Saturday, February 24, 2018

More on Racket-tailed Birds

About a week ago, I posted an article on this blog about racket-tailed birds. http://avianmusing.blogspot.com/2018/02/racket-tailed-birds-whats-all-this.html


Turquoise-browed motmot (Eumomota superciliosa)
Image property of Wikipedia
http://avianmusing.blogspot.com/
During the course of my research, I had contacted Dr. Troy G. Murphy (Trinity University, Texas) about the possibility that three of the closely related species discussed in my posting, Racket-tailed roller (Coracias spatulatus), Common paradise kingfisher (Tanysiptera galatea) and Turquoise-browed motmot (Eumomota superciliosa), had evolved, and thus retained the wag-display from a common ancestor, since all performed the exact same tail-display.

Dr.Murphy was kind enough to respond to my questions with some very thoughtful comments; comments I would like to share with you here.

But before I do that, I’d like to invite you to Dr. Murphy’s personal webpage;  www.finchwrangler.com/Troy_Murphy/homepage.html, where you can find many of his free PDF research papers. His lab’s research spans behavioral ecology and evolutionary biology, with an emphasis on animal communication and the evolution of conflict resolution.

Paul-

I really enjoyed reading your email. Thanks for reaching out. I haven’t thought about motmots much for over a decade so it is nice to think about them again. As per your question, my view is that it is highly unlikely that a tail display trait would be ancestral to these diverse groups. There has been just too much time between the divergence of these groups for an ancestral behavioral trait to still show its face. We know that a lot of avian species have tails that are exaggerated to some extent, mostly in length and color — and we know that these long tails occur in species with rackets, including some of the species you mention (parrots, hummingbirds, birds of paradise, drongos, rollers, pheasants). But most of the species do not show any behavioral wagging of the tail—suggesting that tail exaggeration does not link to display of that tail.

Now when we just consider the Coraciiformes (motmots, rollers, bee-eater, kingfishers, etc.), it would make better sense that behavioral use of the tail in display could be ancestral. But my guess is that this isn’t true here either. Again, because so many species in this group do have exaggerated tails, but don’t use them in display, I think this argues that the display is a recent acquisition in each of the lineages that show it. I believe this is the more parsimonious route to get to the few species that do wag, or similarly display, their tail.

Now an interesting question that has always tugged at me is why the motmots that lack an exaggerated tail (tody, and blue throated motmots) wag their tails. Given that all 11 species of motmots wag, it is easy to infer shared ancestry of the ancestral way display in this clade. But from an adaptive standpoint it remains unclear if the short-tailed motmots can gain much fitness benefit from the wag display — as their tails just aren’t as visible from a distance as those with racket-tips. It seems possible that the tail display in these groups is given to a receiver that is close up, like a mate or a rival, but not oriented to a predator that is some distance away. But this is a project for some student to pursue.

Also interesting is that two other species of motmots that I am quite familiar with (blue-crowned and russet-crowned motmots) do not appear to wag-display in the same context as the turquoise-browed that I published on. The blue-crowned does sometimes seem to wag in response to a predator (to me!), but this hasn’t been studied. But it doesn’t do it so reliably as the turquoise-browed. So there may be additional function to the wag display in this species (i.e., both to predators and mates/competitors). On the other hand, the russet-crowned doesn’t seem to respond to predators with a wag at all, but does use the tail wag in more social contexts during territorial disputes.

So to me, the ancestry of the tail shape is likely ancestral to the Motmotidae, but maybe, just maybe, the selective forces (i.e., the adaptive fitness benefits) that maintain the tail shape in the various motmots is different between the species. Just some thoughts for the campfire.

Thanks again for your email.

Avian Hypertrophied Talons

As easy as it is to find songbirds at a backyard feeder in winter, the same holds true of the predatory hawks that seek them out. The Sharp-shinned Hawk (Accipiter striatus) is one of those hunters that make birds 90% of its diet.

Accipiter’s, as they are known, surprise and capture most of their prey from the cover of forests and thick vegetation. Their victims are typically small, the size of a sparrow or finch. However, they will also pursue larger quarry like thrushes and doves.


Sharp-shinned Hawk (Accipiter striatus) restraining and eating a Mourning Dove (Zenaida macroura)
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
When larger birds are seized, accipiter’s rely on constriction to immobilize prey. During the initial energetic struggles that occur immediately after capture of large prey, the additional grip provided by the hypertrophied talons of D-I and II of accipitrids is vital as the raptor tumbles about while keeping latched into its prey, flapping vigorously, trying to gain the upper hand and pin it to the ground.

As the prey of accipitrids are often consumed while still alive, a firm grip is constantly required to maintain immobilization until the prey is dead, further emphasizing the importance of the hypertrophied talons of D-I and II (source; http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0007999).

We can clearly see these abnormally large talons (D-I and II) on a mummified Sharp-shinned Hawk foot pictured below.

Sharp-shinned Hawk (Accipiter striatus) talon
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
This is even more evident on the foot of the Northern Goshawk (Accipiter gentilis).


Northern Goshawk (Accipiter gentilis) talons
Photo Property of www.nejohnston.org/birds/feet/NorthernGoshawk_1.jpg
http://avianmusing.blogspot.com/

When I think about this manner of prey immobilization, the first thing that comes to my mind is the enlarged sickle-claw on the second toe of the dromaeosaurid, Deinonychus antirrhopus.


Deinonychus antirrhopus
Yale Peabody Museum
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
Deinonychus antirrhopus
Yale Peabody Museum
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
In 2011, Denver Fowler and colleagues suggested a new method by which dromaeosaurids may have taken smaller prey. This model, known as the "raptor prey restraint" (RPR) model of predation, proposes that dromaeosaurids killed their prey in a manner very similar to extant accipitrid birds of prey: by leaping onto their quarry, pinning it under their body weight, and gripping it tightly with the large, sickle-shaped claws. Like accipitrids, the dromaeosaurid would then begin to feed on the animal while still alive, until it eventually died from blood loss and organ failure. This proposal is based primarily on comparisons between the morphology and proportions of the feet and legs of dromaeosaurids to several groups of extant birds of prey with known predatory behaviors. Fowler found that the feet and legs of dromaeosaurids most closely resemble those of eagles and hawks, especially in terms of having an enlarged second claw and a similar range of grasping motion (source; Wikipedia. Also see journal above).

However, to find a species of bird today that best exemplifies the possible behavior and actual structure of the dromaeosaurid sickle-claw, we have to look instead to the Red-legged Seriema (Cariama cristata).

Red-legged Seriema (Cariama cristata)
Image Credit: https://www.hbw.com/ibc/species/red-legged-seriema-cariama-cristata
http://avianmusing.blogspot.com/
The seriema is a mostly predatory terrestrial bird that inhabits grasslands from Brazil to northern Argentina. Its omnivorous diet enables it to eat a variety of foods, which include seeds, wild fruits, grains, but also animals such as rodents, lizards and frogs. Small items are usually swallowed whole, whereas larger game is beaten upon the ground first, then torn into manageable pieces.

How the seriema uses its enlarged, hyperextended second toe claw, in my opinion, is still up for debate. Some say the toe claw is used solely for tearing into larger prey? Others point to the claw as a weapon used to protect itself against potential threats.

Red-legged Seriema (Cariama cristata) hyperextended talon
Image Credit: http://carnivoraforum.com
http://avianmusing.blogspot.com/
Since the seriema engages live prey with its bill, it is often exposed to defensive toxins around its facial area. When this happens, like in the video posted below of a seriema killing a sapo frog, the seriema will use its foot to wipe away the annoying poison. This use of the foot and claw is called scratch-preening, which is usually applied to the head and neck region.


The Red-legged Seriemas abnormally shaggy head and neck feathers (preening), social interactions and prey manipulation, may have been the selective forces behind the evolution, and use of the species sickle-claw.

A feathered Deinonychus, on the other hand, could have utilized the claw in much of the same way as the seriema, co-opted from the raptor prey restraint model of adaptation.


Deinonychus antirrhopus 
Harvard Museum of Natural History
Image Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/

Sunday, February 18, 2018

Rachis-Dominated Tail Feathers

A few years ago, I was given the rare opportunity of studying a partial 120 million-year-old bird fossil from Western Liaoning, China.

An obvious lower half of a bird with one wing, the fossil revealed some defining characters. Located on the plate was a synsacrum, a pygostyle, a small claw on metacarpal 1, and a short metatarsal 1 (hallux) with a large claw that is more recurved than the other pedal claws. The fossil also preserves faint remnants of plumage.

Enantiornithine Bird Fossil
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/

But I also noticed one other feature that looked unusual to me. Coming directly off the end of the pygostyle (partially hidden by matrix) was a near-perfect, even-width impression of what looked to be a possible tail feather. In addition to the even-width nature of the impression, there also appeared to be some indication of feather overlap (if they were in fact actual feathers).

Enantiornithine Bird Fossil
Rachis-dominated feather
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
However, this unique impression clearly lacked the characteristics of what we would consider a recognizable feather. If this was indeed a tail feather, where did the rachis and vanes go? What was this impression?

In my search for information, I found and read an excellent paper titled; Homology and Potential Cellular and Molecular Mechanisms for the Development of Unique Feather Morphologies in Early Birds (Geosciences 2012).


In it, the paper describes how dinosaurs, including birds, possessed diverse and specialized integument. This diversity in plumage increased in the Early Cretaceous, with the dominant avian clade, the enantiornithines, possessing a huge diversity of feather patterns and morphologies. 

Of the number of Cretaceous aged feather morphs that I have been fortunate to examine, two have been directly associated with enantiornithines, while the others have been isolated feathers. These have included pennaceous feathers with proximally undifferentiated vanes, feathers with multiple filaments joined basally and others with large single filaments.

Mesozoic Bird Feathers
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
Mesozoic Feather
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
But the question still remained, is this even-width impression coming off the end of the bird’s pygostyle a possible “tail streamer”, a feather similar to what we see in today’s tropicbirds? Provided below is an excerpt from the scientific paper which nicely describes this peculiar feature;

The preservation of advanced feather structures in the earliest diverging birds and some non-avian theropods suggests that basal avians would have had comparable if not more derived integument with respect to their dinosaurian predecessors. Archaeopteryx lithographica was first identified as a bird mainly on the basis of its large, asymmetric and pennaceous remiges; the morphology and distribution of the wing feathers in this taxon and other primitive birds (e.g., Confuciusornis sanctus) is considered essentially modern. However, some recent studies suggest that although superficially modern in appearance, the remiges of basal birds may have been structurally weaker, raising questions about the flight capabilities of these taxa. Furthermore, the identification of at least two feather types not present in modern birds, and the wide and variable distribution of different feather morphologies among non-avian maniraptorans, suggests that the evolution of modern avian integument is more complicated than suggested by just Archaeopteryx lithographica and warrants further investigation.

The first unique feather type recognized within Mesozoic birds was the elongate and paired “streamer” rectrices (tail feathers) preserved in some specimens of Confuciusornis sanctus. Similar paired feathers were later reported in some specimens of enantiornithines although at first interpretation of these structures was controversial. While some workers regarded these paired rectrices as a primitive stage in the evolution of feathers from elongated scales, others inferred them to be more advanced structures based on inferences that the rachis itself is a derived feather feature. Most recent interpretations have concurred with the latter hypothesis: these paired rectrices are modified pennaceous feathers not present in living birds—they represent an extinct morphotype.

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.

The researchers go on to propose a function for these unusual non-aerodynamic tail feathers; 

Protopteryx fengningensis and most other enantiornithines are thought to have been arboreal. This has led to the interpretation that their elongate tail feathers may have helped them balance in the densely wooded environment in which they lived, similar to the way in which a squirrel uses its tail. Interpretations of the similar feathers present in confuciusornithiforms have instead been dominated by suggestions that they were used for sexual display—their variable presence in the known specimens suggestive of sexual dimorphism. However, recent morphometric studies have not been able to support or reject this hypothesis and the function of these feathers remains controversial. The variation in length and morphology observed among the tail feathers of enantiornithines may suggest they are also related to display, species recognition, or other forms of visual communication. The tail feathers in another group of basal birds, the Jeholornithiformes, also show a morphology which suggests that visual communication may have been the primary function; the wide range of non-aerodynamic tail morphologies among basal birds suggests that this may have been a trend during the early evolution of Aves.

Protopteryx fengingensis
Image property of: www.mdpi.com
http://avianmusing.blogspot.com/

Saturday, February 17, 2018

Racket-tailed Birds; what’s all this racket about?

I am currently in the middle of an amazing book titled; The Malay Archipelago: The Land of the Orang-utan, and the Bird of Paradise. A Narrative of Travel, with Studies of Man and Nature, by Alfred Russel Wallace,1869.


A co-founder of The Theory of Evolution, the Malay Archipelago is considered to be Wallace's most important work and contribution to the theory.

This book covers a range of topics from the unique animal life of the region, to the practices and lifestyles of its peoples, generously illustrated with both full-page wood-engraved plates, maps, and numerous wood-engraved illustrations.

One of those illustrations was that of the Common paradise kingfisher (Tanysiptera galatea). Unlike most kingfishers I know, the paradise kingfisher hunts in forests, with a diet that consists of such invertebrates as earthworms, grasshoppers, beetles, caterpillars, centipedes and occasionally lizards.

Common paradise kingfisher (Tanysiptera galatea)
Image property of orientalbirdimages.org
avianmusing.blogspot.com/
These birds also differ from all other kingfishers (which have usually short tails) by having two middle tail-feathers immensely lengthened and very narrowly webbed, but terminated by a spoon shaped enlargement, as in the motmots and some of the hummingbirds (Wallace).

The kingfisher incidentally was done by T. W. Wood, an English zoological illustrator responsible for the accurate drawings in major nineteenth century works.

Common paradise kingfisher (Tanysiptera galatea)
T.W. Wood
Image credit: Wikipedia
http://avianmusing.blogspot.com/
Woods image held my attention for quite some time, leading me to wonder about the evolutionary purpose of those glorious tail-rackets.  

One would think that the tail-rackets are used for some sort of sexual signal, or as a distraction display against potential predators. Seems like a logical explanation for such eye-grabbing appendages. But is it that straightforward? Should we just accept this mainstream view and move on? Or do we step back and look at the larger picture, searching for possible alternative answers.

Choosing the latter, I took it upon myself to examine six species of racket-tailed birds. They included the previously mentioned paradise kingfisher, Golden-crowned Racket-tail parrot (Prioniturus discurus), Greater racket-tailed drongo (Dicrurus paradiseus), Racket-tailed coquette hummingbird (Discosura longicaudus), Racket-tailed roller (Coracias spatulatus) and Turquoise-browed motmot (Eumomota superciliosa).


Greater racket-tailed drongo (Dicrurus paradiseus)
Image Credit: orientalbirdimages.org
http://avianmusing.blogspot.com/
What these species have in common is that they all possess well-defined racket-tails, distinctive in having elongated outer tail feathers with webbing restricted to the tips. All inhabit subtropical and tropical moist lowland forests.

Most of the above-mentioned species hunt insects and small lizards, except for the parrot and hummingbird. Interestingly, the hummingbird is the only species where the racketed tail does not occur in both sexes.

So why did the racket shaped tail evolve in the first place? What advantages do they provide?

Do the rackets startle prey as the bird drops to the forest floor? Are the rackets a form of camouflage that works by breaking up the outlines of a perch-hunting bird, or in flight? Is it a sign of sexual quality?

One researcher, Troy G. Murphy, Ph.D., believes the tail has evolved to function differently for both sexes in turquoise-browed motmots. Males apparently use their tail as a sexual signal, as males with longer tails have greater pairing success and reproductive success. In addition to this function, the tail is used by both sexes in a wag-display, whereby the tail is moved back-and-forth in a pendulous fashion. The wag-display is performed in a context unrelated to mating: both sexes perform the wag-display in the presence of a predator, and the display is thought to confer naturally selected benefits by communicating to the predator that it has been seen and that pursuit will not result in capture. This form of interspecific communication is referred to as a pursuit-deterrent signal.

Turquoise-browed motmot (Eumomota superciliosa)
Image Credit: Wikipedia
http://avianmusing.blogspot.com/
That might explain the reason why both male and females wag their tail, but it doesn’t explain the reason for a bare-shafted rachis with a feathered tip. Why was this selected among unrelated species?

The male Racket-tailed coquette hummingbird may have convergently evolved the rackets as an aggressive signal toward other males.


Racket-tailed coquette (Discosura longicaudus)
Image Credit: David Stimac/Davidstimac.com
avianmusing.blogspot.com/
The Greater racket-tailed drongo behavior is little more bothersome. A video posted online features a chick-feeding drongo at the nest flicking its long-racketed tail. This comes across to me as more of an advertisement to predators than anything else.


At this moment, I’m not totally committed to any present-day theory.

I did however notice one interesting behavior that may shed light on the close evolutionary relationship of three of these birds. 

As was mentioned earlier, the Turquoise-browed motmot performs a unique wag-display, whereby the tail is moved back-and-forth in a pendulous fashion.


Curiously, the exact same movement (pendulum) and racket-tail is also detected in the closely related Common paradise kingfisher and Racket-tailed roller.

Racket-tailed roller (Coracias spatulatus)
Image Credit: Wikipedia
http://avianmusing.blogspot.com/
https://www.youtube.com/watch?v=gjxi02QpFyE


According to a recently completed study on the avian tree of life, the rollers (Coraciidae) divergence date from the motmots (Motmotidae) and kingfishers (Halcyoninae), occurred around 58 million-years-ago.


If that’s the case, could the wag-display of the racket tail (slow, pendulum swing) imply an ancient avian trait? Did these three species retain this behavior from a common ancestor? Is the wag-display dependent solely on the occurrence of feathers with bare rachises and distal rackets? Still many interesting questions to be asked of racketed-tailed birds.   

Bare feather rachises with distal rackets are not unique to today’s birds. Neither were tail displays. This is nicely discussed in a 2013 research paper titled; Unique caudal plumage of Jeholornis and complex tail evolution in early birds.


Feather ornaments in Mesozoic birds are common: the basal bird Confuciusornis and several species of enantiornithine possess racket plumes, with no other pennaceous tail feathers. Although the length, morphology, and probable dimorphic nature of these racket plumes preclude a purely aerodynamic function, their aerodynamic costs may have been limited for reasons parallel to those given above for the distal frond of Jeholornis. The partly ornamental nature of the tail plumage of Jeholornis, and of the racket plumes known in some other Mesozoic taxa, indicates that sexual selection was an important influence from almost the earliest stages of avian evolution. Documentation of the unique frond-and-fan tail of Jeholornis adds to the growing body of evidence that basal birds resembled their living counterparts in using a remarkably diverse and advanced array of feather types and configurations to optimize flight and engage in social signaling, with many integumentary features likely playing key roles in both flight and display.


Caudipteryx zoui
Image property of Peter Schouten
with paid permission
http://avianmusing.blogspot.com/

Saturday, February 10, 2018

The Megapodes; adaptations to underground incubation

In 2002, I met my wife-to-be on a birdwatching trip to Big Bend National Park in Texas. A year later, and before I knew what hit me, I was married and on my way to Australia on a three-week honeymoon.  

Before I depart to any far-off birding destination, there is always a list of species in the back of my mind that I consider “must-see-birds”.

For our visit to eastern Australia, the list included the Cassowary (Casuarius casuarius), with its skin-covered casque on their heads, the Satin Bowerbird (Ptilonorhynchus violaceus), which build specialized bower structures, and the Laughing Kookaburra (Dacelo novaeguineae), famous for its staccato vocalizations.

Strangely, out of all the species we had encountered, the one that brings back some of the most vivid memories is the Australian Brush-turkey (Alectura lathami).

Australian Brush-turkey (Alectura lathami)
Photo Credit: en.wikipedia.org
http://avianmusing.blogspot.com/
No, there was nothing outwardly special about this bird, it looked and acted much in the same way as our turkey’s do back home. Despite its name and their superficial similarities, the brush-turkey is not closely related to North Americas Wild Turkey.

What is special about this bird is its nesting behavior.

The Australian brush-turkey is a common, widespread species of mound-building bird from the family Megapodiidae. It is the largest extant representative of the family Megapodiidae and is one of three species to inhabit Australia. We were also fortunate to find another species of megapode called the Orange-footed scrubfowl (Megapodius reinwardt).

Orange-footed scrubfowl (Megapodius reinwardt)
Photo Credit: en.wikipedia.org
http://avianmusing.blogspot.com/
Both species build large nests on the ground made of sand, leaf litter and other debris where the heat generated by the decomposition of organic material serves to incubate the eggs. The brush-turkeys mound can measure 1 to 1.5 meters high and up to 4 meters across, whereas the scrubfowls may reach 4 meters in height and over 8 meters in diameter. Personally, no one could have ever prepared me for such a sight, it was absolutely overwhelming.


Australian Brush-turkey (Alectura lathami) mound-nest
Photo Credit: cape-york-Australia.com
http://avianmusing.blogspot.com/
Since then, my interest in megapodes behavior has grown. I even purchased a book shortly after my trip called; The Megapodes, by Jones, Dekker and Roselaar (1995. Oxford University Press), which I highly recommend.


The Megapodes; Jones, Dekker and Roselaar
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
Now and again I am reminded of these fascinating creatures. For example, I just watched one of my favorite megapode video clips (Youtube), featuring the Melanesian Megapode (Megapodius eremita) at its volcanic nesting grounds in New Britain, the largest island in the Bismarck Archipelago of Papua New Guinea.


I also photographed a Maleo (Macrocephalon maleo), a large megapode endemic to the Indonesian island of Sulawesi, in 2016 at the Bronx Zoo in New York City. I believe this is the only megapode I have ever seen in captivity.
Maleo (Macrocephalon maleo) in captivity, Bronx Zoo, NY City
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
Then there was the recent discovery and preservation of in-situ Cretaceous bird eggs, which led researchers to compare megapode nesting methods to other Mesozoic birds and theropod dinosaurs.

It was not long after reading this research paper, that I made it a point to learn more about the different megapode nesting strategies.

For this we turn to the 1995 book, The Megapodes;

Incubation sites: mounds and burrows.

Undoubtedly, the most notable featured shared by all megapodes is their technique of incubation. This involves the utilization of some form of naturally occurring heat to incubate their eggs, rather than the body heat of the adult. Basically, three main sources of heat are used: microbial decomposition of organic matter, geothermal activity, and solar radiation. These are utilized in a variety of ways, and the amount of effort required for their utilization varies greatly. Although most species use only one of these heat sources, some may use several, such species may, for example, construct mounds in some areas, and lay their eggs in burrows in warm soil in other areas. Birds that gather piles of organic matter to be used as an incubation site are called “mound builders”; those that tunnel into pre-existing locations in volcanic areas or hot sands are called “burrow nesters”.  
Megapode mound-nest 
The Megapodes; Jones, Dekker and Roselaar
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
Megapode burrow-nest
The Megapodes; Jones, Dekker and Roselaar
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
Adaptations to underground incubation.

Megapodes exhibit a surprising and interrelated array of physiological, ecological, and behavioral adaptations related directly to the special conditions of their unique incubation technique. Perhaps the most remarkable of these adaptations are those associated with the incubation process itself. This is because the egg, the developing embryo within, and the newly hatched chick must cope with conditions dramatically different from those associated with any normal nest. Most critically, the gaseous environment surrounding the egg is extremely humid and is very low in oxygen and very high in carbon dioxide. Megapodes have solved these serious problems by means of several specializations of their eggs and their physiology.

Megapode eggshells are very thin compared to those birds of similar size. In addition, the pores in the shell through which the gases pass actually change shape during incubation, becoming wider as the growing embryo assimilates the calcium for bone formation. This progressive change in pore shape is a very unusual phenomenon in birds and greatly facilitates gas exchange between the embryo and the atmosphere immediately surrounding the egg. Therefore, despite the extreme humidity and high gas pressures within the incubation site, the embryo’s tissues develop at rates similar to those of birds incubated in a normal nest.

Although the rates of growth of the megapode embryo are similar to those of other birds, the chick that finally hatches is relatively large. This is associated with the very long period of incubation which may be between 50 and 70 days. During this time the chick continues to develop within the egg, finally hatching by cracking through the eggshell with its feet rather than by using an egg-tooth as in other birds. The hatchling may spend many hours or even several days battling upwards through the material of the incubation site. The chick that eventually emerges is, in term of its behavioral and physiological capabilities, the most advanced of any bird; it is able to run, feed, regulate its body temperature, find food, and even fly on the day of hatching. This extreme precociousness is both a necessity and a consequence of the specialized incubation technique; unlike any other birds, young megapodes receive absolutely no assistance from their parents and must live independently from the moment of emergence.  

For those who are interested in seeing megapodes, the easiest species to observe are the two we found Australia; these are both mound builders. The Australian Brush-turkey is found in many locations in southern Queensland, where it is common in National Park picnic grounds and even in the suburbs of large cities. In tropical Australia, Orange-footed Megapodes are conspicuously present around many resorts and islands used by visitors.


Thursday, February 8, 2018

Avian Images in Snow

It’s sort of easy to become inspired by birds. They have colorful plumage, sing beautiful songs, raise their young around us humans, and above all, they fly.

But I also find inspiration in a host of other ways. One of those is through bird tracking and sign. Some of you may recall that I have touched upon this topic once before, but this posting is slightly different.

With winter not letting up any time soon, I’ve been on the heels of many species (actually their hallux), trudging knee-deep after my favorite photographic subject; impressions of birds in snow.

These images can vary immensely, due to the depth of the snow, and other conditions that may influence track and trail characteristics.


American Crow (Corvus brachyrynchos) foot impression with digital pads
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
A fresh coating of snow is like a stretched canvas, and the birds are its artists.

For me, its not necessarily the identification of the trackmaker itself, rather, it’s how the footprints are positioned, and the story surrounding them that is being told.  

Some of these stories can be exciting, such as an owl’s isolated body impression in the middle of an open field. Did it hear a vole tunneling through the snow?


Barred Owl (Strix varia) in snow
Photo Credit: Mary Holland
naturallycuriouswithmaryholland.wordpress.
While others tell a more straightforward tale of a sparrow searching for fallen seeds in our old flowerbed.

Dark-eyed Junco (Junco hyemalis) foot impression in snow
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
Tracks in snow sometimes make us wonder and ask questions. Why did that crow trek so far during the snowfall? What was it hoping to find?


American Crow (Corvus brachyrhnchos) track impressions in snow
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
In my opinion, one of the most beautiful images in nature is a track that is accompanied by a wing feather impression. These impressions typically occur as a bird lands, or when a wing contacts the snow during the downstroke when a bird takes to the air.


Common Raven (Corvus corax) wing and foot impression in snow
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
No matter how you may be inspired by birds, I hope you can take the time to appreciate these temporary works of nature art.

Song Sparrow (Melospiza melodia) body impression in snow
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/

Wednesday, February 7, 2018

Avian Gaping; an unusual manner of feeding

The month of February is without question a time of transition for many of our local bird species. Signs of spring fill the air with familiar bird song, mated pairs of hawks, nesting eagles and the first sightings of migrant waterfowl on the river.

But the most visible indication that spring is near is the return of the blackbirds to our neighborhoods and parks. The term blackbird loosely refers to a diverse group of about ten species of North American birds that belong to the subfamily Icterinae.

The most familiar of these blackbirds are the Common Grackle (Quiscalus quiscula), Red-winged Blackbird (Agelaius phoeniceus) and Brown-headed Cowbird (Molothrus ater). They can easily be found in wide open spaces, carpeting lawns and cemeteries as they search for grains, weed seeds, fruits, and insects.  Sometimes they are joined by non-blackbird species, notably European Starlings (Sturnus vulgaris) and American Robins (Turdus migratorius).

Blackbirds and starlings are not the most striking of species plumage-wise, but what they lack in color, is often made up in sheer numbers and opportunities for behavioral observations.

One of the most interesting feeding behaviors that I have observed among these ground foragers is called “gaping”. Two species, the Red-winged Blackbird and European Starling excel at this activity, which forcibly open their bills, allowing the bird to dig or look for soil invertebrates.

European Starling (Sturnis vulgaris) Gaping
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
Bird species that are powerful gapers have stronger muscles for opening the bill than they do for closing it, so they can generate quite a bit of pressure to open the bill (source: Orians, G. 2014). This action is facilitated by highly developed protractor muscles, or in the photo below, the jaw muscle complex (source: Birds of North America online edition).

Avian Jaw Muscle Complex
Manual of Ornithology; Avian Structure & Function by Noble Proctor
Illustrations by Patrick Lynch
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
This method of searching allows blackbirds and starlings a greater capture rate per individual, a clear advantage among other ground specialists.

Red-winged Blackbird (Agelaius phoeniceous) Gaping
Photo Credit: Greg Lavaty (Birdnote)
http://avianmusing.blogspot.com/

Monday, February 5, 2018

The Avian Heart

One of my all-time favorite ornithology books, Manual of Ornithology; Avian Structure & Function, by Noble Proctor and Patrick Lynch, for years has been my go-to source for avian skeletal, musculature and digestive illustrations.

Manual of Ornithology; Avian Structure & Function by Noble Proctor
Illustrations by Patrick Lynch
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
Noble taught ornithology, biology and botany at Southern Connecticut State University for 34 years and frequently spoke at our local Audubon chapter.


But what I admired most about Noble Proctor was his willingness to answer many of my personal bird questions, no matter how simple, or off-the-wall they may have been. For a young person like myself, that direct connection to a brilliant naturalist made a lifelong impression.

That passion for learning still continues to this day, thanks in part to mentors like Noble.

In keeping with past inquiries, I once again turn to my copy of the Manual of Ornithology, this time for information on an organ that I embarrassingly know little about, the avian heart.

Why the sudden interest in the avian heart? Over the past month, I have had the opportunity to examine and dissect three species of road-killed birds, two of them offered to me by close acquaintances. My interest in the specimens focused solely on the digestive, circulatory and respiratory systems; the removal, and subsequent documentation of organs such as the gizzard, lungs, liver and even the heart.

What I did know about the avian heart prior to dissection is more or less summarized below;

Birds tend to have larger hearts than mammals (relative to body size and mass). The relatively large hearts of birds may be necessary to meet the high metabolic demands of flight. Among birds, smaller birds have relatively larger hearts (again relative to body mass) than larger birds. Hummingbirds have the largest hearts (relative to body mass) of all birds, probably because hovering takes so much energy (source; http://people.eku.edu/ritchisong/birdcirculatory.html).

Dark-eyed Junco (Junco hyemalis) heart
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
However, I think this is a wonderful time, and opportunity for us to take a closer look at this organ, and to expand on this general knowledge (start of manual text).

The external anatomy of the avian heart.

The avian heart is quite similar in its major features to the hearts of mammals. Both birds and mammals have true four-chambered hearts that completely separate pulmonary and somatic circulation. But the avian heart differs in several ways from the mammalian heart. The most distinctly avian feature, mentioned above, is the rightward orientation of the aortic arch (rather than the leftward, as in mammals). In addition, in birds the brachiocephalic vessels branch off the aorta at the base of the ascending aortic arch. The aortic arch is thus relatively smaller than it appears in mammals, where the brachiocephalic vessels branch off the top of the aortic arch. Because they supply massive pectoral arteries, each brachiocephalic artery is nearly equal in diameter to the aortic arch.

Manual of Ornithology; Avian Structure & Function by Noble Proctor
Illustrations by Patrick Lynch
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
The avian arrangement of the anterior veins entering the heart is similar to that found in reptiles. Two large precava veins meet in a sinus venous just before entering the right atrium. There is no single superior vena cava, as found in mammals. As in the mammalian heart, however, the venous blood that flows from the posterior regions of the body collects into a single inferior cava (postcava) that enters the right atrium.

The internal anatomy of the avian heart.

Because both birds and mammals are homoiothermic, their hearts must work efficiently to supply the body tissues with enough oxygen to support a high metabolism. Hence, both have developed a four-chambered heart that separates the circulation of oxygenated and unoxygenated blood. Even in such advanced reptilian groups as the crocodilians the heart mixes some arterial and venous blood and is thus less effective in keeping the oxygen content of arterial blood high.

Manual of Ornithology; Avian Structure & Function by Noble Proctor
Illustrations by Patrick Lynch
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
The internal details of the avian heart are remarkably similar to these found in mammals, with the prominent exception of the right-oriented aortic arch. Blood from the anterior and posterior body flows into the right atrium via the precava and postcava veins. From there it moves through the tricuspid valve and into the right ventricle. In both birds and mammals, the right ventricle is typically much less muscular than the left ventricle, although it may equal the left ventricle in volume. This is because blood flowing from the right ventricle into the pulmonary arteries must not damage the lungs by entering them at too high a pressure. Oxygenated blood from the lungs returns to the heart via the pulmonary veins, the only “red” veins of the body. The pulmonary veins empty into the left atrium. From there blood flows through the mitral valve and into the left ventricle. The left ventricle is the major engine of blood circulation and does most of the real work of moving blood throughout the body and maintaining blood pressure. The walls of the left ventricle are very muscular and contain small papillary muscles that control the opening and closings of the mitral valve. Blood flows out of the left ventricle via the aortic valve, a complex valve with three semilunar cusps. Just above the aortic valve two small coronary arteries branch from the aorta to supply the heart muscle with oxygen and nutrients (end of manuals text).    

The removal of these three bird hearts were unfortunately done in a haphazardly fashion. Instead, I should have consulted the Manual of Ornithology first before attempting such an extraction. My dissection resulted in the failure to retain and observe the major blood vessels entering and leaving the heart. These included the delicate pulmonary veins, precavas and postcava.

However, I did notice a small difference between two of the dissected bird hearts that I feel is worth mentioning.

In a direct comparison between a Mallard (Anas platyrhynchos) and Barred Owl (Strix varia), the size of the duck’s heart (6cm) is nearly twice as large as the owls. The overall measurements of each species can vary, but may on occasion overlap in both length (50cm), and weight (1000g). Why the discrepancy in heart size?

Barred Owl (Strix varia) heart
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
Mallard (Anas platyrhynchos) heart
Photo Credit: Paul Cianfaglione
http://avianmusing.blogspot.com/
In this case, locomotion is the answer. The flight of the Mallard is described as strong and usually direct; at takeoff, 10-12 wing beats/s. Can spring vertically from water surface when alarmed by flapping wings downward onto surface. Descends steeply when necessary, braking by beating wings horizontally and almost hovering just before alighting.

Whereas the flight of a Barred Owl is portrayed as light, buoyant, and noiseless; can glide gracefully and skillfully among branches of trees. Forests with open understory and low stem density of canopy trees allow for easy flight; uses specific flyways.

In short, the Mallards large heart is necessary to meet its high metabolic demands of its flight style.