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Ask The Biologist: Why Are Some Fawns Bigger Than Others?

Back To "Ask The Biologist?"QUESTION: My trail camera took this picture on Aug. 29, 2010. I have a series of these photos showing two fawns with spots and two adult does. The large fawn appears as big as the does and is considerably larger than the other fawns in all photos. Any idea why it is so large, or is there something different about it? — Bob Rufo, Woburn, Mass.

Ask The Biologist

ANSWER: My first thought was that the larger fawn might be a buck, as buck fawns tend to be larger than doe fawns. However, in magnifying the image, that doesn’t appear to be the case. The best I can do is speculate based on the image. What I think you are seeing is three generations of the same family.

A doe fawn typically remains with her mother through the fall, winter and early the next spring. The mother will drive off her yearlings shortly before giving birth to new fawns the next spring. However, it is not at all uncommon for the yearling doe to rejoin her mother and her new fawns later in the summer.

This doe group might separate briefly during the rut, but will often join up in the winter and remain together until the following spring. Over time, this cycle creates groups that contain several generations.

In areas of exceptionally good habitat and ample food, it is not uncommon for doe fawns to be bred their first fall. This often occurs during the second rut, a month later than the peak rut, when most adult does are bred. As a result, the younger deer will give birth a month later than the older deer.

It is very likely the adult does in your photo are mother and daughter, and the smaller fawn is the older doe’s granddaughter. Given the size difference, it’s possible the smaller fawn was born to a yearling doe. Or, her mother simply might have mated later than her grandmother. As a result, the smallest fawn was born a month later than her grandmother’s fawn, which would explain the size difference.

