Monday, January 30, 2017

Sclerotic Rings; still in the dark about their true function

The avian skeleton is a complex structure of specialized bones, many of which have evolved specifically for the purpose of flight. Those that are not familiar to us include features that are very rare or unknown among mammals.

These features include splints of ordinary bone that develop in connective tissue to stiffen parts of the neck and backbone (Source; Kaiser W. Gary, The Inner Bird, Anatomy and Evolution 2007), as well as the well-developed hyoid apparatus, a combination of three bones that give support to the avian tongue.

Red-tailed Hawk vertebrae with bone splints
Even within the bird’s eye there are plates of unfamiliar bone called the sclerotic ring. Set around the pupil, birds share this unusual eye reinforcement with their dinosaurian relatives and primitive reptiles (Source; Proctor and Lynch, Manual of Ornithology 1993).

Books on the osteology of birds, however, as a rule merely refer to the sclerotic rings in passing, sometimes taking casual notice of the number of plates but giving no consideration to details of shape or arrangement.

Prior to this, the only knowledge I had with scleral rings was that of the specialized eyes of an owl, which have a uniquely tubular shaped ring that looks and function something like my spotting scope.

Sclerotic Ring of an owl
Image Credit: studyblue.com
But according to a recent National Geographic article that I just discovered titled, “How we know Velociraptor hunted by night”, the sclerotic ring has apparently become an important research tool in determining when extinct animals would have been active.


Comparing data from 164 living animals, 23 dinosaurs and 10 extinct reptiles, researchers Lars Schmitz and Ryosuke Motani now believe that they can say for sure when Velociraptor, and other predatory dinosaurs like Microraptor, hunted based on the size of their scleral ring opening and eye socket.


Protoceratops scleral ring
Photo: Lars Schmitz
Accompanying the article are convincing comparative photos of diurnal plant-eating Protoceratops and Diplodocus who sport thick, narrow-holed scleral rings, with skulls of crepuscular and nocturnal creatures such as the purported Velociraptor and a gecko, who clearly have wider openings to their scleral rings.

Velociraptor scleral ring
Photo: Lars Schmitz

At first glance, this made perfectly sense. For predators that hunt in the dark, the wider the opening, the more light is allowed to enter. 

But as a citizen scientist and birdwatcher, I had to see this for myself. I scoured through my collection of bird bones looking for a specimen, finally locating my only intact scleral ring from a road killed Northern Flicker.  

Northern Flicker
Photo Credit: Paul Cianfaglione
The Northern Flicker is a common, primarily ground-foraging woodpecker that occurs in most wooded regions of North America. It is diurnal in its habits, foraging for ants and other insects by probing and hammering in soil with their powerful bills (Source; Bird of North America Online Edition).

Under the microscope, the flicker’s sclerotic ring is composed of a number of individual plates, slightly overlapping to form a bony ring. The size of the ring in relation to the skull appeared large to me, with an opening, according to this study, that would most likely classify it as firmly crepuscular. But could that be an accurate assessment?  

Northern Flicker sclerotic ring within the orbit
Photo Credit: Paul Cianfaglione
 
Northern Flicker sclerotic ring
Photo Credit: Paul Cianfaglione

As my suspicions grew about the findings, I learned that other researchers were also questioning the data, methods, and interpretations of this study. See comments below;


In short, they believe the data shows that orbit and scleral ring morphologies of diurnal and nocturnal birds and lizards overlap to a degree that precludes confident reconstruction of activity pattern in fossil taxa.

After reading the National Geographic blog post (A Blog by Ed Yong), observing the flicker’s sclerotic ring and then seeing the rebuttal, I had to wonder, were researchers once again purposely ignoring certain species in their studies? Many of the smaller insectivorous birds including the warblers, hummingbirds and flycatchers migrate large distances, usually at night. How then would they categorize a neo-tropical migrant? As diurnal, crepuscular, nocturnal? All of the above? How would their sclerotic rings measure up in this study?

Did Velociraptor occasionally hunt in the fashion of an acciptiter like a Sharp-shinned Hawk? A diurnal hunter who uses the early morning darkness to its advantage on unsuspecting Mourning Doves at my bird feeder.

 
Sharp-shinned Hawk kill at dawn
Photo Credit: Paul Cianfaglione
Maybe Velociraptor did hunt morning, noon and night. Despite the questions attached to this theory, I still find the association (weak) between the sclerotic ring and nighttime activity very interesting.   

Monday, January 23, 2017

Fossilized Avian Gastric Pellet

A couple months ago, I posted on my blog a description of a 120 million-year-old partial bird fossil from Western Liaoning, China, detailing a feature which appeared to be a possible tail feather coming directly off the end of a pygostyle.

Partial Enantiornithine Fossil
Photo Credit: Paul Cianfaglione
It turns out that this unusual feature, partially hidden by matrix, was part of an even-width impression of a rare “rachis dominated” tail feather.

Rachis Dominated Tail Feather
Photo Credit: Paul Cianfaglione
In addition to this remarkable extinct form of streamer-like feather, the fossil revealed a synsacrum, a pygostyle, a small claw on metacarpal 1and a short metatarsal 1 (hallux) with a large claw that is more recurved than the other pedal claws. The fossil also preserves other faint remnants of plumage.

 
Small Claw on Metacarpal 1
Photo Credit: Paul Cianfaglione
If that wasn’t enough, I also noticed one other feature on this half-bird plate. Located near the lower left corner of the fossil, and loosely associated with the bird itself, is what looked to be a yellowish, densely concentrated, mass of possible bone. To my untrained eye, this unified aggregation seemed to include some small rib bones (along the edge) and many other bits-and-pieces.  

Fossilized Avian Gastric Pellet
Photo Credit: Paul Cianfaglione
I thought to myself, could this be a regurgitated gastric pellet of fish bones?

In my search for answers, I decided to contact an expert in the field to help me understand what this curious feature was all about. The researchers reply;

From the photo’s you sent, it is most likely to be a gastric pellet of fish bones. I have outlined a string of fish vertebrates which are preserved in lateral view. By the way, this bird belongs the Enantiornithines, the same avian clade as was reported in a recently published paper.

Fossilized Avian Gastric Pellet with String of Fish Vertebrate
Photo Credit: Paul Cianfaglione

The abstract from the paper;

ABSTRACT: Modern birds differ from their theropod ancestors in lacking teeth and heavily constructed bony jaws, having evolved a lightly built beak and a specialized digestive system capable of processing unmasticated food. Enantiornithes, the most successful clade of Mesozoic birds, represents the sister group of the Ornithuromorpha, which gave rise to living birds. Nevertheless, the feeding habits of enantiornithines have remained unknown because of a lack of fossil evidence. In contrast, exceptionally preserved fossils reveal that derived avian features were present in the digestive systems of some non-enantiornithine birds with ages exceeding 125 million years. Here, we report a new piscivorous enantiornithine from the Early Cretaceous Jehol Biota of China. This specimen preserves a gastric pellet that includes fish bones. The new enantiornithine, like many modern piscivores and raptors, seems to have swallowed its prey whole and regurgitated indigestible materials such as bones, invertebrate exoskeletons, scales, and feathers. This fossil represents the oldest unambiguous record of an avian gastric pellet and the only such record from the Mesozoic. The pellet points to a fish diet and suggests that the alimentary tract of the new enantiornithine resembled that of extant avians in having efficient antiperistalsis and a two-chambered stomach with a muscular gizzard capable of compacting indigestible matter into a cohesive pellet. The inferred occurrence of these advanced features in an enantiornithine implies that they were widespread in Cretaceous birds and likely facilitated dietary diversification within both Enantiornithes and Ornithuromorpha. Wang et al. discover a new Early Cretaceous enantiornithine bird preserving a pellet including fish bones. This finding represents the first evidence that some enantiornithine birds were piscivorous and that distinctive features of modern avian digestive system were well established in some Early Cretaceous birds.




Life reconstruction of the fish-eating enantiornithine bird 
[Credit: SHI Aijuan]

Read more here;

Tuesday, January 17, 2017

Avian Perception

In a first-ever study to find clear cognitive changes in birds from urbanized areas compared to rural areas, researchers from McGill University have recently reported key differences in problem-solving abilities, accessing food, and temperament (bolder) among city birds versus suburban birds. Their conclusion, birds living in urban environments are smarter than birds from rural environments.

Since I live and work in both of these environments, the results from this study came as no real shocker.

Driven by the need to locate food, the mind of a city bird is continuously stimulated by a myriad of human caused activity. This activity typically leaves the local streets scattered with garbage and other edible items. For an urban based crow or starling, obtaining food is much easier and requires far less energy than the same bird working a handful of widely-spaced suburban homes. This is especially important during the frigid, energy-depleting months of winter. But there are risks involved with being an urban resident.

City environments present birds with many dangerous challenges. How birds perceive the world about them determines many choices, including how they forage, how they avoid hazardous materials, as well as recognizing potential predators.

Perception is defined as the organization, identification, and interpretation of sensory information in order to represent and understand the environment (Source; Wikipedia).

Birds combat these threats by relying on many of their fine-tuned senses for survival, such as sight, hearing and touch.

In the case of the American Crow, its success around the city also has to do a lot with their complex social lives, long life spans and large brains. In fact, corvids and our own species share qualities, which have enabled both of us to adapt to changing environments and to flourish.

 
Fish Crow
Photo Credit: Paul Cianfaglione

In a book I’m currently reading called “Gifts of the Crow, How Perception, Emotion and Thought Allow Smart Birds to Behave like Humans”, authors John Marzluff and Tony Angell wonderfully explore the neurobiology of crows with accompanying stories that show how humans and crows have an ongoing connection, a cultural coevolution, which has shaped both our species for millions of years.

The books premise, and its relevance to this articles post are nicely summarized here; there, relays from the eyes, ears, mouth and skin transport their view of the world to the brain stem and into the brain, which uses emotion to integrate and shape diverse information and past experience to guide a bird’s behavior and enhance its survival and reproduction. Its brain allows the bird to learn quickly, to accurately associate rewards with dangers with environmental cues, and to then combine what it knows with what it senses and to draw conclusions leading to a more informed response.

As complex and involved as this may sound, these behavioral responses are surprisingly available to us each and every day. This is especially true for birds in urban environments, which make some of the easiest and most rewarding subjects to study.

In the hopes of drawing a response from the local birds at work, I recently placed a bag full of stale bread out in the middle of our parking lot. Secretly I stood (I thought)) behind a garage door window, watching how these interactions among humans and city birds might eventually play out.    

A single House Sparrow, who happened to be sunning itself nearby, spotted the old bread first and quickly came over to investigate. At about the same instant, an American Crow swooped in to intercept the spoils, but suddenly jumped back when it caught wind of my presence.

The crow flew over to the top of a nearby telephone pole, where it peered down at me, the sparrow and the bread. It suddenly began calling very loudly, as if recruiting others from around the area.

American Crow
Photo Credit: Paul Cianfaglione
Within minutes, two more crows arrived and landed beside the noisy bird. Things remained at a standstill until the sparrow decided to start dragging one of the pieces of bread to safety under a car. Were the crows being overly cautious in their plot to take-over the bread? I waited, and waited, and waited some more. The crows refused to budge. I thought to myself, maybe if I move to another vantage point, this will change the crow’s behavior? In the time that it took me to reach the other window, the three crows had dropped down to the ground, and taken off what was left of the bread.     

So why did these three crows hesitate to come down for the bread in the first place? Did my presence behind the garage window raise alarm bells? Were these inexperienced, juvenile crows sensing a possible trap, or perhaps these were adults with a memory of past dangers in these circumstances?

The next day finds more crows in my parking lot, but this time they appear bolder and more confident around people. To see if I could recreate the same behavior as yesterday, I decided to walk back into work, grab a handful of water crackers, and toss them out the same garage door. Within seconds, five crows had descended onto the food.  Three of the birds picked up and immediately took off with a cracker, while the other two ate right there on the spot.

American Crow
Photo Credit: Paul Cianfaglione
The crows that remained watched me very carefully, but most certainly recognized the obstacle that separated us from them. Quite a difference in perception from the day before! Were these crows seasoned adults?

The behavior of crows in my suburban yard is slightly different. Their response to being discovered is unchanged, but instead of flying a short distance to a nearby tree or telephone pole, the crows fly much further away and sometimes out of sight. Why is this? What is this subtle change all about? Is this behavior a direct response from being harassed by unwelcoming homeowners? Quite possibly. Or is the competition for food far less demanding in the suburbs, and worth the few extra meters of safety to properly assess the situation? Remember, the same crow in the city who retreats too far from its coveted food source, may return to find it’s no longer there!
Suburban American Crows feeding on cornbread
Photo Credit: Paul Cianfaglione 
Soon after the crow observation, a beautiful immature Red-shouldered Hawk came flying in on quick wing beats and landed right next my tube-feeder. It perched motionless for a while on a low branch with its long tail dangling below. At first glance, this slender species of woodland hawk could easily be mistaken for one of our bird-hunting specialists called accipiters.

 
Immature Red-shouldered Hawk
Photo Credit: Paul Cianfaglione

In spite of this, the birds at the feeder carry on as if the hawk was not even there. Remarkably, each and every bird recognized the hawk as no threat at all, rendering the situation as temporarily safe. How did they make the identification so quickly? For species that typically specialize on fewer resources, could these smaller-brained woodland birds be as aware of their surroundings as the urban birds?  

It appears to me, that the same principles that guide crows in our cities also applies to forest dwelling birds; the brain allows the bird to learn QUICKLY, to accurately associate rewards with dangers with environmental cues, and to then combine what it knows with what it senses and to draw conclusions leading to a more informed response.

Finally getting back to the McGill University paper for a moment, a study which claims birds living in urban environments are smarter than birds from rural environments, life in the city changes cognition, behavior and physiology of birds to their advantage.

Are the researchers leading us to believe that city birds have the edge over their country friends, simply because they can exploit human made conditions? Of course, the fact is that in their narrowly focused experiments, urban birds do outperform the competition. For researchers, feedback is critical, and the corvids provide an obliging hand. To me, this study was more of a rehashed confirmation than anything else.

But is it really fair to compare problem solving in the city with problem solving in the forest, and then paint the underdog as inferior in intelligence?  

Corvids are without question intelligent birds. Internet articles comparing the intelligence of crows with apes are not uncommon, and lead into other related studies such as “Crows Better at Tool Building Than Chimps”, “Crows Makes Wire Hook to Get Food” and “Crafty Crows Found to Be Right-handed”

Ravens, jackdaws and New Caledonian crows! So, what about our suburban birds? How intelligent are they? Do we have any other way, besides these so-called innovative tests, to truly measure intelligence in and out of nature?  

If we are to define the smarts of a bird based on how well they exploit new human resources, then how would a researcher measure the intelligence of a Merlin (Falco columbarius), a small falcon who literally does a cerebral about-face, year-after-year?

 
Merlin
Photo Credit: Paul Cianfaglione
The Merlin, whose breeding habitats include deep, secluded forests, will then spend winters in major cities hunting starlings, sparrows and pigeons. Does a Merlin’s time in an ever-changing urban landscape make for a smarter, more effective hunter? Are these falcons associating Walmart parking lots, apartment buildings and suburban sprawl with feeding opportunities, the same way crows, pigeons and gulls do? How often does a Merlin in an urban environment solve critical problems, or are they just mechanically designed to kill?

 
Ring-billed Gulls
Photo Credit: Paul Cianfaglione

American Crows feeding in an urban setting
Photo Credit: Paul Cianfaglione
How about other avian tool users like the Galapagos Island woodpecker finches, who use cactus spines to impale inactive insects from crevices and holes. Or the Brown-headed Nuthatch who uses pieces of wood bark as a wedge to expose hidden insects (Source; Wikipedia). Are these bird’s problem solvers? Where do these species stand on the intelligence ladder?

As researchers glow at the crow’s continued willingness to provide clues to their intelligence, it may be a good time for us as individuals to reexamine our own observational habits.   

Since we are, in one form or another, all birdwatchers, our goal should always be to learn as much as we can about each and every species. This entails patience, persistence and most of all, perception of the natural world.