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Harvard Forest Symposium Abstract 2007
- Title: Dynamics of a non-irruptive deer herd in Massachusetts
- Primary Author: John McDonald (U.S. Fish and Wildlife Service)
- Abstract:
White-tailed deer (Odocoileus virginianus) populations across much of the species range in eastern and central North America rebounded over the past century from low levels to become locally or regionally overabundant. Many researchers have documented deer population increases and the resulting effects of high deer densities on local plant and forest communities, other wildlife, human activities, and on the physical condition of the deer themselves. Historically, public hunting has been used by state fish and wildlife agencies to manage deer populations but was often applied conservatively and the harvest of antlerless deer (e.g., females and male fawns) was strictly limited or prohibited completely when the goal of management was restoration of deer. In many places, this fostered a hunting culture that was (and remains) opposed to antlerless deer harvest. Often, conservative hunting seasons and antlerless harvest restrictions remained in place until deer numbers had risen to a point where liberal seasons and bag limits, when applied, were ineffective at reducing deer numbers to desired levels. In Massachusetts, deer have been hunted continuously since 1910 and until 1966 hunters were allowed to take 1 deer of either-sex. Since 1967, hunters have been required to have permits to take antlerless deer in some or all seasons, but there has never been a prohibition on antlerless deer harvest and in the past decade seasons, bag limits, and antlerless deer permit numbers have been dramatically increased. Estimated deer densities on the Massachusetts mainland now range from 12 to 30 deer per square mile, with most management zones having less than 20 deer per square mile. However, based on several local examples potential deer densities are much higher, comparable to states to the south where high deer numbers are a chronic issue.
We examine historic trends in Massachusetts deer numbers by using harvest sex and age data gathered at mandatory check stations between 1985 and 2006 to reconstruct the male and female deer populations in 3 mainland areas of Massachusetts. Our hypothesis is that the culture of either sex deer hunting in Massachusetts, coupled with timely liberalization of hunting, resulted in adequate antlerless deer harvests over time that prevented widespread deer overabundance. Total deer harvests during the period ranged between 5,000 and 11,000 per year; sex was determined for all legally harvested deer and age was typically determined for 30% to 40% of the overall harvest. This technique requires some assumptions about the proportion of mortality due to hunting in order to provide true estimates of the population but in the absence of this knowledge we believe the resulting trends to be accurate if the absolute numbers are biased. We did estimate cause-specific mortality rates for radio-collared deer in 4 study areas in Massachusetts between 1997 and 2005 to examine the proportion of annual mortality due to hunting (typically <50% in each study area). We combined these datasets in a simulation model to examine the effects of alternative management schemes (e.g., 0 antlerless harvest, ½ the observed antlerless harvest rate, 2X the observed antlerless harvest rate, varying the timing of harvest liberalization) on the resulting trends in deer populations. The model randomly selected survival rates for male and female deer separately and estimated reproduction for females in 3 age classes (fawn, yearlings, and adults) to derive pre-hunting season population estimates that could be compared to those observed based on the actual check station data.
- Research Category:
