Remsen, J.V. 1975 Bewick's Swan Olor bewicki Jan. 15 ventral view of lower mandible (cont) it was not clear if this yellow streak was actually that bright yellow or slightly tinged pink Associating with the Bewick's was a peculiar imm. bird with a large, fairly sharply defined whitish patch at the base of the upper mandible in same position as the yellow on the Bewick's, but not nearly as extensive. Perhaps a 2nd winter Bewick's? De- definitely different from any Whistling Swan I'd ever seen. possible 2nd. winter Bewick's Swan or Bewick's X Whistling Also present were two adult birds which may have been hybrids - they had yellow patches on the upper mandible intermediate between the fine streak of Whistling and the large patches of the Bewick's. Could this one Bewick's have been breeding for several years with the same population of Whistlings or is this the expression of some former genetic contact between Bewick's and Whistlings? I could conceive of a situation in which one wayward Bewick's Swan intermingles with a local population of Whistlings and breeds with them