Nebraska Bird Review 
13 
increments from one day to the next. 
Other characteristics selected as good 
age criteria were tarsus length, 
growth of the spinal tract and 
growth of the femoral tract. Hol¬ 
comb and Twiest (unpub. b) reported 
total length, alar tract projection, 
alar tract growth and spinal tract 
growth as the criteria used to calcu¬ 
late age in Redwings. 
The stepwise-regression was used 
to select from 35 variables those 
which would be suitable for predict¬ 
ing age. The resulting equation was 
Age (in days) = -4.67 + .32 
Tarsus length -f- .11 Total length 
.11 Spinal tract feather length 
-j- .16 Femoral tract feather length. 
The Standard Error of Estimate 
is .49 which means that most pre¬ 
dictions of age will be within one 
day of the correct age. 
If a nestling was found that had a 
tarsus length of 13mm, total length 
of 67mm, spinal feathers 5mm and 
femoral feathers 5mm, the age would 
be: 
Age = -4.67 + .32 (13) + .11 (67) 
+ .11 (5) + .16 (5) = 8.21 days 
Other criteria which may be help¬ 
ful in deciding the correct age would 
be the timing of feather projection 
and fringing. These aid one in de¬ 
ciding the minimum age of a nest¬ 
ling. 
Since the formula is only reliable 
to within one day most of the time, 
one might be able to be more precise 
by looking at Table 4. In this in¬ 
stance, the table would probably only 
verify what we already know; that 
is, if the nestling has the capital 
tract fringing, it is at least seven 
days of age. However, if the capital 
tract was not fringing, it would be 
likely that the formula gave the 
wrong value (for it is accurate most 
of the time) and that the nestling is 
six days of age. 
Another example of age calcula¬ 
tion would be of a nestling with 
values of 9mm and 54mm for the 
tarsus and total length, respective¬ 
ly, and the femoral and spinal tracts 
not projecting. 
Age = -4.67 -|- .32 (9) -f .11 
(54) = 4.15 days 
Table 4 shows that some nestlings 
do have the femoral and spinal tracts 
projecting by day four and most of 
them have them projecting by day 
five. This particular nestling is prob¬ 
ably three or four days of age and 
one could usually eliminate the 
probability of its being five days old. 
On the other hand, if this nestling 
has the ventral tract projecting, it 
is at least four days old and, in¬ 
deed, is probably four days of age. 
The value of this formula is per¬ 
haps more important because it re¬ 
quires only a few measurements that 
can be taken with a small milli¬ 
meter ruler or, preferably, calipers. 
g. Age, appearance and behavior 
of young at fledging. The mean time 
of fledging for 117 Goldfinches was 
12.3 days. They usually left the nest 
a little earlier when there were more 
nestlings in the nest. One left the 
nest between days eight and nine 
from a nest containing six young. 
Five of six young leaving the nest 
between days nine and 10 were from 
nests containing five or six nest¬ 
lings. The only three nestlings leav¬ 
ing between days 15 and 16, were 
from a nest of three. They had been 
in a nest of six and grew slowly 
until two died of starvation (one 
each on days 10 and 12) and an¬ 
other died after falling from the 
nest. 
The range of nestling periods was 
between 8.5 and 15.5 days. Walkin- 
shaw (1939) reported that young 
Goldfinches fledged between the ages 
of 11 and 15 days with a mean of 
12.88 days for 25 birds. He reported 
them often sitting on the rim of the 
nest or nearby branches and flying 
to distances of 100 feet. 
One first-hatched nestling weigh¬ 
ed 9.2 grams on day 11; on the fol- 
