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What’s on the menu for Allegheny woodrats?
It’s difficult for a population to persist when its main food source has disappeared.
Allegheny woodrats (Neotoma magister) faced this firsthand when American chestnuts were extirpated and forests transitioned to become oak-dominated about 100 years ago. These oaks sometimes fail to produce the mast that the species consumes, which may be a contributing to their range-wide decline.
In a recent study published in the Journal of Wildlife Management, researchers looked at Allegheny woodrats’ hard mast preference in Indiana and also studied their response to increases in artificial mast availability.
“The reason for the chestnuts’ decline is chestnut blight,” said Timothy Smyser, a biologist in the wildlife genetics program at the National Wildlife Research Center. “It’s a fungal pathogen that was introduced from Asia, like white-nose syndrome from Europe. It became airborne and then spread rapidly throughout the range.”
The American Chestnut Foundation has been working for the last 30 years to create blight resistant chestnuts by crossing blight resistant Chinese chestnuts with American chestnuts, he said.
To learn more about the woodrats food preferences, Smyser and his team built wooden boards and drilled small holes into them where they placed seeds from oaks, hickories and chestnuts. They labeled the holes — which kept the seeds from rolling off the board — with letters and numbers to keep track of which seed was in which hole. “It was like a Battleship board game board,” Smyser said. The team monitored the boards with camera traps to see which seeds the woodrats chose as well as which seeds other animals such as mice consumed.
Smyser compares the situation to the wide range of ice cream flavors available at Baskin Robbins, for example. “You have a preferred flavor of ice cream, and you order that flavor over the other flavors,” he said. “If they’re out of that ice cream, you choose something else.” Here, researchers were looking at what woodrats were selecting and what they were choosing from based on availability.
Smyser and his coauthors found the woodrats preferred red oak and black oak seeds over chestnut — a finding that could help managers prioritize recovery efforts for woodrats, according to Smyser. “Specifically, conservationists were anticipating that as soon as we have established a blight-resistant American chestnut, the woodrat population will once again flourish.” But based on the woodrats’ preferences revealed in the study, this might not be the case.
In Indiana, the presence of hard mast such as acorns was not a limiting factor for woodrats. But Smyser suggests that in other areas this might not be true; managers should first consider the abundance and diversity of mast-producing species in the overstory to make sure there’s enough mast to support woodrat populations. Then, he said it’s important to evaluate whether those species of oak are producing mast that particular year. “Some years there are acorns everywhere and some years it’s hard to find acorns,” he said. Finally, managers should decide if they need to supplement sites with acorns, he said. “Here, there was no need for supplementation,” he said.