22 



THE OOLOGIST. 



Devoted to Birds and Birds' Eggs 



THIRD PUBLICATION YEAR. 



S. L. WILLAED, EDITOR, 



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MAY, 1877. 



THREE PAPERS ON THE BREED- 

 ING HABITS OF BIRDS. 



II. VIPOSITION. 



"DEFORE the eggs are laid, the nest is 

 unoccupied for a short time after being 

 finished ; those requiring the most labor and 

 the use of materials which it is necessary 

 should be left to the atmosphere to toughen, 

 are often allowed to remain unoccupied for 

 from one to four or five days. 



With the majority of birds, the deposi- 

 tion begins on the day of the completion of 



the nest. At this stage the temperature of 

 the body of the female increases, and does 

 not attain its maximum heat until incuba- 

 tion is commenced. The period of deposi- 

 tion of the eggs varies with the species, 

 though with most birds they are laid at the 

 rate of one each day until the completion 

 of the set ; other species deposit one egg on 

 each alternate day. Some observers main- 

 tain that with many species considerable 

 reliance may be placed in the weather, as 

 to the frequency of deposition ; in other 

 words, if the weather be dry or moist, warm 

 or cold, the eggs are laid either daily or 

 duo-daily in accordance with the advantage 

 to be derived from certain phases of the 

 weather. However true this may be of 

 some species, it is not applicable to all, as 

 a regularity of deposition occurs with many 

 that nothing less than severe disturbance 

 would affect. A point of some interest is, 

 that, with birds which always lay the same 

 number of eggs in a clutch, the length of 

 time occurring between each deposition is 

 the same, allowing of course room for a 

 few exceptions. For instance, under fa- 

 vorable circumstances the Wood Thrush 

 always lays four eggs ; oviposition with this 

 bird takes place regularly, one egg being 

 laid a day. With many, especially some 

 of the water birds, great irregularity in 

 the number of eggs in a set is observa- 

 ble,, yet as far as can be ascertained, they 

 deposit them with no degree of uniformity 

 as regards frequency. 



When more than one brood is reared in 

 a season by birds which commonly incubate 

 but once, the number of eggs in a clutch 

 generally diminishes with the number of 

 sets laid. Thus, a Wood Thrush will de- 

 posit four eggs at first, while a second lit- 

 ter* may comprise but three, and often a 



*lN his "Birds of Eastern Penn." Mr. Gent- 

 ry states that but a single brood is reared by 

 this bird in a season, and mentions a nest tak- 

 en on the loth of July, as the "labor of birds 

 whose early eftbrts had been frustrated." Cer- 

 tainly the WoodThrusli very frequentlj^ rears 

 two broods in a season, as the circumstance 

 of finding sets of very slightly incubated eggs 

 in nests Avhich gave abundant evidence of 



