Bill Deformities

I’m seeing more bill deformities “out there” than I used to and that disturbs me.  The latest example was a Sage Thrasher we found on Antelope Island four days ago.   This is what a normal bill on a Sage Thrasher looks like.  Notice that the upper mandible is slightly longer than the lower one with a curved tip at the terminus and that both mandibles fit together tightly showing no evidence of a gap between them.     But in this thrasher the upper mandible is significantly shorter than the lower and the curve of the two mandibles doesn’t match so they don’t fit together well, leaving a gap.  This is definitely not a temporary, voluntary position of the bill as I have about a dozen shots of the bird over a period of about a minute that show the same thing.  The two mandibles never fit together cleanly and the upper one is definitely shorter.     With this head turn you can see the other side.  I can only imagine how this would interfere with normal preening as the bird attempts to draw the individual feathers through the bill to lock the barbs together.     An extreme crop of the previous image.  Notice how the back of the mandibles touch each other and prevent the rest of the bill from coming together because their curves don’t match along the entire length of the bill.  At first I thought that the end of the lower mandible looked damaged or eroded but perhaps there’s just something on the bill that…

Continue reading

Red-winged Blackbird With a Crossed Bill

  This morning while out photographing birds at a local wildlife refuge I came across this Red-winged Blackbird with a strongly crossed bill, which of course is not typical of the species.  I’ve seen a few mildly crossed bills in this and other species in the past but never one quite this pronounced in a species where it isn’t “normal”.   Red-winged Blackbird with a crossed bill, perched on curley dock    There are species of birds in North America that have crossed bills as a species trait – the Red Crossbill and the White-winged Crossbill.  Their crossed bills are an adaptation for extracting seeds from cones.  Seeing this RWBB with a crossed bill naturally got me thinking about evolution.  Variations occur throughout nature since each individual inherits a different combination of genes from its parents.  This  particular variation would likely be selected against in RWBB’s and would not persist since they do not typically pry seeds from cones.  However, one can see how this same variation in the ancestors of todays crossbills would be the genetic fuel for the crossed bill trait they all exhibit today.  Ron  

Continue reading