246 Bird - Lore 



The time required for the passage of an egg from the ovary to the exterior is 

 somewhat less than 24 hours, so that, ordinarily, one egg is laid each day at 

 about the same time until the number is complete. With the laying of the last 

 egg, incubation ordinarily begins, though with a few birds like the Owls and 

 Bitterns that are less regular in laying their eggs, incubation sometimes starts 

 sooner and the young do not all hatch at the same time. Obviously this is a 

 disadvantage to the young that hatch late, for it does not give them all an 

 equal chance. The period of incubation varies with the size of the egg, larger 

 eggs ordinarily requiring longer to hatch than smaller ones, though there are 

 some minor exceptions to this rule. Thus, while the Sparrows require but twelve 

 or thirteen days, the Hummingbird requires fourteen or fifteen — as long as 

 the Robin. The Least Bittern requires 18 days, the Ruffed Grouse 21, the 

 Mallard Duck 28, and the Canada Goose about 35 days to hatch. The exact 

 time required is not known for many of our common birds, and this is a place 

 where even the school child can add to our knowledge by watching the progress 

 of the nests which he discovers. Little is known, likewise, concerning the care 

 given to the eggs by many birds, how they are turned and how often, which 

 parents incubate, when each incubates, and for how long. There is scarcely a 

 bird whose nesting activities have been described in detail. Ordinarily, the 

 female does most of the incubating and the male stands guard when she leaves 

 to feed, but occasionally, even in such brightly colored birds as the Rose- 

 breasted Grosbeak, the male seems to share the duties equally, and with the 

 Phalaropes, the female allows the male to assume the entire task. The number 

 of observations that can be made upon a nest that is favorably situated is 

 unlimited and is in itself a sufficient argument against the taking of the eggs 

 for a collection. The eggs themselves are interesting, but what happens to 

 them is still more so. — A. A. A. 



QUESTIONS 



1. What is the best way to identify birds' eggs? 



2. How many different kinds of birds' eggs can you recognize? 



3. Does each family of birds have a type of coloration for the eggs? What is the 

 type for the Thrushes, Sparrows, Warblers, Vireos, Blackbirds, Flycatchers, Crows, 

 Woodpeckers, Kingfishers, Doves, Owls, Herons, Shorebirds? 



4. Do you know of any exceptions to the type in each case? 



5. What birds lay white eggs and why? 



6. What birds lay protectively colored eggs and why? 



7. What birds lay conspicuous eggs and why? 



8. How do you account for the origin of color on birds' eggs? 



9. Is the coloration of each species of birds' eggs constant and how do you account 

 for plain eggs when they ought to be spotted or abnormally marked eggs? 



10. Is the number of eggs laid by each species of bird constant? 



11. What determines the number of eggs that a species lays? 



12. Can the number of eggs which a bird normally lays be increased? 



13. How much variation is there in the shape of birds' eggs and how do you account 

 for their various shapes? 



