1954). Ina paper by Lack and Arn (1947), as reported by Lack, 
1954, on the Alpine Swift (Apus melba) a correlation was drawn 
‘bpetween clutch size and Sinateal rate. 
In summary: both hereditary factors and environmental 
factors influence the clutch size, 
I have spent much time on these events since the sur- 
vival of the egg in the nest is almost completely dependent on 
the success of the parent in displaying the proper behavioral 
responses to various situations, and in coping with her en- 
vironment. Manipulation of these responses can result in 
thwarting of the sustentation of the embryo. We find in the 
field that although adverse weather conditions, wind, rain, 
temperature and humidity may play a part in the success of the 
brood that the parent compensates for most of these impinge- 
ments. Moring and Bryant (1954) submitted domestic chicken eggs 
at various incubation stages to -10°F. temperatures for various 
lengths of time. Prior to the 17th day, a temperature of -10°F, 
for 85 minutes showed very little effect on hatchability. It 
is hard to imagine this situation occurring in the field. 
Romijn and Lokhorst (1955) showed that egg temperature is 
slightly cooler than the environment up to the 10th day of in- 
cubation, and slightly warmer than environmental temperature 
from about the 12th day on. MacMullan and Eberhart (1953) 
working with wild pheasants showed that as the temperature is 
lowered, the endurance of the embryo became shorter; the older 
the embryo, the more vulnerable to exposure it became. These 
authors showed that tolerance to cold in pheasants was very 
great and that embryo mortality in the wild attributable to cold 
is precluded by the attentiveness of the parent. Severe cold 
and rain at the time of hatching, however, is definitely a 
decimating agent. 
Kessler (1960) and Farner (1958) showed that there is 
greater attentive efficiency on the part of the parent as in- 
cubation progresses. Kessler reported that pheasant egg temp-~- 
eratures under the incubating parent did not reach a high point 
until the 12th, 13th, or 14th day. Farner working with the 
Yellow-eyed Penguin (Magadyptes antipodes) observed that the 
temperature of the egg increased from the 2nd to the 15th day. 
This rise in temperature coincided with the vascularization of 
the ventral apterium. He suggests that this relatively long 
warm-up period may play a part in the relatively long incubation 
period of this species. Farner's review of the literature re- 
vealed that this is common in other species. It was shown by 
Holstein (1950), as reported by Farner (1958), that the peak 
temperature in Goshawks (Accipter gentilis) did not come until 
the 22nd day. The Sparrow Hawk (Falco sparverius) has a similar 
warming-up period. Bergmann (1946), also reported by Farner 
(1958) working with turnstones, showed that the temperature in- 
creased from 30°C. to a maximum of 38=@40°9C. by the 18th day. All 
these birds have a relatively long incubation period. 
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