An Aberrant Bald Eagle (Haliaeetus Leucocephalus) with Multiple Anatomical Abnormalities

Vertebrate Anatomy Morphology Palaeontology 7:101–110 101 ISSN 2292-1389 An aberrant bald eagle (Haliaeetus leucocephalus) with multiple anatomical abnormalities Jeremy J. Klingler1,* and Christine N. Glasmann2 1School of Biological Sciences, University of Utah, 257 South 1400 East, Salt Lake City, Utah, 84112, USA; [email protected] 2Department of Integrative Biology, University of California Berkeley, 3040 Valley Life Sciences Building, Berkeley, California, 94720, USA; [email protected] Abstract: 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. INTRODUCTION induce multiple abnormalities in developing embryos, such as stress bars and polydactyly, as seen in a blue-fronted Genetic diversity and variation is important in a species’ Amazon parrot (Amazona aestiva) nestling (Herrara and evolutionary fitness and is often viewed in a positive light. Berkunsky 2017). Although there are many accounts of However, some genetic discrepancies can severely hinder polydactyly, there is surprisingly little information on the an animal’s ability to execute tasks vital to its survival, such musculoskeletal anatomy that makes up these physical as prey capture or locomotion. Polydactyly is a condition abnormalities. For instance, with the duplication or expres- in which a vertebrate exhibits additional phalanges. This sion of additional digits, do the tendons also duplicate or physical abnormality, and more generally any physical are there aberrant connections where the muscles/tendons abnormality, may be the consequence of environmental insert? The omission of these studies represents a serious conditions, genetics, or unknown reasons (Pourlis 2011). deficit in our understanding of aberrational anatomy. Here, Among birds, polydactyly has been well-documented in we describe a juvenile bald eagle (Haliaeetus leucocephalus) domestic as well as wild species (e.g., Reichnenau 1880; with polydactyly and multiple other abnormalities. We Coale 1887; Lönnberg 1907; Bebe 1910; Ester 1937; compare the anatomy of the abnormal bird with that of a Cole 1942; Landaver 1946; Taylor and Gunns 1947; developmentally normal bald eagle of similar age. Kummerloeve 1952; Cooper 1984; Fox 1984; Heidenreich 1997; Trinkaus et al. 1999; Samour 2000; Vedde 2000). Polydactyly can come with a multitude of other abnormal- METHODS ities (Hollander and Levi 1942). In pigeons, for instance, Two juvenile bald eagle specimens, one abnormal and one alongside polydactyly, Hollander and Levi (1942) ob- normal, were dissected (fresh, frozen, and thawed). The served other characteristics including short nestling down, abnormal specimen (specimen number 2017-01134; acces- defective plumage, an undershot beak, and shortened legs. sion number N1715533 Pennsylvania Animal Diagnostic Extreme environmental stressors, such as wildfires, can Laboratory System) was a 14-week old female nestling Published September 3, 2019 *corresponding author. © 2019 by the authors; submitted May 15, 2019; revisions received August 27, 2019; accepted August 28, 2019. Handling editor: Robert Holmes. DOI 10.18435/vamp29351 Vertebrate Anatomy Morphology Palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/VAMP Article copyright by the author(s). This open access work is distributed under a Creative Commons Attribution 4.0 International (CC By 4.0) License, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. No additional restrictions — You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. Vertebrate Anatomy Morphology Palaeontology 7:101–110 that had never fledged. This specimen’s nest was from ies, and body contour feathers exhibited peculiar bifurcations Columbus, New Jersey near an area that had recently been wherein the feather’s rachis split in two somewhere along cleaned up of arsenic contamination; however, there was no the rachis forming two distinct feathers emerging from one evidence of toxins in the body. Thus, the deformities may central stem. In at least three feathers, it was observed that the have been genetic or developmental in origin. This bird rachis split in a left-right manner (Fig. 2A). More common- was captured and brought to the Mercer County Wildlife ly, the feathers split in such way as to produce a front-back/ Center (New Jersey) after it was found when the nest had overlapping bifurcation (Fig. 2B, C). Sixth, some primary and fallen out of the tree. Evaluation of the bird concluded that secondary feathers were missing (i.e., never formed; Fig. 2D). although it could perch and use all toes on each foot, it Issues such as deep cutting stress bars curved primary remiges, was not a viable candidate for release given the discovery and the absence of primaries and secondaries would severely of numerous anatomical anomalies, and the inability to impact the animal’s ability to generate lift and properly fly. extend its wings. The bird was anesthetized with isoflurane, Forearm and then humanely euthanized with pentobarbital injected intravenously. The normal specimen (band number 17- M. extensor carpi radialis: This muscle has a tendin- 1208; accession number N1714552 Pennsylvania Animal ous origin on the distal end of the humerus on the lateral Diagnostic Laboratory System) was a male with the plum- epicondyle, and the muscle inserts on the extensor process age and development of a recent fledge (11–16 weeks). This of the carpometacarpus. This muscle acts to extend the car- animal was found weak and emaciated, was diagnosed with pal joint at the wrist. The muscle courses along the dorsal disseminated aspergillosis, and was humanely euthanized. surface of the radius and its belly is about as long as half The normal specimen was found in Annapolis, Maryland, the length of the forearm before it becomes a stout tendon and is therefore not related to the deformed specimen. distally towards the carpometacarpus. Overall, this forearm Specimens were worked on under the following per- muscle is quite normal in the aberrant specimen, except mits: MCWC Federal Wildlife rehabilitation permit in one respect. In the right muscle of the abnormal bird #MB777794; MCWC NJ Wildlife rehabilitation permit exists a bizarre, anomalous, extra tendon stemming from #2017-2192; MCWC NJ Endangered species permit #ES2017038; and MCWC NJ Wildlife salvage permit #SB2016037. Upon completion of the study, both specimens were sent to the National Eagle Repository (Commerce City, CO, USA). Both specimens were dissected to compare the anatomical differences between certain regions of interest, particularly the wings and feet. Anatomical terminology follows the Handbook of Avian Anatomy: Nomina Anatomica Avium (Baumel et al. 1993). RESULTS The following section details all the significant issues the abnormal bald eagle specimen exhibits that would impair normal function contrasted with the normal condition. Feathers Numerous abnormalities are associated with the feathers. First, many feathers (primaries, secondaries, and retrices) exhibited stress bars indicative of poor nutrition, stress, and/or general illness (Fig. 1A). Many of these feathers had deeply cutting stress bars which cut off the ends of the barbs. Second, some primary remiges retained the sheath along the rachis (Fig. 1B). Third, some primaries of the right forelimb exhibited severe curvature laterally rather than exhibiting straight-to-slight medial curvature (Fig. 1C). Fourth, some Figure 1. Feather anomalies. A, stress bars; B, extended primary feathers on each wing were ingrown in the follicle of sheath on rachis; C, curvature of primary; D, ingrown the calamus (Fig. 1D). Fifth, numerous primaries, secondar- feather. Arrows indicate these features. 102 Klingler & Glasmann—Aberrant bald eagle Figure 2. Feather anomalies. A, bifurcated feather exhib- Figure 3. A, dorsal view of the extra tendon of the m. iting a left-right split; B, bifurcated feather displaying a extensor carpi radialis. Arrow points to the extra tendon; B, front-back split; C, another bifurcated feather with a front- line drawing of the dorsal forearm musculature of the bald back split; D, missing feathers can be seen on the wing eagle. (image

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