Wednesday, August 15, 2018

Avian Mobbing; influence and variability.

Its an all too familiar site that even the most casual of bird observer will recognize. A Red-tailed Hawk (Buteo jamaicensis) perched majestically on a neighborhood light pole. Beside it, a highly agitated Northern Mockingbird (Mimus polyglottos) doing its best to make it go away.

Northern Mockingbird 'mobbing' Red-tailed Hawk
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Northern Mockingbird 'mobbing' Red-tailed Hawk
Photo Credit: Paul Cianfaglione
Northern Mockingbird 'mobbing' Red-tailed Hawk
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Our interpretation for this type of behavior is pretty straightforward. The predatory hawk, most would speculate, is either a threat to the mockingbirds young, or to the mockingbird itself.

Unfortunately, the end results of these interactions often go unseen. So, I’m often left asking, does being overly aggressive toward a predator really work at lessoning the threat?

In Ornithology, the term used to properly describe this aggressive behavior is called ‘mobbing’, and is done singly or in groups, depending on the species.

Mobbing occurs mostly during the height of the breeding season as a way to distract and encourage a predator to relocate to another area. Also referred to as the ‘move on’ hypothesis (Curio 1978), previous studies have confirmed that predators are profoundly distressed by mobbing and avoid the areas where they have been harassed. The ‘move on’ hypothesis appears to be most clearly linked to territoriality (Pavey and Smyth1998).

Before I get into some sure examples of avian mobbing, I’d like to touch upon a study that recently came out (July 2018) implying that ‘American Crows (Corvus brachyrhynchos) are always the bullies when it comes to fighting with Common Ravens (Corvus corax)’.

The study used more than 2,000 publicly collected and submitted observations from across North America via eBird to analyze the interspecific aggression between crows and ravens. From these records, it was determined that crows were the predominant aggressor. Crows primarily attacked in small groups rather than one-on-one confrontations with ravens. The breeding season was when most of the attack observations were made, suggesting that nest predation by ravens influences this behavior. Aggression during the winter is potentially explained by crows preemptively deterring nest predation and defending resources needed for nesting later in the year (source; Sciencedaily).

The results of this study offered little in the way of surprises. Nest predation by ravens is undoubtedly the cause of the crow’s aggression. But does this aggressive behavior toward ravens really translate to lower incidents of nest predation? Some of you will be surprised to learn that the answer is no.

Despite the crow’s best parental efforts, ravens are still successful at providing a steady flow of crow nestlings to their own growing young.

In retrospect, one should probably ask; do ravens knowingly coincide their egg hatching with that of crows? Crow nestlings appear to be an important and well-timed resource. In fact, an overlap in chick raising is curiously supported by the species annual cycle of breeding (source: Birds of North America Online). 

American Crow annual cycle of breeding
Image Credit: Birds of North America Online
https://avianmusing.blogspot.com/
Common Raven annual cycle of breeding
Image Credit: Birds of North America Online
https://avianmusing.blogspot.com/
So, are ravens in any way influenced or intimidated by crows? The answer may lie where the two species interact outside of the nesting season.

In my backyard, a small flock of crows will freely surrender their food source to a single large raven, returning only when it has long departed. In this setting, ravens are clearly the dominant species and are not intimidated by the presence of crows, even when heavily outnumbered. 

Common Raven at a backyard feeding station
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
This may explain why ravens are so effective at securing crow nestlings. Do crow’s offer any resistance when confronted by a prowling raven? Why does ‘mobbing’ fail in this situation?

Crows, on the other hand, may have better luck intimidating, or ‘moving on’ less active Red-tailed Hawks and Great Horned Owls (Bubo virginianus).  

Not only are the hawks and owl’s threats to the nest, they pose danger even to the adults at times.

Crow mobbing aimed at these predators can be particularly harsh, sending hawks into the paths of moving cars or buildings.

One of the most disturbing attacks that I have ever witnessed happened at a local cemetery, where a Great Horned Owl was observed being harassed at its daytime roost. Surrounded closely by a crowd of angry crow’s, the terrified owl slipped off a branch, lodging its neck tragically into the fork of a tree. 

Great Horned Owl death as a result of avian 'mobbing'
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Is the death of a dangerous predator the intended outcome of every avian ‘mobbing’? Probably not. But it is for all intents and purposes, a result many birds would gladly welcome.

Birdwatchers will often tell stories of a more familiar form of ‘mobbing’ in some of our smaller bird species.

Warbling Vireo (Vireo gilvus) eggs for instance are often the target of opportunistic Blue Jays (Cyanocitta cristata), yet I have seen vireos on more than one occasion, successfully mob and distract jays well away from their leaf-hidden nests.

One of the simplest ways to find roosting Northern Saw-whet Owls (Aegolius acadicus) in winter is by listening and following the scolding calls of Black-capped Chickadees (Poecile atricapillus) and Tufted Titmice (Baeolophus bicolor). 

Black-capped Chickadee (Poecile atricapillus)
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
David Allen Sibley writes in his book, The Sibley Guide to Bird Life and Behavior; parids are social, bold, and inquisitive, traits that endear them to humans but make them among the most tenacious and aggressive songbirds when mobbing owls or other predators. Chickadees and titmice usually take the lead in announcing the presence of a small owl.

Does being overly aggressive toward a predator really work at lessoning the threat? In the vast majority of cases, ‘mobbing’ is an effective way of protecting eggs, nestlings and themselves.

The unusual crow-raven relationship is little bit harder to understand, and accept. The crow’s overall population however seems little affected by this ‘taking’ of birds.

One has to wonder if the raven’s sudden expansion into more urban areas has to do more with the presence of nesting crows than anything else.

Tuesday, August 7, 2018

Owl Cervical Vertebrae; adaptive features for head rotation.

The owl has been a part of pop culture for as long as I can remember, from movies to television to advertising. Today, owls continue to dominate our society, so much that we don’t even realize that they are around us. By that I mean on top of shopping mall buildings, car dealerships and even in our gardens, replica owls are used as decoys to repel unwanted pests, animals and rodents. 


Owl Decoy
https://avianmusing.blogspot.com/
What makes the owl decoy so effective as opposed to other predatory birds? Is it their large eyes? Angry expression? Fearsome reputation? All are classic owl traits. But it’s the rotating head that really sets them apart; a distinctive life-like feature and a realistic profile. I jokingly ask, what good is an owl decoy if it can’t fully rotate its head?

So how does an ‘real’ owl spin its head around? What major biological adaptations are known today to allow for such a unique behavior? 

For this, I turned to a new book that I just recently completed titled; The Ascent of Birds, How Modern Science is Revealing their Story, by John Reilly (2018). 

The Ascent of Birds by John Reilly (2018)
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
It is here in chapter 10 that the author nicely describes the ‘The Owl’s Story’; revealing a number of the owls previously unknown and unique adaptations, including its ability to rotate its head.

Given that owls are closely related to raptors and mousebirds, it is likely that the earliest species were diurnal and relied primarily on sight to obtain their prey. As a result, all owls have large eyes that are very efficient at capturing and processing light. They are not spherical organs, as in most birds, but elongated structures, held in place by bony protuberances known as sclerotic rings. Such large, forward-facing eyes provide owls with an improved depth perception, but they are essentially fixed and cannot be moved within their sockets. To compensate, all owls can rotate their heads through 270 degrees in either direction without having to move their bodies. For us, this would mean turning our head to the left so that we end up looking over our right shoulder. Not a maneuver I suggest you try, as your delicate blood vessels would be severely damaged, resulting in a major stroke or even death. So how do owls manage it?

To find out, a team from John Hopkins University School of Medicine, led by medical illustrator Fabian de Kok-Mercado, injected radio-opaque dye into the bloodstream of dead owls and took a series of CT scans while the head was twisted. The results revealed a number of previously unknown and unique adaptations. Firstly, the owl’s cervical vertebrae contain transverse foramina (‘holes’ for the vertebral arteries and veins) that are much larger than those of other species, including humans. In our neck, the foramina are roughly the same size as the blood vessels, whereas in the owl they are almost 10 times the diameter of the arteries, with the extra space acting as air sacs that cushion the vessel during twisting motion of the head. Furthermore, the last few cervical vertebrae lack transverse foramina, an anatomical adaptation that provides the cord-like arteries with some slack when the head rotates.

Owls also possess connections or anastomoses between their carotid and vertebral arteries, a feature that ensues a constant blood flow to both sides of the brain even if the vessels on one side of the neck are occluded. Finally, the main arteries – carotid, mandibular and maxillary – contain contractile reservoirs that are hypothesized to ensure an uninterrupted blood supply to the brain and eyes, even during the most extreme of head movements. It seems that the ‘wise old’ owl has not just evolved one answer to the neck-twisting problem; it has come up with a whole raft of solutions (end of book citation).

These were extraordinary findings, so much so that I felt compelled to see it for myself.

First, I compared three avian cervical vertebrae side-by-side; a Barred Owl (Strix varia), Mallard (Anas platyrhynchos) and an American Crow (Corvus brachyrhynchos). The claim made in the book regarding the owl’s cervical vertebrae containing transverse foramina that are much larger than those of other species, is still a mystery to me. The holes, in relation to the size of the cervical vertebrae, appeared nothing out of the ordinary. 

From top to bottom; Barred Owl, American Crow and Mallard Cervical Vertebrae
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Avian Foramen transversarium
Handbook Of Avian Anatomy (1993); Baumel and Witmer
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
I was however more intrigued by the fact that the last few cervical vertebrae were reported to lack transverse foramina altogether. This was a feature that should be easy to detect. 

Barred Owl (Strix Varia) Cervical Vertebrae
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/

Surprisingly, my inspection of the cervical vertebrae instead revealed holes on the transverse processes, albeit very narrow ones.

Barred Owl (Strix varia) 14th Cervical Vertebrate
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
What was going on here with the owl’s last few cervical vertebrae? Why the retention of holes? Could the existence of holes in the transverse processes imply a more recent evolutionary adaption for extreme head and neck rotation?

Given their other set of raptor-like characteristics, large eyes, binocular vision and powerful talons, one could envision head rotation along with the unequal positioning of their ear openings for acute hearing, as adaptations later evolved by owls for a more successful nocturnal existence.  


John Reilly mentions in his book that 40% of extant species are commonly active in daylight, especially around dawn and dusk, only two are truly diurnal, a fact largely dictated by prey preference.

Why retain holes in the transverse processes if they are bypassed and no longer of use? Were today’s owls forced into a nocturnal lifestyle, not long ago, by more aggressive daytime competitors like hawks and corvids?

I believe this is a reasonable idea, loosely supported by this final snippet;

‘Most of the early owl lineages, however, were subsequently displaced by other bird orders, and only two survived: Barn Owls (Tytonidae) and the typical or ‘true owls’ (Strigidae). At the time, the Strigidae would have resembled the Spotted Owl or the Tawny Owl, and their marked diversity of morphology and anatomy only evolved during the last 15 million years (The Ascent of Birds, How Modern Science is Revealing their Story. Reilly J. 2018).  

Thursday, August 2, 2018

Brazilian Merganser (Mergus octosetaceus). All Birds Considered.

Inspired by David Attenborough’s book, The Life of Birds, is a monthly spin-off segment of my blog called “All Birds Considered”, which I hope will bring attention to some of the more unusual, and lesser known birds of our world.

The Life Of Birds by David Attenborough
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Species; Brazilian merganser (Mergus octosetaceus)

Introduction; The Brazilian merganser (Mergus octosetaceus) is a duck in the typical merganser genus. It is one of the six most threatened waterfowl in the world with possibly fewer than 250 birds in the wild and currently 4 kept in captivity at 2 different Brazilian locations. The origin of its name is from its long, sharp-edged beak that has a great number of teeth-looking edges.

Brazilian Merganser (Mergus octosetaceus)
Image Credit: Wkipedia
https://avianmusing.blogspot.com/


Population; The total world population for Brazilian mergansers is believed to be less than 250 birds. Originally, the duck's geographical distribution comprised central-south Brazil and adjacent regions in Paraguay and Argentina. Currently, all confirmed populations are located in Brazil and a more recent population in Argentina and information on most populations is very scarce. The Brazilian Merganser population in the Serra da Canastra region is the most significant and best known, with populations occurring hundreds of kilometers away from each other. There are 47 individuals—28 adults and 19 young—in the Serra de Canastra region as of 2006. Most mergansers are found in the Serra da Canastra National Park. 70 birds have been seen near the park's headquarters in Rio São Francisco. In Jalapão region are estimated 13 individuals in Novo river on 2009/2010 (four couples and some solitary adults).

In 2002, the species was also found on the Arroyo Uruzu in Misiones, Argentina, the first record in the country for ten years, despite extensive surveys done by local researchers conducted throughout previous years. The bird was last reported seen in 1984 in Paraguay, where very little habitat remains, however, some local reports show that a few individuals may still be living in the area.
Description; Narrow bill. Head, neck and long crest black with green sheen. Back blackish; breast, flanks, and belly finely barred dark and light grey. Wings blackish with white secondaries and a white line through wing-coverts.

Voice; The Brazilian mergansers are generally silent birds, but may make barking calls in certain situations. Four calls have been recorded. A harsh krack-krack acts as an alarm call emitted in flight. Males make a barking dog-like call, females make a harsh rrr-rrrr and the contact call ia a soft rak-rak-rak. Ducklings give a high pitched ik-ik-ik.

Behavior; The species spends the days interspersing foraging and resting periods. Generally, they rest on rocks or branches which are projected out of water, as well as on river beaches. They also can stay in the water motionless or with very slow movements.

Brazilian Merganser (Mergus octosetaceus)
Image Credit: Wikipedia
https://avianmusing.blogspot.com/
Habitat; Streams and rivers in sub-tropical forests.

Justification of Red List category; Critically Endangered (IUCN 3.1) The Brazilian mergansers are very sensitive to habitat degradation and loss primarily due to human actions. A major threat to the birds' survival is the issue of silting of rivers caused by the expansion of farming activities, mining, watershed degradation and soil erosion, as well as deforestation.

Source:

https://neotropical.birds.cornell.edu

Wikipedia

The Life of Birds by David Attenborough, 1998.

Birds of Southern South America and Antarctica. 1998. Martin R. DE LA Pena and Maurice Rumboll

Tuesday, July 31, 2018

Avian Nutrient Foramen (Canals)

I recently read an online article which defined scientific inquiry as being a gathering of information through the use of human senses — seeing, hearing, touching, tasting, and smelling. Inquiry encourages people to question, conduct research for genuine reasons, and make discoveries on their own.

In an inquiry-based learning, people aren't waiting for the teacher or someone else to provide an answer — instead, they are actively seeking solutions, designing investigations, and asking new questions.

There is no better place, in my opinion, for this type of inquiry-based learning than with the inner bird.

Just the other evening, while going over the bones of an American Robin ((Turdus migratorius), I noticed a peculiar hole located on its tibiotarsus, about a third of the way down the shaft roughly the same level as the end of the fibular crest. 

American Robin (Turdus migratorius)
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
No, its not the first time I have noticed such an opening, but it is the first time that I have ever made a concerted effort to learn more about their true purpose.   

All bones possess larger or smaller foramina (openings) for the entrance of blood-vessels; these are known as the nutrient foramina and are particularly large in the shafts of the larger long bones, where they lead into a nutrient canal, which extends into the medullary cavity. The nutrient canal (foramen) is directed away from the growing end of bone. The growing ends of bones in upper limb are upper end of humerus and lower ends of radius and ulna. In lower limb, the lower end of femur and upper end of tibia are the growing ends. The nutrient arteries along with veins pass through this canal. In long bones the nutrient canal is found in the shaft (source; Wikipedia).

Bone Nutrient Foramen Diagram
Image Credit: Wikipedia
https://avianmusing.blogspot.com/
Below are a few examples of nutrient canals from our above-mentioned American Robin, and an American Crow (Corvus brachyrhynchos); the humerus, coracoid, ulna and femur respectively. 

American Crow (Corvus brachyrhynchos) left, and American Robin (Turdus migratorius) bones with nutrient foramen
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
American Crow (Corvus brachyrhynchus) humerus nutrient foramen
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
American Crow (Corvus brachyrhnchus) coracoid nutrient foramen
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
American Robin (Turdus migratorius) ulna nutrient foramen
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
American Robin (Turdus migratorius) femur nutrient foramen
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
One of the more interesting bits of information to come about from my inquiry included a past study on the nutrient canal size of extant animals, in comparison to dinosaur fossils.

"One of the big controversies among paleobiologists is whether dinosaurs were cold-blooded and sluggish or warm-blooded and active. Could the size of the foramen be a possible gauge for dinosaur metabolic rate?", says Professor Roger Seymour from the University of Adelaide School of Earth & Environmental Sciences.

"On a relative comparison to eliminate the differences in body size, all of the dinosaurs had holes in their thigh bones larger than those of mammals," Professor Seymour says.

"The dinosaurs appeared to be even more active than the mammals. We certainly didn't expect to see that. These results provide additional weight to theories that dinosaurs were warm-blooded and highly active creatures, rather than cold-blooded and sluggish."

Professor Seymour says following the results of this study, it's likely that a simple measurement of foramen size could be used to evaluate maximum activity levels in other vertebrate animal groups, both living and fossils.

Wednesday, July 25, 2018

Cedar Waxwing (Bombycilla cedrorum). Are their wing-tips really made of wax?

The Cedar Waxwing (Bombycilla cedrorum) is arguably one of the most beautiful birds in North America. It is also one of the most common, occurring year-round in both rural and urban areas. 

Cedar Waxwing (Bombycilla cedrorum)
Image Credit: Wikipedia
https://avianmusing.blogspot.com/
Cedar Waxwings are very sociable, often seen in massive flocks. The sociality of individuals within winter flocks and the lack of territoriality during the breeding season also are associated with the reliance of this species on locally superabundant fruit crops. Voracious feeding on fruits by large flocks and a high degree of mobility make this waxwing an especially effective disperser of the seeds of fruiting plants (source: Birds of North America Online).

As its scientific name implies; cedrorum is Latin for "of the cedars", the Cedar Waxwings favorite food crop from the native red cedar tree.

Its common name “waxwing” also relates to the red cedar seed, which is covered in a white-waxy substance. The large consumption of cedar seed is believed to be a useful, and convenient source of wax secreted by the bird to the tips of their secondary feathers. 

Eastern Red Cedar (Juniperus viginiana)
Image Credit: illinoiswildflowers.info
https://avianmusing.blogspot.com/
Interestingly, the red secretions (colored by pigments found in other berries) on the secondaries of Cedar Waxwings increase in number and size with a bird's age. Experts suggest that the red waxy feather tips act as an important signal in mate choice and social organization.

Cedar Waxwing (Bombycilla cedrurum) secondary feathers
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
If we could for just a moment go back over these evolutionary steps; the cedar seed becomes covered in a protective wax, a Cedar Waxwing eats the wax covered seed, the ingested wax is secreted to the wingtip pigmented in red, finally giving rise to mate choice and social organization; it would be hard to argue against, or sway from this type of reasonable interpretation.

I agree, at first glance it does appear as if the wingtips were made out of a wax-like material, even under a stereo-microscope. But the more I thought about feather secretion, the more skeptical I became. Could wax really secrete out of the tip of a thin feather rachis? I had to have a closer look. 

Cedar Waxwing (Bombcilla cedrorum) secondary feather wingtip
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Sacrificing one of my own feathers, I focused my attention toward the base of this so-called secretion, looking for a telltale sign that may suggest a definitive droplet. What I discovered instead were actual feather barbs growing off the side of this wax-like base. Do feather barbs grow off wax secretions?

Cedar Waxwing (Bombycilla cedrurum) secondary feather wingtip
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Cedar Waxwing (Bombycilla cedrurum) secondary feather wingtip
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
There was also a pattern of barb termination characteristically seen at the tip of other feather rachises, where under a microscope one can observe two or three smaller barbs coming together to form the rachis tip. These terminal barbs seemed to grow normally onto and meet at the droplet. 

I also detected a blending of the rachises dark coloration directly onto the base of this wax-like substance. Is this significant? Can a feather rachis evolve odd looking appendages just about anywhere along its shaft? The answer to this question I believe is yes.

Back in August of 2017, I wrote an article about a similar appendage on the feather rachis of a deceased Hoatzin (Ophisthocomus hoazin). Here, I found not one, but three separate (different feathers) protrusions growing from the rachis itself, the black coloration bleeding into a lighter colored swelling. 

Hoatzin (Ophisthocomus hoazin) feather rachis
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Hoatzin (Ophisthocomus hoazin) feather rachis
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
The reason for this evolutionary accompaniment is still unclear, but it does appear to be a growth from the rachis, rather than from an outside source. See article below;


My continued examination of the droplet also included the handling and turning the feather on its side. Nowhere did this droplet feel like hard wax, nor was it stiff in any way. In fact, it felt thin as the rachis tip, soft and pliable. 

Cedar Waxwing (Bombycilla cedrurum) secondary feather wingtip sideview
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
The final inspection of the red droplet required total mutilation. This I did by pulling off the terminal half of the appendage and cutting it into a number of small pieces. What was revealed from the fragments, in my best judgement, were indications of tiny barb-like structures. Did the rachis reabsorb the barbs?

What does all this tell us about these red adornments on the waxwings secondary feathers? Are the tips secreted wax? Or are they simply an extension of the feather rachis itself?

In my opinion, the red tips at the end of the Cedar Waxwings secondaries are most likely a continuation of the feather, dominated, or reabsorbed by the rachis.

A “rachis dominated” feather is typically used to describe the rectrices of some 120 million-year-old Mesozoic birds. Below is a short remark, and a link to a past blog posting regarding this long extinct feather form. 

Changchengornis hengdaoziensis
Image Credit: Peter Schouten
https://avianmusing.blogspot.com/
Typically referred to as “rachis dominated”, the proximally ribbon-like portion of the feather in basal birds is a large rachis that continues almost to the end of the feather, distally bounded laterally by the vane, as in modern pennaceous rectrices. The rachis of the distally pennaceous portion is continuous through the unbranched vane portion of the feather in Mesozoic birds.

Sunday, July 22, 2018

Avian Mud Nests

The American Cliff Swallow (Petrochelidon pyrrhonota) is one of the most social land birds of North America. These birds typically nest in large colonies, and a single site may contain up to 6,000 active nests. Cliff Swallows originally were birds of the western mountains, where they still nest underneath horizontal rock ledges on the sides of steep canyons in the foothills and lower elevations of the Sierra Nevada and Rocky and Cascade mountains. In the past 100 to 150 years, these birds have expanded their range across the Great Plains and into eastern North America, a range expansion coincident with the widespread construction of highway culverts, bridges, and buildings that provide abundant alternative nesting sites. New colonies continue to appear each year in areas where Cliff Swallows were previously unrecorded as breeders (source: Birds of North America Online).


Cliff Swallow (Petrochelidon pyrrhonota) 1894
Image Credit: Wikipedia
https://avianmusing.blogspot.com/
This is the exact situation here in interior Connecticut, where twenty years ago Cliff Swallows were an uncommon sight and a bird worth reporting. Today, Cliff Swallows are a regular breeder in my area, but by no means nest in large colonies. At best, the species nesting status is believed limited, with a success rate that’s very low.

There are a few obvious reasons for this poor success rate. First; when Cliff Swallows do choose to nest in a colonial manner, they are widely spaced, making them more susceptible to nest predation by trained corvids, or nest displacement by aggressive House Sparrows (Passer domesticus).

If that doesn’t take them out, maintenance crews with water hoses often do, at private businesses where stucco and brick buildings are a favored foundation for their mud nests.

In this case, the second nesting attempt now becomes the alternative site, where Cliff Swallows search for out-of-the-way schools or libraries which bring less attention. This year’s second nesting attempt also brought with it some interesting personal observations.

The first dealt with the construction styles of both the first and second mud nests. Before losing their initial design, Cliff Swallows had affixed a narrow mud ledge below an overhang, extending the walls until a complete dome was created. With this plan came a narrow entrance tunnel, which pointed downward for added protection. 

Cliff Swallow (Petrochelidon pyrrhonota) Nest
Image Credit: http://www.ccbbirds.org
https://avianmusing.blogspot.com/
The second nest however is more rudimentary, again affixed to corner overhang, but this time in a less protective open cup. Constraint on available breeding time had led to a more limited construction method. 

Cliff Swallow (Petrochelidon pyrrhonota) Nest
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/

The texture of the mud itself was also an interest of mine. How do swallows transport mud and create such wonderful surface designs? 

Cliff Swallow (Petrochelidon pyrrhonota) mud nest close up
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/

Birds gather mud in their bills along the bank of a stream, lake, or temporary puddle, usually at a site within 0.5 km of the colony but sometimes several kilometers distant. A bird brings a mud pellet back to the colony and molds it into the nest with a shaking motion of the bill. The shaking causes a partial liquefaction of the mud, disperses moisture, and allows fresh mud to overrun small air spaces, resulting in a stronger structure when dry (source: Birds of North America Online). 

Cliff Swallow (Petrochelidon pyrrhonota) building nest
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Cliff Swallows (Petrochelidon pyrrhonota) building nest
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
This shaking motion and dispersal of moisture can be recreated by taking a handful of semi-moist dirt, packing it into a ball, alternating it from hand-to-hand, which turns the balls outer surface more wet.   

It’s an amazing construction method used also by the Barn Swallow (Hirundo rustica). Other birds incorporate mud into their nests, and when they do, depending on the location, appear to be more helpful. 

Barn Swallow (Hirundo rustica) and mud nest
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
The American Robin (Turdus migratorius) often uses the ledge located over my front door to raise young. Some robins use a mud base, others do not. Those that use mud, are almost always successful. Those that do not find it impossible to keep nest material secured to the ledge.

The Eastern Phoebe (Sayornis phoebe), like the Barn Swallow affix their nest to a roofs wood beam or pipe using a strong, adhering mud base.

The Rufous Hornero (Furnarius rufus) takes nest building with mud to another level. Rufous Horneros are incredible architects that build domed nests out of mud and straw; these nests are 20 to 30 cm in diameter and 20 to 25 cm tall.

Rufous Hornero (Furnarius rufus) and nest
Image Credit: Wikipedia
https://avianmusing.blogspot.com/
Recent studies suggest that the mud nest of the Rufous Hornero works as an incubation chamber that likely evolved to help resolve the incubation-foraging trade-off in the very seasonal and hot regions where the bird evolved. See study here; https://www.ncbi.nlm.nih.gov/pubmed/25526648

Friday, July 20, 2018

Dinosaurs. A Concise Natural History; Third Edition. A Pictorial Book Review.

The first time I ever set eyes on the book Dinosaurs. A Concise NaturalHistory; by David E. Fastovsky and David B. Weishampel, it was sitting behind the counter of a local museum called Dinosaur State Park, in Rocky Hill Connecticut.

Dinosaurs. A Concise Natural History. Third Edition.
By David E. Fastovsky and David B. Weishampel
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Curious, I asked a volunteer at the museum if the book was for sale. She replied no, but kindly asked if I would like to thumb through the pages. It didn’t take me long to realize that this publication was not going to be your traditional Dinosaur read. 

Dinosaurs. A Concise Natural History. Third Edition.
By David E. Fastovsky and David B. Weishampel
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Dinosaurs. A Concise Natural History. Third Edition.
By David E. Fastovsky and David B. Weishampel
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Published in 2016, Dinosaurs; A Concise Natural History is an innovative look at what is presently known about the evolution and extinction of dinosaurs, both avian and non-avian.

Designed and organized with the college student in mind, Dinosaurs (in their own words) promises to make science exciting and understandable to non-science majors through its emphasis on scientific concepts rather than endless facts. Fully updated and now integrating the theme of feathered dinosaurs, this beautifully illustrated, lively and engaging text will encourage students to ask questions and think like a scientist.

I couldn’t agree more, that’s exactly what this book has accomplished. Below is a brief example of what is to be expected within the pages of this book.

Stuff n’ feathers!

A look at the modern biota, without understanding its evolutionary history (preserved in the fossil record) leads to some very erroneous ideas about the “why” of many features. For example, pneumatic bones and feathers are commonly singled out as marvelous adaptations to maintain lightness and permit flight. Well, they surely are marvelous, they clearly maintain avian lightness, and there is no doubt that feathers work well for flight. But did pneumatic bones and feathers evolve for lightness and flight, respectively?

In both cases, now that we have a sense of bird ancestry, the answer is a resounding, “No”! Hollow bones are a saurischian character (even the names Coelophysis and Coelurosauria contain a reference to the hollow bones in these non-flying dinosaurs), and pneumaticity is likely related to efficient breathing (as implied above, we will see this again in immense, ponderous sauropods which you can safely assume didn’t fly). Avian pneumaticity likely developed long before there were things we would call birds. Modern birds inherited pneumaticity, unidirectional breathing, feathers and a host of other “bird” features from non-avian theropods, even though these features were further refined in modern birds.

Most of us would say that the purpose of feathers is flight. We agree; feathers are used for flight, but we doubt that they evolved for that purpose, particularly as many non-flying, non-avian dinosaurs had them. This, in turn, provides a real insight into what the origin of feathers was all about. One striking feature of all feathered dinosaurs, flying or no, are skeletal designs suggesting very active, commonly predatory, lifestyles. With feathers most primitively appearing on non-flying theropods, we infer that feathers likely provided the insulation that is a prerequisite for warm-bloodedness, allowing theropods to maintain high levels of activity for extended periods of time; an attribute that was eventually used for flight. Feathers undoubtedly were useful in a cursorial, predatory lifestyle. It is perhaps not coincidence that the most highly evolved feathers are flight feathers; other feathers, such as monofilamentous feathers and down, likely represent earlier stages in feather development, and graced the coats of more primitive non-avian theropods.

But insulation for warm-bloodedness as the real reason for the origin of feathers doesn’t completely satisfy, either, because many of the early feathers that we’ve seen are monofilamentous and may not have insulated very well. But as we all know, modern birds are brightly colored, highly social, and visually acute. Moreover, we know that at least some non-avian theropods were highly social creatures. We also know that ancient feathered theropods, non-flying and flying, had distinctive patterns and colored markings. Could feathers, at first, have been at least as much for display as for insulation?

Recall that in Chapter 5 we discussed the sensory importance of feathers. Here, then, is a hypothetical, but plausible, scenario for the evolution of feathers: widely distributed (across the skin), monofilamentous feathers could have first arisen for tactile sensation. Color might have appeared as a byproduct, or an even driving force, of evolving theropod sociality, associated with denser packing of the feathers. Still more densely packed, multifilamentous (downy) feathers might then (or concurrently) have evolved as a means of insulation. And finally, flight feathers may have ultimately evolved, associated with small size and a very active lifestyle. That is simply a scenario; however, what we know for sure, now, is that early feathers weren’t about flight!

This sort of clear and concise (as the books title implies) writing occurs throughout the entire book. Each chapter, such as; Who are the Dinosaurs? Theropoda III: the origin and early evolution of birds, and Ornithopoda: mighty Mesozoic masticators, contain chapter objectives, summaries, selected readings and topic questions. 

Dinosaurs. A Concise Natural History. Third Edition.
By David E. Fastovsky and David B. Weishampel
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/

The graphic design of this publication is also wonderful. With its mix of easy to interpret cladograms, color CT-scans and excellent fossil photographs, every page seems to offer new and exciting visual information. 

Dinosaurs. A Concise Natural History. Third Edition.
By David E Fastovsky and David B. Weishampel
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/

If that wasn’t enough, British freelance paleoartist John Sibbick provides a number of original black-and-white reconstructions of prehistoric life. Sibbick’s use of scientifically accurate environments, and animal behavior in his artwork is some of the best I have ever seen. Wow! 

Dinosaurs. A Concise Natural History. Third Edition.
By David E. Fastovsky and David B. Weishampel
Artist: John Sibbick
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Dinosaurs. A Concise Natural History. Third Edition.
By David E. Fastovsky and David B Weishampel
Artist: John Sibbick
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
On its third printing since 2009, Fastovsky and Weishampel do their best to stay up-to-date with today’s new scientific developments.

No longer is it just about digging up prehistoric bones from the ground. Dinosaur study instead deals with more far- reaching topics such as brain reconstructions (Stegosaurus), jaw mechanics (Heterodontosauridae and Ceratopsian), thermoregulation, nesting and feather coloration. All of these are effectively touched upon in this book.

Dinosaurs. A Concise Natural History. Third Edition.
By David E. Fastovsky and David B. Weishampel
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
One has to wonder, is another update and edition not far on the horizon? Recent discoveries in 100 million-year-old Burmese amber may set the wheels further in motion.

A personal favorite of mine was the section on Mesozoic birds. Fastovsky and Weishampel do a very nice job describing some of the critical steps in early avialan evolution. The evolution of Aves from the primitive avialan condition, represented by Archaeopteryx, through the remarkable avian discoveries recently made in China, culminates in an easy to decipher cladogram on page 182. 

Dinosaurs. A Concise Natural History. Third Edition.
By David E. Fastovsky and David B. Weishampel
Photo Credit: Paul Cianfaglione
https://avianmusing.blogspot.com/
Dinosaurs. A Concise Natural History, is without a doubt, one of the more lively and interesting Dinosaur books on the market. I highly recommend it.