An aberrant bald eagle (Haliaeetus leucocephalus) with multiple anatomical abnormalities

Genetic abnormalities, especially polydactyly, are quite common among birds. Although there are numerous accounts of anatomically abnormal birds with polydactyly, few written anatomical descriptions have elucidated whether or not these physical aberrations extend to the musculoskeletal structure of the feet. Here, we present the findings of a dissection of a 14-week old female bald eagle that exhibited polydactyly and numerous other aberrations and discuss the functional impact these aberrations would cause. The specimen displayed a myriad of feather anomalies including missing feathers (i.e., had never grown in), ingrown feathers, stress bars, and most strikingly, bifurcated feathers wherein two feathers were seen to grow out of one rachis. Further, an extra, anomalous tendon was observed stemming from the tendinous origin of the m. extensor carpi radialis. The carpometacarpi were unable to reach full extension, stopping at less than 140º, and had phalanges bent downward at 45º. This mobility is limited in comparison to that of a normal bird. Most notably, the specimen exhibited polydactyly with one extra hallux on each foot. Several tendons of the left foot were seen to have aberrant connections as well.