White Swan Question (Angela P.)

[Tracey Kast]

>
>Can someone help me answer this question, my e-mail is angnix at gmail.com:
>
>We are on Upper Crooked Lake in Delton, MI and there is a swan family this
>year with 3 babies.  Two babies are grey and the other is white - both
>parent swans are white.  Can you tell me why one is white?  I have a theory
>that one is a different gender than the other two, but would like the real
>answer.

Mute Swan cygnets can indeed come in two color morphs. The gray ones are 
called "Royals" and they are typical to the species. The morph also tends 
to have dark legs/feet. The white morph cygnets are called "Continental" 
and occur mostly in NA and part of Europe (i.e., Poland) and they have 
pinkish legs and feet. Both morphs can be found in one brood, as you have 
noticed. The white morph cygnet is a result of a sex-linked recessive 
"leucistic" form (allele) of the gene.

Since female swans, like other birds, are the heterogametic sex (XO like 
human males (XY) and not like human females (XX), the sex-linked gene will 
show up most frequently in females. So, although not 100%, there is a good 
chance that the white cygnet is a female (in the same way that 
color-blindness shows up more frequently in humans males than females). The 
two gray cygnets could be any gender.

Note: the leg/foot color of cygnet is retained in the adult.

Tracey

***************************************
Tracey L. Kast
Environmental Education Coordinator
W. K. Kellogg Bird Sanctuary
Michigan State University
12685 East C Avenue
Augusta, MI 49012

Phone: (269) 671-2181
Fax: (269) 671-2474  
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