SREL Reprint #0014




Weights and Weight Variations in Summer Birds from Georgia and South Carolina


Norris, R. A. and D. W. Johnston


Statistical data are presented on weights of 576 specimens representing 97 species of birds.  All were collected in summer, from 1947 to 1956, in southern Georgia and adjacent parts of South Carolina.  The general procedure and manner of presentation of data are explained.  The data are broken down into three categories:  species, sex, and age (adults versus fully fledged immatures). For each category represented by more than one weight, the mean value with the standard error is given both for weight and for sub-seasonal period of collection.  For more or less fat specimens, semi-quantitative indications of fat condition are provided; these aid in the interpretation of certain weight values.  Data for certain species are subjected to further analysis.  In four species, males are significantly heavier than females; in four others there is no significant difference between the sexes.  By our criterion (the validity of which is discussed), the difference between the means of compared samples, if it is to be regarded as significant, must equal or exceed 7 per cent of the weight of the male, or the difference must show a P-value that is no greater than .10.  Among compared samples, immatures in most instances average slightly heavier than adults.  The coefficients of variability of weight samples, if compared sex for sex, are on the whole significantly higher (P=.10) for immatures than for adults.  This marked variability is due in part (heavily irradiated one) hatched, and two days later both parents were watched as they fed their young.  It was clear that both cared for the young throughout the nestling period.  When I visited the box on June 8 in order to band the nestlings, both the male and female came fairly close and issued scolding notes.  Three days later the young departed from the nest.  Like the bluebirds, the female titmouse showed no signs of radiation sickness.



Norris, R.A. and D.W. Johnston. 1958. Weights and weight variations in summer birds from Georgia and South Carolina. The Wilson Bulletin 70:114-129.



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