From the Field

Connecting YOU with Wildlife – Pennsylvania Game Commission


5 Environmental Factors Influencing Turkeys

turkey an poult.Dingel

PGC Photo: Jake Dingel

Turkey populations in Pennsylvania as well as the entire Northeast region have been declining during the past decade.

Five factors influence turkey populations and the interactions of these five factors have changed over the last 25 years. These factors are: habitat, weather, predation, disease and hunting mortality.

During the 1990s turkeys exhibited rapid population expansion facilitated by a combination of: restoration (trap & transfer), suppressed predator populations (much more trapping than today and rabies was more evident), more controlled hunting seasons, and a more diverse landscape than exists today.

5 environmental factors have changed since turkey population restoration, which likely negatively affect turkey populations.

  1. Landscape level habitat changes, that is, a decline in: amount of interspersion of different habitat types (too many mono-cultures), habitat quality (particularly due to exotic species replacing native species), mast-producing trees (particularly oaks and cherry), younger age-class forests (therefore, less food diversity for wildlife), nesting brood cover for turkeys (due to the above and to declines in shrubby and herbaceous cover)
  2. Unpredictable weather (climate change), which has caused more extreme weather events with more spring rain and winter precipitation,
  3. Increased predator densities and wider distribution –  Predation typically only limits local turkey populations. But, high predation rates may be symptomatic of a landscape with poor habitat quality causing turkeys and their young to be more vulnerable to predation,
  4. Unforeseen effects from disease – we currently do not know the effects of disease on productivity, immunity, & energy assimilation, and how disease may interact with other population influences, such as habitat & weather,
  5. Harvest regulations (thereby changing hunting mortality) – spring harvest of males after breeding has occurred (such as PA’s regulations) have proven to be sustainable. However, fall hunting mortality can affect populations due to harvest of hens. Our recent 5-year study showed that fall harvest rates of hens in Wildlife Management Units (WMUs) with 2-week + 3-day Thanksgiving seasons are 2-7%, and in WMUs with 3-week + 3-day Thanksgiving seasons are 4-9%. When populations were expanding research showed that a 10% harvest rate was sustainable. Now that populations are declining, the sustainable harvest rate obviously is lower, but what that rate is we are not sure. Therefore, we have been decreasing fall season length to decrease the harvest rate.

The interaction of these factors, such as a high fall harvest rate coupled with poor poult production due to adverse spring weather with poor habitat quality, predation and minor disease, impact populations. Several consecutive years of this add up to severely limit the population.

What the new ‘normal’ turkey population level will be in the years ahead depends on how these interactions play out. However, we all can help turkey populations.

What we all can do to help turkeys:

Improve habitat quality (this helps buffer the negative effects of the other factors), help protect existing habitat, report any potentially diseased turkeys so we can monitor disease more intensely, begin trapping furbearers (selling furs can provide some income too)(this won’t eliminate predation but will help keep it in check on a local level), and during fall turkey season, if given the opportunity, harvest a young-of-the-year bird because the adult females have the highest nest success the following spring.

Mary Jo Casalena, Wild Turkey Biologist

Pennsylvania Game Commission

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