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  • Alaskan island wolves caused a deer population to plummet

    Alaskan island wolves caused a deer population to plummet

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    Newswise —

    Historically, wolves and sea otters likely lived in the study area, Pleasant Island, which is located in an island landscape adjacent to Glacier Bay about 40 miles west of Juneau. The island is about 20 square miles, uninhabited and accessible only by boat or float plane.

    During the 1800s and much of the 1900s, populations of sea otters in this region were wiped out from fur trade hunting. Unlike wolves in the continental USA, Southeast Alaskan wolves were not hunted to local extinction. Only in recent decades, particularly with the reintroduction and legal protection of sea otters, have the populations of both species recovered and once again overlapped, providing new opportunities for predator-prey interactions between the two species.

    Wolves on an Alaskan switched to primarily eating sea otters in just a few years, a finding scientists believe is the first case of sea otters becoming the primary food source for a land-based predator. Using methods such as tracking the wolves with GPS collars and analyzing their scat, the researchers found that in 2015 deer were the primary food of the wolves. By 2017, wolves transitioned to primarily consuming sea otters while the frequency of deer declined.

    Sea otters are this famous predator in the near-shore ecosystem and wolves are one of the most famous apex predators in terrestrial systems. So, it’s pretty surprising that sea otters have become the most important resource feeding wolves. You have top predators feeding on a top predator.

    The researchers studied the wolf pack on Pleasant Island and the adjacent mainland from 2015 to 2021. Gretchen Roffler, a wildlife research biologist with the Alaska Department of Fish and Game, and others from the department collected 689 wolf scats, many along the island’s shoreline.

    Once the scat is collected, members of Levi’s lab in Oregon used molecular tools, such as DNA metabarcoding and genotyping of the scat, to identify individual wolves and determine their diets.

    Roffler also captured and placed GPS collars on four wolves on the island and nine on the mainland. The researchers were curious whether wolves were traveling between the mainland and island, considering other scientists have found they are capable of swimming up to eight miles between land masses. Both the GPS collar data and genotypes of the scats confirmed they were not, indicating that the island wolf pack is stable and that the island is not a hunting ground for mainland wolves.

    Locations from the GPS-collared wolves also provide evidence that the wolves are killing sea otters when they are in shallow water or are resting on rocks near shore exposed at low tide. Roffler and her crew have investigated wolf GPS clusters on Pleasant Island for three, 30-day field seasons since 2021 and found evidence of 28 sea otters killed by wolves.

    “The thing that really surprised me is that sea otters became the main prey of wolves on this island,” Roffler said. “Occasionally eating a sea otter that has washed up on the beach because it died, that is not unusual. But the fact that wolves are eating so many of them indicates it has become a widespread behavior pattern throughout this pack and something that they learned how to do very quickly.

    “And from the work we are doing investigating kill sites, we are learning that wolves are actively killing the sea otters. So, they aren’t just scavenging sea otters that are dead or dying, they are stalking them and hunting them and killing them and dragging them up onto the land above the high tide line to consume them.”

    Shortly after wolves colonized Pleasant Island in 2013, the deer population on the island plummeted. With the wolves having consumed most of the deer, their main food source, Levi said he would have expected the wolves to leave the island or die off. Instead, the wolves remained and the pack grew to a density not previously seen with wolf populations, Levi said. The main reason, he believes, is the availability of sea otters as a food source.

    The findings outlined by the same researchers showed that wolves were eating sea otters. This was documented throughout the Alexander Archipelago, a group of Southeastern Alaskan islands which includes Pleasant Island.

    The research has now expanded to study wolves and sea otters in Katmai National Park & Preserve, which is in southwest Alaska, about 700 miles from Pleasant Island. Early research indicates that wolves are also eating sea otters there. In fact, at that location three wolves were killing a sea otter near the shore.

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    Oregon State University

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  • Cheetah marking trees are hotspots for communication also for other species

    Cheetah marking trees are hotspots for communication also for other species

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    Newswise — Marking trees are important hotspots of communication for cheetahs: Here they exchange information with and about other cheetahs via scent marks, urine and scats. A team from the Cheetah Research Project of the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) now showed that several mammalian species on farmland in Namibia maintain a network for intra- and interspecific communication at cheetah trees. Black-backed jackals, African wildcats and warthogs visited and sniffed the cheetahs’ “places to be” more frequently than control trees, the team concluded from photos and videos recorded by wildlife camera traps in a paper in the scientific journal “Mammalian Biology”. A common prey species of the cheetahs, however, avoided these hotspots.

    Many mammalian species use scent marks, urine or scats to communicate with each other. By doing so, animals leave, receive and exchange information on territory ownership, reproductive receptiveness, health status or diet. Whether and how such olfactory communication is also used by other species than the one having placed the information is not well understood. Scientists from the Leibniz-IZW Cheetah Research Project now observed nine cheetah marking trees and nine similarly looking control trees on farmland in Namibia with wildlife camera traps. They found that some species visited and sniffed cheetah marking trees more frequently than control trees, suggesting they gain important information from cheetah markings. Other species exchanged information at the same frequency at cheetah marking trees and control trees. This indicates that they used prominent trees for their own communication. The scientists concluded that mammals on Namibian farmland maintain communication networks within and between species
    During the 65-day survey period, 29 mammalian species visited the cheetah marking and the control trees. There was a higher diversity of species at cheetah marking trees than control trees, but most species visited the trees only a few times. For the analyses only species which visited, sniffed or marked the trees at least 20 times were included. In this subset, 13 species visited, 9 species sniffed and 1 species left information at the cheetah marking and control trees.

    With African wild cats (Felis lybica lybica), black-backed jackals (Lupulella mesomelas) and warthogs (Phacochoerus africanus) two small carnivore species and one omnivore rarely preyed by cheetahs visited and sniffed cheetah marking trees more frequently than control trees. „ Small carnivore species might visit cheetah marking trees to assess when cheetahs last visited the area and/or to feed on undigested prey remains in cheetah scats”, says Dr Sarah Edwards, first author of the paper. “Warthogs on the other hand are omnivores and opportunistic scavengers, so they might also feed on undigested prey remains in cheetah scats. Additionally, warthogs are the only species that left olfactory information and did this at the same frequency at cheetah marking and control trees. This suggests that warthogs use large trees as sites for their own communication”, Edwards adds.
    In contrast, common duikers (Sylvicapra grimmia), a common and important cheetah prey species, visited cheetah marking trees less frequently than control trees. Leopards – the top predator in the study area – on the other hand, sniffed, urinated, scratched and rubbed body parts at both cheetah marking trees and control trees. “Although leopards visited the trees less than 20 times, it is possible that they used conspicuous trees for their own olfactory communication and at the same time demonstrated at cheetah marking trees their presence towards cheetahs”, says Dr Bettina Wachter, senior author of the paper and head of the Cheetah Research Project.

    Interspecific communication has mainly been described between prey and predator or between carnivore species. It often involves prey animals or small carnivores that sniff at markings from predators. While prey animals normally do not mark at predator marking sites, small carnivores and other predator species might counter-mark existing scent marks. If counter-marking is done at conspicuous sites, it might be directed to conspecifics rather than to different species. “In our investigation, we monitored nine cheetah marking trees and nine similar looking control trees nearby on farmland in central Namibia with wildlife cameras. These trees were all conspicuous, isolated, prominent specimens, typical for cheetah marking trees. We used this paired tree setup to investigate whether mammalian species visit these trees for interspecific and/or intraspecific communication”, explains Dr Jörg Melzheimer, initiator of the wildlife camera trap survey.
    By using a paired survey design, the scientists demonstrated that some species gain important information from other mammalian species. “Thus, it is likely that mammals maintain communication networks across species”, Wachter and Melzheimer conclude. “These networks might be laid out along cheetah marking trees and also along communication locations of other species such as latrines of brown hyenas or spotted hyenas. Investigations on the interspecific communication of various species in different populations and ecosystems will likely uncover more details on the complexities of communication networks.”

    In a previous paper, Melzheimer, Wachter, and colleagues showed that marking trees are important hotspots of intraspecific communication for cheetahs and how they work. They used this to demonstrate that detailed knowledge of the spatial ecology and communication of the big cats can help reduce human-wildlife conflicts. This work was published in December 2020 in the “Proceedings of the National Academy of Sciences of the United States of America”.

     

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    Forschungsverbund Berlin e.V.

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