INHIBITION OF AVIAN EMBRYO SUSTENTATION 

Raymond P. Coppinger 
Inhibition of avian embryo sustentation does not have 
as strict a demarcation in the annual cycle of the avian species 
as do the other papers presented in this symposium but has an 
overlap into other areas of the behavior and physiology of birds. 
The ultimate success or failure of progeny does not occur ex- 
clusively during that period spanning egg deposition and chick 
emergence from the egg. Therefore, in order to handle the 
sub ject comprehensively, I will consider that period in the 
annual cycle which begins at the time the potential parent is 
ready to take up breeding territory, and ends roughly at the time 
the “embryo" is ready to leave the territory. 
1. External stimuli regulating nesting cycle. 
Although the reproductive activities are triggered 
in the spring, there are many environmental factors that have a 
regulatory effect on the success or failure of the nests. It 
has been confirmed by Wolfson (1959) that the lengthening of the 
light period in the spring initiates the reproductive activities 
and causes and regulates the gametogenesis of many species of 
birds. Marshall (1954) recognizes this light factor but qualifies 
its affect upon the complexity of events in the sexual life of 
the bird. Environmental factors--potential predators, weather, 
food, and the availability of nesting sitesemware a few of the 
factors which regulate, augment, or inhibit the nesting activi- 
ties. Marshall T1954) showed that on Jan Mayan Island, most 
species never successfully nested because of disturbance by the 
fox population. However, even these non-breeding birds went 
through a gametogenic cycle. 
Kluijver (1961) found that a cold spell set back the 
egg production of the Black-capped Chickadee (Parus atricapillus) 
for a week in Massachusetts. Some of these birds had already 
begun to nest, but they ceased laying activity during the cold 
weather; others were suspected to be ready, but postponed laying 
until after the cold period. Kluijver noticed the same thing 
in previous studies,Kluijver (1951), of the Great Tit. Paynter 
(1954) reported that a severe storm caused Tree Swallows 
(Iridoprocne bicolor) to cease laying for a brief period or even 
to abandon nests after an egg had been layed. This does not 
necessarily mean that the swallows did not renest elsewhere. 
In some bird species, ovulation may not take place 
until the traditional food supply becomes abundant, even though 
the birds may be physiologically ready. Marshall (1954) pointed 
out considerable evidence that most bird species breed at the 
height of the protein food supply, requisite for the rapid 
growth characteristic of passerine birds. 
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