Relative Length of the Intestinal Canal

The Bird Digestive System

The Bird Digestive System

Intestine and Villi

Relative Length of the Intestinal Canal

Intestinal Fold or Loop Types

Intestinal Loops and Fold Characteristics in Bird Groups

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Continued from Intestine and Villi

The capacity of the Intestinal Canal depends upon the nature of the bird's food.  In order to compare its length in different forms we require a unit by which to arrive at its relative proportions.  The length of the whole vertebral column, or even the distance from the tip of the bill to that of the tail, has been frequently used; but this gives only faulty results, since the length of the neck is obviously not correlated with that of the intestine.  Numerous measurements and comparisons led 19th Century naturalist Alfred Newton to adopt as the unit the distance from the first thoracic vertebra (i.e. from the root of the neck) to the anus, and thus the quotient of the absolute length of the intestine from the pylorus to the anus is the relative length of the gut. This relative length is very constant in a species, and was considered to often give results of considerable taxonomic value.

Of course "short-gutted" and "long-gutted" are arbitrary expressions; but, if we assume that a relative length not exceeding 5 indicates a short, and one of more than 8 a long gut, we find that the Intestinal Canal is very short in all purely frugivorous and insectivorous birds, while it is very long in those which live upon fishes, carrion, grain, and grass. It must, however, be remarked that, according to the nature of the food, a short intestinal canal is often compensated by its width either wholly or in part, as of the rectum, or by the presence of large caeca. Consequently all these points had to be considered in using the features of the intestine for taxonomic purposes. Caeteris paribus, the relative length of the canal is as good a character as many others, and occasionally by it alone closely-allied species can be determined. The table below shows the measurements of the intestine in a few forms of Newton's day.  For more information Bronn's Klassen und Ordnungen des Thier-Reichs Vogel,  pages 590-661 and 700, gives the respective measurements of nearly 400 birds.

Absolute Length Length of
of Intestinal Canal.
1 caecum./ Rectum

Absolute Relative
cm.  cm. cm.
Struthio camelus 70  820 1430 20
Casuarius indicus  13  28 180 3-4
Spheniscus minor  2 7 223 16
Anser cinereus, var. dom. 24 18 260 12
Procellaria leachi  0.2 1.5 29 5
Ardea cinerea 0.5 10 212 10
Gallus bankiva, var. dom. 17-20 8-11 136-170 8-10
Syrrhaptes paradoxus  12 10 80 9
Columba Livia, var. dom. 0.8 4 108-132 11-13
Pandion haliaetus  0.3 9 300 18
Astur palumbarius. 0.7 7 108 6
Corythaix persa  0 - 42 3-4
Cypselus apus 0 - 17 3
Corvus corax 1.4 5 120 8
Manucodia atra 0.5 3 29 2-3
Passer domesticus  0.2 2 21 5-6

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