Tag Archives: strategy

Meet the Woodpecker That Impersonates a Snake

göktyta.PNG

( National Geographics; 19 september 2018)

The Eurasian wryneck can’t put a spell on you, as people once believed, but it does have a few tricks up its sleeve.

This bird’s motto is fake it till you make it. Or in this case, fake it until the threat of being eaten has passed.

That’s the strategy of Eurasian wrynecks, small brown woodpeckers native to Europe, Africa, and Asia. When spooked, they bend and twist their head from side to side, often while hissing, to imitate a forest snake.

“Whenever you catch a wryneck, they usually wiggle with their neck to imitate some kind of snake,” says Anders Nielsen, a student at the University of Copenhagen, who shot the video at Denmark’s Gedser observatory, where scientists capture wrynecks each summer and apply leg bands to monitor their population.

“Moving its head and throat from side to side … it looks pretty strange.”

Once considered otherworldly and a sign of magical powers, the odd behavior is now known to be a form of self-defense, he says. And it’s something of a genius strategy: If you’re not scary yourself—perhaps, you don’t have sharp talons, quick speed, or a powerful bite—impersonate an animal that’s more terrifying. Why not a snake? (See how snakes, spiders, and other animals fool their prey.)

In the hand of a bird bander, the display might not be so convincing. But shrouded in the shadows of a dark tree cavity, where these birds nest, the disguise is sure to trick stoats, goshawks, and other feather-hungry predators, says Kenn Kaufman, a renowned bird expert and field editor at Audubon magazine.

“If you’re a wryneck sitting inside a cavity, writhing around and looking and sounding like a snake is likely to make just about any predator retreat,” he says. “The more snakelike it looks and sounds, the more effective the defense could be.”

One Weird Woodpecker

Wrynecks are in the woodpecker family, but they don’t exactly fit in—at least at first glance.

For one, they don’t peck wood. Instead, they nest in holes that other species have laboriously excavated for themselves. And unlike their tree-drilling brethren, wrynecks forage on the ground, using exceedingly long tongues to slurp up fat-rich ants. (Related: How woodpeckers can thrive in leafy suburbs.)

 

But while they don’t look or act like your typical backyard woodpecker, wrynecks share important features with them, including a long, flexible neck packed with muscles. (Related: Why woodpeckers don’t get headaches.)

It’s these underlying woodpecker features that make snake mimicry possible, Kaufman says.

“Even though the wrynecks are not digging holes, they’ve got the woodpecker family characteristics, such as really complex vertebrae,” he says. “Since they’re not pounding on trees, they can put those morphological traits to use in other ways, such as by being contortionists and moving their head in every which way.”

In other words, wrynecks have repurposed their family strengths—which most species use for hammering out homes and digging up grubs—to imitate a snake when they feel threatened. And they did so over thousands of years of evolution that selected for “accidental” snake-like traits, Kaufman says.

“There wasn’t any conscious attempt at the start, like ‘gee, I’ll try to look like this other species,” he says. “Selection is likely favoring wrynecks becoming more and more snake-like, just like in other cases of mimicry.”

And there are plenty of other snake mimics in the animal kingdom. The hawkmoth caterpillar can inflate a serpent head, the mimic octopus has eight limbs that each double as sea snakes, and burrowing owls are known to produce a long, hissing noise. Heck, there are even snakes that imitate snakes.

A Bird for Bewitching

Today, you’d be lucky to spot a wryneck in the woods. They’re elusive, well-camouflaged, and in decline. But centuries ago, its shrill cry might have sent you running.

Due to its odd movements, this humble-looking woodpecker—known then as the jynx bird—was once thought to wield magical, perhaps even evil powers. In fact, that’s where our modern word jinx (“one that brings bad luck”) comes from.

Other sources suggest it was also used for love spells. According to the book Birds: Myth, Lore and Legend, hopeless romantics would nail an open-winged wryneck to a spinning top called an iynx, which they would twirl “amid incantations to excite sexual love.”

Thankfully, that practice has long been retired. But the wryneck’s scientific name, Jynx torquilla (from the Latin torqueo, “to twist”) has forever preserved its spellbinding past and head-turning talent.

 

Advertisements

Birds of all feathers work together to hunt when army ants march

ruddy_woodcreeper.jpg
(SD, Drexel University 19 June 2017)
Army ants scare up a lot of food when they’re on the move, which makes following them valuable for predator birds. But instead of competing and chasing each other off from the ant “raids,” as scientists had thought, birds actually give each other a heads up when the ants are marching, according to a new Drexel University study.

For more than a decade — from 2005 until 2016 — Sean O’Donnell, PhD, a professor in Drexel’s College of Arts and Sciences, observed army ant “raids” and the birds that follow them. He hoped to find out whether birds really were aggressive toward each other during the ant marches or whether they actually cooperated to access the food (other insects and bugs) that ants rustle out of hiding.

After observing 74 swarms in Costa Rica, it seems birds are much more likely to play nice with each other.

“Overall, the results strongly supported facilitation — species help each other to exploit shared resources,” O’Donnell said of his study that was recently published in Biotropica.

In watching for the raids and the flocks that “attend” them, a key to avian cooperation may be what are termed “bivouac-checking” birds. These are birds that perch near the sites where army ants make their nests (bivouacs) and watch to see where and when the ants move. Birds that fall into that category include the ocellated antbird and the blue-diademed motmot.

The prevailing thought has been that these specialized birds liked to keep the ant colonies they watched to themselves, not allowing other species to horn in on their finds.

But a frequent high diversity of species in flocks following the ant columns showed O’Donnell that birds that didn’t specialize in tracking army ants (like the migrant species Kentucky warbler) were allowed to join and hunt.

So when bivouac-checking birds see the movement of the columns and take off, other birds take the cue. They either know birds like the ocellated antbird follow ant columns or recognize vocalizations the specialized birds make when chasing the colonies.

“Birds may use each other as a way of finding army ant raids, which are very hard to locate in the forest because they are widely spaced and the ants are mobile,” O’Donnell said. “Observations suggest some birds are attracted to other birds at raids, and birds may even follow each other when moving among raids of different ant colonies.”

However, there did seem to be some bullies.

O’Donnell noticed some pairs of species were almost never found in flocks together despite, independently, being ant-chasers. That indicated that these bird species might chase each other off as competition, or just avoid each other entirely. Pairs that seemed to be unable to be around each other included the blue-throated toucanet and the brown jay, as well as the wood thrush and the white-eared ground sparrow.

“These antagonistic pairs were often species of very similar body size or feeding behavior,” O’Donnell explained. “Perhaps these species do compete very strongly at army ant raids.”

All in all, finding that birds largely work together to forage at army ant raids seems to demonstrate that cooperation is a better survival strategy than trying to keep food from the raids for their own species.

“Having other birds around may be an advantage because there are more eyes and ears to detect predators,” O’Donnell said. “If the raid is hard to monopolize, and food is very abundant there, then the costs of allowing other birds to attend may be low, further favoring positive species interactions.”

Fuel loads acquired at a stopover site influence the pace of intercontinental migration in a boreal songbird

(Camila Gómez, Nicholas J. Bayly, D. Ryan Norris, Stuart A. Mackenzie, Kenneth V. Rosenberg, Philip D. Taylor, Keith A. Hobson & Carlos Daniel Cadena 13 June 2017)

 

Although migration is an adaptive behaviour in a wide range of animals1,2,3, it is also thought to impose significant costs on individuals4. Studies on various migratory birds5,6,7, mammals8 and fish9 provide evidence that mortality can be higher during migration than during stationary periods of the annual cycle. In addition, work on birds10, 11 and insects12 indicates that migrating individuals often undergo significant metabolic and behavioural adjustments to fulfil the high energetic demands of migration. Time spent and energy used during migration can also determine subsequent breeding success10, 12,13,14,15, emphasizing the high costs that individuals pay when migrating. Because migration is costly, migratory organisms are expected to maximize their fitness behaviourally via minimizing either the time spent, energy consumed, or the risks incurred during migratory journeys16, 17.

In terms of time, the highest cost of migration is generally thought to be experienced during stopovers rather than during periods of flight18, 19, and birds rely on the time spent at stopover sites to rest and refuel for the next leg of their journeys20. Optimal migration theory provides a framework to study stopover behaviour and its consequences by testing whether migrants are time- or energy-minimizers using data on fuelling rate, stopover duration, fuel loads and potential flight ranges17. Individuals attempting to minimize the overall time spent on migration are expected to maximize the amount of fuel they can acquire at each stopover in the shortest time possible. A key consequence of this strategy is that it maximizes the distance that can be flown between stopovers18, 21. Consequently, the fuel loads (amount of fat carried) of a time-minimizer should be tightly linked to local conditions at stopover sites as well as to the conditions expected ahead because these conditions influence fuelling rates18, 21. Furthermore, stopover durations in time-minimizers are expected to have been shaped by or to respond directly to experienced fuelling conditions17, 18. Larger departure fuel loads should allow for longer flights and a faster overall pace of migration because individuals acquiring sufficient fuel in the shortest time possible will need to make fewer stopovers and be able to take more direct routes to their destination, including being able to fly over physical barriers or large areas of unsuitable habitat such as deserts or oceans rather than circumventing these areas22.

Read more