shell and the dense markings as well as in more round shape, contrary to the latter which are creamy as a whole and sparcely marked, being pointed at one end. The breeding season is also earlier in Marcus population as suggested by the dates of collected eggs.
