Tuesday, March 29, 2016

The Developing Bird Egg

     The Eastern Bluebird (Sialia sialis) is a common species of open and semi-open habitats. Easily recognized by their brilliant blue plumage, bluebirds are a familiar sight in my Connecticut neighborhood, perch-hunting for insects from tree snags, mailbox poles and stonewalls. 

     My own yard not only provides excellent feeding opportunities, it provides bluebirds with a place to nest and raise young. In a typical breeding season, our lone nest box will produce two clutches of eggs.  

     After a successful spring nesting, a second attempt was soon underway. As activity inside the box increased, I confirmed that a new clutch of five eggs were placed.

Eastern Bluebird Nest and Eggs
Photo Credit: Paul Cianfaglione
However, in the days to follow, the lively activity that had preceded the egg laying had all but ceased. Suspicious, I decided to check the box one more time. What I discovered was truly upsetting. The bluebirds had abandoned the nest box and five eggs due to a large infestation of sugar ants.

     Frustrated, I removed the nest and prepared the box for another possible nesting attempt. I brought the infested nest down to the woods to discard it properly and bury the eggs. As I was carefully picking out each individual bluebird egg to set it down on the ground, one of them had broken in my hand. The photograph below is what I found inside the broken egg.

Eastern Bluebird Embryo
Photo Credit: Paul Cianfaglione

     Wanting to know more about the development of an egg, I turned to one of my favorite books; Manual of Ornithology (Noble Proctor and Patrick Lynch, 1993) for some enlightenment. I’d like to share with you some information from the book which helped me better understand the structure and development of an egg.


     {The avian egg is a miracle of natural engineering. Light and strong, it provides everything a developing bird embryo needs from just after the ovum is fertilized until the chick hatches.

     The avian egg is a self-contained womb in which the embryo is protected and provided with the food and nutrients it needs to develop and hatch. But the egg is not a completely closed system, shutting off all outside contact. Birds, even as they are developing in the egg, are warm-blooded animals, with all of the metabolic activity that homoiothermy demands. The chick within the egg must be able to respire, to exchange gases and water vapor with the outside world, or it will suffocate.

     The bird egg must allow an efficient exchange of gases to support the growing chick, allowing waste gases out and oxygen in. The avian eggshell is not simply a coating of calcium carbonate but a complex laminate of mineral crystals embedded within a web-like matrix of material similar to collagen fibers. Reptiles, birds and mammals are called amniotes because the eggs of all three groups develop within an amniotic membrane. The amniotic membrane forms an enclosed, watery environment that protects the developing fetus and allows it to exchange gases with the surrounding world (Carey 1980, 1983; Romanoff and Romanoff 1949).

      The yolk of the egg supplies the embryo with nutrients, storing food until the chick hatches. The yolk sac surrounding the yolk is another embryonic membrane. The yolk is approximately 30 percent lipids (fats), 15 percent protein, and 55 percent water. Fat, not protein, is the primary food in bird eggs. This gives bird eggs a significant advantage over reptile eggs, in which the primary nutrients are stored as protein, because when broken down, fats yield more metabolic energy and water per unit than do proteins. They can thus survive in much drier environments than reptile eggs}.  

     The age of the embryo, from the information gathered, is anywhere between eight to twelve days old, given the size of the formed digit and toe plates.

     Despite the loss of our five bluebird eggs, I feel there is always a way to take a bad situation and extract something positive from it.  Learning about egg structure and the developing embryo was certainly an eye opening experience, as was the actual embryo in my hand.

     I also realized that I needed to be a better steward to the birds I provide for. Whether it be a hummingbird feeder or a nest box, periodic inspections and cleaning helps ensure a birds health and nest productivity.

     Finally, I would like to thank the late Noble Proctor and Patrick Lynch for publishing this outstanding book. The writing is excellent and easy to understand, and the drawings are exceptional.  Roger Tory Peterson’s foreword to the book says it best; “A gold mine of facts…Every library and biology department, as well as every birder, should have a copy close at hand.”  I couldn’t agree more.

Wednesday, March 23, 2016

Quill Knobs under the Microscope

     My first foray into the world of the inner bird was some years ago with the acquisition of a friends fossil bird bone collection from the Peace River in Florida (Pleistocene in age). As a seasoned bird watcher, I knew a great deal about field identification, but little else about a bird’s hidden skeleton. With over a hundred fossil bird bones strewn across my desk, this would be the perfect opportunity for me to take my own advice and “go beyond the field mark”.

     Determined to put a name to each bone, I decided to sit down with a strong cup of coffee, my old Leica microscope and a copy of the book, Avian Osteology by B. Miles Gilbert (1985).

Every evening was spent carefully comparing and measuring bones. With each identification came a newfound appreciation for the bird beneath the feathers.

     I positively identified coracoids from a Common Loon (Gavia immer) and Great Blue Heron (Ardea Herodias). A carpometacarpus from an American Coot (Fulica Americana). A tarsometatarsus from a Canada Goose (Branta Canadensis) and Pied-billed Grebe (Podilymbus podiceps). As time went on, my ability to recognize and identify avian bones grew stronger and stronger.

     Of all the fossil bones, one in particular caught my attention, the ulna. Together with the radius, the two bones form the support for the forearm. In the hand, the ulna reveals small, boney bumps along its trailing edge. These bumps are called quill knobs, which is where the secondary feathers of the wing attach directly to the bone.

     Provided below are two photos of Pleistocene bird ulnas, as well as quill knobs on both fossil and extant birds.

A likely ulna of a Pleistocene Mallard (top) and Teal sp.
Photo Credit: Paul Cianfaglione
Quill Knobs on a Pleistocene Teal sp.
Photo Credit: Paul Cianfaglione

Barely discernable quill knobs on a Yellow Warbler ulna
Photo Credit: Paul Cianfaglione
Quill Knobs on a Northern Flicker
Photo Credit: Paul Cianfaglione

According to a recent article, the discovery of a fossil ulna from a theropod dinosaur called Velociraptor mongoliensis, was shown to have boney quill knobs (“Feather Quill Knobs in the Dinosaur Velociraptor” by Turner A.H., Makovicky P.J., Norell M.A. Science 317:1721, 2007). The finding of quill knobs on Velociraptor, Turner notes, indicates the dinosaur definitely had feathers. This is something we’d long suspected, but no one has been able to prove. Even though the Mongolian Velociraptor’s short arms suggest that this species was unable to fly, its feathers likely had other uses such as territorial or courtship displays, temperature control or shielding eggs.

Image property of AMNH

Saturday, March 19, 2016

Are these fossil tracks avian, or non-avian?

Ever since the discovery of the first complete fossil of Archaeopteryx lithographica in Solnhofen, Germany, scientists have proposed an evolutionary connection between birds and dinosaurs, based largely on its unique skeletal features and of course feathers.

So close were these features that a featherless skeleton of an Archaeopteryx was for years misidentified as a small theropod called Compsognathus.

The hypothesis that dinosaurs and birds were close relatives was strengthened even more by Yale Universities John Ostrom in 1964, with the discovery of a new theropod called Deinonychus antirrohopus.

Yale Peabody Museum
New Haven, Connecticut
Photo Credit: Paul Cianfaglione
Shortly thereafter, Ostrom described many similarities between Deinonychus and Archaeopteryx including the semi-lunate carpal bone of the wrist, reduction of digits on their hands, hollow bones, wishbone and many others. Ostroms recognition of the dinosaurian ancestry of birds began what is now known as the dinosaur renaissance.

Like no other period in the history of paleornithology, the last three decades has seen a spectacular rate of fossil bird discoveries in Cretaceous rock worldwide. Most spectacular of all has been the discovery of fossils from Early Cretaceous formations in the Chinese province of Liaoning. In addition to the primitive birds, Liaoning has produced some incredibly feathered bird-like dinosaurs, which have helped close the morphological gap between theropods and birds. The unearthing of fossils in China further supports Ostroms ideas that species like Deinonychus were particularly closely related to birds.

As a fossil collector, I often seek out information, and sometimes acquisitions, which help me better understand the origins of birds. One such acquisition was that of a fossil trackway from the Hell Creek Formation in Montana.

Cretaceous Bird Tracks
Photo Credit: Paul Cianfaglione
They were acquired through a prep lab and described as follows; {these fossil tracks are of a large prehistoric bird similar to today’s Great Blue Heron or Sandhill Crane. They are a snapshot in time 70 million years ago of a large freshwater lake shoreline with ripple marks recorded as they foraged for food alongside their next of kin the dinosaurs}. At present, the track record of Mesozoic birds appears to be associated mainly with Cretaceous lacustrine deposits and various coastal deposits (Lockley, M.G., Rainforth, E., Mesozoic Birds; Above the head of Dinosaurs, 2002; pp 405-418).

Unlike body fossils, dinosaur and bird tracks record the active movements of ancient organisms. A series of two or more consecutive tracks by the same animal is known to researchers as a trackway or trail (Kuban, G.J., An Overview of Dinosaur Tracking, 1994). My goal at this time was to gather as much information as possible from the trackway in hopes of determining if the track maker was indeed avian as described, or a small theropod.

I turned to my best reference at hand, “The Track Record of Mesozoic Birds and Pterosaurs; An Ichnological and Paleoecological Perspective” (Lockley, M.G., Rainforth, E., Mesozoic Birds; Above the head of Dinosaurs, 2002; pp 405-418).

Lockley and Rainforth describe their methods below on how to identify the tracks of birds and how not to confuse them with the pes tracks of nonavian dinosaurs; {The following criteria are useful, although not foolproof, in determining whether tracks were made by birds or other track makers, but, given that almost all fossil bird are those of waterbirds, it is to this group that these criteria apply: (1) general resemblance to the tracks of neornithines (modern birds); (2) small size; (3) slender digit impressions with indistinct differentiation of the pad impressions; (4) wide divarication angle, approximately 110-120 degrees between the outer digits; (5) caudally directed hallux (digit 1), oriented up to 180 degrees from middle forward digit; (6) slender claws; and (7) claws on the outer digits curving distally away from the middle digit}.

Smaller theropods also make relatively long and narrow digit impressions, ending in sharp claw marks. However, theropod digits are often held closely together in a V-shape, with well-defined toe pads, like the track pictured below. 

Connecticut Valley Dinosaur Track
Photo Credit: Paul Cianfaglione

My fossil trackway measures 39 inches (99 cm) long by 18 inches (46 cm) wide. There are 14 negative tracks on the slab, with the largest measuring 4.75 inches (12.07 cm) long by 5 inches (12.7 cm) wide. There appears to be four separate trails on the plate; the longest stride length is measured at 12 inches (30.38 cm), pad impression to pad impression. Each track was highlighted by the lab with an organic material for esthetic value. The material used to highlight the tracks, unfortunately, fails to paint an accurate picture of the fossil imprint. Despite the fossils deceptive appearance, the negative digit impressions (to the touch) are very slender, with small pad impressions.

Cretaceous Bird Tracks
Photo Credit: Paul Cianfaglione
Two of the tracks show the presence of what appears to be a small, angled hallux strike. The divarication angle of the tracks are approximately 110 degrees between the outer digits.

Cretaceous Bird Tracks
Photo Credit: Paul Cianfaglione

Track reports of possible avian affinity from both the lower Cretaceous to the upper Cretaceous have increased significantly in recent years. All descriptions appear to be those of waterbirds and in most cases are essentially indistinguishable from the tracks of modern birds.

Of utmost interest to me were the reports of tracks from the western United States and Canada. Lockley and Rainforths chapter in Mesozoic Birds provide tantalizing accounts in western Alberta of high concentrations of smaller bird’s tracks in association with larger bird tracks. Large tracks, approximately 16 cm long and 17 cm wide, have been recently reported from the Dunvegan Formation of western Canada (94-100 ma).

Another large fossil bird track was found in the Woodbine Formation of Texas (95 ma). These tracks (image below) lack hallux impressions, and the step is long; the track maker may have been a crane-like bird.

Lockley, M.G., Rainforth, E., Mesozoic Birds; Above the head of Dinosaursaption

The Lance Formation in eastern Wyoming (69-66 ma) has revealed a diverse avian track assemblage. The presence of four distinct bird track morphotypes includes a relatively large fossil track measuring 9.5 cm long and 8.3 cm wide.

I also sought out track information of extant birds. Mark Elbroch and Eleanor Marks book called; “Bird Tracks and Sign, A Guide to North American Species”, provided me with many comparable track photos of shorebird, heron and game bird species. Of particular interest was the track of the Sandhill Crane (Grus canadensis).

Sandhill Crane
Photo credit Anthony Martin

The Sandhill Cranes track measures 4.75 inches (12.07 cm) long by 5 inches (12.70 cm) wide, matching the largest tracks on the Hell Creek trackway. Stride length measures approximately 12 inches (30.38 cm), again equal to the Hell Creek plate. The divarication angle of the cranes track was unavailable, but it appears in the book to approach 110 degrees between the outer digits. Elbroch and Marks note the presence of both toe 1 (hallux) and the metatarsal pad is dependent upon depth of substrate. In shallow substrates, the hallux tends to be absent altogether, and the metatarsal will show lightly, if at all.

Lockley and Rainforth conclude their chapter in Mesozoic Birds with an interesting discussion; {We readily admit that the identification of bird and pterosaur tracks is sometimes controversial. There is somewhat less consensus regarding the identification of bird tracks, owing to their similarity to the tracks of theropods. Even so, we are unaware of any efforts to refute the claims that most of the bird tracks reported herein (Cretaceous period) are attributable to shorebirds. This seems to be because shorebirds consistently have relatively small, slender tracks with large divarication and their tracks look just like the tracks of their Tertiary and recent contemporaries. It is also clear that the Cretaceous shoreline habitats in which these bird tracks are found evidently lack the tracks of diminutive animals with pedal characteristics that indicate theropod affinity, with which waterbird tracks could easily be confused. Moreover, despite the lack of skeletal evidence for Early Cretaceous shorebirds, it is becoming abundantly clear that birds, as a whole, underwent a significant radiation from earliest Cretaceous times onward. Not only is the track record chronologically consistent with the timing of this radiation, but it suggests that the track record of shorebirds is currently more complete than the osteological record}.

As pleased as I am about my possible avian trackway, I have to realize that there is still a small degree of uncertainty among scientists concerning the accurate identification of fossil tracks. Hopefully, the widespread revival of interest in feathered dinosaurs will continue to stimulate a similar interest in the study and interpretation of ancient bird tracks. I encourage anyone who is fascinated by fossil tracks to take the time and visit an actual tracksite, including Dinosaur State Park in Rocky Hill, Connecticut and the incredible Hitchcock Ichnology Collection at the Beneski Museum of Natural History in Amherst, Massachusetts.
Beneski Museum Of Natural History
Amherst, Massachusetts
Photo Credit: Paul Cianfaglione
Avian or Non-Avian??
Beneski Museum Of Natural History
Photo Credit: Paul Cianfaglione

Monday, March 7, 2016

Bird Feathers; their multifunctional use

     With seed in hand, I make an early hour pilgrimage to the feeders by the woods, cursing the freezing temperatures and biting winds. But this late February morning is a bit different. A twittering sound from up above rings of the familiar sound of the American Woodcock (Scolopax minor). I pause for a minute to admire the woodcock’s trills and whistling wingbeats as it displays at dawns first light.

     Distracted by the moment, I continue to the feeders, oblivious of the thirty or so Mourning Doves (Zenaida macroura) scattered about in the still dim light. In one loud whistle, the doves burst into the sky, leaving me with a bucket of seed on the ground and an irregular heartbeat.

     A short time later, a Red-bellied Woodpecker (Melanerpes carolinus) is heard tapping in my yard, excavating a hole at the top of a freshly broken oak tree. Its two outer tail feathers are clearly observed, used as a brace to stabilize the bird as it probes.

Red-bellied Woodpecker Nest Hole
Photo Credit: Paul Cianfaglione
Besides allowing for flight, birds are able use their feathers for a number of different tasks. Listed below are five additional functions, and the important role that these feathers play in a bird’s daily life.


     As we have just discovered, birds are fully capable of making sounds with their feathers. The sound of the woodcocks spring flight display is produced by air passing through their three outermost primaries. The alarm signals of a frightened Mourning Dove is again caused by air vibrating through the tips of the flight feathers.
Mourning Dove
Photo Credit: Paul Cianfaglione

The most interesting of feather sounds is made by male Ruffed Grouse (Bonasa umbellus). The male grouse proclaims his territory from a fallen log by actively engaging in a drumming display. Compressed air beneath each wingbeat creates the dampened drumming sound.

As a prop 

     The stiff tail feathers of woodpeckers and the Brown Creeper (Certhia Americana) allow these species to brace themselves against tree trunks while foraging. Among the most unusual of foraging methods is the drilling of sap wells by the Yellow-bellied Sapsucker (Sphyrapicus varius).

  Thermoregulation, retaining heat during cold weather

     The cold winter weather poses a major risk to birds. As warm-blooded animals, birds depend on body heat generated by the metabolic processes to maintain a high level of activity regardless of the environmental conditions (The Inner Bird, Kaiser. 2007). Unfortunately, this heat diffuses into the external environment unless the bird is properly insulated. Birds are entirely reliant on their plumage for such insulation. By fluffing out their contour feathers, birds can retain body heat by trapping warm air between the feathers and the skin, creating a natural insulation against the cold. At rest, birds will also tuck their heads into its feathers to conserve heat, like this Canada Goose (Branta Canadensis) pictured below.

Canada Goose tucked in and resting
Photo Credit: Paul Cianfaglione

Visual signals

     Birds employ a number of behaviors for the sole purpose of display and signaling. A species plumage itself is a type of communication. Feathers are most effective when they contain striking colors and shapes. The Red-winged Blackbird (Agelaius phoeniceus) is a common sight in wetland habitats throughout Connecticut. The male’s distinctive red shoulder patches are a visible warning to other males to “keep away” during territorial defense.
Red-winged Blackbird display
Photo Credit: Paul Cianfaglione

The Mandarin Duck (Aix galericulata), on the other hand, uses two oddly shaped “sail feathers” along its flanks to attract females. However, the male will molt his colorful feathers into a cryptic form after breeding in mid-summer. This drab, female-like appearance is called an eclipse plumage.
Mandarin Duck Sail Feather
Photo Credit: Paul Cianfaglione


     As a means of protecting themselves from predators, birds have evolved specific feather colors which allow them to effectively blend into their surroundings. A bird’s wing-spots and stripes can help break up its outline and virtually make it disappear. The Killdeer (Charadrius vociferous), for example, uses tones of brown, black and white to become one with an open field as it sits on a clutch of three eggs.
Killdeer sitting on eggs
Photo Credit: Paul Cianfaglione