Wyoming Fish and Wildlife irrigates fields in the Sunlight Basin Wildlife Habitat Management Area, 40 miles northwest of Cody, to provide forage for elk. Forum contributors Chris Wilmers and Taal Levi show that the non-migratory elk use the irrigated fields more heavily during drought years. Migrating elk do not receive this subsidy.
"I think Middleton has an intriguing idea, and it might be what's happening. We offer another hypothesis that also fits the data that they have. He says it's climate change on the summer range and more predators on the summer range. I think it's because there is irrigation that provides the sedentary elk with food. And I think it's also that there is predator control outside the park," said Wilmers.
While wolves and grizzlies have been thriving inside the park, predator control measures have intensified outside the park, Wilmers said. "My hypothesis is that in that crucial winter period, the migrants are coming down to range that the resident elk have already been feeding on all summer, and now they are competing for in the winter," he said. To distinguish between these two stories would require hypothesis testing, he said pitting them against each other and testing them with more data.
Jack Massey, Sarah Cubaynes, and Tim Coulsen of Oxford University joined the conversation with their contribution "Will central Wyoming elk stop migrating to Yellowstone, and should we care?" The trends in vegetation and predator differential across the park boundary are compelling, they commented, but have those factors caused the change in elk demographics? Middleton et al.'s data cannot answer those questions, the Oxford group wrote. "We don't wish to sound critical of the huge effort they have put in. Nonetheless, despite their hard work, their data on elk condition and pregnancy rates come from a relatively small number of animals
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Ecological Society of America