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Epizootic of Beak Deformities in Alaska: Investigation of an Emerging Avian Disease

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Epizootic of Beak Deformities in Alaska: Investigation of an Emerging Avian Disease Epizootic Of Beak Deformities In Alaska: Investigation Of An Emerging Avian Disease Item Type Thesis Authors Van Hemert, Caroline Download date 24/09/2021 21:40:22 Link to Item http://hdl.handle.net/11122/9139 EPIZOOTIC OF BEAK DEFORMITIES IN ALASKA: INVESTIGATION OF AN EMERGING AVIAN DISEASE By Caroline Van Hemert RECOMMENDED: Dr. Colleen Handel Dr. John Blake r. &dsan Sharb^m^h ' / )r. Todd O’Hara, Advisory Committee Co-Chair Dr. Diane 0!Bri<n, Committee Co-Chair Dr. Mark Lindberg, Chahrf Wildlife Program, DepartmenLQf Biolog/and Wildlife APPROVED: Dr. Paul Layer, Dean, College of^NaturaTSciences and Mathematics. x. Lawrence Duffy, Dean of tile Graduate School _________________________ , -2LP/3L __________ Date EPIZOOTIC OF BEAK DEFORMITIES IN ALASKA: INVESTIGATION OF AN EMERGING AVIAN DISEASE A DISSERTATION Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Caroline Van Hemert, B.A., B.S, M.A. Fairbanks, Alaska May 2012 UMI Number: 3528856 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI 3528856 Published by ProQuest LLC 2012. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 A b s t r a c t The sudden appearance of morphological abnormalities in a wild population is often associated with underlying ecological disturbances, including those related to introduction of new pathogens or pollutants. An epizootic of beak deformities recently documented among Black-capped Chickadees (Poecile atricapillus) and other resident bird species in Alaska has raised concern about underlying causes. This dissertation describes results from several recent studies of what we have termed “avian keratin disorder.” The primary objectives of the research were to characterize the physiology and pathology of beak deformities and to address specific ecological questions related to this emerging avian disease. In a study of beak growth rates in captive chickadees, I determined that accelerated epidermal growth is the primary physical mechanism by which beak deformities develop and are maintained. Affected birds also exhibited high rates of mortality and skin lesions, suggesting that this disorder significantly compromises individual health. I used radiography, histopathology, and electron microscopy to describe the pathology of avian keratin disorder. As part of this effort, I established baseline information about normal passerine beak and claw structure and developed methods for processing hard-comified tissues. The suite of lesions that I observed in affected chickadees does not correspond with any known avian diseases, suggesting the presentation of a novel disorder in wild birds. In addition, the detailed characterization of gross and microscopic changes has allowed me to eliminate a number of likely etiologies, including nutritional problems, microbial pathogens, and select toxicants. As a complement to diagnostic pathology, I conducted field studies to investigate possible causes and patterns of occurrence of beak deformities. I used stable isotope analysis to investigate the association between diet and beak deformities. I found that winter dietary patterns differed between chickadees with normal beaks and those with beak deformities, but that such differences are more likely a result than a cause of avian keratin disorder. My field research on Northwestern Crows in Alaska confirmed high prevalence of a nearly identical condition to that observed in chickadees. These findings indicate that avian keratin disorder affects multiple, ecologically-distinct species across a large geographic area. Together, the studies presented in this dissertation provide new insights and identify priority research areas for a rapidly emerging disease in V Table of Contents Page Signature Page............................................................................................. Title Page..................................................................................................... Abstract........................................................................................................ Table of Contents ....................................................................................... List of Figures.............................................................................................. List of Tables ............................................................................................... Acknowledgments...................................................................................... ........................ xiii Introduction ................................................................................................. .......................................... 1 CHAPTER 1. Evidence of accelerated beak growth associated with avian keratin disorder in Black-capped Chickadees (Poecile atricapillus)........................................... 5 1.1 Abstract........................................................................................ ........................... 5 1.2 Introduction ............................................................................................................. 6 1.3 Materials and Methods ................................................................ ........................... 8 1.3.1 Field methods ...................................................................... ........................... 8 1.3.2 Captive experiment........................................................................................ 8 1.3.3 Statistical analyses....................................................................................... 10 1.4 Results .......................................................................................... .........................11 1.4.1 Beak morphology and observations............................................................11 1.4.2 Beak growth......................................................................... ........................ 13 1.5 Discussion.............................................................................................................15 1.6 Acknowledgments ....................................................................................................18 1.7 Literature Cited ........................................................................................................ 18 CHAPTER 2. Microanatomy of passerine hard-cornified tissues: Beak and claw structure of the Black-capped Chickadee {Poecile atricapillus) ................................... 27 2.1 Abstract .................................................................................................................... 27 2.2 Introduction.............................................................................................................. 28 2.3 Materials and Methods ............................................................................................ 32 2.3.1 Sample collection............................................................................................32 2.3.2 Laboratory methods........................................................................................33 2.4 Results.......................................................................................................................36 2.4.1 Beak microanatomy........................................................................................36 2.4.2 Claw microanatomy........................................................................................41 2.5 Discussion................................................................................................................ 43 2.5.1 Techniques...................................................................................................... 43 2.5.2 Form and function...........................................................................................46 2.6 Acknowledgments ....................................................................................................49 2.7 Literature Cited ........................................................................................................50 CHAPTER 3. Pathology of avian keratin disorder in Black-capped Chickadees {Poecile atricapillus)..............................................................................................................69 3.1 Abstract .................................................................................................................... 69 3.2 Introduction.............................................................................................................. 70 3.3 Materials and Methods ............................................................................................ 71 3.3.1 Study animals.................................................................................................. 71 3.3.2 Radiography....................................................................................................72 3.3.3 Histopathology................................................................................................72
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