Science

Common Poorwill, Uncommon Habit

It hibernates. 

We can already hear you: "Say what? The Common Poorwill hibernates? You have GOT to be kidding. Birds don't hibernate!" 

We're not kidding. Named "The Sleeping One" by the Native American Hopi tribe, the Common Poorwill (Phalaenoptilus nuttali) has a tendency to lie around all winter. This small, black and gray nightjar spends the colder months concealed in piles of rocks. It's not completely asleep, like, say a bear; instead, it's very greatly slowed down--a state called "torpor," in which metabolism and body temperature are reduced for days or even weeks. While some hummingbirds experience daily, short-term torpor in order to conserve energy, the Common Poorwill is the only bird known to have long bouts of it, which some scientists call hibernation. 

The Common Poorwill is nocturnal, which is rare in itself. Its habitat ranges from British Columbia and southeastern Alberta down to northern Mexico via the western United States. It prefers dry, open areas with grasses or shrubs; it also likes sparsely vegetated, stony desert areas. It is in the southernmost part of its range that the poor-will has most often been seen its long torpor bouts, usually in extremely cold and extremely hot weather, and sometimes even while incubating eggs. 

The Lewis & Clark expedition found torpid (or hibernating) Common Poorwills in North Dakota back in 1804. Dr. Edmund Yaeger described them in California in 1948.

In torpor, the poor-will's body temperature as been measured as low as 40°F, with a respiration rate reduced by 90%. That's pretty cool, huh? (In more ways than one.)  

 

Female Songbirds: Quiet for Good Reason

Female birds are capable of song in 71% of songbird species, So how come we don't hear them as often as we hear the males? New research indicates that sometimes female songbirds have good reasons to stay quiet. 

Sonia Kleindorfer, a behavioral ecologist at Flinders University in Adelaide, Australia, studied the singing patterns of female and male Superb Fairywrens (Malarus cyaneus), a small Australian songbird species. Like the females of many species, female Superb Fairywrens often sing for territorial defense, sometimes even when they're on their nests. They use a melody known as a "chatter song." The male uses it too, but he is not as often near the nest when he sings.  This is a key difference, since singing alerts predators such as rodents, cats, and foxes. Kleindorfer investigated whether male singing or female singing poses a greater risk.

During the nesting seasons of 2013 and 2014, Kleindorfer and her colleagues monitored male and female singing on and near 72 wild Superb Fairywren nests, as well as the eggs and chicks in the nests. The scientists counted a nest as “attacked” if eggs or chicks vanished in under 25 days. In other words, if eggs disappeared unhatched or chicks disappeared before they were capable of fledging, researchers assumed they'd been eaten. 

Kleindorfer's team leaned that both males and females sang the chatter song more often when they were just beginning to nest. They sang it less often when they had eggs and chicks in the nest, and with one major gender difference: The males sang away from the nest and the females near or inside it. In fact, some females never sang at all, and some sang only in response to their noisy mates. To put it differently, the females sang less when doing so would endanger their nests. Proof? The scientists baited artificial nests with quail eggs and broadcast female chatter songs infrequently (six calls per hour) and frequently (20 calls per hour). Predators ate the eggs at 40% of the "frequent" nests, but at only 20% of the "infrequent" nests: the quieter nests were safer for the kids. 

Jordan Price, a behavioral ecologist at St. Mary’s College of Maryland, posits that danger to the nest could be the reason that female songbirds of other species sing far less than their partners—or not at all—when they're the primary on-nest parents. It's even possible that, generally, male songbirds sing not to attract mates but simply because there's no reason for them not to. The females, on the other hand, have to be more wary. 

The Nocturnal Kiwi Bird

Instead of shivering while we think about winter, let's contemplate a bird who lives where it's summer right now: New Zealand's kiwi bird.  

There are five species of kiwi, all of them endangered, all of them flightless. They have no tail, only rudimentary wings, and nostrils at the end of their long, slender bills. As if those traits aren't weird enough, they are also nocturnal. We here at Talkin' Birds wonder whether they ever star in New Zealanders' ghost stories, but never mind.

Kiwis emerge from caves in the evenings to forage for food. Perhaps because they're active at night, they have lost their color vision and have gained an acute sense of smell. Interestingly, they also have a lower body temperature and slower metabolism than other birds. 

Fewer than 3% of the world's bird species are nocturnal. Researchers from the University of Leipzig and Max Planck Institute for Evolutionary Anthropology estimate that the kiwi became nocturnal about 35 million years ago, after its ancestors came to New Zealand. Why? They're not sure, but perhaps other bird species crowded them out of daytime food resources and they had to adapt. These researchers have sequenced the kiwi genome for the first time ever. Their findings recently appeared in Genome Biology, so take a look.

Too-Dark and Too-Light Birds

We can rely on our field guides, right? All birds of the same species and gender look the same?

Wrong. When it comes to color, an occasional bird may be darker or lighter than the others of its species. That's when you find yourself looking back and forth between the bird and your field guide and saying, "It SOUNDS like that one and it ACTS like that one and it's in a whole FLOCK of them--but it's the wrong color!" 

So what's going on?

If a bird is darker than usual: It's "melanistic" or a "dark morph." These birds possesses an excess of dark pigment, called melanin, in their feathers. They are sometimes so dark that their markings are impossible to see. Therefore, it's best to identify them by sound, behavior, and association with other birds. Some species, such as red-tailed hawks and ferruginous hawks, have regularly occurring instances of such birds. These more common dark birds are known as dark morphs.

Melanistic and dark morphed birds have a couple of advantages over normally colored birds. First, their dark feathers absorb sunlight more easily in cold climates, helping them stay warmer than normal birds. Second, darker birds generally have an easier time with camouflage. The disadvantage of excess melanin? It makes feathers brittle, so they break easily.

if a bird is lighter than usual: It's albino or "leucistic." These birds lack dark pigmentation.

Albino birds—very rare—are unable to produce melanin at all. They may have red markings only (red pigment is unaffected) or they may look completely pale, and their eyes appear pink or red. Since their eyes have no protection from UV light, they don't see very well. Their poor eyesight and light coloring make it unlikely that they'll survive until adulthood. 

Leucistic birds might lack either of two kinds of melanin, or their bodies simply might not be able to deposit melanin in their feathers. They appear lighter than others of their species, making them easier for predators to see. Their feathers tend to wear out quickly. 

So next time you see a bird that looks darker or lighter than the picture in your field guide, remember that it might be one of these variants. And let us know!

 

Merry Christmas Bird Count

Back in the 19th century, what we now know as the Christmas Bird Count (CBC) was the Christmas Side Hunt. The winning hunter would be the one who brought back the most prey. So how did this hunt get to be a bird census? More importantly, how do you tell who wins?

Back then, Americans were much more interested in hunting than in conservation. However, even the most driven hunters were beginning to notice that certain bird species were in decline. In 1900, the ornithologist Frank M. Chapman (officer of the very young Audubon Society) proposed a Christmas Bird Census instead of the traditional Christmas Side Hunt. That year, twenty-seven birders all over North America counted 18,500 birds in 89 species. A new Christmas tradition had begun.

So who wins the Christmas Bird Count? You guessed it: everybody, especially the birds. CBC data, gathered by citizen scientists for over a hundred years, provides an indispensable long view of the health and distribution of bird populations all over North America. 

Want to learn more, see the data archives, maybe get involved yourself? Signups begin every November, and the single-day counts take place starting a couple of weeks before Christmas. Check out the Christmas Bird Count on the Audubon website here

Migration Knows No Boundaries—and That's a Problem

Imagine you're a migrating bird. You've got to get to your winter home by molting season. You and your flock need to stop and refuel. Your senses and your memory tell you that this very spot is where you landed last year for water and a quick bite. But what's that? A parking lot? Now what are you going to do? 

A new study in the journal Science reveals that more than 90 percent of migrating birds find themselves in this situation (and worse) because of poorly coordinated conservation efforts around the world. Of the 1,451 bird species studied, 1,324—91 percent—traveled through areas that were not safeguarded from development. This means these birds may well have encountered the situation above. Further, eighteen species found themselves in unprotected breeding areas, and two species had no protection anywhere they went. 

“Migratory species cover vast distances and rely on an intact series of habitats in which they can rest and feed on their long journeys," conservation scientist Richard Fuller of the Australian Research Council's Centre of Excellence for Environmental Decisions (CEED) and the University of Queensland told the Associated Press. "If even a single link in this chain of sites is lost for a species, it could lead to major declines or even its extinction."

The United States and Great Britain signed the Migratory Bird Treaty in 1916 (with Great Britain signing for Canada) to protect birds that cross their international boundaries. Similar treaties have been made with Mexico (1936), Japan (1972), and Russia (1976). This is a good start, but habitat destruction is worst in North Africa, Central Asia, and the coastlines of East Asia. In these regions, the safeguarded areas—if any—do not overlap enough to provide a migration route for birds. One example of a bird at risk is the Bar-tailed Godwit. This well-traveled bird migrates from the Arctic to Australia and New Zealand, making stops in China, North Korea, and South Korea. Its population is dwindling because of the loss of habitat along its route.

The protection of migrating wildlife is a concern for all countries. We here at Talkin' Birds imagine it could bring about cooperation among people who don't usually cooperate. Meanwhile, if we could, we would donate all our frequent-flyer miles to the Bar-tailed Godwit.

 

 

Zebra Finch Pairs Seem to Discuss Child-Rearing Inequalities

Like humans, some bird species mate for life and rear chicks together. But do they squabble like we do when one partner seems to be slacking off? The answer seems to be yes.

A forthcoming article in the Biological Journal of the Linnean Society describes research on vocalizations between Zebra Finch mates (Taeniopygia guttata) when they're incubating eggs. Zebra Finch couples share all chick-rearing responsibilities, including sitting on the nest before the chicks hatch. They sit in shifts about a half-hour long; while one sits, the other goes in search of food. When it's time to change shifts, the finches have what sounds like a conversation. Researchers were curious about whether this finch-to-finch conversation would change if one spouse were late returning to the nest for his or her turn. 

Working with twelve pairs of Zebra Finches incubating eggs in a large aviary, researchers trapped the male of each pair at the beginning of a foraging shift and detained him for an entire hour. Remember, his spouse was home on the nest, expecting him to return in a half hour. She did not leave the nest while waiting. Instead, she and the male had a, um, rapid conversation when he finally returned, vocalizing at each other faster than usual. (We imagine a heated argument.)

Are you wondering whether a female took extra time away from the nest if her spouse came back late? The answer: only if the male didn't talk with her much. If the late-arriving male initiated only a short conversation, the female would fly off for up to an hour. However, if the male took the time to "talk" longer with the female, she'd come back in 30 minutes. In other words, it looked as if the female got back at the male only if both spouses did not talk long enough to sort things out. 

No word on what the unhatched chicks thought about these delayed arrivals and arguments. Perhaps a next-generation study is in order.

Few Answers (So Far) Concerning West Nile Virus in Bird Populations

 A new study in Proceedings of the National Academy of Sciences indicates that West Nile virus (WNV) is killing millions of birds every year in North America, but few clear patterns are yet visible. 

West Nile Virus (WNW), which arrived on this continent about 16 years ago from Africa, is carried by mosquitoes. It can infect and kill people, but birds are its preferred host. Because North American bird populations had not previously encountered WNV, they had not developed any resistance to it. Therefore, the virus spread across the entire continent in only five years, leaving millions of birds dead. Earlier studies had shown that other factors, such as climate and habitat, influenced the virus's effect on various bird species. For instance, it was found that birds in urban environments seemed more likely to contract it, for reasons that are still unknown.

A team of scientists analyzed 16 years of data collected from 1992 to 2007 at more than 500 Monitoring Avian Productivity and Survivorship (MAPS) stations across the United States. (MAPS data after 2007 weren't included because they have not yet been processed.) Using this information, the scientists were able to determine whether and how the virus first affected various bird populations and whether their numbers have recovered or are still declining. They studied a quarter-million birds from 49 species, focusing on adults.

Twenty-three of the species studied were negatively affected. Some initially suffered huge declines. For example, Red-Eyed Vireo (Vireo olivaceus) populations dropped about 29% in the year they first encountered the disease. As expected by disease ecologists, their numbers subsequently recovered. Ryan Harrigan, an infectious disease biologist at the University of California, Los Angeles (one of the study's authors) explains, “Everyone builds up immunity, and the impact tends to wane.” Eleven of the 23 affected species in the study experienced this type of recovery. 

 

But the other twelve species were not so lucky: their populations are still declining for unknown reasons. For example, populations of Warbling Vireos (Vireo gilvus) dropped only 8.7% when they contracted WNV. But instead of recovering, they've continued to drop every year by roughly the same percentage.

To try to understand why some species overcome the disease better than others, the researchers compared their habitats. Here, too, results were mixed. Ten species, including the Spotted Towhee (Pipilo maculatus) and Song Sparrow (Melospiza melodia), did not show significant losses among adults, but eleven other species in these same urban areas did. The scientists also studied whether closely related species were affected similarly by WNV. Again, the pattern was mixed. Researchers are now looking more closely at regions where certain species are still dying to see whether they can spot the reason. And they have no idea why WNV did not affect at least three species, the black-capped chickadee (Parus atricapillus), American robin (Turdus migratorius), and house wren (Troglodytes aedon). Meanwhile, Staffan Bensch, an animal ecologist at Lund University in Sweden, wonders whether the virus might even be benefitting some songbird species by killing off jays and crows, which prey on them.

One further area of concern is that the virus may be causing particular harm to birds with smaller populations and ranges--that is, endangered birds. No answers are presenting themselves at this time. The researchers say that finding them will require more long-term data of the type collected at the MAPS stations. Ultimately, they hope that understanding the behavior of WNV in bird populations will help us understand its behavior in human populations.

For further reading, check out the study: http://www.pnas.org/content/early/2015/10/27/1507747112

 

Shells and Feathers: Climate Change Affects All

If you've ever had difficulty finding a date, consider the plight of the loggerhead turtle. Although this species has been around for more than 60 million years, climate change is threatening their future reproduction. Researchers from Florida Atlantic University have just published the results of a four-year study in the journal Endangered Species Research.

The sex of sea turtles is defined when they're still in their eggs, which develop in underground nests. Warmer conditions produce females and cooler conditions produce males. The research team documented rainfall, nest temperatures, and other measurements at a loggerhead turtle nesting beach in Boca Raton over the course of four years. The majority of the loggerhead hatchlings entering the northwestern Atlantic come from this area. Most of the hatchlings in the sampling were female, suggesting that nest temperatures were not sufficiently cool year-round to produce males.

"If climatic changes continue to force the sex ratio bias of loggerheads to even greater extremes, we are going to lose the diversity of sea turtles as well as their overall ability to reproduce effectively," says Jeanette Wyneken, Ph.D., professor of biological sciences in FAU's Charles E. Schmidt College of Science.

A mama loggerhead lays roughly 105 eggs per nesting season, which spans April to October. Only one in 2,500 to 7,000 sea turtles makes it to adulthood. A female would have to nest for more than 10 nesting seasons (over the span of 20 to 30 years) just to replace herself and possibly one mate. 

 

How Do Owls Turn Their Heads?

An interesting fact about owls: they cannot move their eyes! In order to follow the movements of their prey, they have to turn their heads. Owls can turn their heads up to 270 degrees, or three-quarters of the way around. If we did that we'd rupture blood vessels and cut off the blood supply to our brains. So how do owls do it?

Researchers at Johns Hopkins University, led by medical illustrator Fabian de Kok-Mercado, M.A., found major biological adaptations in owls' bones and arteries that prevent injury when they rotate their heads. 

The team studied the heads and necks of Snowy, Barred and Great Horned Owls after they'd died from natural causes. They discovered that one of the major arteries nourishing the brain passes through bony holes in the vertebrae (neck bones). The hollow cavities are about 10 times larger across than the artery traveling through them. The researchers say that this extra space allows the artery to move when it's twisted. Twelve of the 14 vertebrae in the owl's neck were found to have this adaptation.

Among the team's other findings: small vessel connections between the carotid and vertebral arteries that allow blood to be exchanged between them. We humans don't have these connections. The researchers say they allow for uninterrupted blood flow to the brain even if one route is blocked when the neck rotates.

No word on whether your high school math teacher had any of these adaptations. Better to assume she simply had eyes in the back of her head.

Want to hear more about owls and their amazing necks? We did a Science Corner piece about it on the radio show of December 8, 2013. Click here to listen!