Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

The greening of polar bears in zoos


POLAR BEARS (Thalarctos maritimus) normally have creamy-white fur, presumably an adaptation for camouflage in a snowy environment. However, during the summer of 1978, the fur on the back and sides of three adults in the San Diego Zoo turned green, though the animals remained otherwise healthy. (Of these bears, one female was born in the zoo in Calgary, Alberta, Canada, in 1966 and was transferred to the San Diego Zoo in 1969; a second female was born in the wild, having been caught at Spitzbergen in 1951; the third, a male, was born in the San Diego Zoo in 1970.) This phenomenon, though less marked, has been noted in several previous summers, both here and in zoos elsewhere, for example, in Cologne, Germany (C. Hill, personal communication). The coloration was particularly evident on the flanks, on the outer fur of the legs and in a band across the rump: fur on the head and belly and inner sides of the legs was white. We first supposed that the colour was due to green algae such as Chlorella or Scenedesmus on the surfaces of hairs, growth of such algae being promoted by the presence of nitrogenous wastes in the waters of the bears' pool. (The pool in the exhibit area, which contains 12,500 gallons of tap water, is drained and cleaned twice weekly.) However, microscopic examination of samples of hair taken from the three San Diego bears and from a similarly green polar bear in the zoo at Fresno, California, revealed that this was not so. The outer surfaces of the hairs appeared clean and smooth, except for the normal squamation. The coloration was clearly attributable to the presence of algae inside the hairs, specifically in the hollow medullae of many of the wider (50–200 µm), stiffer guard hairs of the outer coat. (The thinner (<20 µm) and more undulant hairs of the under coat, which were not hollow, were colourless.) Some of the lumina were apparently filled with air, but many of these hollow spaces were partly occupied by masses of small greenish cells, which we describe here.

Your institute does not have access to this article

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. Wildman, A. B., The Microscopy of Animal Textile Fibres (Wool Industries Research Association, Leeds, 1954).

    Google Scholar 

  2. Maertens, H. Beitr. Biol. Pfl. 12, 439–496 (1914).

    Google Scholar 

  3. Lewin, R. A. & Cheng, L. Phycologia 14, 149–152 (1975).

    Article  Google Scholar 

  4. Edgren, R. A., Edgren, M. K. & Tiffany, L. H. Ecology 34, 733–740 (1953).

    Article  Google Scholar 

  5. Johnson, B. W. & Johnson, P. A. US Mammal Commission Rep. MMC-77/05 (Washington, DC, 1978).

  6. Scheffer, V. B. Pelage and surface topography of the northern fur seal. North American Fauna No. 64 (1961).

  7. Weber van Bosse, A., Natuurk. Verh. ser 3, 5, 1–23 (1903).

    Google Scholar 

  8. Sanderson, I. T. The Monkey Kingdom: Introduction to the Primates, 19 (Hanover House, New York, 1957).

    Google Scholar 

  9. Nemoto, T. Whales Res. Inst. (Tokyo), Sci. Rep. 11, 99–132 (1956).

    Google Scholar 

Download references

Author information

Authors and Affiliations


Rights and permissions

Reprints and Permissions

About this article

Cite this article

LEWIN, R., ROBINSON, P. The greening of polar bears in zoos. Nature 278, 445–447 (1979).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing