The following is my translation of an article called: Das spezifische Gewicht der Vögel, Käfer und Schmetterlinge von Ingenieur Bruno Rheinisch. It appeared in a German popular science magazine, Kosmos Handweiser für Naturfreunde 1910, Heft 7, Seiten 261-262. I'm not aware of any previous translation.
Trevor Dykes.

The specific weights of the birds, beetles and butterflies by Engineer Bruno Rheinisch
It was some 9 years ago (1899) when, in Hamburg-Ottensen, I began with my first investigations into the specific weight of bird bodies, and I spoke with the Curator of the Zoological Garden about my intentions, and he gave me the address of a famous ornithologist in Switzerland. The student of birds informed me that he was delighted that this question had finally found interest, but he was unable to help with any numbers, as he only knew of enquiries on wild birds performed for very informal purposes.

As more exotic material was unavailable, I limited myself to calculating the specific weight of a pigeon and a yellowhammer.

The pigeon had a body volume of about 0.5 cubic dcm = 0.5 litres. The absolute weight turned out to be 0.325kg, and so the specific weight was 0.325 / 0.5 = 0.65 for a pigeon.

Whether this value should be termed small or large can only be judged in comparison to a further value.

My own body then weighed 70kg. Measurement of displaced water from a bath tub revealed a volume of about 63 cubic dcm. This meant my body had a specific weight of S = 70 : 63 = 1.1.

As far as the specific weight goes, the human body would be nearly twice as heavy as that of a pigeon.

The specific weight of atmospheric air compared to that of water has been calculated as S = 0.00129. In accordance with this, the human body would be about 1,000 times heavier than the same volume of air, and the bird body examined about 500 times heavier as a similar volume of air.

With later comparisons of wing size relative to body size of butterflies, I also examined the conditions for beetles and, specifically, the ladybird, as this species was most readily available. This led me to also establishing a specific weight for the ladybird.

The absolute weight was found to be 0.5g and the volume was 1.25 cubic dcm; and this gives a specific weight of S = 0.4.

Calculating the specific weight of butterflies was not part of my intention. This was partly due to the difficulties in obtaining enough large specimens, but also because of the difficulty of assessing the volume. However, chance helped me in the shape of a caterpillar of a Privet hawk moth. This had hatched in its prison and fell into my hands as a suitable research object in May 1906. The Privet hawk moth caterpillar had an absolute weight of 3g and a volume of 4 cubic dcm, S = about 0.75. At the end of May, the Hawk moth crept out weighing 2g with a volume of around 3.5 cubic dcm. This gave S = 0.57.

The results in summary:

Pigeon	S = 0.65
Ladybird	S = 0.4
Privet hawk moth	S = 0.57

These produce an average of about S = 0.54. When it is taken into account that, if a better set of scales for letters were available, then it could be said that bird, beetle and butterfly appear to have a certain affinity of specific weight.

Is this the case for all birds, or significant differences detectable when it comes especially to birds? Certainly, it seems likely that, should one consider lightly built birds, eg. the swallows, then a specific weight of S = 0.35 may be found, whereas the domestic chicken and partridge, which can only reach low heights with much difficulty, could show S = 0.7 and more. The yellowhammer that I caught weighed 27g and had a body content of some 48 cubic dcm. That provided a specific weight of about 27 : 48 = S = 0.56, a value which is near to the average of S = 0.54. It would be of interest to me to hear whether others have undertaken investigations of this nature.

An index of more of my translations of old Kosmos articles can be found at:

Kosmos Translations Archive

A number of Mesozoic (and post-Mesozoic) location summaries can be found at Localities.