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Some species are covered instead by scutes. They mostly spawn a large number of small eggs with little yolk which they broadcast into the water column. The upper jaw is formed from the pterygoids and vomers alone, all of which bear teeth. You should have a nice round pile of…. Behind these are the orbits, and then an additional pair of capsules enclosing the structure of the inner ear.
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Feeding and caring for dogs for me is as important as feeding and caring for a child. My dogs ARE my children. And that includes their treats as well. The pet food industry is a huge money making machine, and unfortunately, we Americans are led astray by their advertising, their lack of information of contents and origin, and the lack of regulation of food processing. I am stepping down. But I hope more dog owners will find your site and heed your comments. It is up to US the owners and care takers to get the best for our dogs.
My best friend is a 13 year old female Rottie. When she does throw up, It comes up with very little effort or distress. Sometimes its undigested food, sometimes its white stuff…. Everything else about her seems fine.
Gums are red, eyes are fine, personality is normal. She was, for a few weeks feed bread, by neighbor who was dog sitting…He meant no harm…but…bread is bad for dogs digestive systems, yes? Hi Grace, I came in search of a possible solution to help my pup gain some weight and stumbled upon your question.
The symptoms of your gal match the symptoms of the condition that my 10 month old pup is afflicted with. Another form of it is neurological. The nerves that tell the muscles of the esophagus to move food down cease to do so. I have to liquify my pups food and feed him on stairs so that gravity can help get his food into his stomach, but otherwise he leads a very normal life.
I started feeding her boiled chicken and rice and my once very fussy eater gobbled it up. Blood is gone, stools are becoming more solid. I want to try one of your diets — not sure if it should be raw or cooked; I want to stick to chicken at least at first because of the colitis. Also, what about switching between chicken and beef — can you do that, or do you have to do the 24 hour fast?
Switching between homemade dog food recipes does not require a fast. I just posted a chicken and rice dog food recipe that may work for you. Any other advice to make her more healthy and have more normal stools would be appreciated.
Linda PS Sadie says thanks for the delicious recipe — no more fussy eating! I feed him a liquid diet in an upright position 4 times per day and he gets LOTS of exercise. Thank you very much for your time and possible advice.
You may want to try the chicken and rice dog food recipe. Pass this through a blender and it should be ok. Dogs metabolize fat well.
High carbohydrate content in kibble seem to be more responsible for weight gain. I have just start my research about raw foods. I have a 5 year old Great Pyrenees who is having difficulties having bowel movements.
I have taken him to the vet multiple times and after many enemas and laxatives he seemed fine. However, they have told us to start putting metamucil on his food regularly as he would not eat the high fiber diet we started putting him on.
This worked for a couple of weeks, now he is back to the way he was backed up and we have to give him more laxatives. Someone mentioned to me that raw food may help with his digestion.
Poor boy is in pain. Is the raw food diet good for this sort of thing? Thanks for your time. Have you ever tried probiotics to help his digestive tract? Yes, I started giving it to him when he started having problems. He is still having difficulties. I have been reading more about the raw food diet and I am becoming more nervous about it. I read how if your not balancing the meals appropriately then you can cause more problems.
Its so hard to tell what is legit. I will keep researching before I switch over. If I find anything I will also update you. If you are nervous about feeding raw dog food then just feed him cooked. Try feeding the chicken and rice dog food recipe or the easy cooked dog food recipe.
Your dog will love either and both are very nutritious. This is my first time on your website and I love that easy recipe with the eggshell and all! Now I put the used eggshell in my stale bread, cracker mix for the birds as they need it for digestion but I never thught you could do that for dogs. Thanks for letting other animal lovers know about the positive benefits of a natural food diet for our beloved pets. I mean really, if the commercial dog food is all that great and healthy then why does it say NOT fit for human consumption?
Hmmm, now I have an issue with that! Treat our furry critters as we want to be treated also! Thank you so much and my 3 APBT just love their natural food fare! They whine like your 2 didin the video but they are so healthy and happy and just full of energy. Yes they love fish especially salmon. What a life they have! God Bless you and yours. I have an 8 month old Cavachon. She started having diarrhea here and there about 6 weeks ago.
We had her poop tested at the vet but no parasites. She had been eating Diamond Puppy. We switched to chicken and rice and diarrhea got better. Interesting note, on chicken and rice, she no longer ate her poop. Whenever we tried to put her back on Diamond Puppy, diarrhea would come back.
So, back to chicken and rice. During that time, she ate part of a yard ornament and was given meds to make her vomit. After that, she had diarrhea even staying on chicken and rice. The vet gave her antidiarrheal meds for 10 days and it finally went away. Meanwhile, she was still on only chicken and rice. After several days with nodiarrhea, I tried to give her a little Diamond Puppy again mixed in with chicken and rice and it started to come back again.
I came across your cooked dog food recipe. I ordered Dinovite and Licochops. Before making the full recipe, I gave her a little Dinovite in her chicken and rice for the past 3 days.
Her diarrhea is back. I also caught her trying to eat her poop again. Not sure if there is something in the Dinovite that makes her want to eat her poop.
I am currently making your cooked dog food recipe, but want to know your opinion on how to proceed since she will be starting while she already has some intestinal upset. Other than the diarrhea , she is acting happy and healthy. Is her diarrhea watery or is she just having frequent softer stools?
I would try her on the chicken and rice dog food recipe or the easy cooked dog food recipe and follow the introductory methods.
Then give her system time to adjust. She loves sweets and breads. She constantly has stomach issues. I give her a puppy multivitamin and she eats grass daily. She gets treats that have no artificial flavors, colors or preserves.
What I want to know is if there is anything else I can do to help her with the stomach issues. Any info would be greatly appreciated. Try the easy cooked dog food recipe or the chicken and rice dog food recipe and see how she does. I have a MinPin, Grace, whom is 2 years old.
She is absolutely our baby. Sometime in November, I was cutting the red ring off of our bologna. I laid the small ring of paper on my table, and Grace ate the red paper.
I have not seen her poop out the paper. Can she actually digest this paper or should I take her to the vet? I certainly do not want her to go through surgery, yet, I cannot stand to lose her. I would appreciate any comment, as I am very concerned about my Grace. Hi — Thank you very much for your informative website. My husband and I own an 8. He has always been very healthy. I changed him to a home cooked diet of cooked chicken breast; brown rice and sweet potato. He loves the food; but was losing a lot of weight.
I found your website about 2 weeks ago and substituted the rice for white potato in addition to adding hard boiled eggs. He is currently on Omega supplements; however his Vet recommended to supplement safflower oil for fat — I see that you recommend extra virgin coconut oil. Although his weight is still in the healthy range; he has gone from 75 lbs to 65 lbs in the past 3 months since the diet change. His recent bloodwork is excellent and energy level is good — I just feel like he is very thin.
I am concerned about giving him the right fats. Try adding the Supromega fish oil or Lickochops , both are great fat sources. Virgin coconut oil also does not stress the pancreas. Dear Ed what do you reccomend for a dog who has a high ph of 6 and is not producing enough acid on her own to keep from getting sturitve stones and is getting constant bladder infections she has gone through surgery to remove the stones and is a special deit of royal canin urinary so wet and dry and for six months was given a clean bill of health by her vet but now she has and infection again and crystals im being told by her vet that its time to possibles start her on a monthy antiboitic treat meant to hopefully get her system back on track which im really concerned about.
Neither have any known health problems and no skin issues. Can I start her on the raw diet right after that? Yes, cats can eat a raw diet safely just eliminate all the carbs because they have no use for them at all. I started him on a grain free kibble and mixed in raw meat with his food , enzymes a other supplements and for 4 years he has been fine. I do know that kibble and raw digest at different rate. I give him beef heart, tongue and liver.
He has recovered nicely and became my service dog now at 9 I am training another and he is now in semi retirement he will never fully retire until he passes on. Lately he has not been very good at eating his meals oh he is feed twice a day half in the a.
GSD are prone to bloat. He will eat if I give him some of what I am eating and he will eat the raw meat alone so my question what to do about feeding a raw diet. I have 4 dogs and with the constant increase in meat prices it is hard to put all on a raw only diet.
When you feed a raw meat and bones based diet bloat is not a problem. This is because the raw maenad bonds not swell like kibble. Currently I am feeding my dogs raw chicken leg and thigh quarters. I grind them using the meat grinder I show on this site because both my dogs are missing teeth. The chicken is 69 cents per pound. You must be logged in to post a comment.
My name is Ed Lukacevic and I'm an incurable animal lover! I have spent my life working with birds, reptiles, horses and especially dogs. Optimum nutrition for the animals in my care has been my passion. March 19, at 9: What about corn on the cob?
Log in to Reply. They perch on sturdier portions of a branch and use their long beak to reach their food. So, the beak must be rigid enough to resist bending and twisting forces, but has to be light or the bird couldn't get off the ground. The lightweight strength of the toucan's beak is due to a matrix of bony fibers and drum-like membranes sandwiched between an outer layer of keratin.
The interior of the beak is rigid "foam" composed of bony fibers and drum-like membranes sandwiched between outer layers of keratin. Woodpecker shock-absorbing system -- Woodpeckers are known to drum hard woody surfaces of trees at a rate of 18 to 22 times per second with a deceleration of g humans can lose consciousness at g-forces as low as 4 to 6 g.
Woodpeckers have four structures that help absorb mechanical shock and prevent brain damage: A woodpecker's hyoid extends posteriorly from the floor of the oral cavity, goes behind the neck, divides into two bands, goes around the back of the skull, and inserts at the front of the skull.
This allows woodpeckers to extend their tongues well beyond the tip of the beak when foraging, but this arrangement also helps distribute mechanical vibrations when drumming. The spongy bone is thought to evenly distribute mechanical vibrations before they propogate to the brain.
Yoon and Park Yoon and Park built a shock-absorbing device with mechanical 'woodpecker' analogues that consisted of glass beads embedded in a steel-encased aluminum cylinder. They shot it with an airgun and found that the new device protected its contents electronic equipment at forces up to 60, g. To evenly distribute load and cut down on vibration, like the hyoid, they added a rubber layer.
Woodpecker's head inspires shock absorbers. The unequal length of the upper and lower parts of woodpecker beaks the lower being longer directs the force of impact downwards, away from the brain, when it hits the tree red coloration indicates the greatest force or stess; blue indicates the least force or stress. Time after impact proceeds from upper left 0. The hyoid of woodpeckers loops over top of the skull to completely surround their skulls.
The hyoid helps direct the stress of impact below and around the skull and brain and also acts like a 'safety belt', helping to keep the brain in place. It is the movement of the brain inside the skull during impact, more than the blow itself, that causes concussions. If the brain is held in place, injury risks are greatly reduced. As in the above figure, time after impact proceeds from upper left to lower right Figures from Wang et al.
Built to peck - Segment 2. Built to peck - Segment 4. Built to peck - Segment 5. Built to peck - Segment 6. Built to peck - Segment 7. The capillary ratchet mechanism. Surface tension transport of prey by feeding shorebirds: They peck at the surface, picking up droplets of water with prey inside.
Because their beaks point downward when feeding, gravity must be overcome to get those droplets from the tip of the bird's long beak to its mouth.
This feeding strategy depends on surface tension. As the beak opens and closes, each movement propels the water droplet one step closer to the bird's mouth. Specifically, when the beak closes, the drop's leading edge moves toward the mouth, while the trailing edge stays put. In this stepwise ratcheting fashion, the drop travels along the beak at a speed of about 1 meter per second.
The efficiency of the process, called the "capillary ratchet," depends on beak shape, and long, narrow beaks, like those of phalaropes, are best suited to this mode of feeding. Serin Serinus serinus with a seed positioned in its bill.
Note how the tongue is used to hold the seed in position From: Their data provide the first detailed description of this highly specialized foraging technique. They recorded no or a very low deceleration when Gannets entered the water, which underlines the remarkable streamlining of this large bird.
Birds use their momentum to travel underwater at an average descent rate of 2. After chasing prey, birds developed an upward momentum before gliding passively back to the surface, making use of their buoyancy to complete the dive at the lowest possible energy cost. Check the Gannet videos at ARKive. Aerial insectivores -- Swifts depend on flying efficiently and maintaining high speed.
Hawking insectivores, like flycatchers , depend on perches located near prey, but they must be able to accelerate rapidly and be very maneuverable. Swallows combine these two strategies; they are fast, maneuverable and able to accelerate when necessary Warrick Although not part of the digestive system in an anatomical sense, some birds, like hawks and owls , use their feet and talons to capture prey.
Typically, raptor prey are killed by the talons of the contracting foot being driven into their bodies; if required, the hooked bill is used to kill prey being held by the talons. The raptor digital tendon locking mechanism -- Digital tendons form a mechanical-locking mechanism in many birds that must maintain a degree of grip force, including perching, hanging, tree-climbing, and raptorial species.
In raptors, powerful hindlimb muscles produce a strong grasp, and a tendon locking mechanism TLM helps sustain grip force. The components of the digital TLM include a 'textured' pad on the ventral surface of each flexor tendon that contains thousands of minute, rigid, well-defined projections called tubercles see figure below.
The neighboring portion of the surrounding tendon sheath contains a series of transversely running plicae folds that often have a proximal slant i. When the flexor tendons are pulled taut, and the digits flexed, the tubercle pad moves proximally over the stationary plicae on the sheath.
When resistance to digital flexion is met, the locking elements intermesh and engage and the friction produced prevents slippage of the tendons. This permits digital flexion to be maintained with little or no muscular involvement E inoder and Richardson Action of the avian digital TLM: This shows the movement of the talon a , flexor e and extensor d tendons, ungual phalanx b , and the movement of the ventrally located tubercle pad f relative to the stationary plicated sheath g and phalangeal bone c From: Einoder and Richardson Each raptor has a unique force production, along with a different time of activity, that would allow for a degree of prey specialization.
Great Horned Owl foot. B Great Horned Owl. The relation between rate of success and direction of movement for a food item that was pulled forward a , backward b and sideways c. Direction of prey progression — dotted arrow 1 , direction of owl flight — dashed arrow 2 , and direction to which the owl had to move its head or trunk — solid arrow 3.
Owl picture from Knudsen Movement and direction of prey affect raptor success rate -- Shifferman and Eilam tested a novel idea, that rather than maximizing their distance from a predator during close-distance encounters, prey species are better off moving directly or diagonally toward the predator in order to increase the relative speed and confine the attack to a single available clashing point.
They used two tamed Barn Owls Tyto alba to measure the rate of attack success in relation to the direction of prey movement. A dead mouse or chick was used to simulate the prey, pulled to various directions by means of a transparent string during the owl's attack. This failure to catch prey that move sideways may reflect constraints in postural head movements in aerial raptors that cannot move the eyes but rather move the entire head in tracking prey. So far there is no evidence that defensive behavior in terrestrial prey species takes advantage of the above escape directions to lower rates of predator success.
However, birds seem to adjust their defensive tactics in the vertical domain by taking-off at a steep angle, thus moving diagonally toward the direction of an approaching aerial predator. These preliminary findings warrant further studies in Barn Owls and other predators, in both field and laboratory settings, to uncover fine predator head movements during hunting, the corresponding defensive behavior of the prey, and the adaptive significance of these behaviors.
Barred Owl primary - leading edge below and trailing edge above. The silent flight of owls -- Noise is generated by vortices produced when air flows over a bird's wing and larger vortices produce more noise. Wings with small saw-toothed projections vortex generators , like those on the leading edge of owl wings, generate many small vortices instead of large vortices and produces less aerodynamic noise.
In addition, the fringe feathers at the trailing edge of the wing with fewer hooklets at the ends of the barbs help to break up the sound waves that are generated as air flows over the top of their wings and forms downstream wakes, and the soft down feathers located elsewhere on the wings and legs of owls absorb the remaining sound frequencies above 2, hertz and make owls completely silent to their prey.
As a bonus, with high angles of attack and at slow speeds, vortex generators stick out of the stagnant air near the surface of the wing, and into the freely moving air outside the boundary layer. This surface layer is typically quite thin, but dramatically reduces speed of the airflow towards the rear of the wing. The vortex generators mix the free stream with the stagnant air to get it moving again, providing considerably more airflow at the rear of the wing and helping to prevent stalling.
This process is referred to as 're-energizing the boundary layer. Unpredictable predators -- The use of space by predators in relation to their prey is a poorly understood aspect of predator-prey interactions. Classic theory suggests that predators should focus their efforts on areas of abundant prey, that is, prey hotspots, whereas game-theoretical models of predator and prey movement suggest that the distribution of predators should match that of their prey's resources.
If, however, prey are spatially anchored to one location and these prey have particularly strong antipredator responses that make them difficult to capture with frequent attacks, then predators may be forced to adopt alternative movement strategies to hunt behaviorally responsive prey. Roth and Lima examined the movement patterns of bird-eating Sharp-shinned Hawks Accipiter striatus in an attempt to shed light on hotspot use by predators.
Their results suggest that these hawks do not focus on prey hotspots such as bird feeders but instead maintain much spatial and temporal unpredictability in their movements. Hawks seldom revisited the same area, and the few frequently used areas were revisited in a manner consistent with unpredictable returns, giving prey little additional information about risk.
But why wouldn't Sharp-shinned Hawks focus their hunting on the areas with the most potential prey bird feeders? One possibility is that behaviorally responsive prey diminish the "hotspot" quality of feeders. Although feeder hotspots are sources of abundant prey, the individuals at such feeders generally benefit from group vigilance as a result of these higher densities.
As a result, the vulnerability of the prey may actually be lower at feeders than at other locations. In addition, unpredictable movement may reflect a sort of "prey management" by predators, whereby predators spread their hunting activity over multiple areas in an effort to avoid inflating the antipredator behavior of their prey.
This hunting strategy may be effective when prey are anchored to high-resource areas such as feeders and use antipredator behaviors, such as high vigilance, that reduce a predator's attack success if it attacks frequently and predictably. Seabirds are choking on ocean plastic video. The tongues of cormorants and other fish-eating species are small because these species swallow prey whole and tongues are not needed to manipulate or position food in the oral cavity.
Dorsal view of the surface of the lower bill of a Great Cormorant Phalacrocorax carbo. Arrow shows the tongue with sharpened tip. Scale bar, 12 mm. Lateral view of the cormorant tongue. The tongue and the small anterior and posterior areas of the mucosa of the bill are covered by white keratinized epithelium. Black arrow shows short base of the tongue. White arrow shows the median crest on the dorsal surface of the tongue. A, anterior; B, posterior.
Scale bar, 3 mm Source: Detailed view of the horny tip left of the Guadeloupe Woodpecker tongue in vivo position Villard and Cuisin Dorsal view of the tongue of the Spotted Nutcracker Nucifraga caryocatactes. Arrows show two elongated processes of the apex.
A, apex, B, body, R, root, LP, laryngeal prominence. Scale bar, 3 mm. Lateral view of the tongue of the nutcracker. Arrow shows elongated processes, pointed diagonally, B, body, R, root. Hummingbird tongues are fluid traps, not capillary tubes -- Hummingbird tongues pick up a liquid, calorie-dense food that cannot be grasped, a physical challenge that has long inspired the study of nectar-transport mechanics. Existing biophysical models predict optimal hummingbird foraging on the basis of equations that assume that fluid rises through the tongue in the same way as through capillary tubes.
Rico-Guevara and Rubega found that hummingbird tongues do not function like a pair of tiny, static tubes drawing up floral nectar via capillary action. Instead, the tongue tip is a dynamic liquid-trapping device that dynamically traps nectar by rapidly changing their shape during feeding.
In addition, the tongue—fluid interactions are identical in both living and dead birds, demonstrating that this mechanism is a function of the tongue structure itself, and therefore highly efficient because no energy expenditure by the bird is required to drive the opening and closing of the trap. These results rule out previous conclusions from capillarity-based models of nectar feeding and highlight the necessity of developing a new biophysical model for nectar intake in hummingbirds.
Hummingbird tongue tips twist to trap nectar. How the hummingbird tongue really works with videos. Close encounters with possible prey. You want to live 10—20 years. You are peering under leaves, poking into rolled ones, searching around stems, exploring bark crevices and other insect hiding places.
Abruptly an eye appears, 1—5 cm from your bill. The eye or a portion of it is half seen, obstructed, shadowed, partly out of focus, more or less round, multicolored, and perhaps moving. Now, a safe few meters away, are you going to go back to see whether that was food?
Associated body patterns often suggest other head and facial features, which in turn enhance the eye-like nature of the spots. None of these patterns exactly matches the eyes or face of any particular species of predator; but, even when quickly and partially glimpsed, all give the illusion of an eye or face. These false eyes are mimicking the eyes and faces of such predators of insect-eating birds as snakes, lizards, other birds, and small mammals, as perceived at close range by the insectivorous birds in their natural world.
Note the distended throat of this American Kestrel. Pigeons generally lay two eggs one day apart, which hatch 18 days after they are laid. A similar substance is produced by flamingos and male Emperor Penguins.
The normal function of the crop is food storage. Pigeon 'milk' also contains IgA antibodies and antioxidants carotenoids. The avian stomach is divided into 2 parts:. Photomicrograph 50X of a cross section through the proventriculus showing folds of mucous membrane P ; deep proventricular glands GP ; capsule connective tissue around the glands arrow head ; muscle layer m ; serosa connective tissue with blood vessels S , and the lumen L From: Photomicrograph X of longitudinal section of the gizzard showing folds of mucous membrane lined by simple prismatic epithelium P ; simple tubular glands Gs in the lamina propria constituted by connective tissue Lp ; secretion of glands S that are continuous with the cuticle or koilin ; C , part of muscle layer m , interpersed with bundles of connective tissue Tc From: Photomicrograph X of the koilin of an Eclectus Parrot Eclectus roratus.
Note the regular, columnated structure of the koilin layer K and its association with the glandular epithelium E of the ventriculus From: De Voe et al. A, koilin, B, crypts, C, glands that secrete koilin, D, epithelial surface, E, desquamated epithelial cells, 2 Mucosa of the gizzard. A, koilin, B, secretion in gland lumens and crypts, and 3 Koilin layer.
A, secretion column, B, koilin-layer surface, C, horizontal stripe indicating a 'pause' in secretion of the koilin, D, cellular debris. Eglitis and Knouff Vultures of the seas -- Animals are primarily limited by their capacity to acquire food, yet digestive performance also conditions energy acquisition, and ultimately fitness.
Optimal foraging theory predicts that organisms feeding on patchy resources should maximize their food loads within each patch, and should digest these loads quickly to minimize travelling costs between food patches. GPS-tracking of 40 Wandering Albatrosses from the Crozet archipelago during the incubation phase confirmed foraging movements of between — km, giving the birds access to a variety of prey, including fishery wastes.
Using miniaturized, autonomous data recorders placed in the stomach of three birds, the first-ever measurements of gastric pH and temperature in procellariformes were obtained. Such low stomach pH gives Wandering Albatrosses a strategic advantage because it allows a rapid chemical breakdown of ingested food and rapid digestion. This is useful for feeding on patchy, natural prey, but also on fishery wastes, which might be an important additional food resource for Wandering Albatrosses.
It is likely that this physiological characteristic evolved as a response to a diet largely composed of squid, and to a patchy distribution of this food resource resulting in large, infrequent meals.
The strategy of Wandering Albatrosses is to cover long distances rapidly and at low costs to increase the probability of encountering dispersed prey patches whose distribution is unpredictable. Knots with large gizzards consumed far more molluscs with shells than the birds with smaller gizzards. Birds with smaller gizzards simply couldn't feed fast enough.
By allowing them to crush more shell per gizzard-full, larger gizzards gave birds the edge. Thus, even though it is energetically costly for the knots to maintain a larger gizzard, when the bird needs to get the most out of its crunchy diet, it's a price worth paying. So, the birds' gizzards enlarge as they fatten for migration. Because the molluscs' shells stay the same size as the molluscs shrink, the amount of shell a bird must process to eat its fill also increases.
But with their larger gizzards, the birds can still make the most of even the crunchiest winter diet! Within 14 days, they showed a doubling of the size of their gizzards. Red Knots have strong muscular gizzards for feeding on molluscs. A shift back to a mussel diet induced about a doubling in gizzard mass in just a few days. As the knots were fed progessively smaller mussels day 22 to day 46 that are easier to crush, gizzard mass again declined.
A switch back to a soft food pellet diet caused a further decline in gizzard mass. Finally, a switch back to a mussel diet again cause a rapid increase in gizzard mass From: Piersma and Drent Ostrich Struthio camelus stomach. Note how particle size of material in the gizzard ventriculus is smaller than in the proventriculus due to the grinding action of the muscular walls plus small pebbles gastroliths.
The capacity to reduce particle size is related to the metabolic demands of a species. Therefore, particle size reduction is often considered the key digestive difference between ecto- and endotherms that allows endotherms to rely on shorter digesta retention times without losing digestive efficiency, and hence facilitate the high level of food intake necessary to meet their increased metabolic requirements.
In contrast, adaptations for chewing intrinsically increase the weight of the head. The use of the gizzard system has the potential advantages that intake rate is not limited by chewing, that no investment in dental tissue is necessary, and that dental wear is not a determinant of senescence as observed in mammals. The absence of age-dependent tooth wear might even be a contributing factor to the slower onset of senescence in birds as compared to mammals.
On the other hand, the use of a gizzard requires the intake of suitable grit or stones—an action that represents, in the few studies where this has actually been quantified in birds, a relevant proportion of feeding time Fritz et al. Gastrointestinal tracts of a carnivorous hawk, an omnivorous chicken, and 4 herbivorous birds. Note larger size of crop in omnivore and herbivores, and particularly in hoatzin.
Ceca are small in hawks and relatively large in grouse. Although ceca are relatively small in Hoatzins , Emus, and Ostriches, an expanded foregut Hoatzins , a much longer midgut Emus , or a much longer colon Ostriches compensates for this From: Stevens and Hume Over-reliance on the passive pathway provides metabolic advantages and ecological constraints.
It does provide birds with an absorptive process that can deal with rapid and large changes in intestinal sugar concentrations. The passive pathway is also energetically inexpensive to maintain and modulate. However, passive absorption through the paracellular pathway is dependent on concentration gradients.
In the absence of a transport system that selects which materials to absorb, this non-discriminatory pathway may also increase vulnerability to toxins, and thus constrain foraging behavior and limit the breadth of the dietary niche of the birds. Another problem is that when luminal sugar concentrations are lower than those in plasma, glucose may diffuse back into the lumen.
Cross-section of the intestine ileum of a Spotted Tinamou Nothura maculosa. Villi are lined with columnar epithelium EP , including goblet cells arrows that secrete mucus. The muscle layer includes longitudinal fibers MI on the perimeter, circular fibers Mc , and additional longitudinal fibers at the base of the villi muscularis muscosae; MM From: Chikilian and de Speroni Blue-headed Parrots at clay lick.
Meyer-Rochow and Gal determined that the pressures involved could be approximated if they knew the 1 distance the feces traveled, 2 density and viscosity of the material, and 3 shape, aperture, and height of the anus above ground. How penguins choose the direction of defecation, and how wind direction factors into that decision, remain unknown. Avian Pancreas tissue Source: The Avian Digestive Tract.
Avian geophagy and soil characteristics in southeastern Peru. Luminal morphology of the avian lower intestine: Histological aspects of the stomach proventriculus and gizzard of the Red-capped Cardinal Paroaria gularis gularis. Comparative study of the digestive system of three species of tinamou.
Crypturellus tataupa, Nothoprocta cinerascens , and Nothura maculosa Aves: Journal of Morphology Journal of Experimental Zoology Rictal bristle function in Willow Flycatcher. Dysplastic koilin causing proventricular obstruction in an Eclectus Parrot Eclectus roratus. Journal of Avian Medicine and Surgery Anatomy and physiology of the digestive system in fowl.
Pages in Proc. An histological and histochemical analysis of the inner lining and glandular epithelium of the chicken gizzard. American Journal of Anatomy