Factors Influencing Local Variation of BaId Eagle Densíty in North-central Saskacchewan by Elston H. Dzus A thes i s presented to the University of Manicoba in partial fulfillrnént of the requirements for the degree of MasEer of Sc ience in the DepartnenE of Zoology Winnipeg, Mani toba (c) Elston H. Dzus, L988 Perniseion Ìta8 been granted L'autorieatíon a êtê accordêe to the National Library of å la Bíbliothèque nat íonate canada to nl crof i lm th I s du canada de nÍcrofílner thesis and to lend or sell cette thèse et de prêter ou copi es of the f i l¡n. de venilre des exenplaires du film. The author (copyright owner ) L'auteur (tftulaire du droi t hag regerved other dr auteur ) se réserve les publ l cat lon rlghts, and autrea droits de publ í cat ion; neither the thesiE nor nl Ia thèse nÍ de longe extensive extracta from it extraits de celle-ci ne nay be printed or otherwiEe doivent être ímprimêa ou reproiluced without his/her autreBent reproduits sana Bon written pernieslon. autorisation écrite. rsBN 0-31-5-47966-3 FACTORS INFLUENCING LOCAL VARIATION OF BALD EAGLE DENSITY IN NORTH-CENTRAL SASKATCHEWAN BY ELSTON H. DZUS A thesis submitted to the Faculty of Craduate Studies of the University of Manitoba in partial fulfìllment of the requirenlents of the degree of I"fASTER OF SC IENCE o 1988 Permission has been granted ro the LIBRARy OF THE UNIVER_ SITY OF MANITOBA to lerìd or sell copies of this thesis. to thE NATIONAL LIBRARY OF CANADA tO MiCrOfìINI thiS thesis and to lend o¡ sell copies of the film, and UNIVERSITy MICROFILMS to publish an abstract of this thesis. The author ¡eserves other publication rights, aud neither the thesis no¡ extensive exlracts from it may be printed or other- wise reproduced wjthout the author's r,¡/ritten pernrissiol. ABSIRACT The ínfluence of nesting habitat, prey resources and hurnan âctivity on local variations of Bald Eagle (Haliaeetus leucocephalus) density was examined in 1986 and 1987 on Besnard and Neneiben Lakes in norÈh-central Saskatcher¿an. Eagle density and the number of active breeding areas on Besnard Lake was Èwo to three times greater Lhan on Nemeiben Lake. Differences in water area or area of foresL within 200 m of shore accounLs for â facEor of l.14 of the variation in eagle numbers, leavíng the najority of the density differences Eo be explained by other factors. Bald Eagles preferred to nest in large trees close Eo shore in rnixed-r¿ood stands dorninaEed by coniferous Lrees. Treed rock, muskeg and even-aged coniferous stands \.¡ere avoided. Trembling asPen (lgg¡Igg tremuloides) was the preferred species for nesting on Lhe rnâinland, while ¡,¡hite spruce (ELçgê glauca) was preferred on islands. PêrcenÈ of suicablê forest habiÈat !¡ithin Ehe zone in which most ea8les nesE (200m fron shore) was almost identical on Besnard (35%) and Nerneiben (36%) lakes and thus forest nesting habitat was not likely a fâcLor lirniting eagle numbers. f invêstigated food resource leveLs by neEting fish in both lakes, and examining records on conmerc ial/sports - fisher ies , and biological surveys. Cisco (çgeg,glgs artedíí) , ân imPortant Prey specíes for eagles, were nore numerous and Ìarger on Besnard Lake. Other indices of aquatic fauna and fish populacions Portray Besnard Lake as nuch rnore productive. Differences in the Prey base was the nost likely factor limiting eagle densiEy on Nemeiben Lake. iv I compared eaglet gro\,¡Lh and hatching order of the sexes on Nerneiben Lake to thaÈ on Besnard Lake. Inflection Points in growEh curves and feather emergence were earlier in ¡¡ales than females. Second-hatched fernales, in rnixed-sex broods, on Nerneiben Lake gained weighE slower than males on both lakes, and had lnflection points which were nuch laLer than those of females on Besnard Lake. Míxed-sex broods, r.¡ith fenales hatchÍng second, !¡ere rare on Besnard Lâke, buE common on Nerneiben Lake; the production of such broods rnay be an âdaptive response !o lower food levels. I investigated human activiLy on the lakes through questionnaires dÍstríbuted to cottage or,¡ners and analysis of carnpground occuPancy. Hunan activity has been nore íntense on Nemeíben Lake for a longer period than on Besnard Lake. Human activÍty rnay have influenced the eagle populations, but did not account for aIÌ of the variatÍon. ACKNOI¿LEDGEI{ENIS This research project has resulted from the cooperation and assistance of numerous people and agencies. I extend sincere apprecia- tion fírst to Jon Ìf. Gerrard, rny supervisor and nenLor. His knowledge of and unending enthusiâm for Bald Eagles was inspiring. I arn also very grateful for the friendshíp which developed with cary R. Bortolott, \,¡ho suggested I investigate eaglet growth and provlded considerable supporc and effective criEicisn through the field research and preparation of this thes is . The diversity of this project benefítted from people with a broad array of Eechnical expertise. I thank the followÍng people in various branches of Saskatchewan Parks, Recreation and Culture for advice and use of equiprnent: forestry (D. Lindenas and D. Bernier), wildlÍfe (T. tleins) and fisheries (R. Wallace and D. Walton). The counsel and loan of equípment of K. Mills is much âppreciated, as Ís Lhe sLatislical and conputer advice of C. Schwarz and F. Spiring. J. SLewarL provided useful crilicism regarding analysis of the forest nesting habiEat; R. Clark assisted in questÍonaire development. G. Reid drafted the figures. I an also fortunaEe Eo have had the assislance of nany hard-working and intelligent research assistants: T. Jacobson, D. Johannesen, J.Kiteley, G. LeaÈhers, C. Lofstrom, D. Longaker, A. and T. Leighcon, Ëhe Nagy's and the Gerrard's. D. Richert, J. Polson and pilot, R. McPherson provÍded expertise on the aerial surveys. My fellow scudents and friends in the Department of Zoolo'y provided a stimulating atmosphere in t^'hich Èo \tork, v1 Special mentíon is due the Hleck's (Gary, Shirley, David, Christa and Toots) for the loan of Eheir cabín while we r¡orked on Nerneiben Lake and for their friendship and Lnterest in this ProjecÈ. I also thank P. Broten, A. and J, Broten, and J. McOonnell for theír Lodging and hospitality. The cooperaÈíon and service of che lodge ovmers (the Sln's, Talbourdet's, Gunn's, Cunningharn's ând Lindskog's) was rnuch appreciated. I thank rny conrnitEee members, R.A. Bodaly, T.D' Galloway and S'G. Sealy for comments and criticisms which irnproved this thesis. This projecË r¡as funded by a World Wíldlife Fund (Canada) grant Èo J.M. Gerrard. Personal support nas provided by a NaLural Sciences and Engineering Research Council posEgraduate scholarship' I am graceful to these insLitutions for theÍr suPPort. Most importantly, I would lÍke to acknowledge the continuing love and supporÈ of my farnily, for without them, this Process of education and research would be arduous. I'fy ParenEs, Jack and Alice Dzus, have always supported and inspíred my interests in wÍldlife research. My ln- laws, the lùawryk's, províded considerabLe moral and logistic suPPort and developed a keen interest in the "eagle Projecc". And Èo my wife and friend, Connie, and our young nan, Zaènary: for Èhe late nighcs, early mornings, windy days, miles of Erekking .... ' . .Thank-you' . CONTENTS ABSTRACT. iw ACKNOIILEDGEI{ENTS. '....... vi colvrEMs ' " " ' 'viii LIST OF TABLES. Xi Lrsr oF FTGIJRES ' ""''xiii CHAPTER 1: General lntroduction and PoPulation Status of Bald Eagles on Besnard and Neneiben L¿kes.. I 1.1. Introduction... 1 1.2. study Area... ... - -.. '. 2 1.3. Objectiwes..... 3 1.4. t{ethods. 4 1.5. Results. r 1.6. Discussion..... 7 CHAPTER 2: Selection and Availability of Forest Nesting Habitat.... l0 2.1. InEroduction... 10 2.2. l,lethods. 10 2.2.1. Nest-Site Selection ... ' '. " 10 2.2.'i..1. Habitat Analysis. 10 2.2.1.2. HabitaÈ Utilization- availability. Lz 2.2.2. SuiÈable Nesting HabitaÈ. ..... -. L2 2.3 . Results. 13 2.3.1. Nest-site selection 13 2 .3 .LL. Habitat AnalYsis . 13 2.3.L.2. Habitat Utilization- awailability. L6 2.3.2. Suitable Nesting Habitat. 20 2.4. Discussion..... viii 2.5. sr¡Enary. 26 CHAPTER 3: Físh PopulaËions.... 27 3 .1. Introduction... 27 3.2. Haterials and l{ethods 29 3.3. Results. 3l 3.4. Discussion...,. ..""" 36 3.5. Sunmary. 43 CIIAPTER 4: Growth of Nestling BaId Eagles. 44 4.1. Introduction... ."""' 44 4.2. Methods. 45 4.3 . Results. 49 4.3.1. Intersexual Comparisons for Neueiben Låke Eaglets' 49 4.3.2. Ínte'tlake Conparisons . 51 4.3.2.L. Culnen. 57 4.3 .2.2 . IJeight. 57 4.3.2.3. Feather DeveloPment. 61 4.4, Discussion..... """" 61 4.5. Suunary. 65 CHAPTER 5: Sex Ratios of Nestling Bald Eagles. 66 5.1. Introduction... 66 5.2. Hethods. 67 5-3- Results. 67 5.4. Discussion..... 69 5.5. Sunnary. 73 CHAPTER 6: Hunan Activity 74 6-1 InLroducLÍon. , . 7¿+ 1X 6 ,2. Methods. 75 6.2.1. Canpground Occupancy...,.. ......... 75 6.2.2. Nest-site Location. .....',. 76 6.2.3. Questio¡maire. 76 6.2.4. Research-Related Disturbance. 77 6.3, Results. 77 6.3.1. Canpground Occupancy...... 77 6.3.2. Nest-site LocaLion. 80 6.3.3. Questionnaire Responses. 80 6.3.4. Research-Related Disturbance. 88 6,4. Discussio¡I. 92 6.5. Su-nrnary. 99 CONCLUSI6NS. ... 101 LITERATURE CITED.. ... 105 APPENDIX 1. Mean Height and Basal Area of Balsaa Fir, Black Spruce and Ithite Spruce on NesÈ and Random Point Transects on Besnard and Nemeiben lakes.. ...... '. 116 2. Relative Density of White Birch, TreEbling Aspen, l{hite Spruce, Black SPruce and Balsam Fir, and Abolute Density (Species Gonbined) on Nest and Random Points Transects on Besnard and Neneiben lakes.