Growth Patterns in a Post-juvenile Population of Short-tailed Shrews (Blarina brevicauda)

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Abstract
Growth patterns in shrews were studied to learn if seasonal fluctuations in size occurred. Over 400 specimens were aged on the basis of tooth wear. When cranial height was analyzed by month of capture, seasonal, cyclic changes were evidenced. Average skull height varied from a maximum in the 1st spring of life, to a minimum during the winter, and then to an intermediate value in the 2nd spring. When the same data were graphed according to age, the magnitude of the fluctuations was decreased by about 50%. The height of the cranial cavity decreased during the 1st 4 months, then remained at a constant level. Parietal bone thickness increased throughout life. Spring-born individuals were larger in the above measurements at any given age than fall-born specimens. The seasonal fluctuations apparent at the population level did not exist at the individual level, and were caused by the interrelated effects of a decreasing cranial cavity, an increasing thickness in the skull bones, and a differential growth rate between spring- and fall-born individuals. Correlations of long bone weight, body length and body weight supported the conclusions drawn from cranial measurements.

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