Auriculares and the Sonus Feather

A detailed study of bird auriculares

Species count: 53

Orders: 14

Measurements: 795

Plucked feathers: 3952

Feather Series

• A Review of Nomenclature for Avian Color Aberrations
• Feather Basics
• There Are Nine Types of Feathers
• Morphology and Morphometric Characterization of Barn Owl External Sound Related Adaptations
• Auriculares and the Sonus Feather

site under construction with disjointed sections

• note that interpretations have not been posted to species level
  
• this page being updated as research progresses
• first sections published 3/11/24;
• dust protector 3/16/24
• types of auricular feathers 4/1/24
• sonus afterfeather 4/2/24
• meatus 4/3/24
  
• meatus scaling 4/4/24
• not just auriculares 4/29/24
  
• research details by order 5/13/24
  
• study species updated, details posted to each species page, no interpretation 5/22/24
  
• calamus 7/7/24
  
• White-breasted Nuthatch, species #53 8/9/24
• Bald Eagle study — I succeed in getting access permission to study a Bald Eagle. Timeline is based on availability. This is a watershed moment for the auricular study. 8/30/24
• current initiatives — evolution and the Palaeognathae (ostrich, kiwi, tinamou), update to the Barn Owl article
  

Auricular Definition

Auricular feathers cover the bird’s ear which is inferior and posterior to the eye. These feathers are also called ear coverts or an ear patch. Currently auriculares are a subset of contour feathers. Auriculares are not usually noticeable but occasionally a bird will raise them.

Types of Auricular Feathers

To date the research has found four types of auricular feathers. All birds in the study group except the Ostrich, have sonus feathers (author’s term) of various morphologies. The Ostrich has bristle feathers for ear coverts and the American Kestrel has some bristles amongst its sonus feathers. The Costa’s Hummingbird has some contour feathers covering its meatus. Finally, all the sources agree that there are filoplumes associated with all feathers. The sonus is no exception. 

From left to right, an Ostrich bristle feather, a Barn Owl sonus feather, a Costa’s Hummingbird contour feather, and the far right, a Peregrine Falcon meatus showing filoplumes.

Meatus

The meatus is the external opening to the ear canal. It is situated slightly behind and below the eye. All of the birds in the study, with the exception of the Barn Owl, have auricular feathers covering the meatus. The Barn Owl has a pre-aural flap, called an operculum, covering the meatus which itself is covered by sonus feathers. The meatus of the Ostrich (OSTR) and the Ring-necked Pheasant (RNEP) are covered by different types of auricular feathers. In both cases, although not discernible in the picture for the RNEP, the meatus can be seen through the auriculares. 

Notice in the RNEP series that the sonus feather is fully splayed in the first frame. This is due to static electricity. When covering the meatus they lay compact resulting in greater coverage. Once the sonus is plucked, measuring the width would not be a valid measurement.

The Barn Owl (BANO) has the only bare meatus in the study group. It is bordered by the ruff, operculum and specialized sonus feathers. The Greater Roadrunner (GRRO) has the largest meatus in relation to its skull size in the study group. 

The Dark-eyed Junco (DEJU) and Abert’s Towhee exemplify the most common look of the meatus and the surrounding auriculares, sonus in this case.

Meatus Scaling

Measurements were made of the meatus to calculate its area and the skull to estimate volume (see methods). A ratio was calculated and plotted. When plotted, the ratios for the Great Horned Owl and the Ostrich caused a loss of fidelity for data on the x-axis. The pictures on the right of the graph estimate where the ratios would plot to the y-axis. 

As the skull reduces in size (left end of X-axis) the meatus becomes relatively larger (top end of Y-axis). This indicates that there is a limit to reduction in meatus area as the skull gets smaller. The meatus of a hummingbird is 6 times larger than an ostrich on a relative scale. 

An interesting article about estimating t-rex brain size introduced me to the concept of scaling.¹³ As seen in the above graph, it is difficult to compare a hummingbird to an Ostrich. Comparing an elephant to a mouse would make the x-axis kilometers long.¹⁴ To allow for comparisons of Ostriches to hummingbirds a log-transformation chart is used. The same data as the graph above is used for this next graph. 

In this graph the orange points are hummingbirds which visibly seem to fit with the Ostrich plotted on the upper right. The data interpretation says that as skulls get larger the meatus area gets proportionately smaller. 

The yellow diamonds belong to the five ducks in the study. In comparison to other species with the same skull size, the ducks have a smaller than expected meatus area. This would fit if a smaller meatus helps protect the duck’s ear from water. The two lowest duck points on the graph are diving ducks, further supporting the evolutionary pressure to protect the ear.
The data point below and to the right of the ducks belongs to the chicken. Domestic chickens are raised in tight quarters without predators. Over 70 billion chickens are raised each year compressing evolutionary changes. A smaller meatus would seem a likely outcome.

Calamus

The calamus or quill is the proximal end of a feather that is seated in the follicular cavity below the surface of the skin. 

During feather development the pin feather is fed nutrients via blood supplied by the axial artery through the dermal papilla into the pulp.  

Once the feather has matured, the dermal papilla is absorbed back into the body and the calamus becomes hollow. This feature allows the storage of ink for a quill pen. The feather at this point is a collection of dead cells, like the tip of your fingernail. Close inspection of the mature calamus shows bands called “pulp caps” as seen on this Barn Owl primary covert.

These pulp cap rings are the remnants of the blood vessels that supplied the feather with nutrients while it was growing.
Using the Barn Owl as the paradigm for optimal hearing, one of its many unusual traits is the exceptionally long calamus on the auriculares and ruff feathers surrounding the meatus.

The calamus serves as the anchor that secures the feather to the bird’s skin. Under the skin, surrounding the calamus, are erector and depressor muscles and ones that control sideways movements of constriction and expansion.
I postulate that, like the baseball bat analogy in following picture, the greater the length of the calamus (using two hands), the greater control of the feather’s position.

The long calamus is an evolutionary adaptation that helps the Barn Owl control its operculum and ruff which are moved independently to isolate the source of the sound. Since control of feathers surrounding the meatus enhances hearing in owls, it would be anticipated that other orders would have this trait.
Review of the orders examined in this research reveals an interesting hierarchy. With the simple rule that a proportionally longer calamus implies control of auriculares and better optimize hearing, ducks have the smallest percentage of calamus to total shaft length at 7% followed by hawks at 8%, passerines at 9%, dove at 17% and ground birds at 18%. As in other traits, ducks sacrifice hearing for waterproofing. Hawks hunt primarily by sight while the hunted, doves and ground birds, use hearing as a defensive tool.

All birds can raise their feathers like the Bald Eagle (Fig. 6). I conjecture that the length of the auricular calamus is related to the bird’s ability to singularly control just the ear coverts as shown by the doves.

Another function of a long calamus is structural. The frame of a hand fan gives rigidity to the surface thus holding its shape.    

The meatus of the Long-eared Owl is exceptionally large with each about a third of the circumference of the head. Shaped like a colon (Fig 7), the walls of the meatus are stabilized by feathers with long calami.

The Barn Owl uses auricular calami for structural support of its operculum which can be raised or lowered independently.

Sonus Feather Morphotypes

Sonus Afterfeather

Afterfeathers (hypopnea) are a secondary feather growing from the dorsal side of a contour feather. It emerges at the base of the vane. The barbs are plumulaceous that sometimes attach to a rachis as in this case. Their appearance is like a downy feather and serves the same purpose. The afterfeather’s rachis was bent away from the contour feather for this photograph. 

Modified afterfeathers are found on some sonus feathers. They do not have the downy attributes of a contour afterfeather but have the same emergence location. The microscopy of a sonus afterfeather pulled from a Peregrine Falcon (PEFA) shows a sonus type structure. The first frame shows the afterfeather rachis emerging from the sonus feather at its proximal end. The other three frames show the proximal, medial, and distal portions of the afterfeather. Note the lack of barbs.

Four orders displayed this morphotype across all the species studied within that order. Piciformes’ Acorn Woodpecker (ACWO) and Gila Woodpecker (GIWO). Falconiformes’ American Kestrel (AMKE) and Peregrine Falcon PEFA. Accipitriformes’ Cooper’s Hawk (COHA), Harris’s Hawk (HASH), Sharp-shinned Hawk (SSHA) and Red-tailed Hawk (RTHA). Anseriformes’ American Wigeon (AMWI), Common Goldeneye (COGO), Green-winged Teal (GWTE), Lesser Scaup (LESC), and Norther Shoveler (NSHO). Conclusions on function and prevalence across these orders have not yet been made. 

Questioning Auricular Attributes

Ear protection, wind dampening, reflecting or directing sound are all attributes given to auricular feathers. In Lederer’s study of bristle feathers he observed “attributes seem to be casually accepted without definitive evidence.”⁹

Dust Protector

It is puzzling to read that primary purpose of Barn Owl (BANO) auriculares is to protect the ruff from dust.¹² The immediate reaction is to question the environment of raptors as being dusty. Two birds that thrive in a dusty environment are the Curve-billed Thrasher (CBTH) and Rufous Hummingbird (RUHU). The CBTH forages for food by sweeping the ground turning over rocks and litter and sometimes pecks into the dirt like a woodpecker. The RUHU harvests bugs and nectar from flowering plants subjecting its face to pollen and dust. A hummingbird will feed over a thousand times per day.

These are the sonus auriculares from the three species.

 

The BANO’s feather is open with no discernible barbules while the two species from a dusty environment show growth along the rachis and developed barbules. A close up look follows.

 

It is clear that the sonus feathers for the CBTH and RUHU are adapted to account for the dust environment. If the primary function of the BANO sonus feather is dust protection, why not have similar adaptations shown in the other two species. More puzzling is why the sonus feather completely covers the area inside the ruff. A sub optimized dust protector on the cheek of a bird would be better served by an ordinary contour feather if protection is its primary function.
Review of sonus morphotypes indicates there are adaptations to a dusty environment for some species. It shouldn’t be concluded that this is the feather function for all species.

Reflecting or Directing Sound

Wind Dampening

Sensory Feathers, Mechanoreceptors

Filoplume

The filoplume is the third type of feather structure; pennaceous and plumulaceous are the other two. A filoplume is a hair-like feather that has a long bare rachis (shaft) with a small narrow vane at the distal end. The vane consists of one to six short barbs with sparse barbules. They come in various lengths depending on the feather they are supporting.

Filoplumes grow from their own innervated follicle.¹ They are attached to sensory receptors in the skin that detect air pressure, wind and feather movement. Disturbance of a filoplume enlarged tip creates a vibration that is magnified and transmitted by the long, thin shaft to sensory corpuscles at its base.⁴

Every bird has at least one filoplume per wing, tail or body feather. Flight feathers have up to 12 filoplumes each.³ When grown at the base of a flight feather they are shielded from direct airflow as they do not protrude from under the coverts. They sense the movement, condition, or integration of the companion flight feather.¹   

An experiment was conducted on a Golden Eagle, where a rectrix was clipped above the calamus. This species molts feathers every two to three years. The clipped feather was replaced prior to the next molt cycle indicating that the filoplume sensed the missing feather.¹

Some filoplumes in Pelecaniformes, Procellariformes, and Passeriformes visibly project beyond the surrounding contour feathers.⁴ A review of bird skins was undertaken to find protruding filoplumes extending beyond the contour feathers. 117 North American oscine species (song birds) were found to have this feature. Most occurrences were found on the nape and less frequently on the crown. It is speculated that they detect airflow, feather ruffling, and drag during flight controlling contour feathers that are out of sight and not accessible to preening.²

Bristle feathers

Bristle feathers are found on many species. They are whisker-like feathers typically found around the mouth, eyelids and nares. Bristle feathers maybe unbranched or branched. The branched bristles can have minimum barbs at the base to more elaborate structures as found on nightjars. Some birds have both types of structures as shown in the next picture. It was positively correlated that as bristle numbers increase so too the length.⁸

Bristles are sensitive to touch and vibrations. They assist in foraging, burrowing nests, obstacle avoidance, protection from airborne particles, and sense airflow. Some websites state that bristles are used to funnel food. That was dispelled in an article about Willow Flycatcher bristles.¹⁰ Although feathers are dead cells; the bristle feather sits in an innervated follicle connected by muscle tissue within the dermis. The follicle contains Herbst corpuscles, vibration-sensitive mechanoreceptors, that are sensory nerve endings found only in birds.⁷

A recent study of bristles states that lower and upper rictal bristles were present in the most recent common ancestor (MRCA ~ 108 mya) of avian phylogeny. This feather is diverse with differences in shape, size and position within the same order, family and genera and is sexually monomorphic. In a sample of 1,000 bird species, about a third had bristles. Nocturnality is a predictor of both the presence and length of the bristle feather.⁶

It was postulated by Küster in 1905 that bristle feathers may be able to sense sound and used in tracking prey.⁹

click here to see a collection of bristle feathers

Adornment feathers

Whiskered Auklets have three prominent white face plumes and a longer thin crest on its forehead. The crevice dwelling seabird that is active at night was put through a series of experiments involving a totally dark maze. The experiments indicated the elongated facial feather adornments have a mechanosensory use for orientation. When the plumes were taped down, there was a 275% increase in the head bumping the sides of the maze.⁴

This Tufted Puffin excavates burrows up to 5 feet deep. Can the assumption be made that it too has mechanosensory plumes?

Peafowl Crest

This section is a summary of a study on peafowl crests thus all paragraphs are cited to the same source.¹¹

Studies in mammals and arthropods sensory hairs and antennae have found that they have mechanosensory roles in sound detection. Besides the enervation at the base, mechanical structures and vibrational response play a critical role. These structures are frequency-matched to the stimulus source like a caterpillar sensing an approaching wasp.

Bird feathers, like bristles and filoplumes, are known mechanosensors that enable birds to respond to mechanical stimuli. When sound related, feathers are frequency-tuned to their stimuli providing an advantage to filter irrelevant sounds. These feathers have a resonant frequency, vibrating at the maximum to the energy transferred by the sound wave they are tuned to.   

Tests on peafowl crests demonstrate that they have mechanical properties. The resonant frequency of these feathers matches the frequencies emanating from tail rattling during social displays. The resulting hypothesis is that birds receive and respond to vibrotactile cues in a wider variety of scenarios.

Morphologically Similar

Research Details by Taxonomic Rank

Order definitions taken from Wikipidia

Struthioniformes

• an order of birds with only a single extant family, Struthionidae, containing the ostriches

Ostrich OSTR

Anseriformes

• an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae, Anseranatidae, and Anatidae, the largest family, which includes over 170 species of waterfowl, among them the ducks, geese, and swans.

Northern Shoveler NSHO, dabbling duck

American Wigeon AMWI, dabbling duck

Green-winged Teal GWTE, dabbling duck

Lesser Scaup LESC, diving duck

Common Goldeneye COGO, diving duck

Galliformes

• an order of heavy-bodied ground-feeding birds that includes turkeys, chickens, quail, and other landfowl. Gallinaceous birds, as they are called, are important in their ecosystems as seed dispersers and predators, and are often reared by humans for their meat and eggs, or hunted as game birds.

Gambel’s Quail GAQU

Wild Turkey WITU

Ring-necked Pheasant RNEP

Chicken CHIC

Chukar CHUK

Columbiformes

• an order of birds that includes the very widespread and successful doves and pigeons, classified in the family Columbidae

Rock Pigeon ROPI

White-winged Dove WWDO

Mourning Dove MODO

Cuculiformes

Greater Roadrunner GRRO

Apodiformes

• contains three living families: the swifts, the treeswifts, and the hummingbirds.

Black-chinned Hummingbird BCHU

Anna’s Hummingbird ANHU

Costa’s Hummingbird COHU

Rufous Hummingbird RUHU AHYM

Rufous Hummingbird RUHU HYF

Gruiformes

• an order containing a considerable number of living and extinct bird families, with a widespread geographical diversity. Gruiform means “crane-like”. Traditionally, a number of wading and terrestrial bird families that did not seem to belong to any other order were classified together as Gruiformes.

Sandhill Crane SACR

Charadriiformes

• a diverse order of small to medium-large birds. It includes about 390 species and has members in all parts of the world. Most charadriiform birds live near water and eat invertebrates or other small animals; however, some are pelagic, others frequent deserts, and a few are found in dense forest. 

Wilson’s Snipe WISN

Accipitriformes

• an order of birds that includes most of the diurnal birds of prey, including hawks, eagles, vultures, and kites, but not falcons.

Sharp-shinned Hawk SSHA

Cooper’s Hawk COHA

Harris’s Hawk HASH

Red-tailed Hawk RTHA

Strigiformes

• Owls are birds from the order Strigiformes, which includes over 200 species of mostly solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers adapted for silent flight.

Barn Owl BANO

Flammulated Owl FLOW

Western Screech Owl WESO

Great Horned Owl GHOW

Northern Pygmy Owl NOPO

Ferruginous Pygmy Owl FEPO

Burrowing Owl BUOW

Long-eared Owl LEOW

Piciformes

• Nine families of largely arboreal birds make up the order Piciformes, the best-known of them being the Picidae, which includes the woodpeckers and close relatives. The Piciformes contain about 71 living genera with a little over 450 species, of which the Picidae make up about half.

Acorn Woodpecker ACWO

Gila Woodpecker GIWO

Falconiformes

• The order Falconiformes is represented by the extant family Falconidae and a handful of enigmatic Paleogene species. Traditionally, the other bird of prey families Cathartidae, Sagittariidae, Pandionidae, Accipitridae were classified in Falconiformes.

American Kestrel AMKE

Peregrine Falcon PEFA

Psittaciformes

• Parrots, also known as psittacines, are birds with a strong curved beak, upright stance, and clawed feet. They are conformed by four families that contain roughly 410 species in 101 genera, found mostly in tropical and subtropical regions.

Rosy-faced Lovebird RFLO

Passeriformes

• A passerine is any bird of the order Passeriformes which includes more than half of all bird species. Sometimes known as perching birds, passerines generally have an anisodactyl (having the first toe directed backwards and the other three toes directed forwards) arrangement of their toes, which facilitates perching.

American Crow AMCR

W

Cactus Wren CACW

Curve-billed Thrasher CBTH

European Starling EUST Adult

European Starling EUST Adult

Hermit Thrush HETH

House Sparrow HOSP

House Finch HOFI

Pine Siskin PISI

Lesser Goldfinch LEGO

Dark-eyed Junco DEJU

Savannah Sparrow SAVS

Abert’s Towhee ABTO

Yellow-rumped Warbler YRWA

Northern Cardinal NOCA

Sonus Feathers Are Not Just Auriculares

In the Strigiformes order, sonus feathers are found throughout the facial disk. This Barn Owl is labeled where feather samples are taken.

This Barn Owl feathergram displays the sampled feathers. Note none of the feathers were ear coverts.

Positions 4 through 6 are bristle feathers. Positions 1, 2, 7, and 8 are all sonus variations. Eight owls are compared in the following feathergrams. The Ferruginous Pygmy Owl and Northern Pygmy Owl are both diurnal. Although the Burrowing Owl is considered crepuscular, its ruff feathers and its leading primary have diurnal traits.   

Position 1 feather comparison

Position 2 feather comparison

The night hunters clearly have sonus feathers on their cheeks.

Position 7 feather comparison

The nocturnal species continue to show reliance on the sonus feathers above the eye.

Position 8 feather comparison

In all four feathergrams the Barn Owl is very consistent with light and open feather structure. Its presence throughout the facial ruff indicates the importance of this feather structure in the Barn Owl’s sound sensitivity.

Study Species

click on species to get study details

Ind	Common Name	Code	Species	family	order
1	Ostrich	OSTR	Struthio camelus	Struthionidae	Struthioniformes
29	Northern Shoveler	NSHO	Spatula clypeata	Anatidae	Anseriformes
33	American Wigeon	AMWI	Mareca americana	Anatidae	Anseriformes
43	Green-winged Teal	GWTE	Anas crecca	Anatidae	Anseriformes
50	Lesser Scaup	LESC	Aythya affinis	Anatidae	Anseriformes
64	Common Goldeneye	COGO	Bucephala clangula	Anatidae	Anseriformes
77	Gambel’s Quail	GAQU	Callipepla gambelii	Odontophoridae	Galliformes
79	Wild Turkey	WITU	Meleagris gallopavo	Phasianidae	Galliformes
93	Ring-necked Pheasant	RNEP	Phasianus colchicus	Phasianidae	Galliformes
94	Chicken	CHIC	Gallus gallus	Phasianidae	Galliformes
100	Chukar	CHUK	Alectoris chukar	Phasianidae	Galliformes
111	Rock Pigeon	ROPI	Columba livia	Columbidae	Columbiformes
129	White-winged Dove	WWDO	Zenaida asiatica	Columbidae	Columbiformes
131	Mourning Dove	MODO	Zenaida macroura	Columbidae	Columbiformes
134	Greater Roadrunner	GRRO	Geococcyx californianus	Cuculidae	Cuculiformes
169	Black-chinned Hummingbird	BCHU	Archilochus alexandri	Trochilidae	Apodiformes
171	Anna’s Hummingbird	ANHU	Calypte anna	Trochilidae	Apodiformes
172	Costa’s Hummingbird	COHU	Calypte costae	Trochilidae	Apodiformes
174	Rufous Hummingbird	RUHU	Selasphorus rufus	Trochilidae	Apodiformes
207	Sandhill Crane	SACR	Antigone canadensis	Gruidae	Gruiformes
283	Wilson’s Snipe	WISN	Gallinago delicata	Scolopacidae	Charadriiformes
521	Sharp-shinned Hawk	SSHA	Accipiter striatus	Accipitridae	Accipitriformes
522	Cooper’s Hawk	COHA	Accipiter cooperii	Accipitridae	Accipitriformes
534	Harris’s Hawk	HASH	Parabuteo unicinctus	Accipitridae	Accipitriformes
543	Red-tailed Hawk	RTHA	Buteo jamaicensis	Accipitridae	Accipitriformes
547	Barn Owl	BANO	Tyto alba	Tytonidae	Strigiformes
549	Flammulated Owl	FLOW	Psiloscops flammeolus	Strigidae	Strigiformes
551	Western Screech Owl	WESO	Megascops kennicottii	Strigidae	Strigiformes
553	Great Horned Owl	GHOW	Bubo virginianus	Strigidae	Strigiformes
556	Northern Pygmy Owl	NOPO	Glaucidium gnoma	Strigidae	Strigiformes
557	Ferruginous Pygmy Owl	FEPO	Glaucidium brasilianum	Strigidae	Strigiformes
559	Burrowing Owl	BUOW	Athene cunicularia	Strigidae	Strigiformes
564	Long-eared Owl	LEOW	Asio otus	Strigidae	Strigiformes
580	Acorn Woodpecker	ACWO	Melanerpes formicivorus	Picidae	Piciformes
581	Gila Woodpecker	GIWO	Melanerpes uropygialis	Picidae	Piciformes
605	American Kestrel	AMKE	Falco sparverius	Falconidae	Falconiformes
612	Peregrine Falcon	PEFA	Falco peregrinus	Falconidae	Falconiformes
626	Rosy-faced Lovebird	RFLO	Agapornis roseicollis	Psittaculidae	Psittaciformes
716	American Crow	AMCR	Corvus brachyrhynchos	Corvidae	Passeriformes
792	White-breasted Nuthatch	WBNU	Sitta carolinensis	Sittidae	Passeriformes
803	Cactus Wren	CACW	Campylorhynchus brunneicapillus	Troglodytidae	Passeriformes
813	Curve-billed Thrasher	CBTH	Toxostoma curvirostre	Mimidae	Passeriformes
823	European Starling	EUST	Sturnus vulgaris	Sturnidae	Passeriformes
842	Hermit Thrush	HETH	Catharus guttatus	Turdidae	Passeriformes
887	House Sparrow	HOSP	Passer domesticus	Passeridae	Passeriformes
950	House Finch	HOFI	Haemorhous mexicanus	Fringillidae	Passeriformes
961	Pine Siskin	PISI	Spinus pinus	Fringillidae	Passeriformes
962	Lesser Goldfinch	LEGO	Spinus psaltria	Fringillidae	Passeriformes
999	Dark-eyed Junco	DEJU	Junco hyemalis	Passerellidae	Passeriformes
1014	Savannah Sparrow	SAVS	Passerculus  sandwichensis	Passerellidae	Passeriformes
1019	Abert’s Towhee	ABTO	Melozone aberti	Passerellidae	Passeriformes
1093	Yellow-rumped Warbler	YRWA	Setophaga coronata	Parulidae	Passeriformes
1116	Northern Cardinal	NOCA	Cardinalis cardinalis	Cardinalidae	Passeriformes

General Methods

Prior to starting the study I obtained a Scientific Activity License from the state of Arizona that is good for one year and can be renewed. The fee is $70/year. In order to get access to birds from a rehab facility I was requested to get a federal license. The federal license is good for three years at a cost of $100. Both licenses require annual reporting. The possession of feathers and other parts of native North American birds without a permit is prohibited by the Migratory Bird Treaty Act (MBTA). There is no exemption for molted feathers, birds that hit windows or road kill.

Record provenance of each carcass collected which will be used in the annual report.

A note about measurements. All of the measurements are approximate and used to make broad observations. Other than the use of a caliper, ruler measurements round to the nearest millimeter.

Biometrics 

Length of the bird

Length of the primary

Skull volume — length of skull is measured from the base of the maxilla (upper bill) to the back of the  skull. Width and height measured at the maximum of each.

Meatus area

 

Eye orbit to meatus — the distance from the edge of the eye orbit to the meatus is measured. When working with a northern shoveler I notice that the meatus was significantly further away from the eye than the 3 other, non aquatic, species showed.

An ancillary task is accounting for any bristles. Bristles are an important subset of data for this study.  Their relevance will be explained in the analysis section. 

click here for photos of bristle feathers

Close up picture of the auricular area is taken.

If an owl, a picture is taken of the facial disk if a close-up field photo isn’t available. The photo is used to map feather sampling.

Pluck auriculares

Auricular feathers were plucked from the closest to meatus out. The plucking stopped when the tip of the next feather no longer covers any part of the meatus.

Feathers are placed on a photo album page in the approximate order they were plucked. Plucked feathers are counted. Some birds have relatively uniform feather length while others have a mixture of short and long feathers. The feather count is subjective, counting large and small feathers (with period in front of the number). 

Feather measurements

Sonus feather length and width

Barb spacing = rachis length / (number of barbs on one side – 1)

The rachis is measured. The barb pairs are counted in two groups, the shorter ones (S-count) starting at the calamus up to the first full length barb. The longer ones (L-count) are the remainder up to the tip of the feather.

Barb angle is measured using the general direction of the barb. The angle will typically be smaller where the barb meets the rachis. Pictures are placed on top of an on-line tool.

https://www.ginifab.com/feeds/angle_measurement/

Morphology of the vane, barbs and barbules are noted. Three sets of microscopic views are made of a feather at three magnifications. The first view is of the aftershaft just above the calamus. The magnifications are 50X, 150X, and 300X.

The second view is the middle of the vane to the outside edge. This look provides observations on barbule growth. Magnification is at 50X. Note that barbule growth increases towards the distal end of the barbs.

This third view is of the crown of the feather. Note the significant barbule growth. The magnifications are 50X, 150X, and 300X.

Equipment Used

Macro Photography

Camera — Canon 5D Mark IV

Lens — Canon Macro Lens EF 100mm F2.8

Flash — Macro Ring Light

Remote Switch — SMDV wired remote shutter release

Tripod head — Benrousa 3-way geared head

Tripod — Manfrotto 190X

Lightpad

AGPtEK light pad

Microscopes

Edmund Scientific 300X microscope and reflected light illuminator.

Amazon WiFi microscope

Micro Photography

Dissecting Kit

Magnifying work light

Indispensable for close up work. This link is for the latest model.

illuminated-magnifying-lamp

Digital caliper

Home Depot Husky caliper

 

Ethics Statement

No birds were killed for this study. Some birds, based on condition, were set out for neighborhood owls. Provenance of the birds is maintained and reported annually (while license is valid) to Arizona Game and Fish Department and U.S. Fish and Wildlife Service. All feathers will be donated to an educational institution upon completion of the study.

Acknowledgements

Ted Bodner — BS Biology, MS Pathology, professional bird guide, professional photographer, mentor for 14 years

TED’S PHOTOGRAPHY WEBSITE 

Laurie Nessel — editor for the Maricopa Audubon Society’s quarterly magazine Cactus Wren-dition and monthly newsletter — published articles, requested support for birds from members.

https://www.maricopaaudubon.org/

Wild at Heart Raptor Rehab facility — supplied 11 raptors and Greater Roadrunner

https://www.wildatheartraptors.org

Damon “Rooster” Cogburn — generously supplied an ostrich, if you live in Arizona take the kids to this wonderful ranch

Rooster Cogburn Ostrich Ranch

Elizabeth Farquhar — editor of Desert Rivers Audubon Society’s quarterly magazine and newsletter. Published request for birds.

Desert Rivers Audubon

References

1 Rohwer, VG, Rohwer, S, Kane, L. (2021) Filoplume morphology covaries with their companion primary suggesting that they are feather-specific sensors. Ornithology 138, 2021, pp. 1–11

2 Clark, Jr., GA and de Cruz, JB. (1989) Functional  interpretation of protruding filoplumes in oscines. The Condor 91:962-965

3 Devokaitis, Marc (2020) The Most Mysterious Feather: Filoplumes. Cornell “https://www.allaboutbirds.org/news/the-most-mysterious-feather-filoplumes/#”

4 Seneviratne, S.S. and Jones, I.L. (2008) Mechanosensory function for facial ornamentation in the whiskered auklet, a crevice-dwelling seabird. Behavioral Ecology · July 2008, 784-790

5 Conover, R. & Miller, E. (1980) Rictal bristle function in willow flycatcher. Condor, 82, 469–471

6 Delaunay, MG, Brassey, C, Larsen, C, Lloyd, H and Grant, RA. (2022) The evolutionary origin of avian facial bristles and the likely role of rictal bristles in feeding ecology. Scientific Reports  (2022) 12:21108

7 Delaunay, M.G., Larsen, C., Lloyd, H., Sullivan, M., and Grant, R.A. (2020). Anatomy of avian rictal bristles in aprimulgiformes reveals reduced tactile function in open-habitat, partially diurnal foraging species. Journal of Anatomy, 237:355–366

8 Delaunay, M.G., Charter, M. & Grant, R.A. (2022) Anatomy of bristles on the nares and rictus of western barn owls (Tyto Alba). Journal of Anatomy, 241, 527–534

9 Lederer, R.J. (1972) The role of avian rictal bristles. The Wilson Bulletin, 84(2), 193–197

10 Conover, R. & Miller, E. (1980) Rictal bristle function in willow flycatcher. Condor 82, 469–471

11 Kane SA, Van Beveren D, Dakin R (2018) Biomechanics of the peafowl’s crest reveals frequencies tuned to social displays. PLoS ONE 13(11): e0207247. 

12 Koch UR and Wagner H. (2002) Morphometry of Auricular Feathers of Barn Owls. European Journal of Morphology, Vol. 40, No. 1, pp. 15–21

13 Novak, S. (2024) Beasts with Brains. Discover, January 2024, 44-45.

14 West, G. Scaling Biology with Geoffrey West. May 2022, Thinking Tools Podcast #25.

Ancillary Topics

 

blank