Angel Wing

Angel wing is a developmental wing deformity primarily affecting waterfowl, in which the last joint of the wing becomes twisted outward, causing the flight feathers to project away from the body rather than lying flat against the bird's side. This condition, also known as slipped wing, crooked wing, or dropped wing, results in a distinctive appearance where the wing tips stick out at an unnatural angle, often resembling the outstretched wings of an angel, hence the common name. The condition most commonly affects geese, ducks, and swans, though it can occasionally occur in other bird species. Angel wing is seen in both wild and captive waterfowl populations, with particularly high prevalence in birds fed inappropriate diets by well-meaning humans in parks and urban areas.

The underlying cause of angel wing relates primarily to nutritional imbalances during the critical period of rapid wing growth in juvenile birds. Diets excessively high in protein and calories, particularly from sources like bread, crackers, and other human foods commonly fed to waterfowl in public areas, cause the flight feathers to grow faster than the underlying wing structures can support. The weight of these heavy, rapidly developing feathers causes the carpal joint to twist outward before the bones and connective tissues have adequately strengthened. Once the wing has grown into this abnormal position and the bones have hardened, the deformity becomes permanent without intervention.

The impact of angel wing on affected birds ranges from cosmetic concerns to life-threatening disability depending on severity and whether one or both wings are affected. Birds with angel wing cannot fly normally, if at all, making them vulnerable to predators, unable to migrate, and dependent on their immediate environment for survival. In the wild, this condition significantly reduces survival rates and quality of life. Affected birds may struggle to escape danger, find food, or reach suitable habitat. The condition does not cause direct pain in most cases, but the functional impairment has serious consequences for the bird's welfare and survival.

Angel wing is one of the few avian orthopedic conditions that can potentially be corrected if detected and treated early enough during development. In young birds where the bones have not fully calcified, splinting or taping the wing into the correct position while correcting the diet can allow normal development to resume. However, timing is critical, and once the bones have hardened, typically by eight to ten weeks of age depending on species, correction becomes impossible without surgical intervention, which carries its own risks and limitations. Prevention through proper nutrition remains the most effective approach, making education about appropriate feeding of waterfowl an important public health message for bird welfare.

The primary cause of angel wing is nutritional imbalance during the rapid growth phase of juvenile waterfowl, specifically diets that are excessively high in protein and calories while being deficient in essential vitamins and minerals. When young birds consume diets significantly higher in protein than their natural food sources would provide, particularly from sources like bread, popcorn, chips, and other human foods, their feathers grow at an accelerated rate that outpaces the development of supporting musculoskeletal structures. The flight feathers become disproportionately heavy before the carpal joint and associated bones, tendons, and ligaments have developed sufficient strength to support them properly, resulting in the characteristic outward rotation of the wing tip.

Genetic factors appear to play a role in susceptibility to angel wing, with some birds developing the condition despite being fed appropriate diets while others consuming poor-quality food remain unaffected. Certain bloodlines and species seem predisposed to the condition, suggesting a heritable component to the weakness in carpal joint development or the metabolic response to dietary excesses. In domestic waterfowl breeding programs, avoiding breeding from affected individuals can help reduce the incidence of angel wing in subsequent generations. The interaction between genetic predisposition and environmental factors means that some birds require particularly careful nutritional management during development to avoid the condition.

Environmental and husbandry factors significantly influence the development of angel wing in both wild and captive settings. In parks and urban areas where well-meaning people regularly feed waterfowl bread and other inappropriate foods, the incidence of angel wing is markedly higher than in natural populations with access only to appropriate food sources. Captive waterfowl raised on commercial poultry feeds formulated for chickens or turkeys may receive excessive protein levels compared to their natural diet, increasing angel wing risk. Overcrowding and competition for food can lead some birds to consume more than their share, exacerbating nutritional imbalances. Limited access to natural foraging opportunities deprives birds of the varied, balanced diet that would support normal development.

Risk factors for angel wing include species, age, growth rate, and feeding practices. Larger waterfowl species including geese and swans appear more susceptible than smaller ducks, possibly because their larger wing size makes the weight discrepancy between feathers and supporting structures more problematic. Male birds may be affected more often than females in some species, potentially related to their typically larger size and faster growth rates. The highest risk period corresponds to the rapid feather growth phase, typically between two and eight weeks of age, when flight feathers are actively developing. Birds with access to unlimited high-calorie food during this period face the greatest risk of developing the condition.

The mechanism of angel wing development involves a cascade of events beginning with excessive nutritional intake. High protein and calorie consumption stimulates rapid growth of blood feathers, particularly the primary flight feathers of the wing. These developing feathers are heavy due to their blood supply and keratin content. As the feathers grow and gain weight, they exert an outward rotating force on the carpal joint. In normal development, the bones, cartilage, and supporting soft tissues would strengthen at a pace matching feather growth. However, with accelerated feather development, the carpal joint cannot adequately support the feather weight, and the weakest point in the developing joint gives way, allowing the twist to occur. Once the wing has rotated and the bones subsequently harden in the abnormal position, the deformity becomes fixed.

Early warning signs of angel wing development can be detected by observant waterfowl keepers and wildlife rehabilitators during the critical growth period. The first indication is often a slight outward rotation of the wing tip that becomes apparent as the flight feathers begin emerging from their sheaths. The wing may appear to droop slightly lower than normal or not fold as tightly against the body as the opposite wing. Some asymmetry in wing carriage, with one wing appearing longer or more prominent than the other, warrants close examination. During this early stage, the flight feathers may appear disproportionately large compared to the rest of the developing wing, creating a heavy appearance at the wing tip. Catching the condition at this earliest stage offers the best opportunity for successful correction.

As angel wing progresses, the common symptoms become increasingly obvious and unmistakable. The last section of the wing, containing the primary flight feathers, rotates outward and often upward, creating the characteristic appearance that gives the condition its name. The affected wing cannot be folded normally into the resting position against the body, instead protruding outward at an angle ranging from mild to nearly perpendicular to the body axis. The flight feathers stick out awkwardly, often drooping toward the ground rather than lying smoothly over the secondary feathers and body. In severe cases, the feathers may drag on the ground when the bird walks, leading to feather damage and soiling.

Behavioral changes associated with angel wing relate primarily to the functional impairment the condition causes. Affected birds may be unable to fly or may show markedly reduced flying ability compared to normal flock members. When attempting flight, birds with angel wing often show asymmetric wing beats, veering or circling rather than flying straight. Some affected individuals appear reluctant to attempt flight, perhaps having learned from unsuccessful previous attempts. During swimming, which is less affected by the wing deformity, birds may still be able to function relatively normally, though wing position in the water may appear abnormal. Social position within flocks may be affected, as flight-impaired birds cannot keep up with or escape from more dominant individuals.

Physical signs of angel wing extend beyond the obvious wing positioning to include secondary effects of the condition. The affected feathers often become damaged, broken, or soiled from dragging on the ground or catching on objects. The skin and feather follicles in the affected area may show irritation or injury from abnormal positioning and contact with environmental surfaces. Birds attempting to compensate for the abnormal wing position may show altered posture or gait. In bilateral cases where both wings are affected, the bird may have a distinctive hunched or abnormal standing posture. Weight distribution while standing may shift as the bird accommodates the protruding wing or wings.

Symptom progression in angel wing follows a predictable pattern if left uncorrected. Initial mild rotation worsens as feather growth continues and the weight of developing feathers increases the rotational force on the carpal joint. Once feathers reach full development, the rotation typically stabilizes, though it does not improve without intervention. In young birds, the deformity may appear to fluctuate somewhat as growing feathers are molted and replaced, but the underlying joint malposition persists. Adult birds with established angel wing maintain a stable deformity that does not worsen with age but also cannot improve without surgical intervention. Secondary complications including feather damage and skin irritation may develop or worsen over time without management.

Emergency symptoms related to angel wing are relatively uncommon since the condition itself is not acutely life-threatening. However, certain situations warrant immediate veterinary attention. If the affected wing becomes caught on fencing, vegetation, or other objects and the bird injures itself struggling to escape, emergency care may be needed. Open wounds, bleeding, or obvious fractures associated with the abnormal wing require prompt treatment. Signs of infection in damaged skin or feathers, including swelling, discharge, or spreading redness, need veterinary evaluation. In wild or semi-wild settings, birds with angel wing that cannot escape predators or access food and water due to their disability may be found in crisis situations requiring immediate intervention.

Initial examination for suspected angel wing begins with visual assessment of wing position and carriage. An avian veterinarian or experienced waterfowl keeper can typically identify the condition based on physical appearance alone, as the characteristic outward rotation of the wing tip is quite distinctive. The examiner will observe the bird at rest and in motion, noting how the wing is held, whether it can be folded normally, and the degree of rotation present. Both wings should be compared, as bilateral involvement does occur and affects treatment planning and prognosis. The veterinarian will ask about the bird's age, diet history, and when the abnormality was first noticed, as this information is crucial for determining whether corrective treatment is still possible.

Diagnostic tests for angel wing are relatively straightforward compared to many avian conditions. Physical manipulation of the wing allows assessment of joint mobility and helps determine whether the carpal joint can be manually repositioned to a normal orientation. In early cases where correction may be possible, the joint typically maintains some flexibility. Radiographic examination may be performed to evaluate the skeletal structures, assess bone development, and identify any secondary changes or concurrent conditions. X-rays reveal whether the bones have fully calcified, which is the primary determinant of whether non-surgical correction remains possible. In some cases, the degree of soft tissue involvement and the exact anatomy of the deformity can be better characterized through imaging.

Differential diagnosis for angel wing includes other conditions affecting wing position and function in birds. Wing fractures, while typically causing a different appearance, can produce abnormal wing carriage that might initially be confused with angel wing. Joint luxations or dislocations can alter wing position and may co-occur with angel wing in birds that have sustained trauma related to their disability. Neurological conditions affecting wing control can cause abnormal wing carriage but typically present differently and include other neurological signs. Congenital wing deformities unrelated to angel wing occasionally occur and may be distinguished by their presence from hatch rather than development during the growth period. Feather cysts or masses affecting the wing can alter its appearance but are usually palpable on examination.

Diagnosis confirmation for angel wing is primarily clinical, based on the characteristic physical findings and history consistent with the condition. The typical presentation includes outward rotation of the last wing joint with inability to fold the wing normally, occurring in a juvenile waterfowl with a history of inappropriate diet or observed during the critical developmental window. Once the characteristic appearance is identified and other conditions ruled out, definitive diagnosis is established. Staging or grading the severity helps guide treatment recommendations, with assessment including the degree of rotation, presence of secondary changes, and whether ossification of the bones has occurred. Photography or video documentation of the wing position can help track changes over time during treatment or monitor for progression.

Emergency and immediate treatment for angel wing focuses on early intervention during the brief window when correction remains possible. For juvenile birds caught in the early stages of development, the wing can often be manually repositioned to its correct orientation and stabilized using various wrapping or splinting techniques. The standard approach involves gently rotating the wing tip back to the normal position, then securing it against the body using veterinary wrap, bandaging tape, or specialized wing wraps. The wrap holds the wing in position while allowing continued blood flow and feather development. This treatment must begin before the bones have fully hardened, typically before eight to ten weeks of age in most waterfowl species, to have reasonable success.

Medical management of angel wing primarily involves dietary correction combined with physical restraint of the wing. All bread, crackers, popcorn, and other inappropriate foods must be immediately eliminated from the diet. Affected birds should receive species-appropriate waterfowl feed formulated for their life stage, supplemented with natural forage including grasses, aquatic vegetation, and appropriate protein sources like insects and small invertebrates. The protein content of the diet should be reduced to appropriate levels for the species. Some practitioners recommend supplementation with vitamin D, calcium, and other nutrients that support bone development, though evidence for specific supplementation protocols is limited. Dietary correction alone, without physical restraint of the wing, is unlikely to reverse established deformity.

Surgical options for angel wing are limited and generally reserved for cases where conservative treatment has failed or the condition was not identified until after bone ossification. Surgical procedures may involve cutting and repositioning the carpal joint, removing portions of affected feathers or bone, or in some cases amputating the affected portion of the wing. These procedures carry significant risks including infection, blood loss, anesthetic complications, and failure to achieve functional improvement. Even successful surgery rarely restores normal flight ability, and the primary goal becomes improving wing position to enhance quality of life and reduce secondary complications. Surgery should only be performed by veterinarians experienced in avian orthopedics and waterfowl medicine.

Supportive care during angel wing treatment includes environmental modifications to facilitate healing and prevent injury. Birds undergoing wing wrapping should be housed in clean, dry environments where bandages will not become soiled. Swimming access may need to be restricted during treatment to keep wrappings dry, though supervised brief water access for bathing and normal waterfowl behaviors can be beneficial. Soft, non-abrasive substrate reduces the risk of bandage damage and skin irritation. Affected birds may need separation from aggressive flock members who might disturb bandages or stress the patient. Nutritional support ensures adequate intake during the treatment period.

Alternative and complementary treatments for angel wing have limited evidence but may be considered as adjuncts to standard care. Physical therapy involving gentle stretching and range-of-motion exercises may help maintain joint flexibility during the treatment period. Hydrotherapy, allowing supervised swimming once wraps are removed, can support recovery of normal wing function. Some practitioners use supportive devices or prosthetics to help position the wing during healing. Natural foraging opportunities and environmental enrichment support overall health during recovery. These approaches should complement rather than replace established treatment methods.

Treatment decisions for angel wing depend on multiple factors including the bird's age, severity of deformity, and intended disposition. For young birds caught early, aggressive treatment with wing wrapping and dietary correction offers good chances of significant improvement or complete resolution. Older birds with established deformities have limited treatment options, and decisions must weigh the potential benefits against treatment stress and risks. Wild birds intended for release must achieve sufficient wing function for survival, making treatment decisions particularly consequential. For permanently disabled birds, decisions about ongoing care, placement in appropriate sanctuary settings, or humane euthanasia must consider quality of life, available resources, and the bird's welfare.

Recovery timeline for angel wing treated with wing wrapping and dietary correction typically spans two to four weeks of active treatment, though the total rehabilitation period may extend considerably longer. The wing wrap is usually maintained for one to three weeks, depending on the bird's age and response to treatment. During this period, the wrap should be checked daily for proper position, adequate circulation, and signs of complications such as swelling, discharge, or feather damage. Some practitioners recommend periodic wrap removal to assess progress and allow brief periods of normal wing movement before rewrapping. After wrap removal, the wing position should be monitored closely for any return of rotation, with additional treatment periods as needed.

Post-treatment care following angel wing correction focuses on maintaining the improvement achieved and supporting normal development. The corrected diet must continue throughout the bird's growth period and ideally for life to prevent any nutritional factors that might affect wing health. Gradual reintroduction to water and normal activities allows the bird to regain strength and coordination after the period of restricted movement during wrapping. Physical therapy encouraging normal wing use, including wing stretching, flapping exercises, and eventually flight practice, supports functional recovery. Regular monitoring for any recurrence of wing rotation ensures early detection if additional treatment becomes necessary.

Prognosis for angel wing varies dramatically based on when treatment is initiated. Birds treated during the first few weeks of life, before significant bone ossification has occurred, have excellent chances of complete or near-complete correction with diligent treatment. Success rates decrease rapidly with age, and birds treated after bone hardening typically achieve limited improvement. Unilateral cases generally have better outcomes than bilateral involvement. The bird's overall health, cooperativeness with treatment, and absence of concurrent conditions also influence outcomes. Even with successful correction of the deformity, some birds may show subtle differences in wing carriage compared to unaffected individuals.

Long-term outlook for birds recovering from angel wing depends on the degree of correction achieved and ongoing management. Birds achieving complete correction can enjoy normal quality of life with full flight capability. Partial correction may allow improved wing function while leaving some cosmetic abnormality. Birds with residual deformity may still live satisfactory lives in appropriate captive settings where flight is not essential. For wild birds, the long-term outlook depends heavily on achieving sufficient function for survival, including escape from predators, migration if applicable, and normal foraging and social behaviors. Permanent flight impairment generally makes wild birds non-releasable, requiring either permanent sanctuary care or humane euthanasia. Captive birds can often live full lifespans with appropriate accommodations for their disability.

Environmental prevention of angel wing centers on ensuring waterfowl have access to appropriate natural food sources while limiting access to harmful human foods. In public parks and natural areas, educational signage discouraging bread feeding and explaining its harmful effects can reduce the incidence of angel wing and other diet-related conditions. Providing designated feeding areas with appropriate waterfowl feed gives well-meaning visitors an alternative way to interact with birds without causing harm. Maintaining natural habitat features that support diverse food sources allows waterfowl to meet their nutritional needs through foraging. For captive waterfowl, proper housing design ensures birds cannot access inappropriate food sources from visitors or other animals.

Quarantine protocols are less relevant for angel wing specifically, as the condition is not contagious. However, new waterfowl entering collections should be evaluated for angel wing and other developmental or congenital conditions that might affect their welfare or suitability for breeding programs. Assessing wing conformation during quarantine allows early detection of subtle cases and informs decisions about housing, breeding, and management. Birds with angel wing should generally not be used for breeding due to the potential genetic component, though this decision depends on the severity of deformity and the importance of other traits the bird possesses.

Dietary prevention is the cornerstone of angel wing prevention and involves providing species-appropriate nutrition throughout development. Young waterfowl should receive feeds specifically formulated for their species and life stage, with protein levels appropriate for normal rather than accelerated growth. For ducks, protein content of starter feed should be approximately twenty percent, decreasing to sixteen to eighteen percent as birds mature. Geese and swans have similar requirements with species-specific variations. Natural foraging opportunities supplementing commercial feeds provide varied nutrition and behavioral enrichment. Absolutely avoiding bread, crackers, chips, and similar human foods is essential, as even occasional feeding of these items during the critical growth period can trigger angel wing in susceptible individuals.

Health maintenance supporting proper wing development includes regular assessment of growing birds to detect early signs of angel wing while correction remains possible. Daily observation of juvenile waterfowl during the two to eight week age window allows prompt identification of any wing abnormalities. Weighing growing birds and comparing growth rates to species standards helps identify individuals with accelerated growth that might indicate excessive nutrition. Maintaining appropriate stocking density reduces competition that might lead to overconsumption by dominant individuals. Providing adequate exercise opportunities supports normal musculoskeletal development throughout the body.

Early intervention when angel wing is suspected offers the best chance of successful treatment. At the first sign of wing tip rotation or abnormal wing carriage, affected birds should be evaluated and treatment initiated immediately if appropriate. Delay of even a few days during the rapid growth phase can make the difference between successful correction and permanent deformity. Bird keepers should have wrapping materials and appropriate feed on hand before the start of breeding season so treatment can begin without delay if needed. Establishing relationships with avian veterinarians familiar with waterfowl medicine ensures access to expert guidance during the critical treatment window.

Daily management of waterfowl with permanent angel wing deformity focuses on accommodating their disability while maintaining quality of life. Feeding stations should be positioned at ground level and easily accessible, as affected birds may have difficulty competing with normal flock members at elevated feeders. Water sources for drinking and bathing must be designed for safe entry and exit, with gentle slopes or ramps rather than steep edges that could trap a bird unable to use wings for balance. Daily monitoring ensures affected birds are eating and drinking adequately and not being excluded from resources by more mobile flock members. Observation for damage to the affected wing from dragging, catching on objects, or attacks by other birds allows early intervention before serious injury occurs.

Home environment modifications for birds with angel wing include housing design that minimizes hazards related to their disability. Smooth, rounded corners reduce the risk of wing tips catching on structures. Appropriate spacing between fence posts or cage bars prevents wings from becoming trapped. Soft, clean substrate reduces damage from feathers dragging on the ground. Shelter design allows easy access for birds that cannot fly, with ground-level entry points rather than elevated roosts or platforms. If predator protection is needed, ground-level secure housing rather than elevated shelters accommodates flight-impaired birds. Companion birds housed with affected individuals should be selected for compatibility and non-aggressive temperament.

Quality of life for birds with angel wing can remain good despite their disability when appropriate accommodations are provided. Waterfowl are naturally social and continue to enjoy flock interactions, courtship behaviors, and daily activities regardless of flight impairment. Swimming ability typically remains largely unaffected, and access to appropriate water for swimming, bathing, and natural behaviors is important for welfare. Environmental enrichment including varied terrain, foraging opportunities, and appropriate vegetation supports natural behaviors and mental stimulation. While flight is not possible, exercise through walking and swimming maintains physical condition and supports overall health.

Monitoring and ongoing care for birds with angel wing includes regular assessment of the affected wing and overall health status. The wing should be examined periodically for any progression of deformity, skin damage from feather dragging, feather condition, and signs of infection or irritation. Regular trimming of damaged feathers may reduce drag and improve comfort. Veterinary evaluation should occur if any wounds develop, if the wing position changes, or if the bird shows signs of pain or distress. Weight monitoring ensures adequate nutrition despite any competitive disadvantages in feeding situations. Overall health care including parasite management, vaccination where applicable, and attention to any concurrent health issues remains important.

Caregiver support resources for those managing waterfowl with angel wing include avian veterinarians experienced with waterfowl, waterfowl rescue organizations, and online communities focused on waterfowl care. Educational materials about angel wing prevention and treatment help caregivers understand the condition and make informed decisions. Financial considerations for ongoing care are typically modest for angel wing specifically, as the condition does not require expensive medications or frequent veterinary visits once stabilized. Emotional support may be needed for caregivers of severely affected birds, particularly when difficult decisions about quality of life must be made. Connecting with others who have successfully managed birds with angel wing provides practical advice and encouragement.

High-risk species for angel wing include larger waterfowl that experience rapid growth rates and develop correspondingly heavy flight feathers during their developmental period. Domestic and wild geese are particularly susceptible, with various breeds of domestic geese and wild species including Canada Geese and Greylag Geese commonly affected. Swans including Mute Swans and Trumpeter Swans develop angel wing with concerning frequency, particularly in populations with access to human-provided foods. Among ducks, larger domestic breeds such as Pekin ducks and Rouen ducks show higher susceptibility than smaller species. The combination of rapid growth, heavy adult body size, and proportionally large flight feathers creates conditions favoring angel wing development in these species when nutritional imbalances occur.

Moderate-risk species include medium-sized waterfowl and some non-waterfowl species that may develop angel wing under certain circumstances. Mallards and Muscovy ducks occasionally develop the condition, particularly in urban settings where inappropriate feeding is common. Smaller domestic duck breeds have lower incidence but are not immune. Some non-waterfowl species including certain cranes and wading birds may develop similar wing deformities related to nutritional factors, though these cases are less common and may have somewhat different underlying mechanisms. The key risk factors across all affected species remain excessive protein intake during rapid growth and genetic predisposition to carpal joint weakness.

Screening recommendations for waterfowl keepers include regular assessment of growing birds during the critical developmental window. Daily observation of wing carriage in birds between two and ten weeks of age allows early detection of any rotation. Comparing wing position and development between clutch mates or flock members helps identify individuals showing abnormal development. Any bird showing even subtle asymmetry or outward rotation should be immediately evaluated and treatment considered. Breeding stock should be selected from lines without history of angel wing, though the genetic component is not fully understood and cannot be completely controlled. Pre-purchase examination of waterfowl includes assessment of wing conformation to avoid acquiring affected individuals.

Commonly co-occurring conditions with angel wing relate primarily to the nutritional imbalances that cause the primary condition and the secondary effects of living with a wing deformity. Obesity frequently accompanies angel wing in birds fed excessive calories, creating additional health concerns including fatty liver disease, cardiovascular strain, and reduced mobility. Metabolic bone disease can result from the same dietary imbalances causing angel wing, particularly calcium-phosphorus imbalances and vitamin D deficiency. Birds with angel wing may develop skin wounds or infections secondary to wing dragging and abnormal feather wear. Social stress and injuries from aggressive flock interactions may affect flight-impaired birds unable to escape dominant individuals.

Conditions with similar symptoms to angel wing include other developmental wing abnormalities and acquired wing injuries. Congenital wing deformities present from hatch may resemble angel wing but have different underlying causes and are typically not correctable through the methods used for angel wing. Feather abnormalities including fault bars and abnormal feather development can create appearance changes that might initially be confused with angel wing. Wing fractures or joint injuries can cause abnormal wing carriage, though the presentation and history typically differ. Neurological conditions affecting wing control produce functional abnormalities that may superficially resemble the wing drooping seen in angel wing but include other neurological signs and affect the wing differently.

Potential complications of angel wing develop over time if the condition is not corrected and include both direct effects of the deformity and secondary problems related to living with the disability. Chronic skin irritation and wounds develop where damaged feathers drag on the ground, creating risk of infection and chronic discomfort. Progressive feather damage makes the wing increasingly unsightly and dysfunctional. Birds unable to fly face increased predation risk in environments with ground predators. Inability to migrate affects survival in wild populations of migratory species. Social difficulties within flocks can lead to stress, inadequate nutrition, and increased disease susceptibility. Reproductive complications may occur if wing deformity interferes with mating behaviors or if affected individuals are selected against by potential mates.