Date: 2/22/26 11:13 pm From: David McNeely via Inland-nw-birders <inland-nw-birders...> Subject: Re: [inland-NW-birders] Crossbills
The bill curve direction is due to a simple genetic relationship. There is one genetic locus (point on a chromosome where a gene resides) for bill curve direction, and two forms of the gene (two alleles). Right curving of the mandible (lower bill) is dominant. So if a bird with two right curving alleles mates with one with two left curving alleles, 3/4 of the offspring will have right curving bills, while 1/4 have left curving bills. A paper in the Auk explains this, but my browser will not let me copy and paste the url. Google crossbill bill genetics and you will find it.
David McNeely
On Sun, Feb 22, 2026 at 10:44 AM Catherine Temple via Inland-nw-birders < <inland-nw-birders...> wrote:
> Yesterday I saw a pair of red crossbills gathering grit in the road so I > took some lovely photos of them. Later I noticed that each birds bill (a > male and female) curved in a different direction. I know a lot has been > said about the difference in bill size and the different "types" based on > the types of cones they eat. But if the birds are the same species or type > shouldn't the bills curve in the same direction? Or is it common to have > left and right curved bills within the same type? Or is this a difference > between male and female? I'm really curious as this is the first time I've > been able to get close enough to see the differences. I've attached a photo > of the pair. Thanks in advance if you can enlighten me. > Catherine > > > -- > > *Catherine Temple* > > *Pet Portrait and Wildlife Artist* > > *Clarkston, WA.(208) 791-7052* > <ctemple99...> > > www.catherinetemple.com > www.flickr.com/photos/ctemple/ > _______________________________________________ > Inland-nw-birders mailing list > send email to: <Inland-nw-birders...> > manage subscription: > https://mailmanlists.us/mailman/listinfo/inland-nw-birders > _______________________________________________ Inland-nw-birders mailing list send email to: <Inland-nw-birders...> manage subscription: https://mailmanlists.us/mailman/listinfo/inland-nw-birders
