Models to assess ability to achieve localized areas of reduced white-tailed deer density

Localized management of white-tailed deer (Odocoileus virginianus)
involves the removal of matriarchal family units with the intent to create
areas of reduced deer density. However, application of this approach has
not always been successful, possibly because of female dispersal and high
deer densities. We developed a spatially explicit, agent-based model to
investigate the intensity of deer removal required to locally reduce deer
density depending on the surrounding deer density, dispersal behavior, and
size and shape of the area of localized reduction. Application of this
model is illustrated using the example of abundant deer populations in
Pennsylvania, USA. Most scenarios required at least 5 years before
substantial deer density reductions occurred. Our model indicated that a
localized reduction was successful for scenarios in which the surrounding
deer density was lowest (30 deer/mi²), localized antlerless harvest rates
were ≥ 30%, and the removal area was 5 mi² or larger. When the
size of the removal area was < 5 mi2, end population density was
highly variable and, in some scenarios, exceeded the initial density. The
shape of the area of localized reduction had less influence on the ability
to reduce deer density than the size. There were no differences in mean
deer density in the same size circle or square removal areas. Similarly,
increasing the ratio of sides (length : width) in rectangular removal
areas had little influence on the ability to locally reduce deer
densities. Situations in which deer density was higher (40 or 50 deer/mi2)
required antlerless removal rates to exceed 30% and took more than 5 years
to considerably reduce density in the localized area regardless of its
size. These results indicate that the size of the area of reduction,
surrounding deer density, and antlerless harvest rate are the most
influential factors in locally reducing deer density. Therefore, localized
management likely can be an effective strategy for lower density herds,
especially in larger removal areas. For high density herds, the success of
this strategy would depend most on the ability of resource managers to
achieve consistently high antlerless harvest rates.