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  Avian Affairs





Dedicated to wildlife rehabilitation.


Avian Emaciation:

Unraveling the Mysteries of Recovery


Louise Shimmel, Director
Cascades Raptor Care Center
Eugene, Oregon 97405


                      Jan White, DVM
                      Wildlife Health Center
                      University of California,
                      Davis, California 95616


Wildlife rehabilitators are routinely faced with animals, usually birds, who have faced prolonged periods of time without food and have lost a substantial amount of weight. Experience has shown that simply feeding these animals their normal diet is counter-productive and often results in fatality. This article sets guidelines for determining when an animal is emaciated, describes various complications of starvation, and delineates a protocol for recovery based on experience with hundreds of birds of prey.


There is perhaps nothing more frustrating to a wildlife rehabilitator than trying to do battle with something you cannot see, and watching an animal starve to death in the midst of plenty.

Lesson number one is to resist the urge to feed them! A bird that has lost, say 30% of its body weight might use its last available calories to break down any food offered, and might very well die before the resulting energy is available on the cellular level. If the calories to digest that food are not available, the food will sit in the crop or stomach and rot, resulting in a proliferation of bacteria, toxemia, and death.

Starvation is, in essence, the prolonged absence of nutrition, and is sometimes found in medical texts under 'inanition' or 'anorexia.' The result is emaciation. One of the many difficult aspects of dealing with emaciation is that it NEVER presents alone: it is either the result of some underlying physical problem, or results in debilitating physical problems (e.g., suppressed immune system, parasite infection, anemia, dehydration, or kidney damage), or BOTH. At times, it is almost a relief to detect an obvious cause of starvation, because those cases where all of the physical systems seem otherwise normal can be a real challenge.

Physical Signs of Emaciation

How can you tell if a bird is starving? There are some subjective and some objective measures.


  1. Breast musculature should be rounded and, with most species, reach the top of the keel bone. Although you can always palpate the keel (leading edge of the breast bone) in a bird that is flying and within its normal weight range, these muscles will feel full and well-developed; in a bird that is starving, these muscles waste away to varying degrees, leaving the keel very prominent. A 'knife-edge' or 'razor' keel is, like it sounds, when you can actually pinch the keel, feeling bone with the pads of your fingers. Other bone, like the lumbar area of the lower back, will also be palpably prominent.
  2. One of the primary signs of prolonged inanition is a lime-green dropping: when the gastro-intestinal tract is empty, there is nothing to mix with the bile that is produced automatically (whether the bird is eating or not) by the gall bladder, and the droppings come out lime-green. Often the droppings are primarily urates; sometimes even foamy in appearance.
  3. And even notice the 'feel' of the bird in your hand compared with your normal experience.


    1. Compare the weight upon intake to normals. Obviously, even this objective measure has an element of subjectivity to it; given the often large size/weight ranges for most species, especially gender size variances, you don't always know to which normal range to compare the bird. An excellent resource book (and essentially the only resource beyond your own records of species' weights in your area) is Body Weights of 686 Species of North American Birds by John B. Dunning, Jr., now available through the International Wildlife Rehabilitation Council. For example, say you receive a bird as much as 30% down in weight. This has an impact on treatment, as will be discussed, but a note of warning on the use of these printed averages; although the referenced book is an excellent resource, it must be used with a grain of caution. It is a compilation of many different surveys, which are referenced in the back of the book, and which also vary by geographic location and time of year. Record-keeping of intake and release weights is critical.

Categories of Emaciation

Treatment protocols vary by the degree of starvation. Category I birds are between 90%-100% of normal; the keel may be slightly prominent but not severe. Perhaps there has been a storm; perhaps the bird has been trapped in someone's garage; perhaps it has been sitting in a daze in a ditch for a couple of days, but in essence it is not in a critical state of starvation. Category II birds are 75%-95% of normal and you will be seeing some complications of prolonged malnutrition, as well as of the underlying injury or disease process, such as anemia. Category III birds are 50%-75% of normal weight and are an extreme challenge to save. By the time you see this degree of wasting in a wild animal, you are seeing a lot of changes inside; some things are no longer functioning well and may never recover. This does not mean that you give up on these birds.

Complications of Starvation

Whether or not there is an underlying injury or disease process, starvation almost always presents along with severe dehydration, anemia, and both ecto- and endo-parasites. Obviously, treatment of the dehydration is imperative and can be addressed in multiple ways. On intake, the author frequently administers subcutaneous fluids in the inguinal flap; IV fluids are difficult to administer, even into the jugular, when veins are collapsed and blood pressure low, but can often be used after SQ fluids have added volume to the system. Oral electrolyte solutions are also used unless there is blood in the mouth or any sign of respiratory compromise, but may or may not be well-absorbed. (The author had at least one case where oral fluids essentially ran right through the system unchanged.) Replacement volume calculations can be found in IWRC's Basic Wildlife Rehabilitation 1AB, a Skills Seminar manual.

Ectoparasites are always treated, by the author, with the application of a pyrethrins-based powder, because these mites and lice can present a risk to other birds in the center. Endoparasites are treated at the discretion of the rehabilitator and veterinarian based on severity of infestation and degree of debilitation.

Anemia will probably respond to general supportive treatment but can also be addressed with iron dextran injections weekly and/or a tonic such as Beecham's Pet-Tinicš orally. Iron should not be administered in the presence of an infection, however, as bacteria find iron exceptionally beneficial and can multiply faster than antibiotics can take care of them1. Get any infection under control before using iron supplements to treat anemia. Severe anemia can be assisted by blood transfusions and the author has used an education bird as a donor, as well as a bird under rehabilitation. The Raptor Center at the University of Minnesota typically transfuses any bird that presents with a PCV of less than 20.

Emaciation Protocol

Successful treatment for emaciation involves rehydration, the calculation of the calories necessary for a slow and steady weight gain, and the various means of supplying those calories. Each of these steps involves choices.


Typically, the author gives nothing but electrolyte fluids during the first eight hours. If, however, the eight hours would stretch into more overnight, she adds an amino acid solution to an oral hydration formula, in order to provide some nutrition. Such solutions contain very few calories, however, and neither do electrolyte solutions. The bird may gain some weight from rehydration, may lose a little since little or no calories are being provided in the first few hours, or may roughly balance out. Do not attempt to provide calories by way of a high percentage glucose solution:

a) their addition makes a solution hypertonic and may actually complicate dehydration

To calculate the amount of fluids necessary to compensate for the deficit and provide the normal daily maintenance levels, see the Fluid Therapy section of the IWRC Basic Wildlife Rehabilitation 1AB Manual3. To rehydrate a bird is a prolonged process and must be continued for the first few days, or as long as any signs of fluid deficit are present, even after emaciation treatment feedings have started.

Calculation of Calories

Different types of animals have different metabolic rates and different caloric requirements. The formula for determining the caloric needs of a bird in your care is as follows:

Animal Factor x (weight in kg) .75   x      basal rate factor = Kcal/24 hrs.

The animal factor is a multiplier based on the metabolic rate of different types of animals; as you would assume, these vary from a reptilian low of 10 to a small bird high of 129. Birds are typically divided into two classifications: passerines (or those weighing 100 gms or less) with an animal factor of 129, and non-passerines (those weighing over 100 gms) with an animal factor of 78.3

This formula is an inverse exponential function of the body weight: i.e., the daily caloric requirement is negatively related to body weight (but not in a straight line) or, as we have all noticed, a kestrel needs to eat far more in relation to its body weight than does an eagle!

The basal metabolic rate (BMR) is defined as the number of calories necessary for an animal at rest, in a thermo-neutral environment  to maintain its body weight. The basal rate factor depends on the age and condition of the bird and is a multiplier of the basal metabolic rate. That is, a healthy adult bird, in order to maintain its body weight in normal activity, needs 2x the BMR; a sick adult needs 3x, in order to maintain body weight AND provide energy for healing; a healthy, growing juvenile needs 4x; and a sick juvenile, 5x.

The IWRC Basic Wildlife Rehabilitation 1AB manual explains this at length and provides examples of these calculations, as well as charts that can be used in the absence of a calculator with a yx key or a square root key.

Whether your bird is a sick adult or juvenile, it is important to start it out on the low end of the scale: providing no more than 1.5-2 x the BMR in the first day of feeding, and gradually working up over several days to the appropriate basal factor of 3, 4 or 5.

What to Feed, How Often, and How Much

Two of the primary decisions to be made are what to use to provide these calories and how to balance the benefit of numerous small feedings against the stress of handling.

Category I and II birds can usually be started (after the initial period of rehydration and often the addition of small amounts of an amino acid solution to second/third fluids and the first few feedings) on Ultracalš , Isocalš Osmolyteš or Ensureš , all of which are easily digested and absorbed, nutritionally complete, isotonic human tube-feeding formulas. They are approximately 1.0 or 1.1 kcal/ml. The author prefers Ultracalš because of the addition of fiber, which has helped to control some of the diarrhea which tends to accompany the use of Isocalš . Category III animals will probably need an elemental diet: a diet made up primarily of the building blocks of nutrition and which takes little or no energy to break down. Some examples are Vivonexš or Tolerexš , human elemental tube-feeding formulas; they are, however, hypertonic, so since they are usually used while the bird is still being rehydrated, care needs to be taken to offset the hypertonicity with extra fluids. In the absence of these products (which are very expensive), the author has used higher quantities of amino acid solutions in conjunction with Ultracalš .

Using Ultracalš as an example, the quantity to feed is easily determined by taking the result of our kcal formula and dividing by 1.1 kcal/ml. That is, a 300 gm starving (and 10% dehydrated) barn owl which received only fluids and then fluids with amino acids in its first 8 hours, would then need in its next 24 hours, 47.6 kcals (1.5 x basal) or 43 mls of Ultracalš . To calculate how much to tube in each feeding, the rehabilitator must factor in both the volume of Ultracalš and the volume of hydration solution (25 ml) needed for a total oral volume of some 68 ml that must be ingested. A rough rule-of-thumb for figuring out stomach capacity of an animal is 55 ml/kg of body weight: for a 300 gm barn owl, that would mean its maximum capacity would be some 16 ml. In order to minimize the risk of aspiration in an already debilitated bird, the author recommends stepping that number down to approximately 12-15 ml/feeding. Thus, dividing the 68 ml of volume needed during this 24 hours by 15, results in 5 (rounded); resulting in a suggested 5 feedings of 13.7 ml each - 8.7 ml of Ultracalš and 5 ml of fluids. If volume is a problem or the bird regurgitates, fluids can be given SQ instead of orally.

Obviously, the daily calorie requirements will go up as the bird is moved up the scale to its necessary 3, 4 or 5x basal and as it gains weight. This can pose a problem; the author tries to ensure that the system of a debilitated bird is clear of food for at least part of each day, usually overnight. This means that an ever-expanding amount of calories and volume needs to be ingested over a period of some 14-16 hours.

Category I and II animals can, by day 3 or 4, have Nutri-Cal‚ added to their diet; it is a low-volume, high calorie supplement which provides 6 kcal/ml. Because it is fat-based (34.5%), it takes a certain amount of energy to assimilate and the bird needs to be able to provide this. Nutri-Cal‚ should be used very judiciously and with caution on a Category III animal. If a Category III bird is moved slowly up the scale to 3 or 4x basal, it may be able to assimilate Nutri-Cal‚ by the time many small meals have exhausted its volume capacity.

When to Add Solids

Two of the most critical elements to monitor in emaciation treatment are blood values: PCV and serum protein. Blood should be drawn on Day 1 (and adjusted heuristically for the false elevation of these values caused by dehydration) and monitored again approximately every other day. PCV provides a reading of anemia; the author has seen birds come in with values less than 10%; from the hematocrit tube (and even better from a blood smear), the rehabilitator can judge whether any anemia is regenerative (amount of immature red blood cells) and whether or not the bird is battling an infection (prominent buffy coat or white cell count). Serum protein, or the amount of circulating protein expressed in grams per deciliter, is a measure representing a fairly complicated interaction between protein synthesis and catabolic rate, or in other words, measures how able the bird is to convert available protein to usable energy. In a bird that has not eaten, serum protein is typically very low. Readings lower than 2 gms/dl indicate an inability to perform that conversion well, and birds with low serum protein should not be fed solid food.

Unfortunately for those of us who might like clear guidelines, the author has also had several birds come in with serum protein at adequate levels who were still unable to process food. Some came in with packed, sour crops; some ate food provided by the author but were unable to process it. With birds with crops such conditions must be handled by removing the rotted food from the crop. If the food which is not being moved along consists of a tube mix, sometimes it can be sucked out through a tube and syringe. It is, however, always better to err on the conservative side and provide solid food in small amounts, even to birds with adequate blood readings and normal droppings, until you are sure they can handle it.

Assuming the bird's serum protein has reached 2 g/dl, the author starts factoring 'solid' food into the tube-feeding mix at an initial rate of 10% of the day's caloric requirements. That is, say our 300 gm barn owl is now up to 350 gm, and his serum protein has reached 2.1 gm/dl; he is at 4x basal (adult bird, recovering from an injury, and trying to gain weight) and so needs 142.5 kcal/day. We want to provide 10% or 14.25 kcal from solids. The author has used Science Diet‚ dry cat food (or dog food) soaked in water or electrolyte solution and then blended, to provide this solid portion. The caloric content varied based on how promptly the mixture was put through the blender after it was softened. The most effective mixture provided 1.6 kcal/cc to add to the Ultracalš . Hill's has now developed a new product called a/dš , specifically for cats and dogs that are unable to eat solid food. Hill's representatives have indicated that they think it is an adequate diet for sick raptors as well, and it provides 1.6kcal/cc. It is a semi-solid food, too solid for tube-feeding as is, but when mixed with Ultracalš provides a good intermediate step. The amount of calories derived from solids (i.e., food that is closer to a natural diet and that is correspondingly more demanding to digest) can be stepped up each day if the bird shows no adverse reactions.


Treatment of emaciation can be a frustrating experience. Once you have a protocol which seems to work, there is a fine line between sticking with success and being willing to experiment when something better presents itself. Like most areas of wildlife rehabilitation, emaciation demands a blend of science, intuition, observation skills, and a willingness to 'fly by the seat of your pants.'

For example, if any bird (thin or not) presents with lime-green droppings and a serum protein of 2.2, the author would initiate her emaciation protocol, starting at 1.5x basal requirements on the first day after the 8 hour rehydration period. How quickly the bird progresses through the steps depends on the recover of blood values, general attitude, weight gain, the condition of the droppings, and indications of what else might be wrong. Poisoning suspects should be given lots of fluids anyway to assist in flushing the system. Birds with broken bones might be switched as fast as possible to solid foods (Ultracalš has a calcium:phosphorous ratio of 1:1) or the tube mix supplemented with calcium or bone meal (Ca:P of 2:1). Borderline cases of diurnals might be started on 'solid' solids because it can be removed, if necessary, from their crop. Solid food that is not being digested cannot be retrieved from the stomachs of those birds without a crop, so a tube mixture with a/dš as the solids (which could be removed, perhaps, by tube if necessary) would be used instead.

It is the author's experience that a starving bird usually shows some dramatic signs of improvement over the first couple of days, probably as the result of warmth and rehydration. By the third day, however, the underlying condition may reassert itself and some birds regress at this point, usually vomiting and often dying. If they make it through the third day, the odds seem to go up for their recovery. If at any step of the process, such as when going from 3x basal to 4, or from 10% solids to 25%, there is an adverse reaction (vomiting or deteriorating blood values), back off and start up again more slowly.

If you lose a bird or make the decision to euthanize it because of the underlying injury, you can learn a lot by making necropsies a regular part of your routine. Finding roundworms in the abdominal cavity or a severely damaged liver can teach you and help to acknowledge that even doing the best you can does not always lead to success.


    1. SCRIMSHAW, Nevin S. 1991. "Iron Deficiency." Scientific American 265(4): 46-53.
    2. DOBBS, Joan. 1983. "Glucose Utilization in an Avian Carnivore, the Red-tailed Hawk, as Measured by Glucose Tolerance Tests." Ph. D. Thesis, Avian Sciences Dept., UC Davis, Ca.
    3. WHITE, Jan, DVM. 1992. Wildlife Rehabilitation 1AB, International Wildlife Rehab. Council, Suisun, CA.


Tolerexš - Norwich Eaton; 80g packets to mix w/ 255ml water to make 300 ml; 1.0 kcal/ml.

Ultracalš - MeadJohnson; 8oz can with 250 kcals; ready-to-use; 1.1 kcal/ml

Isocalš - 8 oz cans; ready-to-use; 1.1 kcal/ml

Nutri-Cal‚ - Evsco Pharmaceuticals; 4.25oz tube; 6 kcal/ml

aA/dš - Hill's Prescription Diet‚ ; 5.5oz can; 1.6 kcal/ml

Amino Acid Solution - Phoenix Pharmaceutical; 25 kcal/100ml

Pet-Tinicš - SmithKline Beecham; bottles of different sizes


Author Profiles

Louise Shimmel has been a wildlife rehabilitator since 1985, when she helped get Willamette Wildlife Rescue and Rehabilitation up and running, overseeing its growth from 100 animals / year to over 2,000 and the establishment of a central care facility. She started working with raptors in 1987 and founded Cascades Raptor Care Center in 1990. Louise has also been an IWRC Board member since 1989 and currently serves as its president. In a past life, Louise received her BA from Stanford, her MBA from the University of Chicago Graduate Schools of Business, spent a year at the London School of Economics, and spent four years as an international commercial banker in various parts of the world.

Jan White, DVM, has been a wildlife rehabilitator since 1975. In that time she has served as the founder and director of the Suisun Marsh Natural History Association, and the operations manager and staff veterinarian for the International Bird Research Rescue Center in Berkeley, CA. Presently, she is the executive director of the IWRC, and a staff research associate at the School of Veterinary Medicine, Davis, CA where she teaches and assists in the development of the Wildlife Health Center.


(Additional emphasis, i.e. font sizing & bolding, by UWS)