October 8, 2013
In 2011, Felix Liechti and his colleagues at the Swiss Ornithological Institute attached electronic tags that log movement to six alpine swifts. The small birds—each weighs less than a quarter of a pound—spend the summer breeding in Europe, then migrate to Africa for the winter, thousands of miles away.
“We wanted to learn about energy demands during migration. We expected to see how often they fly, how often they stop, that sort of thing,” he said.
But a year later, when three of the birds returned to the same breeding site and the scientists removed their tags to collect the data, the electronic tags revealed something unexpected. “When we looked at the data, we were totally blown away,” Liechti said. “During their non-breeding period in Africa, they were always in the air.”
For more than 200 straight days straight, as revealed by his team’s study published today in Nature Communications, the birds stayed aloft over West Africa. The tags only collect data every four minutes, so it’s impossible to rule out the chance that they touched down occasionally in between these intervals—but every single one of the data points collected for more than six months in a row indicated that, at the time, they were either actively flying or at least gliding in the air.
Ornithologists had previously speculated that a closely related common swift was capable of staying in flight for extremely long periods of time, but this is the first time anyone has collected hard data. The new finding was, in part, enabled by developments in technology—this was the first time that this particular kind of sensor, developed by at Bern University, was attached to birds for research.
Its tiny size allowed the researchers to attach it to relatively small birds without interfering with their free movement. The tags solely collected data on acceleration, the
pitch of the bird’s body (the angle of its body relative to the ground) and light hitting the bird at any given time. From the latter, scientists were able to infer latitude, due to the timing of sunrise and sunset.
By comparing the acceleration and pitch data to that of birds under observation, Liechti and the others could match particular data patterns with different types of movement—flying (with flapping wings), passively gliding in the air and resting on the ground. “They stayed in the air for all time they spent south of the Sahara, day and night,” he said. “Sometimes they just glide for a few minutes, so there’s no movement, but the pitch of the body indicates that they’re still gliding in the air.”
It’s still a mystery how the birds are able to physiologically accomplish this feat. The diet aspect is relatively straightforward—they largely feed on airborne insects—but until now, opinions differed over the question of whether birds could sleep while aloft. Sleep patterns in birds are fundamentally different than in mammals, and the difficulty of studying the brainwaves of migrating birds makes it very hard to fully understand how they rest while in motion. But the fact that these swifts never touch down for such a long time indicates that they’re able to rest in midair.
There’s also the deeper (and perhaps more confounding) question of why the birds would bother staying aloft for their entire time in Africa. At this point, it’s pure speculation, but Liechti suggests that diet could play a role. “We observed that the further north they go, the more they stay on the ground at night,” he said. “Additionally, the further north you go, the less insects there are in the air—so it might be related.” He also proposes that staying in air could reduce the risk of predation or perhaps the chance of catching a disease.
Perhaps most exciting is the fact that this finding came after just the first time the new, ultra-lightweight movement sensor was used in avian research. Tagging other sorts of birds that are too small for conventional sensors might tell us similarly surprising things about their movement or migrations habits. “It’s fascinating,” Liechti said, “and it opens up a whole new window for us into these species.”
September 24, 2013
Few examples of parasites in nature are as infamous as the gutsy, lazy cuckoo bird, which lays its eggs in unsuspecting nests so it doesn’t have to bother with rearing its own young. The garish cuckoo chick, oftentimes dwarfing its host parents in size, monopolizes food by mimicking its siblings cheeps but screaming the loudest, and by thrusting its gaping beak out whenever “mom” or “dad” show up with a tasty morsel. The monster chick will oftentimes go so far as to kick its step-siblings out of the nest, issuing a death sentence by starvation, predation or the elements.
But those cuckolded host parents aren’t completely dim. They are engaged in a constant evolutionary sprint with these enemy brood parasites and are continuously adapting new ways to weed out the impostors and confirm their own eggs’ identity. They mentally imprint on their own eggs, for example, and repeatedly scan their nest in a game of which-of-these-things-does-not-belong. If they spot an egg that does not fit their internal template, they throw it overboard.
They also examine their nest to determine proportions of different egg types, favoring the majority since common cuckoos only lay one egg per nest. If there’s three brown eggs and one speckled one, they will surmise that the speckled one must contain an unwanted baby bomb.
One brood parasite, the the diminutive cuckoo finch, uses many of the same strategies, although it belongs to a different biological order of birds than the common cuckoo. Unlike its larger cousins, however, the clever cuckoo finch has developed a novel method for outsmarting those discerning hosts, according to researchers from the University of Cambridge and the University of Cape Town in a new paper published in Nature Communications.
“Interactions between hosts and parasites are often evolutionarily older in the tropics than in the better-studied temperate parts of the world, resulting in sophisticated trickery and counter-defense such as this,” said Claire Spottiswoode, a zoologist at the University of Cambridge and co-author of the paper, in an email.
Rather than simply match her eggs to her victim’s own colors and patterns, the mother cuckoo finch plants a minefield of parasitism, laying several eggs at once to ensure the balance is tipped in her manipulative favor.
“Brood parasites and their hosts are often locked in an ongoing arms race of attack and defense, with each escalating over evolution,” explained Martin Stevens, an ecologist at the University of Exeter (formerly of the University of Cambridge) and lead author of the paper, in an email. “Our work shows that cuckoo finches have a cunning strategy to beat host defenses and trick them into accepting not just one, but often multiple parasitic eggs.”
To arrive at these findings, Stevens, Spottiswoode and co-author Jolyon Troscianko traveled to Zambia. They searched the grasslands for nests built by tawny flanked prinias, a somewhat drab passerine bird that is a favorite victim of cuckoo finches. The prinias lay a lovely array of colored eggs–red, blue, olive and white, of all different speckled patterns–although females stick to one egg color and pattern type throughout their life times.
Rather than mimic those eggs, cuckoo finches rely upon chance luck to get their egg-matching right. ”Adult cuckoo finches and prinia might not be the most exciting birds to look at in terms of their plumage, but when you see how wonderfully colorful and diverse their eggs are, you realize that there must be a remarkable evolutionary battle going on inside the host nests,” Stevens says.
To figure out how the cuckoos manage their deceit, the researchers performed several field experiments. First, they swapped prinia eggs in different configurations between around 50 nests. Some birds received one foreign egg and kept two of their own, while others received one egg and kept three, or two eggs and kept two.
The team recorded how often the birds purged their nests of suspect eggs; which of those eggs they kicked out; and how close a visual match those foreign eggs were compared to their own. They found that the prinias were significantly more likely to reject the foreign eggs than their own eggs. In the few cases that they rejected their own eggs, the foreign eggs were a very close match in color and pattern.
By further statistically analyzing these results, the team was able to break down which factors influence whether or not a host bird rejects or accepts an egg. They found that pattern diversity, pattern size and the proportion of foreign eggs all significantly influenced whether a host bird keeps or dumps a foreign egg.
The more impostor eggs that pop up in a nest, however, the more extreme the color differences need to be for the host bird to pick up on the trick, the researchers found. They ran a model of known cuckoo egg patterns and ratios compared to prinias, and found that cuckoos will randomly closely match egg color and pattern with the prinias about 25 percent of the time.
These predictions were reflected in the real-life nest dramas at play on the savannah. Of 62 prinia nests that cuckoo finches had parasitized, the researchers found that two-thirds contained two or three cuckoo eggs laid by the same female. Tellingly, in just over half of those nests only cuckoo eggs remained, indicating that the host parents likely unknowingly expelled their own unborn chicks.
“By laying several eggs in a host nest, the cuckoo finch causes confusion in host defenses, and when this is combined with effective mimicry, the parasite can outwit the host and help more of its young to be reared,” Stevens says.
Unlike common cuckoos, cuckoo finch chicks don’t actively kill their nest mates, alleviating the possibility that parasitic chicks will engage in a gladiator-like battle for survival against their true brothers and sisters. To confirm this, the researchers kept an eye on around a dozen parasitized nests, watching what happened as the chicks grew older. In 85 percent of those dysfunctional families, two parasitic chicks fledged from a single nest. Avoiding murderous impulses is likely yet another clever adaptation the species has pursued for perfecting its multi-egg laying regime, the team writes, since those chirping nest-mates are more likely than not to be parasitic siblings.
“Tropical species surely still have many more intriguing adaptations yet to reveal to us,” Spottiswoode said. “One of the many reasons we’re lucky to work in Zambia is not only its wonderful study species, but also the help of our brilliant team of local assistants who have found every single nest involved in our field experiments over the last seven years.”
September 11, 2013
There’s a reason children taunt each other with calls of “Chicken!” at the smallest sign of hesitancy. Birds tend to be flighty little creatures, easily spooked at the first sign of danger. In nature–as reflected in pop culture–however, different birds deal with stress in a variety of ways. Diminutive Donald Duck is a mess of nerves, for example, whereas Big Bird is a chill, go-with-the-flow kind of guy.
In fact, in a curious case of art reflecting nature, it turns out a bird’s bird-brainedness is not a matter of personal bravado or cowardliness, but rather of a question of intrinsic smarts, a new study published in the Proceedings of the Royal Society B: Biological Science finds. The bigger the bird brain compared to the body, researchers discovered, the less ruffled that animal becomes under pressure.
When we encounter a stressful situation, whether bird or human, our body responds by flooding our system with stress hormones called glucocorticoids. For people, this fight-of-flight response may produce a racing heart and sweaty palms on the short-term, but if sustained over a long period of time–in the case of an illness in the family, a divorce or a job loss, for example–chronic stress can result in depression, insomnia and a host of other health impacts. Fellow vertebrates such as birds are no exception. How they cope with stress takes a toll on their ability to survive and produce offspring.
Not all species respond in the same ways to stress, however. Birds’ maximum stress hormone levels vary 12-fold across different species. Those species with the lowest stress levels, researchers hypothesized, may also possess the larger brains, which help them keep their feathers on when fear takes hold. Larger bird brains (pdf), past studies already found, correlate with a higher propensity for learning and for dealing with new situations. Evading as well as dealing effectively with problems requires some degree of smarts and the ability to learn, the researchers figured, so stress could be tied to a bird’s brain-to-body ratio–a proxy for intelligence.
To see whether bird brain sizes do indeed relate to their stress levels, an international team of researchers created a global database of stress levels reported in 189 previously published scientific studies for 119 bird species, from penguins to tropical songbirds. Stress levels in these studies were assessed by determining the concentrations of glucocorticoids in the birds’ blood.
Two different stress hormone levels–when birds were first captured and hadn’t had the chance to chemically panic yet, and when birds hit their peak stress levels after being held captive for 5 to 70 minutes–were included in the database. The authors used a statistical modeling technique to analyze the birds body-to-brain ratios compared to the animals’ glucocorticoids. They were careful to take into consideration how and when the stress level data had been attained, such as when the bird was migrating, wintering, preparing to breed or taking care of chicks.
Bird species, they found, share a common stress baseline and peak. In other words, all of Donal Duck’s brethren will be equally skittish, whereas Big Bird’s flock (yes, he has one) wil be relaxed all around. Further confirming their hypothesis, bigger-brained birds, they found, had lower levels of glucocorticoids in their blood than their less cranially-endowed counterparts.
Asio otus, the long-eared owl, for example, lived up to the wise owl stereotype with its large brain. It turned out to have relatively low stress hormone concentrations, as opposed to Calidris pusilla, the semipalmated sandpiper, which sat trembling at the other end of the small brain/high stress spectrum. During the wintering stage, the long-eared owl sported baseline stress levels four times smaller than the sandpiper.
When the owl was most stressed out, it was still relatively super-chill compared to sandpipers: the highest levels of stress hormone in the owl’s blood peaked at concentrations that were 3.5 times lower than peak stress levels found in sandpipers. Peak stress levels–when the avians were at the height of their frenzied freak-out–between these and other species were especially varied between the smart and not-so-bright birds.
Simply possessing a larger body size or living life at a slower pace, the team pointed out, did not necessarily mean a more relaxed outlook; in other words, a hummingbird would not necessarily be less adept at managing stress than an ostrich. Rather, the differences hinge upon that crucial brain-to-body ratio.
In addition to keeping their cool under pressure, the researchers predict that smarter birds likely know danger when they see it, and take measures to avoid it. More work will be needed to confirm this hypothesis, though it does hint at the possibility that, for birds at least, stupid-is-as-stupid-does, whereas the gift of intellect keeps perpetually giving.
August 29, 2013
The Eastern U.S. is home to exactly one population of wild whooping cranes. Each fall, members of the flock migrate more than 3,000 miles, from Alberta, Canada, to the Gulf Coast of Texas. But these enormous, long-lived birds (they can stand up to five feet tall and live as long as 30 years) are endangered, with only about 250 left in the wild.
The Whooping Crane Eastern Partnership is trying to change that. Since 2001, the group has bred cranes at the Patuxent Wildlife Research Refuge in Maryland, brought them to the Necedah National Wildlife Refuge in Wisconsin for nesting, then guided young cranes down to Chassahowitzka National Wildlife Refuge in Florida for the winter with an ultralight aircraft, just like the technique used in the movie Fly Away Home.
After their first migration, the cranes are left to their own devices and are forced to make the trip on their own every year. But to ensure their survival, researchers carefully track and log the precise routes they take each year, using radio transmitters attached to the birds.
For Thomas Mueller, a University of Maryland biologist who studies animal migration patterns, eight years of records collected as part of this project were an especially appealing set of data. “The data allowed us to track migration over the course of individual animal’s lifetimes, and see how it changed over time,” he said.
When he and colleagues analyzed the data, they found something surprising. As they write in an article published today in Science, the whooping cranes’ skill in navigating a direct route between Wisconsin and Florida is entirely predicated on one factor: the wisdom of their elders.
“How well a group of cranes does as a whole, in terms of migrating most effectively and not veering off route, really depends on the oldest bird in the group, the one with the most experience,” Mueller says. The years of data showed that, as each bird aged, it got better and better at navigating, and that young birds clearly relied heavily on the guidance of elders—the presence of just a single eight-year-old adult in a group led to 38 percent less deviation from the shortest possible route between Wisconsin and Florida, compared to a group made up solely of one-year-olds. Mueller’s team speculates this is because as the birds age, they grow more adept at spotting landmarks to ensure that they’re on the right path.
The data also indicate that the flocks are prone to following one particular elder in any given migration, because total group size didn’t correlate with shorter trips. In other words, it’s not the overall migratory skill of the group as a whole that determines the flock’s route, but the expertise of one key elder crane that does so.
For Mueller, this finding helps to answer a question that researchers have been asking for years: Is the ability to migrate thousands of miles genetic, or learned? The research, which didn’t investigate genetics specifically, nonetheless gives credence to the latter.”This is really social learning from other birds, over the course of years,” he says. At the same time, he notes that “there’s also an innate component to it, because after they’re taught the migration once, the birds initiate it on their own every spring.”
These findings could have important implications for the conservation efforts. For one, they vindicate the current model of teaching young birds how to migrate once with an ultralight aircraft, because at this point, there are so few older birds in the breeding flock that can perform their natural role as migratory leaders. By letting the birds migrate on their own afterwards, though, the program allows them to learn from elders and develop their navigation skills.
The work could also provide hope for one of the crane program’s biggest challenges: getting the birds to breed on their own in the wild. Thus far, very few of the human-reared birds have successfully bred on their own after maturation. But if navigation is a skill that’s developed slowly over time, as the birds learn from others, it’s possible that breeding could operate the same way too. As the flock’s population ages as a whole and features a larger proportion of elder birds, the researchers say, they could gradually get more adept at breeding and pass those skills on to others.
July 2, 2013
The problem of antibiotic-resistant bacteria—especially MRSA (methicillin-resistant Staphylococcus aureus)—has ballooned in recent years. Bacteria in the Staphylococcus genus have always infected humans, causing skin abscesses, a weakened immune system that leaves the body more susceptible to other infections, and—if left untreated—death.
Historically, staph with resistance to drugs have mostly spread within hospitals. Last year, though, a study found that from 2003 to 2008, the number of people checking into U.S. hospitals with MRSA doubled; moreover, in each of the last three years, this number has exceeded the amount of hospital patients with HIV or influenza combined. Even worse, multidrug-resistant Staphylococcus aureus (MDRSA) has become an issue, as doctors have encountered increasing numbers of patients who arrive with infections resistant to several different drugs that are normally used to treat afflictions.
It’s clear that these bacteria are acquiring resistance and spreading outside of hospital settings. But where exactly is it happening?
Many scientists believe that the problem can be traced to a setting where antibiotics are used liberally: industrial-scale livestock operations. Farm operators habitually include antibiotics in the feed and water of pigs, chickens and other animals to promote their growth rather than to treat particular infections. As a result, they expose bacteria to these chemicals on a consistent basis. Random mutations enable a small fraction of bacteria to survive, and constant exposure to antibiotics preferentially allows these hardier, mutated strains to reproduce.
From there, the bacteria can spread from the livestock to people who work in close contact with the animals, and then to other community members nearby. Previously, scientists have found MRSA living in both the pork produced by industrial-scale pig farms in Iowa and in the noses of many of the workers at the same farms.
Now, a new study makes the link between livestock raised on antibiotics and MDRSA even clearer. As published today in PLOS ONE, workers employed at factory farms that used antibiotics had MDRSA in their airways at rates double those of workers at antibiotic-free farms.
For the study, researchers from Johns Hopkins University and elsewhere examined workers at several pork and chicken farms in North Carolina. Because the workers could be at risk of losing their jobs if farm owners found out they’d participated, the researchers didn’t publish the names of the farms or workers, but surveyed them about how animals were raised at their farms and categorized them as industrial or antibiotic-free operations.
The scientists also swabbed the nasal cavities of the workers and cultured the staph bacteria they found to gauge the rates of infection by MDRSA. As a whole, the two groups of workers had similar rates of normal staph (the kind that can be wiped out by antibiotics), but colonies of MDRSA—resistant to several different drugs typically used as treatment—were present in 37 percent of workers at industrial farms, compared to 19 percent of workers at farms that didn’t use antibiotics.
Perhaps even more troubling, the industrial livestock workers were much more likely than those working at antibiotic-free operations(56 percent vs. 3 percent) to host staph that were resistant to tetracycline, a group of antibiotics prescribed frequently as well as the type of antibiotic most commonly used in livestock operations.
This research is just the beginning of a broader endeavor aimed at understanding how common agricultural practices are contributing to the development of antibiotic-resistant bacteria. The scientists say that surveying the family members of farm workers and other people they come in frequent contact with would help to model how such infections spread from person to person. Eventually, further evidence on MDRSA evolving in this setting could help justify tighter regulations on habitual antibiotic use on livestock.