Wednesday, March 26, 2014

Analyzing a Trade-Off, Swiftly

Now that we've completely our obsession with Picidae, why don't we switch over to, of all things, swifts (family: Apodidae)? Shall we?

The incredible migration of the Bar-tailed Godwit. Image
credit: USGS Alaska Science Center
If you're a researcher looking to study flight, birds are a pretty good place to start. Birds have achieved flight speeds from 200 miles per hour all the way down to 13, with everything in between. Birds have flown extended journeys well above Mt. Everest and well below the surface of the ocean, mastering flight both in the jet stream and in the most powerful of ocean currents. Certain birds have adapted to completing sustained, unbroken migrations across more than 7,000 miles of the Pacific Ocean in only nine days. Migratory birds in North America that weigh less than an ounce take on flights straight across the Gulf of Mexico twice every year. Some birds fly by barely flapping their wings at all, using thermals to soar across hundreds of miles of mountain range per day. Others flap their wings more than 80 times per second for the hovering precision needed to feed constantly on nectar. Some birds can chase fleeing forest birds through dense tangles of vegetation at 30 miles per hour, while others can pursue duck prey over arctic tundra with sustained flight speeds of 70 miles per hour. Others still can carry loads of fish that weigh up to half the body weight of the avian carrier.

Common Swift - Image Credit: Wikipedia
But perhaps one of the best places to start, amongst the overwhelming variety and splendor of bird's feats in flight, is with the birds that do it the most. Swifts--a family termed Apodidae, derived from the Ancient Greek work for "without feet"--hold the record for spending the highest proportion of their lives on the wing. The record-holder for the longest sustained flight is the Common Swift of Eurasia, ranging between 2 to 4 years of nonstop flight at certain ages.

Swifts provide a frontier to press towards in the understanding of avian flight. Being capable of such sustained flight, however, does not mean being "ideal for flight" in general, though of any bird, swifts would be fairly close to that ideal. Platonism does not work in nature, and we might as well wash that from our brains now. Everything that makes any animal what it is exists purely based on the pre-existing genetic material and how that material adapts to the conditions it finds itself in. Swifts are not ideal for flight. They are ideal for flight in "x" circumstances, or in "x" conditions.

Being able to sustain flight for years means that swifts are able to adapt to an enormous array of conditions aloft, some of which we, as land-bound primates, can't understand. Swifts must adapt to random wind shifts from calm to extreme speeds, shifts in wind direction, changes between rising and falling columns of air, differences between air above water and air above land, rain, hail, snow, sleet, fog, blinding sunshine, and they have to do so while navigating the skies and finding enough food to sustain such an effort.

Pamprodactyly - Image credit:
kidwings.com
But fear not...swifts have a slurry of adaptations to make them such masters of the sky. First, swifts have a body shape to reduce what's called parasitic drag--the drag that is inherent to any body trying to sustain lift in the air. This also means having tiny feet that don't get in the way of airflow. This lends itself to an issue: swifts are incapable of perching, but their feet have adapted to the next best thing. Because swifts can only cling to vertical surfaces of crawl along flat surfaces, they have adapted a unique and muscular toe configuration called pamprodactyly. Swifts are also capable of what's called unihemispheric slow-wave sleep, which means they can sleep with one side (hemisphere) of the brain at a time, leaving the other half awake to control flight and navigation. Behaviorally, swifts collect all of their nesting material from debris in the air, drink in flight, court, and even mate in midair.

Only the sections here labeled with X contain
the swift's arms. The rest of the wings are
feathers, without any bones.
Image from Henningsson et al. 2008
Perhaps the most important adaptations swifts boast is their wings, and even more importantly, how they use them. Swifts have a fairly unique physiology of the wing: the actual arm portion of the wing is extremely short, with the wrist of the wing placed quite close to the body. Most of the wing, then, is the outer wing feathers that go from the wrist and form the tip of the wing: the primaries. In swifts, the bones that control the wingtip are also relatively large. Why? With these relatively small modifications to typical avian wing morphology, swifts have enormous control over the angle and shape of their wings, which allows them to adapt to changing conditions aloft and retain control and maneuverability. Also impressive, swifts share the ability to rotate their wings at the base with hummingbirds. This allows their wings to be fully extended--and thus to generate the most lift--on both the upstroke and the downstroke. With this sort of complexity already present in swifts, a recent study reveals one of my favorite evolutionary phenomena in swifts: a trade-off.

Swifts are renowned both for their gliding flight and their flapping flight, but both require very different physiological adaptations--contrast the wings of predominantly gliding condors with those of predominantly flapping ducks. One would expect, when looking at swifts, that they are equally well adapted to flapping flight as they are to gliding flight. Makes sense right? This way, swifts would be ideal for flapping or gliding.

But remember, there are always more conditions, more variables, to consider. In this case, we know that swifts benefit from the highest possible level of efficiency, and ultimately, this means being efficient with energy. So let's ask the important question. Which kind of flight requires the most energy: flapping, or gliding? The answer to us seems obvious. While gliding is relatively passive, flapping requires constant effort of a complex muscle system and takes much more energy. This discrepancy is where we find the trade-off--in order to maximize efficiency in flight overall, swifts must balance their efficiency at gliding with their efficiency at flapping, because, after all, they can't switch between a body optimized for flapping and a body optimized for gliding every time they switch flight styles!

This is figure 1 from the first study cited below. Dark blue
corresponds to positive lift, or upward motion, which, for
our purposes, means best possible efficiency. 
And like with all trade-offs, evolution handles this one beautifully. Because swifts spend much more energy at flapping, swift wings have adapted more towards efficiency at flapping to minimize this energy cost. They are "flapping-biased". While they may be less efficient at gliding because of this, gliding required less energy to begin with. By minimizing the energy cost of flapping rather than adapting equally to flapping and gliding, the energy cost of flying overall is less for the swifts. It's a balancing act folks, and in this one, leaning toward flapping works best. Isn't that fascinating?!

The level of complexity in animals we can sometimes take for granted, like twittering swifts spiraling overhead, is dumbfounding; we have so much to understand even just outside our bedroom windows. If we could only see the gray of the unknown in the world around us, like some strange, brain-wave-reading Google Glass app, we would see an inordinately gray world.

And in order to clear some of the gray with swifts, the scientists in the above-mentioned study only needed a curious eye, some math, and a stopwatch. Oh and a windtunnel. Don't forget the windtunnel.

Have a great day everybody.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

References:

Henningsson, Per, Anders Hedenström, and Richard J. Bomphrey. "Efficiency of Lift Production in Flapping
     and Gliding Flight of Swifts." PLOS ONE. PLOS ONE, 28 Feb. 2014. Web. 26 Mar. 2014
     <http://www.plosone.org/article/info%253Adoi%252F10.1371%252Fjournal.pone.0090170>.

Henningsson, P., G. R. Spedding, and A. Hedenström. "Vortex Wake and Flight Kinematics of a Swift in
     Cruising Flight in a Wind Tunnel." The Journal of Experimental Biology. The Journal of Experimental
     Biology, 2 Jan. 2008. Web. 26 Mar. 2014. <http://jeb.biologists.org/content/211/5/717.full>.

Tuesday, March 11, 2014

Bio-Control: Tying together our Woodpecker Journey

Photo by scarboroughcruiser
Invasive species are...complicated. Well, actually, they aren't necessarily complicated themselves; the situations they breed are what is complicated. Take the issue of the explosive Asian Carp population in the Mississippi, which consumes much of the food sources required by an enormous set of native fish species to survive at all. Ecological catastrophe will follow if their invasion succeeds in conquering the Great Lakes. House Sparrows, an all-too-familiar species introduced from England in the 19th-century, presents such bellicose competition for nest cavities that they will literally murder Bluebird chicks in a nest box and go on to build their nest on top of their corpses.

But one species in particular, friends, has gotten my attention, and the attention of all those with trees above their heads...trees that may be slowly but surely falling and dying out mysteriously. This invasive is the Emerald Ash Borer (EAB in short). To the chagrin of interstate firewood smugglers, Emerald Ash Borers have pervaded much of North America from their origin in Asia, and, at this point, human efforts have largely been unable to stop their silent incursion.
Adult Emerald Ash Borer
Photo by Dan Small

The problem with invasive species is what makes them invasive. Being
non-native to the area that they are invading, the often face no natural opposition at any level of the ecosystem, and are often able to out-compete native species. Being successful at invading an area means being coincidentally better adapted to exploiting that ecosystem than that ecosystem's natural occupants. It's a bad deal folks, and yes, we should be scared.

The real culprits...the larvae
Photo by David Cappaert
We should be scared because...well...take Chicago After losing an estimated 30 million ash trees in the Eastern half of the continent alone, 17% of street trees in Chicago are the ash trees that the Borers target. This means that on the city-owned property along streets alone, 85,000 trees are up for grabs to our untouchable insect invader. Not enough for you? It is estimated that 300,000 ash trees occupy private property in the city--we are facing significant holes in ecosystems and shade over our heads. Not to mention safety hazards resulting from decrepit, infested trees.
EAB infestation marks by John Marvin
Phelps

Before we move on to the science of birds, what is it that ash borers do to trees, you ask? Ash borers are problematic primarily in their larval stage. In this stage, they live just below the bark in the top layer of wood, burrowing serpentine ruts. These ruts, which I'm sure you've seen, look like tiny squiggled indentations into the wood. Why is this an issue for strong and stoic trees? This top layer of wood is extremely important to the trees and all plants; this is where the plant's vascular system is. Similar to our system of blood vessels and veins, this layer of wood contains cataracts that transport water and nutrients around the plant. Damaging it would be like damaging our blood vessels. And a badly infested tree can be entirely cut through its vascular system.

How do birds play into this, then? Woodpeckers (here they are again) specialize in feeding on larvae within this layer of wood. By preying on larvae and other insects within the bark and top layer of wood, woodpeckers help maintain the trees' health and ultimately the health of the forest. It's a great deal, you guys.

Top to bottom: male Downy and Red-bellied
Woodpeckers by Warren Lynn
But the question is this: do woodpeckers (and nuthatches, for that matter) prey upon Emerald Ash Borer larvae? Normally, part of the success of invasive species is their lack of natural predators in the area they're invading. Asian Carp are a perfect example of this; they have no predators to control their populations. Can we look to woodpeckers as a potential bio-control of invasive EAB's, one that we don't need to interfere with anymore than by preserving healthy woodpecker populations?

Here's the best part. A bunch of middle-schoolers in Ohio helped us find that the answer is a resounding yes. A group of researchers recently conducted a study to answer these questions, in which they established observation plots in Michigan and Ohio to follow the dynamics of the forest ecosystem in response to the Borers. One of these plots lay behind an Ohio middle school, where the researchers reached out to the students to be part of a multi-year citizen science project. Here's how it worked according to an article on this study by the University of Illinois at Chicago:
"A section of trees in the stand behind the school was cut down for examination each year for two years. The students searched for and painted all the holes they found in the bark of each tree—a different color each for large round woodpecker holes, for the characteristic crescent-shaped holes mature emerald ash borers make exiting a tree and for holes made by other insects.
Paint seeped through to dye the stem beneath, and after the bark was stripped the students could identify woodpecker holes that penetrated into emerald ash borer galleries, or into holes made by other bugs. The students tracked the fate of each bug that had been in the tree. Instead of relying on a statistical estimate of the insect population and thus the food source available, every bug and its fate were accounted for."
White-breasted Nuthatch by Brian Howell
And what statistics did the middle school scientists attain? In accordance with the hopes of any fan of ash trees, woodpeckers chose to prey on 85% of the Emerald Ash Borers within an infested tree. This means that woodpeckers are actively altering their prey-selecting behaviors to take full advantage of the new and increasing invasive food source. In a way, the Borers are actively invading right into the mouths of hungry woodpeckers. On top of that, another citizen science project, this one Cornell's Project Feederwatch, revealed that the populations of three woodpecker species and the White-breasted Nuthatch actually increased in areas where the Borers were increasing.

So, is it enough? After all, 85% isn't 100%, and this means that there are still Emerald Ash Borers left over in the wake of woodpecker predation. In a way, it is enough. Woodpeckers will not instantaneously snuff out the population of Emerald Ash Borers...it would be unrealistic to expect them to do so in the first place. If they could have done that, it is certain that they already would have. But they certainly will slow the increase of the Borers, and eventually, slowly but surely, as woodpecker numbers continue to increase, Emerald Ash Borer populations may be expected to decline, which eventually would lead to their disappearance. Be mindful; this is an assumption. But what a sweet dream it is to imagine that nature will do the job of eliminating one of its most virulent pests completely on its own.

What fantastic balance this is.

Like any decent science blog, I'd like to leave you with some questions. This is where we will tie together my previous two woodpecker posts.

First and foremost, think back to the post on Syrian Woodpeckers and their ecological trap within polluted, urban forest tracts. Now think back to the post before where we found that woodpeckers tie the separate continents back together--part of this is their remarkable consistency in foraging method. Everywhere you go, woodpeckers do just that: peck wood. So...
  1. If woodpeckers show this consistency, might woodpeckers around cities in North America also be drawn to polluted areas because of higher concentrations of prey?
  2. If this is a yes, would woodpeckers in urban areas more rapidly eat away at Emerald Ash Borer populations because of greater densities of woodpeckers paired with increased tree infestation?
  3. Would the percentage of Emerald Ash Borers ultimately consumed be higher in urban forest tracts than the 85% found in Ohio?
  4. Finally, if woodpeckers can limit the populations of invasive wood-boring insects and possibly eliminate them, is it possible that this isn't the first time in their evolutionary history that they've done so?

Ultimately, just food for thought. Cheers everybody. You've been great.


- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Here's the article on which this post is based:

Galatzer-Levy, Jeanne. "Emerald Ash Borer May Have Met Its Match." UIC News Center. University of Illinois at 
     Chicago, 16 Dec. 2013. Web. 28 Feb. 2014. http://news.uic.edu/emerald-ash-borer-may-have-met-its-match

Monday, January 27, 2014

Piciform Pictures

So to continue my serendipitous research in Piciformes this month, I was inspired today to do some preliminary research on the Ramphastidae (toucans). One of my most prized possessions is a whiteboard, which I've been using more and more to represent my research. I've used it on everything from ID'ing Sooty from Dusky Grouse, to working out how Pleistocene glaciation affected what are now our neotropical migrants, to this, which is the fruits of my Ramphastid research today:



Here's hoping you enjoy!

Another really cool thing I found during this morning's research is a "tree" of all bird life constructed by Jetz et al. As far as infographics go, I think this one is really beautiful:
By all means, click to zoom. This image is stunningly high resolution.

So what's next? By the end of the month, I'll have another post put together about woodpeckers with an awesome question I've been brewing for a few days now.

So keep your eyes peeled, and more importantly, stay warm!

Saturday, January 25, 2014

Don't Get Too Excited, but Syrian Woodpeckers Like Pollution

Learn about this photo at its source here.
The myriad ways that we affect our environment are pretty dumbfounding, aren't they? Just by releasing chemicals like CO2 and Methane into the atmosphere, we increase the acidity of the ocean, create a runaway greenhouse effect that elevates global temperatures, and deteriorate polar and alpine ecosystems that depend on the existence of ice. We know all this. And there are people that are doing something about it. That's all good. We'll talk about that some other time.

Another effect merely of our pollution of the atmosphere, however, that is of interest to me, is how air pollution affects trees. And all plants, for that matter. When plants, especially trees, are exposed to air pollution, and worse yet forced to grow and develop in it, things go amiss. Trees grown in air polluted areas often grow into weaker forms, with lower quality wood and disrupted processes within the tree. It would be like us trying to grow up with a constant supply of toxic gases at levels that are slightly too high to be healthy in our bloodstream. We would grow up weak and malnourished, regardless of how much food we get.

Syrian Woodpecker by Sergey Yeliseev:
http://flic.kr/p/66rnF2
Now apply this back to trees. In cities, many trees receive plenty of good soil, fertilizers, access to sunlight, and watering from caring gardeners. But with the addition of air pollution, however, something will always be slightly off for the tree. And often, this "slightly-off-ness" manifests itself in a reduction of natural defenses from parasites and insects living within the tree, to the tree's detriment. In its slightly weaker form, polluted trees are worse off at defending themselves from, for our purposes, insects.

If you were wondering when birds come in (because they have to here, right?), we're there. Woodpeckers, specifically Syrian Woodpeckers (Dendrocopos syriacus), were studied around Krakow, Poland, to see how their numbers relate to thirteen urbanized habitats and the amount of pollution in those areas. Because of the air pollution in the study area, trees had reduced defenses and thus harbored more insect life. And all pollution aside, that means food for the Woodpeckers. The study found that:


The number of trees, coverage of woody vegetation, total vegetation cover and level of pollutant emissions were significantly higher in Syrian Woodpecker breeding territories than in the random points. 

 So, counterintuitively, it was found that habitats often thought of as negatively correlated to bird numbers hold a hidden twist...a bit of an incongruity. The pollution of urbanized habitats indirectly holds benefits for insectivorous wood-clinging birds; weaker trees equal higher susceptibility to insect infestation, and that equals a buffet for woodpeckers.

Photo by Rachel Rosen:
http://flic.kr/p/dbaqZA
But this is not a case where we should leap up in victorious arms and yell, "Yes! City's aren't that bad for wildlife!" The effects of atmospheric pollutants still take place on the birds, and more significantly, affect their breeding cycles. We can't negate all the research throughout the years that have exposed the negative effects of urban environments on their avian inhabitants.

In this case, we have what is called an Ecological Trap. Animals, when selecting habitats to live in take in a variety of environmental cues. Quantity of food, cover/shelter, and density of other animals of that same species are some of these cues. In an ecological trap, one or more of these cues appear to be higher in quality to the selector, while others are coincidentally far worse. A good analogy would be selecting a home in a dirty, overcrowded, crime-ridden neighborhood just because it's near a world-renowned yet inexpensive restaurant. Woodpecker foodies are selecting dirty and overcrowded urban environments because they're full of easy-to-access food in decrepit trees. They have been ecologically "trapped".

While we have, in our various human doings, provided a reliable and predictable food source for woodpeckers, we have also created in them a habit of sacrificing the quality of their home for this food source. Now exposed directly to the pollutants of the city, Syrian Woodpeckers and their young are subject to the many detrimental effects thereof.

So what may seem at first to be a hidden positive of existing in the city actually reveals itself to be our confusing of the natural tendencies of the Syrian Woodpecker.

Fascinating, and not a little bit worrying.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Ciach, Michał, and Arkadiusz Fröhlich. "Habitat Preferences of the Syrian Woodpecker Dendrocopos syriacus in Urban Environments: An Ambiguous Effect of Pollution."Taylor and Francis. Bird Study, 24 Oct. 2013. Web. 25 Jan. 2014. <http://www.tandfonline.com/doi/abs/10.1080/00063657.2013.847899#.Um4yvxZy_8s>.