I am looking for recommendations on how to measure bird beak morphology (specifically Passer montanus) such as whether I should simply use calipers or use a computer program.
Also, what is the best morphological feature I can look at to compare the beaks with each other? (e.g. depth, length, etc.)
Lastly, what statistical test would be appropriate to show that there is indeed a significant difference?
Measurement beak significantly different in the various groups birds. Generally accepted to measure several options for beak length. One of the most common is measuring the length of the beak to feathers by using caliper. Thus hold the bird in the hand with the little finger, nameless and middle fingers, and the the thumb and index fix beak (tip). One of calipers pressed to the tip of the beak and hold in this position your thumb and forefinger. Another part touch the tip of the feathers (bill-length to the feather) or nostrils (in the case of measuring the length of the beak to the nostrils (bill-length to the nostrils (nalospi), or to the base of the skull - in the case of measuring the length of the beak to the skull (bill- length to the skull).
Measure the height of the beak is carried out in the widest point closer to the base of the beak. Sometimes the best place one piece calipers in the corners of the lower jaw, and the other as high as possible on the upper jaw.
However, when measuring wedge-shaped beak can be difficult. In many species both parts calipers are placed on one side. In this case, the best measure to take off at an angle of 90˚ to the beak and indicate where in it is made, such as "proximal (ext.) Edge of the nostrils", "feathers", etc. (Svensson, 1992).
The width of the beak
You should avoid soft measuring angles of the beak, and measure its horn part. In carcasses beaks inelastic, so measurements of carcasses and live birds should not be compared. Measurements carried out as the height of the beak - the widest point near the base, placing a sponge calipers on each side (Svensson, 1992).
It depends what kind of samples you have. If you have a 3D scanner then there are programmes which you can use to map the features and compare them.
If you are sampling live birds then I would recommend metal vernier calipers as these will give you the greatest accuracy. Measurements to include would be Bill length ( from the tip of the bill to the skull - just beyond where the feathers end, there are diagrams available online to show this ) and bill depth, depending on species it can vary which measurement you should take, again there are various diagrams online and in bird identification books ( for e.g. Svensson 1992) showing these.
As for the statistics that depends on exactly what kind of questions you are asking but try reading this paper
http://onlinelibrary.wiley.com/doi/10.1046/j.1365-294x.1998.00441.x/epdf
Here are some beak related articles.
http://www.eurekalert.org/pub_releases/2010-02/hu-sme022210.php
http://jacobsschool.ucsd.edu/news_events/releases/release.sfe?id=417
http://phys.org/news/2013-12-functional-importance-dinosaur-beaks.html
http://www.eurekalert.org/pub_releases/2012-04/sicp-mpa040612.php
http://www.scientificamerican.com/article/evolution-of-darwin-s-finches-tracked-at-genetic-level/
https://scienceblog.com/3926/the-birth-of-a-beak/
Regards,
Joachim
http://eprints.whiterose.ac.uk/99452/1/Bright%20et%20al.%202016_SelfArchive.pdf
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