Jumping to conclusions: Local research looks at jackrabbits
Long-legged and quick, the white-tailed jackrabbit is often seen – albeit for split seconds– in the Upper Green River Basin. This fact led a Montana-based biologist on a journey to track the animal and decipher just why it continues to flourish here, while disappearing completely in nearby areas. With almost no documented baseline data, the studies could be crucial – especially with the rabbit's potential effect on coyote predation on lambs and pronghorn fawns.
White-tailed jackrabbits went extinct for unknown reasons in Grant Teton National Park (GTNP) sometime between the 1940s – at the time described as "commonly in the vicinity" – and the 1990s. Studies of coyote scat contents show they underwent a severe population decline from the 1930s to the 1970s and then completely disappeared between the 1970s and the 1990s.
"What's especially peculiar is that jackrabbits are still found on Forest Service land along the Gros Ventre River, and of course they're quite common in the Upper Green River Basin," said Stephan Ekernas, a 33-year-old University of Montana (UM) PhD student who is conducting the study. "That really begs the question of what's different in the national park compared to these other areas and how that might have caused jackrabbits to locally disappear."
This is the basis of Ekernas's dissertation and study, which UM is helping to support, along with the National Park Service, Grand Teton Association (GTA), the Montana Chapter of the Wildlife Society and the Wildlife Conservation Society.
However, even with all the support, he has had some difficulties. After having little luck capturing the animals last summer, he returned in mid-March to try again. "Turns out it's pretty difficult to capture jackrabbits, which is not all that surprising but a severe constraint," he said. "They're pretty difficult to get your hands on and pretty wily."
White-tailed Jackrabbit
While the traps seemed more adept at capturing cottontail rabbits, the snow cover did help with capturing at least one white-tailed jackrabbit, though Ekernas did not get to see it, returning home with frostbite while placing the traps. "That meant no contact with cold for six months," he said. He would have tried earlier, maybe January, but having a newborn baby at home kept him there. Nonetheless, he did not give up.
His research partner Evan Sims, 24, a young UM biologist, took a break from his Montana ski-hill day job to set and check traps on different Sublette residents' land. Last summer's work was mostly on BLM, National Park Service and Forest Service land, said Ekernas. This time he connected with locals to research on different private land and received permission for the Webb, Bryant and Noble properties in the area.
Wolves do not easily tolerate Coyotes in their core territory
No one is sure why jackrabbits disappeared from GTNP, said Ekernas. At a 2005 meeting hosted by the Wildlife Conservation Society and the National Park Service, several hypotheses emerged: deeper snow; greater competition with ungulates (hoofed mammals like elk, deer, pronghorn and bison) inside the park than elsewhere and the loss of wolves, which kill coyotes. When wolves were hunted out in the 1920s, coyote density increased inside the park but not in areas like Sublette County where people run livestock and control them.
Another is disease, but that's hard to test, said Ekernas – who added the GTNP jackrabbit population faced risk factors that go beyond the immediate reasons for the disappearance. "(They were) effectively living on an island," he said, adding that isolation from other populations if their own was stricken left little opportunity for dispersing animals from other areas to recolonize. "That's in pretty stark contrast to what you find in the Upper Green River Basin."
In measuring many factors – ungulate density, coyote density, snow depth and vegetation in the GTNP and in sites where jackrabbits are still found – Ekernas hopes to determine what might have happened.
The second part of the research is to determine consequences of the jackrabbits' disappearance – especially how they affect coyote predation on pronghorn fawns.
"Everyone thinks of jackrabbits as this kind of pest that just eats your hay in the winter, but they actually have pretty strong effects on species that we care about, like domestic sheep, pronghorn and deer," he said. "The reason is that jackrabbits can affect coyote predation on lambs and fawns, which – as any sheep herder knows – can be pretty severe."
In a long-term study on black-tailed jackrabbits, Utah researchers found that coyote predation on domestic lambs increased dramatically in years when jackrabbit density was low, and similar effects were found with snowshoe hares (closely related to jackrabbits), said Ekernas.
Coyotes testing adult Pronghorn
Coyotes just killed this Pronghorns fawn
The idea is that coyotes target jackrabbits instead of fawns when jackrabbits are found at a reasonable density. As a big meal – a "highly energetically profitable food item" – they are available year-round; thus it does not make sense for coyotes to switch targets for a few weeks to focus on fawns.
However, without jackrabbits to feast on, coyotes mainly eat rodents, said Ekernas.
"And if I were a coyote I'd rather eat one fawn instead of a hundred mice."
To check this hypothesis – that jackrabbits by their presence affect coyote predation on pronghorn fawns – he will compare pronghorn fawn survival in areas with and without jackrabbits, namely GTNP, the Upper Green River Basin and the Gros Ventre drainage. The results could be of great priority for GTNP, where only several hundred pronghorn undergo the iconic long-distance migration from the Upper Green to reach their summer fawning grounds in the park.
Even though he has hit some snags – and the difficulty of catching jackrabbits led his PhD committee to express some reservations about logistics and feasibility – Ekernas will return this summer to continue, likely in May or June when the pronghorn arrive.
"I'm going to work on making it more rigorous within a limited budget," he said.
White-tailed jackrabbits went extinct for unknown reasons in Grant Teton National Park (GTNP) sometime between the 1940s – at the time described as "commonly in the vicinity" – and the 1990s. Studies of coyote scat contents show they underwent a severe population decline from the 1930s to the 1970s and then completely disappeared between the 1970s and the 1990s.
"What's especially peculiar is that jackrabbits are still found on Forest Service land along the Gros Ventre River, and of course they're quite common in the Upper Green River Basin," said Stephan Ekernas, a 33-year-old University of Montana (UM) PhD student who is conducting the study. "That really begs the question of what's different in the national park compared to these other areas and how that might have caused jackrabbits to locally disappear."
This is the basis of Ekernas's dissertation and study, which UM is helping to support, along with the National Park Service, Grand Teton Association (GTA), the Montana Chapter of the Wildlife Society and the Wildlife Conservation Society.
However, even with all the support, he has had some difficulties. After having little luck capturing the animals last summer, he returned in mid-March to try again. "Turns out it's pretty difficult to capture jackrabbits, which is not all that surprising but a severe constraint," he said. "They're pretty difficult to get your hands on and pretty wily."
White-tailed Jackrabbit
While the traps seemed more adept at capturing cottontail rabbits, the snow cover did help with capturing at least one white-tailed jackrabbit, though Ekernas did not get to see it, returning home with frostbite while placing the traps. "That meant no contact with cold for six months," he said. He would have tried earlier, maybe January, but having a newborn baby at home kept him there. Nonetheless, he did not give up.
His research partner Evan Sims, 24, a young UM biologist, took a break from his Montana ski-hill day job to set and check traps on different Sublette residents' land. Last summer's work was mostly on BLM, National Park Service and Forest Service land, said Ekernas. This time he connected with locals to research on different private land and received permission for the Webb, Bryant and Noble properties in the area.
Wolves do not easily tolerate Coyotes in their core territory
No one is sure why jackrabbits disappeared from GTNP, said Ekernas. At a 2005 meeting hosted by the Wildlife Conservation Society and the National Park Service, several hypotheses emerged: deeper snow; greater competition with ungulates (hoofed mammals like elk, deer, pronghorn and bison) inside the park than elsewhere and the loss of wolves, which kill coyotes. When wolves were hunted out in the 1920s, coyote density increased inside the park but not in areas like Sublette County where people run livestock and control them.
Another is disease, but that's hard to test, said Ekernas – who added the GTNP jackrabbit population faced risk factors that go beyond the immediate reasons for the disappearance. "(They were) effectively living on an island," he said, adding that isolation from other populations if their own was stricken left little opportunity for dispersing animals from other areas to recolonize. "That's in pretty stark contrast to what you find in the Upper Green River Basin."
In measuring many factors – ungulate density, coyote density, snow depth and vegetation in the GTNP and in sites where jackrabbits are still found – Ekernas hopes to determine what might have happened.
The second part of the research is to determine consequences of the jackrabbits' disappearance – especially how they affect coyote predation on pronghorn fawns.
"Everyone thinks of jackrabbits as this kind of pest that just eats your hay in the winter, but they actually have pretty strong effects on species that we care about, like domestic sheep, pronghorn and deer," he said. "The reason is that jackrabbits can affect coyote predation on lambs and fawns, which – as any sheep herder knows – can be pretty severe."
In a long-term study on black-tailed jackrabbits, Utah researchers found that coyote predation on domestic lambs increased dramatically in years when jackrabbit density was low, and similar effects were found with snowshoe hares (closely related to jackrabbits), said Ekernas.
Coyotes testing adult Pronghorn
Coyotes just killed this Pronghorns fawn
The idea is that coyotes target jackrabbits instead of fawns when jackrabbits are found at a reasonable density. As a big meal – a "highly energetically profitable food item" – they are available year-round; thus it does not make sense for coyotes to switch targets for a few weeks to focus on fawns.
However, without jackrabbits to feast on, coyotes mainly eat rodents, said Ekernas.
"And if I were a coyote I'd rather eat one fawn instead of a hundred mice."
To check this hypothesis – that jackrabbits by their presence affect coyote predation on pronghorn fawns – he will compare pronghorn fawn survival in areas with and without jackrabbits, namely GTNP, the Upper Green River Basin and the Gros Ventre drainage. The results could be of great priority for GTNP, where only several hundred pronghorn undergo the iconic long-distance migration from the Upper Green to reach their summer fawning grounds in the park.
Even though he has hit some snags – and the difficulty of catching jackrabbits led his PhD committee to express some reservations about logistics and feasibility – Ekernas will return this summer to continue, likely in May or June when the pronghorn arrive.
"I'm going to work on making it more rigorous within a limited budget," he said.
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