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A while back I came across a couple of papers that statistically looked at bill length (ratio of bill to head) and "loral angle" of SB vs. LB.  While both of these features overlap between the species, the papers showed that if these measurements are at the extremes of the bell curves (i.e. not in the range where the measurements overlap), you can identify the species with high certainty.

The first paper, authored by someone named Pekka Sarvela from Helsinki Finland, did an analysis of bill length.  The second, authored by Cin-Ty Lee (Rice Univ) and Andrew Birch analyzed something they defined as "loral angle".  I have no idea if either paper was refereed and published in a scientific journal.  However, they both seemed to be decent scientific treatments.  ( @Tony Leukering ,  I know you are an ornithologist.  Have you ever come across these analyses?  Are they worthwhile?)

Anyhow, I marked one of the pictures above to show the measurements as defined in the papers.  The bill length ratio A/B looks to be about 1.3.  Per Sarvela's paper, "Dowitcher is with very high certainty (statistically very significant limit) Short-billed, if the ratio is 1.50 or below."  Just to be clear, if the ratio had turned out to be 1.7 as an example, it would be in the overlap range and not useful to ID the bird.

The loral angle as defined by Lee and Birch is shown in red.  I couldn't find a protractor, but if my trig skills are not totally rubbish after all these years, I get a loral angle of about 30 degrees.  Per their paper, 30 degrees is almost certainly a SB.  Again just as an example, if the angle was 20 degrees, it would be in the overlap range and not useful.

The Lee/Birch paper also says SB bills have a slight droop at the tip.  Seems apparent in this pic.  [The Lee/Birch paper also has lots of other field marks, e.g. plumage, body shape, etc.  These are pretty much above my pay grade...]

 

dowitcher.jpg.c4f3cba26ab81dfa2568d897979731e9.jpg

 

 

 

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So are you saying short-billed, long-billed, or short/long-billed?

38 minutes ago, Jim W said:

A while back I came across a couple of papers that statistically looked at bill length (ratio of bill to head) and "loral angle" of SB vs. LB.  While both of these features overlap between the species, the papers showed that if these measurements are at the extremes of the bell curves (i.e. not in the range where the measurements overlap), you can identify the species with high certainty.

The first paper, authored by someone named Pekka Sarvela from Helsinki Finland, did an analysis of bill length.  The second, authored by Cin-Ty Lee (Rice Univ) and Andrew Birch analyzed something they defined as "loral angle".  I have no idea if either paper was refereed and published in a scientific journal.  However, they both seemed to be decent scientific treatments.  ( @Tony Leukering ,  I know you are an ornithologist.  Have you ever come across these analyses?  Are they worthwhile?)

Anyhow, I marked one of the pictures above to show the measurements as defined in the papers.  The bill length ratio A/B looks to be about 1.3.  Per Sarvela's paper, "Dowitcher is with very high certainty (statistically very significant limit) Short-billed, if the ratio is 1.50 or below."  Just to be clear, if the ratio had turned out to be 1.7 as an example, it would be in the overlap range and not useful to ID the bird.

The loral angle as defined by Lee and Birch is shown in red.  I couldn't find a protractor, but if my trig skills are not totally rubbish after all these years, I get a loral angle of about 30 degrees.  Per their paper, 30 degrees is almost certainly a SB.  Again just as an example, if the angle was 20 degrees, it would be in the overlap range and not useful.

The Lee/Birch paper also says SB bills have a slight droop at the tip.  Seems apparent in this pic.  [The Lee/Birch paper also has lots of other field marks, e.g. plumage, body shape, etc.  These are pretty much above my pay grade...]

 

dowitcher.jpg.c4f3cba26ab81dfa2568d897979731e9.jpg

 

 

 

 

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1 hour ago, BirdNrd said:

So are you saying short-billed, long-billed, or short/long-billed?

 

I'm saying the one bird that I marked up has three field marks that strongly point to short-billed.  I'll defer to the experts as to whether they are conclusive.

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