Migrating Mule Deer: Effects of Anthropogenically Altered Landscapes

Abstract

BackgroundMigration is an adaptive strategy that enables animals to enhance resource availability and reduce risk of predation at a broad geographic scale. Ungulate migrations generally occur along traditional routes, many of which have been disrupted by anthropogenic disturbances. Spring migration in ungulates is of particular importance for conservation planning, because it is closely coupled with timing of parturition. The degree to which oil and gas development affects migratory patterns, and whether ungulate migration is sufficiently plastic to compensate for such changes, warrants additional study to better understand this critical conservation issue.Methodology/Principal FindingsWe studied timing and synchrony of departure from winter range and arrival to summer range of female mule deer (Odocoileus hemionus) in northwestern Colorado, USA, which has one of the largest natural-gas reserves currently under development in North America. We hypothesized that in addition to local weather, plant phenology, and individual life-history characteristics, patterns of spring migration would be modified by disturbances associated with natural-gas extraction. We captured 205 adult female mule deer, equipped them with GPS collars, and observed patterns of spring migration during 2008–2010.Conclusions/SignificanceTiming of spring migration was related to winter weather (particularly snow depth) and access to emerging vegetation, which varied among years, but was highly synchronous across study areas within years. Additionally, timing of migration was influenced by the collective effects of anthropogenic disturbance, rate of travel, distance traveled, and body condition of adult females. Rates of travel were more rapid over shorter migration distances in areas of high natural-gas development resulting in the delayed departure, but early arrival for females migrating in areas with high development compared with less-developed areas. Such shifts in behavior could have consequences for timing of arrival on birthing areas, especially where mule deer migrate over longer distances or for greater durations.

Effects of large‐scale gold mining on migratory behavior of a large herbivore

“…Our movement rate results contradict those found in similar studies of mule deer migration behavior through various types of human disturbances where individuals showed an increase in movement rate through disturbed areas (Lendrum et al 2012, Lendrum et al 2013, Sawyer et al 2013. We believe that these results differed from ours due to the differences in disturbance types from those reported in studies related to natural gas disturbances within migration corridors compared with our results from large-scale disturbance related to gold mining.…”

“…These disturbances include natural gas and oil extraction, open-pit mining, residential developments, restrictive fencing, and recreational development and use (Sawyer et al 2006, Sawyer et al 2009a, Lendrum et al 2012, Lendrum et al 2013, Sawyer et al 2013, Seidler et al 2014. These developments often result in direct or indirect loss of wildlife and habitat, which also influences behavior and habitat use of affected species, and can lead to changes in survival and recruitment (Cole et al 1997, Sawyer et al 2006, Bolger et al 2008, Sawyer et al 2009a.…”

“…Recently, scientists have attempted to quantify the impacts of human disturbances across a variety of migratory ungulates (Lendrum et al 2012, Lendrum et al 2013, Sawyer et al 2013, Seidler et al 2014). Natural gas exploration has been the primary focus of that research because of the recent expansion of exploration across the western United States (Sawyer et al 2006, Sawyer et al 2009a, Beckmann et al 2012, Lendrum et al 2012, Lendrum et al 2013, Sawyer et al 2013, Buchanan et al 2014, Seidler et al 2014.…”

“…Natural gas exploration has been the primary focus of that research because of the recent expansion of exploration across the western United States (Sawyer et al 2006, Sawyer et al 2009a, Beckmann et al 2012, Lendrum et al 2012, Lendrum et al 2013, Sawyer et al 2013, Buchanan et al 2014, Seidler et al 2014. Research in these areas suggests that mule deer increase their movement rates, select habitat types that provide greater amounts of concealment cover, reduce stopover use, and migration route use and width decreased when migrating through areas with high densities of well pads (Lendrum et al 2012, Lendrum et al 2013, Sawyer et al 2013). On winter range, mule deer avoided areas with natural gas fields and shifted habitat use away from disturbance (Sawyer et al 2006, Sawyer et al 2009a).…”

Asynchronous vegetation phenology enhances winter body condition of a large mobile herbivore

“…More specifically, we predicted that individuals inhabiting home ranges with shallower vegetation green-up slopes (slower aggregate rate of vegetation green-up) would experience elongated periods when the vegetation is at peak 6 quality, and that this benefit would accrue during the spring and carry over to winter months resulting in better subsequent winter body condition for these individuals in comparison to those inhabiting home ranges with steeper vegetation green-up slopes (Pettorelli et al 2005c;Lendrum et al 2013;Hurley et al 2014). We also predicted that individuals inhabiting home ranges with an earlier vegetation onset (i.e., a higher value of NDVI in early spring) would have higher winter body condition than individuals occupying home ranges with a later vegetation onset (Pettorelli et al 2005c).…”