This is reprinted from ExoticsCon Proceedings, 2022, written and presented by Renée Schott, DVM, CWR.
It can be difficult for a practitioner to know which wild animals will survive the rehabilitation process to release and which will not. This master class uses data from The Wildlife Rehabilitation Center of Minnesota, one of the largest wildlife rehabilitation centers in the country, to help predict which patients will make it to release and which will not. The goal of this class is to help those in private practice know when to euthanize on admission and when to treat and transfer to a wildlife rehabilitator.
Private practitioners are often regarded as experts across all taxa, regardless of the focus of their practice. Clients and the general public will occasionally call with questions about injured or orphaned wildlife, or may simply show up in the lobby with the animal. It behooves the clinic to be prepared to deal with these scenarios so the finders have resources and options. It is important that clinics are prepared to handle and refer these calls appropriately for the sake of efficiency, the welfare of the wild animal, and the safety of the patients in the hospital. In addition, it is important for private practitioners to be armed with basic triage and euthanasia skills to humanely end the suffering of wildlife that cannot recover.
The Wildlife Rehabilitation Center of Minnesota (WRCMN) admits >19,000 sick and injured wild animals each year. Asterisks (*) below indicate older data from WRCMN and updated data from WRCMN is used during the live class to help others make informed decisions. It is difficult to compare data from one rehabilitation center to another due to differences in location, resources, capacity, species, diseases, etc. For more details about how the data was compiled, please contact [email protected].
Before wildlife is in the lobby or calls start coming in, clinics should prepare by following the steps below.
Find a Wildlife Rehabilitator or Facility to Work With
It is illegal to possess native wildlife without the proper permits. Veterinarians must be working with a permitted rehabilitator in order to possess wildlife they are treating. In addition, most states require rehabilitators to work with a licensed veterinarian to keep their permits active. Rehabilitators are familiar with natural history and veterinarians know veterinary medicine; working together ensures the best outcome for the animal. In addition, rehabilitators can determine when an animal needs to be rescued and when it should be left alone. Calls are best referred to rehabilitators or facilities set up to field these questions, as questions are complicated, and answers aren’t always straight forward.
Where can you refer phone calls or injured patients to? Do you know the addresses or hours of facilities in the area? Who is a contact at your state natural resources or fish and game department and at US Fish and Wildlife? Making a resources sheet and SOPs for your reception will limit miscommunications.
Know the Laws
Typically, each state regulates who can rehabilitate wildlife and how. Federal regulations exist for migratory birds as well. While it is usually legal for veterinarians to treat and/or euthanize wildlife, they must transfer all migratory birds to a licensed wildlife rehabilitator within 24 hours of stabilization1 and they cannot possess other species for more than 24–48 hours unless they are already working with a permitted rehabilitator. There are often additional guidelines and regulations surrounding threated or endangered species. Keep in mind, species that have a hunting season in your area must be treated as food animals; withdrawal times and the list of prohibited medications apply.2 More details about legal responsibilities and restrictions can be found in Duerr and Whittington, 2017.3
For a wild animal to allow capture, it is usually very debilitated. Release proportions vary according to species, age, and injuries, but range from 24–85%.4-7 Euthanasia is common, necessary, and humane. In most areas, the number of animals that need rehabilitation are too numerous for the available resources. When considering the below cases, it is important to consider these resources, the anticipated number/species/age of animals needing rehabilitation, rehabilitator/facility limits, and welfare. The ability of the rehabilitator, facility, or clinic to accept animals for rehabilitation will be dependent on the above factors. If resources (time, space, money, people) are low, the overall ability of the caretakers will diminish which will lower welfare for everyone. Euthanizing the least likely to survive and basing the number of animals in care on resources available, will allow those with the best prognosis to receive the best care and ultimately the best chance at release. Because stretching resources results in a lower standard of care for all, euthanizing more animals on admission in a strategic manner results in an increase in the overall number of animals being released (*).
What Types of Orthopedic Conditions Should Be Euthanized?
Prognoses and treatment options are taxa specific.8 Consider your ability, the ability of the wildlife rehabilitator, and the species. Below are generalizations that apply to most taxa unless specified otherwise.
Necrotic or Old, Compound Fractures
Compound fractures are inherently more prone to healing complications owing to the increased likelihood of contamination and/or infection. Necrotic bone must be removed and in general, most species need to have almost perfect fracture alignment with <10% loss of long bone length. Necrotic bone is almost always accompanied by necrotic soft tissue. Many wild animals (especially birds) have very little soft tissue over certain bones and the loss of that soft tissue means the bones underneath will not heal or will have complications.9 Older fractures are also inherently prone to more complications; if the bone has stopped healing, then all bone ends must be freshened to be stimulated to heal again. In addition, muscles, tendons, and ligaments often have contracted, making reduction difficult. Not only do the bones need to heal perfectly, but all joints need near perfect range of motion. The definition of “old fracture” varies with species, age, and type of fracture. For instance, a two-day old compound, comminuted fracture in a nestling songbird may be considered old, whereas a 7-day old closed, simple, midshaft fracture in a fox may be fresh enough to fix.
Traumatic Joint Injuries
In the author’s experience, wildlife that experience traumatic joint injuries, begin trying to reduce the abnormal movement in the joint by producing fibrous tissue around the joint. This reduces range of motion chronically which leaves the animal non-releasable. In the author’s experience, luxations and sub-luxations (excluding coracoid luxations off the keel, which usually heal well) will almost always heal with reduced range of motion and should be euthanized. In addition, traumatic joint luxations frequently will cause osteoarthritis.9,10
Successful surgical management of elbow luxations in raptors11 and a woodchuck12 have been reported; however, in both papers the possibility of osteoarthritis was not discussed. Unsuccessful treatment of luxations in wildlife are also reported.12,13 Articular fractures need perfect alignment and rigid fixation to prevent secondary degenerative joint disease.14 Wildlife develop reduced range of motion and signs of osteoarthritis within weeks of sustaining an articular fracture, no matter how rigid the fixation and perfect the anatomic alignment. WRCMN euthanizes all traumatic joint injuries that result in intra-articular fractures or luxations/subluxations of joints (excluding coracoid luxations off the keel) because of past experiences (*).
Shoulder Fractures in Aerial Insectivores
In North America, swallow species (including but not limited to Barn Swallows, Hirundo rustica, and Cliff Swallows, Petrochelidon pyrrhonota), swift species (including but not limited to Chimney Swift, Chaetura pelagica, and Vaux’s Swift, Chaetura vauxi), nightjar species (including but not limited to Common Nighthawk, Chordeiles minor, and Eastern Whip-poor-will, Caprimulgus vociferus) have very high metabolic demands; Vaux’s swifts may need to eat >5000 arthropods each day!15 Flight must be perfect in order to accomplish this. A bird with even the slightest flight deficit may die of starvation after release. In addition, most of these species migrate to Central or South America for the winter which also requires sustained flight. To adequately assess pre-release flight ability, these species need a 30’ (swallows/swifts) and 50’ (nightjars) flight cage. Any deficit should be heavily scrutinized. In the author’s and other’s experiences (Veronica Bowers, Native Avian Care, personal communication, 2017) <1% of shoulder fractures in these species will recover to a releasable state. Several species do not eat in captivity and must either be trained to accept handfeeding, gavage, or force fed. All are high stress species. Feather condition must be pristine. Husbandry for these species is complicated and best not undertaken by a novice.
All aerial insectivores with any shoulder girdle (coracoid, scapula, clavicle) fractures are now euthanized at WRCMN due to past experiences, other’s experiences and the intense husbandry care these species require (*).
What Type of Traumatic Eye Injuries Should Be Euthanized?
In general, any condition that will result in permanent vision loss should be considered for euthanasia, even if only in one eye. Prey animals will be left unable to watch for predators, predators may have a difficult time catching enough prey (no live prey testing in captivity is equitable to catching prey in the wild). This is a controversial topic and some wildlife rehabilitation veterinarians and rehabilitators have differing opinions. This author does not release one-eyed animals, with an exception being some aquatic turtle cases. Traumatic eye injuries that result in vision loss include luxated lens (posteriorly and anteriorly luxated), ruptured globes, complete retinal detachment with incomplete reattachment, and any other condition that results in permanent vision loss.
What Types of Other Issues Should Be Euthanized?
Wild animals have evolved to hide signs of pain and to self-repair injuries as much as possible. If they did the opposite, they would likely become prey. Therefore, any condition which has the potential to result in chronic pain in a human, should be assumed to have the potential to result in a chronic pain for the animal, should be grounds for euthanasia of the wild animal for humane reasons. Wild animals cannot receive chronic pain medications or other palliative care in the wild.
Spinal Trauma With No Deep Pain
Most rehabilitators and veterinarians recognize spinal trauma via pelvic limb paresis or paralysis. Because of the anatomy of the spinal cord, loss of deep pain perception indicates a grave prognosis for return to function. In addition, neuropathic pain has been reported in paralyzed companion animals.16 Therefore, animals without deep pain should be humanely euthanized. To test for deep pain perception, use a toe on the limb that is paralyzed/paretic. Pinch the toe; start with a superficial pinch and then slowly pinch harder. Watch for head movement, vocalization, or other indication that the pain sensation made it up the spinal cord and to the brain. Ignore all movement in the limb that is being pinched as the withdrawal reflex may be intact or hyper reflexive, depending on where the lesion is. One cannot discern between the withdrawal reflex and voluntary movement when pinching a toe, and wild animals can have very strong reflexes, so it is imperative to ignore movement in the leg and watch the head of the animal. In addition to spinal trauma, brachial plexus avulsion occasionally occurs. If deep pain is not present in one forelimb of a unilaterally forelimb paralyzed animal, brachial plexus avulsion should be considered. Brachial plexus avulsion will not heal to a releasable state and these animals should be euthanized. Animals with no deep pain in a limb should be euthanized as they will not recover to a releasable state.
Seizing Rabies Vector Species
Rabies vector species (raccoon, coyote, fox, bat, skunk) with abnormal neurologic signs should be considered for euthanasia due to public health concerns. It is important to know your rabies vector species and rabies virus variants in your area and what your department of health requires you to do; they may want the animal tested for rabies or to have the contact of the finder to talk about exposure. Generally, a seizing animal bears a poor prognosis, regardless of species.
Distemper Virus Infection Suspects
Distemper suspect species (i.e., raccoon, coyote, fox) with abnormal neurologic or severe respiratory clinical signs, with or without leukopenia should be considered for euthanasia. Consider the infectious nature of this pathogen and the domestic animals in your clinic which are susceptible. In addition, wild animals have a high probability of permanent neurologic issues even if they survive, which is rare.
Only 6.7% (25) of the 373 adult raccoons admitted to WRC from 2011–2017 were able to be released (*). Treatment was attempted with 68 and 25 (36.8%) of treated were released. While not all of these cases were distemper suspects, adult raccoons are difficult for the public to capture and transport; consider how debilitated this species must be to present for rehabilitation and this bears out in prognosis.
The younger the animal is, the lower it’s chance of survival when being raised in captivity by humans. Reviewing data from previous years can help facilities find which variables are best correlated with survival to release.
WRCMN Data (*):
- Eastern cottontail rabbits (Sylvilagus floridanus): WRCMN received 3133 young cottontails in 2017 alone. Historically, under 65 grams, healthy Eastern cottontail rabbits have <30% chance of release. Under 75 grams, unhealthy Eastern cottontail rabbits have a <30% chance of release. Definition of healthy: mild-moderate dehydration, thin (not emaciated), BAR, no injuries.
- Eastern grey squirrels (Sciurus carolinensis): WRCMN received 1285 young grey squirrels in 2017 alone. Historically, healthy grey squirrels under 40 grams have <30% chance of release.
- Virginia opossums (Didelphis virginiana): WRCMN received 119 young Virginia opossums in 2017. Opossums 20–40 g have a 50% chance of survival.
- Hatchling altricial birds (just out of shell) are euthanized as they have 0% chance of release at WRCMN.
Adult Eastern Cottontails and Eastern Grey Squirrels With Abnormal Brain Neurologic Clinical Signs
Adult Eastern cottontails and Eastern grey squirrels commonly present to WRCMN with abnormal brain neurologic clinical signs (e.g., head tilt, circling, head turn, ataxia). Necropsy results most commonly conclude the etiology to be Baylisascaris procyonis (or a nematode tract through the brain) or head trauma.
WRCMN received 233 adult cottontails with abnormal central nervous system signs in 2017 (*). From 2011–2017, 1727 total cottontail adults were admitted. Of these 641 had abnormal brain neurologic clinical signs. Of the 641, 3.3% were eventually released. Of the ones that were treated, 8% were released. This is compared to all other adult cottontails which had an overall release proportion of 5.5% and a treated released proportion of 19%. This author recommends euthanasia of all adult cottontails with abnormal brain neurologic clinical signs due to the poor release proportion.
WRCMN received 94 adult grey squirrels with abnormal central nervous system signs in 2017 (*). From 2011–10.22.2017, 1295 total grey squirrel adults were admitted. Of these 414 had abnormal brain neurologic clinical signs (such as head tilt, circling, head turn, ataxia, etc.). Of the 414, 8.7% were eventually released. Of the ones that were treated, 16.1% were released. This is compared to all other adult grey squirrels which had an overall release proportion of 10% and a treated released proportion of 29.1%. This author recommends heavily scrutinizing any adult Eastern grey squirrel with abnormal brain neurologic signs before choosing to treat.
Conditions to Not Euthanize (If You Have the Resources)
Mycoplasma gallisepticum Conjunctivitis in House Finches
Mycoplasma gallisepticum (MG) originally spread from the production poultry industry to house finches (Haemorhous mexicanus) in the 1990s17 and is now endemic in the house finch population18. When it first appeared, the poultry industry and biologist were afraid of MG recovered house finches becoming latent carriers and some antibiotics being ineffective;19,20 however, it is very hard for wild house finches to actually transmit M. gallisepticum to domestic poultry21,22 and there is a treatment, that when given appropriately can eliminate the carrier state23. Euthanizing one or even several hundred house finches because they have this disease will not affect the population or disease status. WRCMN treats and releases house finches with presumed MG conjunctivitis according to Mashima et al. 1997.23
Severe Mange in Red Fox
Juvenile red fox (Vulpes vulpes) occasionally are admitted in the fall with severe mange, presumably after having been forced out of maternal territory. While some of these fox are too sick or emaciated with secondary conditions to survive, many can be treated and released.24 These patients require intensive critical care as they are usually severely emaciated, chronically anemic, and have a myriad of other health concerns that will develop during treatment (i.e., refeeding syndrome).
Animal Missing Digits
Certain species can survive well in the wild with missing digits; however, the location and number of missing digits that allow successful release are species dependent.8
How to Euthanize Various Wildlife Species
The techniques described below are used most frequently at WRCMN. They take into consideration the wild animal species, age, and physiology of the animal being euthanized as well as the safety of the handler; priority is given to decreasing apparent animal stress. There are other technique options. In the author’s experience, the methods below have proven reliable and cause the least amount of stress to the animal.
Table 1. Euthanasia choices for wildlife ^a
Eastern cottontail rabbit
0.2 ml (100 mg/ml) ketamine; 0.4 ml (5 mg/ml) midazolam; 0.2 ml (10 mg/ml) butorphanol → mix → give IM → wait 15 minutes. If still alive, put into isoflurane boxb until deceased or mask at 5% isoflurane until anesthetized then IC sodium pentobarbital (390 mg/ml) 0.5 ml
2 ml (100 mg/ml) alfaxalone → give IM → wait 15 minutes.
Prolonged struggling and breath holding when placed in isoflurane box without pre-medications and even more prolonged in the isoflurane face mask/induction box
Other mammal species
Neonate, just weaned
Isoflurane boxb until deceased. They dislike the strong smell and will wipe their faces but are anesthetized within 10 seconds
Young mammals’ brains are very tolerant to hypoxia and they hold their breath and struggle in an isoflurane mask at 5% for several minutes
Breath-holding avian species
3 mg/kg midazolam, 5 mg/kg butorphanol, 5 mg/kg ketamine IM → wait 15 minutes then isoflurane boxb until deceased
Debilitated individuals are often too weak to hold their breath and do well in the isoflurane box ^b
Any (except breath-holding species)
Isoflurane boxb until deceased
Birds have efficient gas exchange in their lungs; they become anesthetized in ∼2 breaths
Raccoons/similar sized canids
0.3 ml (0.5 mg/ml) dexdomitor; 0.3 ml (10 mg/ml) butorphanol → mix → give IM; if seizing, start with 1 mg/kg midazolam → wait 15 minutes, if still alive, put into isoflurane boxb until deceased or mask at 5% isoflurane until anesthetized then IC sodium pentobarbital (390 mg/ml) 3 ml
Debilitated individuals are often too weak to hold their breath and do well in the isoflurane box ^b
15–25 mg/kg alfaxalone IM → wait 15 minutes → 10 mg/kg propofol IV wait 15 minutes → same volume (as propofol) pentobarbital IV wait 15 minutes → pith
Other anesthesia medications can be used but all must induce anesthesia and end in pithing
Chelonian brains are so tolerant to hypoxia 26–28 that reanimation can happen if using anesthetics/pentobarbital alone
a The Wildlife Rehabilitation Center of Minnesota (WRCMN) admits >19,000 sick and injured wild animals each year. Asterisks (*) are used to indicate WRCMN data.
b See isoflurane box euthanasia technique below.
Isoflurane (or Sevoflurane) Via Face Mask
Restrain the patient and place head in mask through diaphragm or hook up vaporizer to an induction box with the animal inside. Start at maximal percentage until patient is fully anesthetized. Then administer appropriate amount of pentobarbital IV or IC.
- Liquid isoflurane is poured into a clear Rubbermaid-type container with a lid. Either do this in a vent hood or ensure container is on the ground/floor and you remain above to prevent accidental inhalation of isoflurane, which is heavier than room air. Ideally, a respirator would be worn to avoid inhalation of all fumes when not in the hood.
- If the animal is fractious, aggressive, or high stress, ideally the container would be big enough for a live trap or kennel. Having several sizes of containers would be ideal for different sized animals.
- Use 1 tbsp liquid isoflurane for every 4 gallons container volume.
- The box should be mostly sealed (but not completely sealed as the gas expands).
- After isoflurane is poured into the container, the animal (or animal in a live trap) can be transferred to the container and the lid replaced.
- Monitor the patient to ensure it quickly lose consciousness.
- Leave patient in the tub for at least 10 minutes to ensure overdose of isoflurane has caused death. Overdose of isoflurane is an approved humane euthanasia method according to the AVMA.25
- Pinkie mammals may need longer depending on their body temperature and age.
- Rock tub before opening to ensure no movement.
- Open tub outside (tub on ground, ensure you are above tub or are wearing a respirator) or in a vent hood.
- Use a stethoscope to ensure heartbeat of the patient has stopped.
- Leave tub outside or in vent hood for at least 10 minutes.
Basic Wildlife Stabilization
During all of these steps, decreasing stress is the most important thing we can do for wildlife. Stress will kill wildlife and often a hands-off protocol is preferable over an invasive one.
Do visual triage. Is there an obvious injury that would render the animal non-releasable? If so, euthanize immediately. Immediately treat any breathing difficulties (place in oxygen chamber) or active hemorrhage (apply bandage to stop bleeding).
Treat thermoregulatory deficits. If animal is hypothermic, warm it up. If animal is hyperthermic, cool it down.
Leave the animal alone! Leave the animal in a quiet, dark room so it can de-stress and relax. This also gives the animal time to adjust internal body temperature.
Give fluid therapy. Assume at least 5% dehydration in all animals admitted. Subcutaneous fluids are fast to administer and a great choice in almost all cases.
Give pain medications. If there is any injury, appropriate pain management is paramount.
Adapted from Schott R. Wildlife rehabilitation: Until the rehabilitator arrives. Proc ExoticsCon. 2020.
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Renée Schott, DVM, CWR
The Wildlife Rehabilitation Center of Minnesota
Roseville, MN, USA