Hunting partnerships, part 2

Humans have formed hunting partnerships with a variety of animals in addition to honey guides, which were noted in last week’s essay. For example, a traditional method of fishing for ‘opelu in Hawai’i involved rhythmical banging on the side of the canoe to attract the attention of great barracudas (the kaku or ‘opelu mama). As a barracuda approached a school of ‘opelu, the smaller prey fish would ball up for mutual protection in a dense school. This made it easier for the fishermen to net them. Presumably the predatory barracuda caught some too. And in southern Brazil, certain pods of bottlenose dolphins herd mullet toward fishermen waiting in the shallows. With tail slaps or quick dives, they signal to the fishermen, when it is time for the men to throw their nets.

Some partnerships are not such free associations: Once common in China and Japan, trained cormorants were used to catch fish. A ligature on the bird’s neck kept it from swallowing big fish, but it could still swallow small ones. And for centuries, falconers have trained raptors to capture various prey animals, generally sharing the prey (or a substitute food) with the birds.

Perhaps the most widespread and well-known hunting partnership involves humans and dogs. For many thousands of years, we have bred these domesticated canines for various roles in hunting prey—there are retrievers, chasers, trackers, attackers, and so on. A very specialized kind of hunting does not involve killing prey but rather finding things. The powerful olfactory senses of dogs are put to work detecting drugs, contraband imports, and some diseases. Some dogs are even trained to locate invasive plants, such as purple loosestrife. Search dogs are trained to find lost persons, living or dead, on land and even in water. Some years ago, a dear canine friend could always find me, hidden in the woods, no matter how my trail circled or backtracked, or find my ‘stuff’ if I happened to drop it along the trail.

In Juneau, the excellent noses of dogs are put to work in bat research. First, a little background on previous work on bats, to set the stage for the participation of dogs. An ADFG research program has been radio-tagging and monitoring bats in the Juneau area for several years, focusing primarily on the common little brown bat (Myotis lucifugus). Radio-tagged bats have been tracked to hibernacula in two places (so far): rocky crevices on steep forested slopes on Douglas Island and on Admiralty Island. The bats begin to hibernate in mid-September or so.

Before settling in for the winter, the bats seem to signal to each other about a prospective location by circling with sharp turns near a particular crevice, reaching a peak in the dark hours of the night in late July, August, and early September. This flight behavior is known as ‘swarming’. It has been well- documented in eastern and midwestern North America, where large numbers of bats circle or ‘swarm’ around cave and mine entrances. In contrast, in our area, each crevice seems to be used by only a few bats, although the circling flight pattern is still called ‘swarming’.

Game cameras are set up near rocky crevices to which the radio-tagged bats have been tracked. The cameras can record the circling flights and sometimes also one or two bats (as well as mice and shrews) crawling into a crevice and staying for a while. Mating presumably occurs at this time, in these crevices, in late summer and early fall, but fertilization is delayed until early spring, when females emerge from hibernation. They emerge before the males do, and go to maternity roosts in warm places such as attics. After a gestation period of about three months, the young are born and can usually be ready to fly in about three weeks.

To expand our understanding of the habitats used by hibernating bats, ADFG bat biologists and volunteer ‘citizen scientists’ do road surveys, listening for bat vocalizations with special bat detectors. These surveys are primarily focused on finding areas of concentrated bat activity at the seasons of entry to (and emergence from) hibernation. Then foot surveys in those areas look for the right kind of habitat; bat detectors are used to see if bats are really at that area and identify the species of bat. If all that points to the presence of bats, trained bat-scent-detecting dogs are brought in, particularly during the time of beginning hibernation (the so-called swarming period), to sniff out the exact crevice housing the bats. When a search dog signals that it has detected the scent of bats at a particular crevice, researchers may look for the distinctive feces of bats in the crevice. To determine if the selected crevice is just a day roost or an actual hibernating site, more equipment is set up in the early fall to detect swarming behavior outside the crevice and eventually determine that the bats are really hibernating there.

So far, the scent-detecting dog searches show great promise for locating hibernacula (although not in the rain), and the method should be tested elsewhere, in other habitats and climates. In the meantime, the method will be used here to locate more hibernacula and develop a clear picture of the habitat needs of the bats. That’s critical information for land managers—and a great application of an ancient hunting partnership between humans and canines.

Thanks to Tory Rhoads, ADFG, for a good conversation about local bat research and the use of sniffer-dogs to locate hibernacula.

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Hunting partnerships

We are accustomed to hearing about wolves or killer whales that hunt in cooperative packs. And sometimes, conspecific animals can work in pairs. In the marshes where I worked long ago, I could sometimes watch two coyotes team-hunting ducks—one to keep the duck’s attention while the other crept up behind. And here, we can see eagles working as a team: one swoops down on a duck, which promptly dives, and the second eagle pounces as the duck resurfaces. Ravens also sometimes work in teams, one bird distracting an eagle that has a fish and the other one dashing in to snatch the fish.

Less well known are hunting partnerships between animals of different species. In a true partnership, both participants obtain some benefit, and that is sometimes difficult to demonstrate. Here are some proposed examples, often with insufficient documentation to make a solid case for a true partnership.

Wolves and ravens. Ravens are so often associated with wolves that they are sometimes called ‘wolf-birds’. When wolves kill a large animal, such as a deer, moose, or elk, they tear open the carcass, which allows ravens to scavenge lots of sizable tasty bits; without the opened carcass, the ravens are limited to snatching eyeballs and maybe part of the tongue. Wolf researchers have observed that travelling wolf packs are commonly followed by ravens, which clearly benefit from the more profitable scavenging.

But do wolves get anything from the attendant ravens? Some observers have claimed that ravens lead wolves to carcasses, but these claims may be more story than fact. One long-time wolf researcher noticed that when ravens accompany wolf packs, they would sometimes fly ahead, in the direction of travel, and wait for the wolves to catch up—which could appear to be leading the wolves. If a gang of ravens yells and calls when they discover a carcass, wolves could notice and might come; then both ravens and wolves could feast. The ever-observant ravens might alert feeding wolves to possible interlopers and disturbances, but how often this would be useful is not known. Maybe the potential value to wolves varies with conditions and location, and we should keep an open mind on this question, awaiting more research.

In an interesting twist on wolf-raven interactions, there are strong indications that the professional-level scavenging by ravens may be important in determining the size of wolf packs. A larger pack is better at fending off marauding ravens than a small pack, so more meat is available to the wolves. Of course, that’s also more wolfish mouths among which to divide the meat, but at least in some cases, the advantage of larger wolf numbers outweighs the disadvantage, so wolf packs are commonly bigger than two or three hunters.

Coyotes and badgers. A study in Wyoming found these two predators interacting in ways that suggested collaboration while hunting ground squirrels. Badgers hunt by digging into ground squirrel burrows, blocking off tunnels, and trapping prey in dead-ends, but sometimes the squirrels escape by emerging above ground. Coyotes there chase and pounce, although sometimes a squirrel dives into another tunnel system, there to be pursued by badger. The coyotes clearly benefited: they caught more squirrels when they were interacting with badgers. Because the badgers catch their prey underground, it is harder to tell what their hunting success might be, but they spent more time underground when they were interacting with coyotes and they might have been feasting. More data needed!

The apparently collaborative hunting typically involved single coyotes, not pairs or trios. They seemed to hear the badgers’ burrowing activity and solicit interaction by scrambling in a particular area or showing play behavior when the badger appeared. However, female badgers with young did not participate, rebuffing soliciting coyotes. The cooperative interaction occurred in sagebrush habitat where coyotes had limited mobility and where the sagebrush roots made badger digging somewhat difficult. Collaborative behavior was not observed where both critters had easy hunting or where coyotes are harassed and shot by humans.

Groupers and moray eels. Groupers are sizable predatory fish that live on coral reefs around the world; moray eels are predators that usually forage at night. Groupers sometimes hunt with moray eels, particularly if they are hungry (well-fed ones don’t do it), and an eel can be coaxed to forage during the daytime. A hungry grouper seeks out a moray eel that’s resting in a hole in the reef. It faces the eel, close-up, shaking its head and flicking its dorsal fin. If the eel is interested, out it comes. If the eel is reluctant to emerge, the grouper signals more vigorously. If the grouper manages to recruit the eel, the eel slithers in and out of crevices in the reef and the grouper lurks about nearby. When the eel flushes a small fish out into the open, the grouper may grab it—or chase it back into a hole where the eel can get it. If the prey fish gets away and hides, and if the grouper knows where it is, the grouper gives a more vigorous head-shake to the waiting eel and they may try again. Both animals feed well when they use this method.

The peacock grouper was introduced to Hawai’i from the Indo-Pacific region. Morays in Hawai’I respond to the foraging invitations of these foreigners, which apparently know how to behave as well as the native groupers. So a new association was established.

Groupers have also been seen signaling to octopuses, which may join in a hunt. They can insert their long tentacles into crevices and scare out the hiding fish. Grouper or octopus may catch the fish.

Honey guides and honey badgers. This is the classic, often-cited example of interspecific foraging partnerships. Honey guides are birds of Africa and Asia that have the unusual habit of feeding on beeswax and larvae, but they cannot open a tree cavity that houses bees. Honey badgers are tough weasel-like omnivores that love honey (and probably bee larvae), sometimes raiding domestic bee hives. Certain species of honey guides are said to lead badgers to bee colonies; the badgers rip them open to expose the comb, with its honey and larvae, and both animals feast. However, there is serious doubt about this collaboration; some scientists report that it is basically a myth, with no factual evidence. However, the honey guides do work with humans that will open the cavity, making the goodies inside available to both bird and human. Honey-hunters of some African tribes use special calls to bring honey guides into action. Obviously, these two interspecific interactions are not mutually exclusive, but the badger connection may need to be verified.

Hunting humans interact with many different animals in collaborative ways; of which, more next time.