Who Ate the Corn? Using Monitoring to Feed Management Decisions

Bosque del Apache National Wildlife Refuge cultivates corn to redistribute sandhill crane (Grus canadensis) and waterfowl populations off of private agricultural fields throughout the Middle Rio Grande Valley in New Mexico.  Corn production on the Refuge also helps the birds maintain their body condition as they migrate and overwinter on and around the Refuge.  The current goal of the Refuge is to produce 1.5 million pounds of corn.  Unfortunately, corn production on the Refuge was low during the summer of 2011, raising concerns about meeting the energetic needs of sandhill cranes and increased crop depredation by waterfowl on neighboring farms.  These concerns have prompted Refuge biologists to investigate causes of crop failure.

Many reasons for poor corn production have been proposed.  It could be crop depredation and damage by elk (Cervus elaphus), mule deer (Odocoileus hemionus), and trespass cattle, as well as ineffective farming practices.  Further, the current drought has put additional stress on the farming program.

A wire exclosure used to exclude elk, mule deer, and trespass cattle allowing Refuge biologists to determine potential corn growth and yield without ungulate depredation and damage.

With Region 2 I&M staff, Refuge biologists are leading a monitoring strategy to quantify three things 1) crop depredation and damage from ungulates, 2) identification of species responsible for crop damage, and 3) determining the stages of plant development in which corn is most vulnerable to depredation and damage.  The approach consists of repeated monitoring of corn depredation and damage in exclosures and treatment plots throughout the summer.  These plots are located across a sample of the Refuge’s corn fields.

The Refuge will tolerate some ungulate depredation and damage to the corn crop.  However, aversion techniques, which are methods designed to prevent and control depredation and damage of crops by wildlife, might need to be deployed if depredation and damage is excessive.  Continued crop monitoring will allow Refuge staff to follow plant development and damage of the crop throughout the summer.  If predetermined thresholds of depredation and damage are exceeded, Refuge personnel will implement aversion techniques on affected farm fields.

SCEP Student, Reggie Perkins, monitors corn growth at Bosque del Apache NWR.

Knowledge gained this summer will inform the Refuge as to how much depredation and damage is occurring, which species is responsible, and which developmental stage of corn is most vulnerable.  These kernels of knowledge will inform an adaptive management strategy as the Refuge builds a better understanding of the scale of the depredation issue, and therefore, can design more informed management actions to mitigate corn damage caused by ungulates.  Crop monitoring will continue over subsequent years, allowing further refinement of management strategies.

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