A comparative study on the chemical consitutions of some bird eggs and the adaptive significance

Abstract

1. With the interest to find out the adaptive influence of ecological factors to be reflected in the egg constitution, the eggs of a few species of herons, sea birds as well as some domesticated birds were compared (also referring the known data given by Romanoffs 1949).
2. Chemical constitution was analysed at Japan Oil and Vitamin Inspection Institute, Tokyo.
3. Eggs of wild birds used were those of the following species: Egretta garzetta and Nycticorax nycticorax (Shinhama colony, Chiba), Larus crassirostris, Uria aalge and Cerorhinca monocerata (Teuri I., Hokkaido) and Calonectris leucomelas (Toshima, Izu Is. Eggs of this species of great interest (Nice 1962) were unfortunately too advanced for chemical analysis).
4. A devise for field egg-inspection by means of a long-type cup (of ice-cream) lined inside with silver paper (for strong light reflection), a flashlight (electric torch) and black cloth to work under, is described and by this test the fresh unincubated eggs could be selected. For inspection of thick and colored shelled eggs perfect darkness was necessary.
5. Yolk color difference was noticed between Sooty Tern (orange) and Noddy (yellow) (Marcus I., Kuroda 1954), among Larus crassirostris (orange), Uria aalge, Synthliboramphus Cerorhinca (yellow) and Cepphus carbo (orange) breeding on Teuri I., and Calonectris (yellow) of Toshima, and between Egretta garzetta (red) and Nycticorax (yellow) of a same colony. It was suggested that fish eaters have yellow yolks, while crustacean food seems to be responsible for orange or even red yolk according to the amount ingested. However, difference in Sooty Tern and Noddy, both eating squids there, might have involved some other genetic factor.
6. The relative yolk weight % for entire egg and egg white is higher in precocial than in altricial birds and in smaller than in larger eggs of the birds of same habit (Romanoffs). The present data support this: the yolk % was low in altricial (semi-altricial by Nice) herons and intermediate in semi-precocial gull, murre and the puffin (Cerorhinca). But, the yolk amount relative to albumen was greater in larger goose eggs than in smaller duck eggs and in larger murre eggs than in smaller puffin eggs. This may reflect the stronger conditions at hatching of goose and murre chicks compared with those of duck and puffin respectively.
7. The shell weight % for entire egg is larger in precocial than altricial, and in larger than smaller birds. The shell is thicker in precocial birds, because chicks hatch in stronger condition (Romanoffs). The thick-shelled Guinea Fowl egg should reflect the adaptation of heat prevention devise for they are laid on tropical dryland, while the shell thickness is adaptively different by the murre populations breeding on rough or smooth rocks (Kartaschew) and the eggs of Teuri population belonged to the thick-shelled type; thickest at the pointed end on which the egg rolls.
8. The amount of water is higher in the eggs of altricial than precocial birds (least so in ducks and geese (Romanoffs)), in which the solid portion is greater. The present data on heron eggs coincided with the reported amount of altricial song birds and pigeons. In the semi-precocial gull and alcids, eggs had precocial type amount of yolk water and rather altricial type amount of egg white water (if Romanoffs' data are referred), thus being intermediate as a whole.
9. The thin-shelled heron eggs were decomposed so soon as three days after having been kept in normal refrigerater. Gull and murre eggs were not affected after 53 days kept in refrigerator, while after 89 days the larger murre egg with extremely thick shell still remained in good shape inspite of the gull egg had been entirely decomposed by this time.