WILDLIFEMONOGRAPHS (ISSN:0084-0173) A Publicationof The WildlifeSociety C t141 ;s ° L @ll I X g r DETERMINANTSOF BREEDING DISTRIBUTIONSOF DUCKS by DOUGLASH. JOHNSONAND JAMESW. GRIER NO. 100 OCTOBER1988 : 0Esu ; e- W$siS :is : > r _> . <<-!A./ t-_I' FRONTISPIECE. Lssser scaup use more permanent wetlands and breed in more northern locations than most of the common North American ducks. (U.S. Fish and Wildlife Service photo) DETERMINANTSOF BREEDING DISTRIBUTIONSOF DUCKS DOUGLASH. JOHNSON U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center, Jamestown, ND 58402 JAMES W. GRIER Zoology Department, North Dakota State University, Fargo, ND 58105 Abstract: Thesettling of breedinghabitat by migratorywaterfowl is a topicof boththeoretical and practical interest.We usethe resultsof surveysconducted annually during 1955-81 in majorbreeding areas to examine the factorsthat affect the distributionsof 10 commonNorth American duck species. Three patterns of settling aredescribed: homing, opportunistic, and flexible. Homing is generallymore pronounced among species that use more stable (more predictable)wetlands, such as the redhead(Aythya americana), canvasback(A. valisineria), lesserscaup (A. affinis), mallard(Anas platyrhynchos), gadwall(Anas strepera), and northern shoveler(Anas clypeata). Opportunisticsettling is more prevalentamong species that use less stable(less predictable)wetlands, such as northernpintail (Anas acuta) and blue-wingedteal (Anas discors). Flexible settlingis exhibitedto variousdegrees by mostspecies. The 10 speciesare shownto fall alonga naturalordination reXecting diSCerent life historycharacteristics. Averagevalues of indicesof r- andK-selection indicated that pintail, mallard, blue-winged teal, and shoveler have the mostfeatures associated with unstableor unpredictableenvironments. Gadwall, American wigeon (Anas americana), andgreen-winged teal (Anas crecca) wereintermediate, and attributes of the divingducks wereassociated with the use of stableor predictableenvironments. Somespecies notablymallard, gadwall, blue-winged teal, redhead, and canvasback tendto fillavailable breedinghabitat first in the centralportions of theirrange, and secondly in peripheralareas. Other species- Americanwigeon, green-winged teal, northern shoveler, northern pintail, and lesser scaup fill theirhabitat in the orderit is encounteredduring spring migration. Age and sex classeswithin species vary in theirsettling pattern. Some of this variationcan be predicted from the matingsystems of ducksin which breedingfemales, especially successful ones, have a greater investmentin habitatresources and are morelikely to returnto the samearea in subsequentyears. WILDL.MONOGR. 100, 1-37 6 WILDLIFEMONOGRAPHS CONTENTS INTRODUCTION 6 Breeding Distributions of the Species 13 Acknowledgments 7 Mallard 1 3 A THEORYOF SETTLING 7 Gadwall 16 Homing 8 American Wigeon 16 OpportunisticSettling 8 Green-vinged Teal 21 FlexibleSettling 8 Blue-winged Teal 21 LifeHistory Characteristics 9 Northern Shoveler 24 METHODS 9 Northern Pintail 24 Survey Design 9 Redhead 24 AerialCounts 11 CanvasUck 27 GroundCounts 11 Lesser Scaup 27 Pond Counts 11 General Patterns 30 Computations 12 Relations with Life History Characteristics 30 Analysisof Pond Counts 12 DISCUSSION 31 Breeding-season Distribution,Wintering Areas, Settling Patterns 31 and MigrationCorridors 12 Fillingthe Habitat 32 Relations of Ducks with Local and Continental Relations to Life History Characteristics 32 Ponds 12 Management Applications 34 Relationsto LifeHistory Characteristics 13 LITERATURECITED 35 RESULTS 13 Dynamicsof the WetlandHabitat 13 INTRODUCTION ing estimatesof the breedingpopulation Thesettling of habitatby migratory birds with measuresof productivity(Martin et withintheir geographic range represents al. 1979). Becausereproduction varies habitatselection on a coarsescale (Johnson widelyamong breeding grounds (Hansen 1980),finer than geographical range, but and McKnight1964, Calverley and Boag broaderthan home range and microhab- 1977, Derksenand Eldridge1980), un- itat. Analysisof settlingbehavior on this derstandinghow ducksdistribute them- scaleraises both biological questions and selvesthroughout their range should pro- managementissues. videuseful information for predicting the Onthe biological side, there is a consid- size of fall populations.At a local level, erablebody of theoryconcerning geo- the effectivenessof land management graphicdistribution of highlymobile an- techniquesto increasenumbers and pro- imals such as birds.Both the ultimate ductionof ducksdepends on the extentto factorsthat influence evolutionary fitness whichducks return to the samearea in in the habitatselected and the proximate subsequentyears or seek out new breeding cuesused by animals to selecthabitats have locations(Hochbaum 1946). beenintensively studied. Life history char- Ourobjectives were to determineeco- acteristicsof differentspecies have been logicaland geographiccorrelates of the relatedto habitatsoccupied by thespecies; breeding distributionsof 10 common muchof the discussionon this topic has speciesof NorthAmerican ducks and to been cast in termsof r- and K-selection relatethese to the life historycharacter- (Pianka1974). Distributions and basic bi- isticsof the species.The speciesare mal- ologyare particularly well studied in ducks lard,gadwall, American wigeon, green- (Johnsgard1975, Palmer1976, Bellrose wingedteal, blue-wingedteal, northern 1980),thus providing opportunities for de- shoveler,northern pintail, all of whichare tailedanalysis. dabblers(Tribe Anatini), and canvasback, Thenature of settlingpatterns of ducks redhead,and lesser scaup, all divers (Tribe is importantto waterfowlmanagers at both Aythyini).T}ais analysis is restrictedto the continentaland local levels.To regulate areain NorthAmerica regularly surveyed hunting,for example,managers predict forbreeding ducks (Fig. 1), and data used the sizeof the fall populationby combin- areresults of thosesurveys. BREEDINGDISTRIBUTIONS OF DUCKS Johnsonand Grier 7 1 0 Fig. 1. Strata used in breedingwaterfowl surveys. We propose3 patternsthat migratory H. Boyd,W. F. Crissey,A. Dzubin,J. L. birdscould use for settlingbreeding hab- Eldridge,R. R. Koford,G. L. Krapu,J. T. itat. We then describethe methodsused Lokemoen,H. W. Miller,J. D. Nichols,T. to gatherand analyzethe data.Distribu- D. Nudds,G. L. Nuechterlein,and A. B. tionsof breedingducks are described and Sargeant.M. R. Milleroffered numerous relatedto winteringareas and migration suggestionsthat improved the manuscript. corridors,local and continentalwetland conditions,and homingand pioneering A THEORYOF SE1TLING tendenciesof each species.We also de- scriberelations among the species and how Migratorybirds, by virtueof theirmo- ourfindings fit with the species' life history bility, have many optionsfor selecting characteristics.We concludewith some habitatin whichto breed(Fretwell and implicationsfor management. Lucas 1969, Gauthreaux1980, Bailey Acknotvledgments.We are grateful 1981).The qualityof a habitathas 2 as- to R. S. Pospahalaand others at the Offlce pects-the ultimatequality and the prox- of MigratoryBird Management, U.S. Fish imatecues by whichthe birdschoose it andWildlife Service, for providing survey (Immelmann1973). data used in the analyses,and to A. D. Ultimatefactors are those that affect Aftonand R. A. Wishartfor use of their long-termsurvival and reproductivesuc- unpublishedinformation on homingof cess.Optimal habitat for survivalof the lesserscaup and Americanwigeon, re- adultmay differfrom the optimumfor spectively.We appreciatethe valuable reproduction;requirements for reproduc- commentson variousdrafts of thisreport tion tend to be morestringent. Not only madeby M. G. Anderson,F. C. Bellrose, mustthe birdbe safefrom predation, but 8 WILI:)LIFEMONOGRAPHS so mustthe eggsand ducklings, life stages OpportunisticSettling thatare highlyvulnerable. Food supplies mustinclude the minimumfor adultsur- Thesecond pattern is fora birdto settle vival,as well as adequate calcium, protein, in the firstsite encounteredalong its mi- andenergy for egg production(Holm and grationpath that appears to offerthe req- Scott1954, Krapu 1979), and nutrients for uisitesfor survival and breeding. This pat- the growthand development of young. ternis akinto the "facultativemigration'> Proximatecues used by ducksto iden- of Pulliamand Parker(1979) and would tify suitablebreeding areas are unknown, be appropriateif habitatconditions are butare thought to be indirectand related unpredictablefrom year to year. More- stronglyto wetlandfeatures. Empirical over,opportunistic settling minimizes any evidencecomes from studies in whichwet- migrationcosts. Dispersal, such as caused landswere created or markedly improved, by opportunisticsettling, is an important oftenleading to large increases in the num- meansof adjustingto majorchanges in ber of breedingducks (e.g., Hochbaum birds'habitats and is especiallyimportant 1946,Hochbaum and Bossenmaier1972, in spatiallyheterogeneous habitats (Gau- McKnight1974). Although ducks typically threaux1980, 1982). One manifestation of usea varietyof wetlandsduring the breed- opportunismis frequentpioneering, the ing period(Dzubin 1969, Dwyer et al. movementof birdsinto habitats that were 1979),many of whichdo not persistfor unavailableor not occupiedduring the the entirebreeding season, the conditions previousyear. Pioneering has been docu- of wetlandsin springoffer good cues to mentedby anecdotesattributing increases pondconditions in thesubsequent