Deer Matrilines—What Are They?
Female white-tailed deer are socially organized together into matrilines, that is, groups of deer related through the maternal line that move, feed and remain together, often for years. These matrilines consist of related females of various ages and their offspring that are led by a matriarch, a founding dominant female whose age and experience provides day-to-day guidance to the group.
Deer marked on three areas of Illinois (Brown-Adams, DeKalb and Piatt counties) allowed us to observe the composition of 12 matrilines through time (five for three generations, five for four generations and two for five generations). Each of these matrilines grew within the large home range of a long-lived dominant female.
Each study area offered deer some refuge protection and contributed to the stability of each matriline. We found that these successful matrilines featured: 1) female dispersals and migrations much lower than in the population as a whole; 2) each matriline developed within a large home range that offered succeeding female generations abundant foraging opportunities and numerous sites to give birth in isolation; and 3) some refuge protection from hunters that enabled members to reach maturity.
Adult females that did not succeed in producing a successful matriline failed because: 1) they lost too many female offspring because of high annual dispersals and/or death rates; 2) they produced too many male offspring in succeeding generations; or 3) their home ranges were small in size, were often situated in landscapes subject to annual hunting pressures or were often located adjacent to high speed highways where deer were often killed. Death of the original matriarch was not a cause of matriline failure as, in each case during our studies, the oldest surviving daughter became the new leader and the matriline continued on the same home range.
We did not find any significant biological effects as matrilines grew larger, at least for the years and matriline numbers we studied. Member survival and female breeding rates were normal for the deer populations we studied.
Studies in Minnesota and New York found that matrilines may persist for at least 20 years if left undisturbed. In present day Illinois, however, where hunting pressures are often quite high, such year-to-year stability is rare without at least some refuge protection. Many public lands are now hunted, reducing matriline numbers each year and making matriline stability difficult to sustain.
Charlie Nixon is a wildlife ecologist retired from the Illinois Natural History Survey. Phil Mankin is a wildlife ecologist retired from the University of Illinois.